Note: Descriptions are shown in the official language in which they were submitted.
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A GREEN PROCESS FOR MODIFYING WOOD
This application claims priority to U.S. Provisional Application No.
62/944,858, filed
on December 6, 2019, and U.S. Provisional Application No. 63/068,211, filed on
August 20,
2020; both of which are herein incorporated by reference in their entirety.
Field of the Invention
This invention generally relates to a green (non-toxic) and environmentally
sustainable process for modifying wood.
Discussion of Related Art
The social and environmental benefits of all-green wood are significant,
including
eliminating the need for the toxic chemical treatment of wooden utility poles,
railway ties,
home construction, boardwalks, and decks, while enhancing strength and fire
resistance
ratings appropriate to be used in areas prone to fire. Considering utility
poles as an example:
the negative economic and social disruption consequences of utility company-
linked
wildfires is extraordinary especially in the Western USA. In 2017 alone,
wildfires in the state
of California killed dozens of people, destroyed thousands of homes and
businesses, and
damaged tens of thousands of other properties ¨ these losses were estimated at
$12 billion.
The record-breaking 2020 fire season has seen enormous wildfires tearing
across California
and other states in the West. More than five million acres have burned across
California,
Colorado, Idaho, Montana, Oregon and Washington State in 2020 year to date.
The costs
for all the wildfires in 2018 are estimated to be over $20 billion, and a
similar calculation
would apply to the costs for the wildfires in 2020. An affordable fire
retardant lumber utility
pole with fire retardant cross arms would have a materially positive impact on
these
statistics.
However, there currently is no all-wood, low price, fully
environmentally
sustainable Class A fire retardant industry-approved utility pole.
Lumber has been treated with solutions of elements and compounds to improve
characteristics and lengthen lifecycle, with varying degrees of success.
Treated wood is
typically referred to as wood that has been treated with preservative
chemicals. A typical
treatment method would include impregnating the wood product with treatment
chemicals
that can result in wood product that is fire resistant, mold resistant, and
insect resistant.
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Many different chemicals have been used for these purposes, including many non-
green,
toxic compounds such as arsenic or copper based compounds, pesticides, etc.
The Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA), requires all pesticides
sold or
distributed in the United States to be registered by the EPA. Most of the
current wood
chemical preservatives (either waterborne or oil-type) are registered
pesticides regulated by
the US EPA. Existing wood products are still made with flammable, toxic to
humans,
environmentally damaging treatment chemicals.
U.S. Patent No. 7,955,711 describes an aqueous solution for the preservation
of
wood and wood products. However, the treatment solution includes chemicals for
insect
and termite repellant to achieve termite and/or insect resistance. These
chemicals are
present in a relatively high concentration of about 1.5 to 9 % by wt., which
can be
environmentally damaging. The 7,995,711 patent also employs an alkali metal
carbonate
(e.g., Na2003) at about 1 to 10 % by wt., which may leave high levels of
Na2003 residual
on the surface of the treated lumber, causing efflorescence on the surface of
the finished
product.
U.S. Patent Nos. 6,303,234, 6,827,984, and 7,297,411 describe a process of
using
sodium silicate solution to create fire retardant products. However, these
patents discuss
the problems of the water solubility and the surface deterioration resulting
from exposure to
air and moisture that are associated with using sodium silicate alone and
require that the
sodium silicate treated wood samples be further treated by the deposition of a
molecular
coating of silicon oxide, in order to avoid the aforementioned problems. This
surface
molecular coating treatment specifically resulted in an internal failure of
the treated lumber
after approximately 40-48 months in various applications in multiple
locations. Additionally,
these patents prefer a high concentration of above 20 % by wt. sodium
silicate, as the flame
resistance tended to increase with increasing the concentration.
U.S. RE40517 describes a process of using sodium silicate solution to create
fire
retardant and moisture resistance products, by applying energy to cause sodium
silicate to
become water insoluble. Similar to the above patents, this patent also prefers
a high
concentration of above 20 % by wt. sodium silicate, as the flame resistance
tended to
increase with increasing the concentration.
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U.S. Patent No. 6,146,766 describes a process of using sodium silicate
solution to
create fire retardant and moisture resistance products, by alternately
applying vacuum and
pressure to cause sodium silicate to become water insoluble. The patent does
not discuss
the concentration of sodium silicate solution at all.
None of the aforementioned patents discusses the disadvantages associated with
employing a higher concentration of sodium silicate impregnation solution.
These patents
are also completely silent regarding the weight ratio of (Si02)/(Na20) of the
sodium silicate
in the impregnating solution and the benefits associated with controlling this
ratio. Moreover,
these patents do not employ a gaseous CO2 fixation technology. Without a
reliable fixation
strategy, the treated wood may have issues relating to longer-term lifecycle
protection of the
wood product. Additionally, these patents do not envision any additional
impregnating
stages and the benefits associate with the additional steps.
Thus, there remains a need to develop a cost-efficient, all-green process for
modifying wood which can eliminate the toxic chemical treatment, yet provide
enhancing
strength properties, increased fire resistance ratings that meet or exceed
international
recognized building and building materials standards, while maintaining other
desirable
properties such as rot, bacteria, and insect resistance. This disclosure
addresses that need.
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SUMMARY OF THE INVENTION
A purpose of this invention is to design and produce totally environmentally
sustainable, green (toxic chemical-free), and break-through performance wood
products that
can be widely utilized across all primary construction and infrastructure
applications. The
production process to produce the wood products utilizes a low cost and
scalable
continuously improving manufacturing process primarily using existing wood
treatment
infrastructure that previously used toxic chemical focused manufacturing
processes.
Existing infrastructure can be rapidly converted to sustainable wood
modification facilities at
a highly compelling return on investment basis such that the entire conversion
investment
can be returned within 12 months. The result is the maintaining of existing
lumber production
and treatment manufacturing facilities, while also economically converting
previously toxic
chemical centric and environment damaging operations into a profitable, long-
term,
sustainable "green" lumber business model. The inventors believe, to the best
of their
knowledge, that the combination of an all-green, low cost, high-performance
lumber product
that is produced in green-tech lumber treatment facilities in the United
States (using U.S.
domestic sourced, responsibly harvested lumber) has not been accomplished
before.
The product is a modified all-green wood, sourced from the largest renewable
US
forests, which uses specialized technology and compounds in a scalable
formulation and
manufacturing process to enhance the performance of everyday wood. The result
is an
industry leading array of performance profiles in a single, very price
competitive product.
The main performance enhancements include rendering the wood resistant to
chemical
leaching, inert, stronger, harder, rot-resistant, termite-resistant,
electrical-resistant, and
importantly a Class A (highest level) fire-retardant material, as compared to
the commonly
available and used alternatives, both the non-sustainable conventionally
treated woods as
well as several high price sustainable chemically and process enhanced woods.
The inventors believe their processes can be used to produce the first Class A
fire
retardant industry-approved utility pole to meet these criteria and to be used
and approved
by the electrical power industry due to the unique combination of product
performance
attributes from the invention, as well as its ability to be manufactured at
prices comparable
to the toxic chemical treated, flammable ones used today. This is a
significant step towards
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electrical utility fire suppression and will result in a reduction in
environmental damage
caused by the highly toxic chemicals currently utilized in utility poles many
of which become
airborne once a wildfire starts and further jeopardize the safety of first
responder fire-fighting
teams and the surrounding communities.
Processes are disclosed for the impregnation of lumber with a solution of
alkali metal
salt, such as sodium silicate (Na2SiO3), along with resulting products. Post
impregnation
stabilization may also be provided. Various methods of stabilization are
disclosed, such as
lowering pH and by the addition of gaseous carbon dioxide (CO2) and
application of an
optional second impregnation treatment of the wood. Post impregnation heat
treatments
are also disclosed. Such processes are useful to fix and stabilize the
impregnation of
lumber.
Accordingly, one aspect of the invention relates to a process for modifying
wood. The
process comprises treating the wood with an impregnating solution comprising
an alkali
metal (or alkaline earth metal) silicate, under conditions sufficient to
impregnate the wood
with one or more of the components of the impregnating solution, wherein the
weight ratio
of SiO2 to alkali metal (or alkaline earth metal) oxide in the alkali metal
(or alkaline earth
metal) silicate ranges from about 2.0 to about 4Ø The process also comprises
adding
gaseous carbon dioxide to the treated wood, in the absence or presence of
water, under
pressure ranging from about 2 to about 1 2 bars, thereby lowering the pH of
the treated wood
to about 11 or below, to stabilize and/or fix the components of the
impregnating solution in
the wood. This process is green, non-toxic as being carried out in the absence
of a pesticide
or biocide, or as being carried out with an environmentally safe boron level
in the
impregnating solution of no more than 1 % by wt.
In one embodiment, the process is green, non-toxic as being carried out in the
absence of a pesticide or biocide. In one embodiment, the process is green,
non-toxic as
being carried out in the absence of a mold repellant. In one embodiment, the
process is
green, non-toxic as being carried out in the absence of a toxic chemical.
In certain embodiments, the alkali metal (or alkaline earth metal) silicate is
sodium
silicate, potassium silicate, or calcium silicate. Typically, the alkali metal
silicate is sodium
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silicate or potassium silicate. In certain embodiments, the weight ratio of
(Si02)/(Na20) of
the sodium silicate in the impregnating solution can range from about 2.1 to
about 3.5, or
from about 2.5 to about 3.5. In certain embodiments, the concentration of SiO2
in the
impregnating solution ranges from about 3 % by wt. to about 15 A. by wt. In
one
embodiment, the concentration of SiO2 in the impregnating solution ranges from
about 3 %
by wt. to about 6 % by wt.
In certain embodiments, the process further comprises, prior to the treating
step, a
step of pretreating the wood by drying the wood and/or applying a vacuum to
the wood, to
achieve a moisture content of the wood of less than about 20%.
In certain embodiments, the conditions sufficient to impregnate the wood in
the
treating step comprise two or more of the following conditions:
the concentration of SiO2 in the impregnating solution ranges from about 3 %
by wt.
to about 15% by wt.;
the weight ratio of (Si02)/(Na20) of the sodium silicate in the impregnating
solution
ranges from about 2.5 to about 3.5;
applying a pressure of about 4 bars to about 20 bars;
treating the wood at a temperature ranging from about 15 to about 100 C;
and/or
treating the wood for a period of time from about 2 to about 4 hours.
The conditions sufficient to impregnate the wood in the treating step may also
comprise three, four, or all five of the above conditions.
In one embodiment, the conditions sufficient to impregnate the wood in the
treating
step comprise the following steps:
the concentration of SiO2 in the impregnating solution ranges from about 5
a/c. by wt.
to about 10% by wt.;
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the weight ratio of (Si02)/(Na20) of the sodium silicate in the impregnating
solution
ranges from about 2.8 to about 3.2;
applying a pressure of about 10 bars to about 20 bars;
treating the wood at a temperature ranging from about 50 to about 80 C; and
treating the wood for a period of time from about 2 to about 4 hours.
In one embodiment, the conditions sufficient to impregnate the wood in the
treating
step comprise the following steps:
the concentration of SiO2 in the impregnating solution ranges from about 5 c/o
by wt.
to about 15% by wt.;
the weight ratio of (Si02)/(Na20) of the sodium silicate in the impregnating
solution
ranges from about 2.8 to about 3.2;
applying a pressure of about 10 bars to about 20 bars;
treating the wood at a temperature ranging from about 20 to about 50 C; and
treating the wood for a period of time from about 2 to about 4 hours.
In certain embodiments, the gaseous carbon dioxide is added under a pressure
ranging from about 6 to about 12 bar for a period of time from about 15 to
about 60 minutes,
to lower the pH of the treated wood to about 9 or below. In one embodiment,
the gaseous
carbon dioxide is added under a pressure ranging from about 2.4 to about 7 bar
for a period
of time from about 15 to about 60 minutes, to lower the pH of the treated wood
to about 9 or
below.
In certain embodiments, the process further comprises, after the treating
step, a step
of applying a vacuum to the treated wood to remove residual impregnating
solution from the
surface of the treated wood and prepare the treated wood for the post-
treatment steps.
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In certain embodiments, the process further comprises, after the treating
step, heating
the treated wood at a temperature ranging from about 50 to about 100 C. The
heating step
comprises heating the treated wood with dry air, saturated water vapor, or hot
water. In one
embodiment, the heating step has a duration of about 2 to about 6 days (or
from about 4 to
about 6 days) and comprises varying the rate of increasing the temperature to
the stabilized
drying temperature and the rate of decreasing the temperature to achieve the
desired
moisture level target.
Another aspect of the invention relates to a process for modifying wood. The
process
comprises:
i) treating the wood with a first impregnating solution comprising an alkali
metal (or
alkaline earth metal) silicate, under conditions sufficient to impregnate the
wood with one or
more of the components of the first impregnating solution;
ii) treating the wood with a second impregnating solution comprising an alkali
metal
(or alkaline earth metal) silicate at a concentration higher than the
concentration of the first
impregnating solution, for a period of time shorter than the treating step i);
and
iii) carrying out one or more of the following post-treatment step(s) to
stabilize and/or
fix the components of the first and/or second impregnating solution in the
wood:
adding gaseous carbon dioxide to the treated wood, in the absence or
presence of water, under a pressure ranging from about 2 to about 12 bars,
thereby lowering pH of the treated wood to about 11 or below, and/or
heating the treated wood at a temperature ranging from about 50 to
about 100 C,
wherein the post-treatment step iii) is carried out after the treating step
i), prior to the
treating step ii), and/or after the treating step ii).
In certain embodiments, the treating step ii) comprises the following
conditions:
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the second impregnating solution comprises an alkali metal (or alkaline earth
metal)
silicate at a concentration of about 10 to 15 A, by wt.;
treating the wood for a period of time from about 10 to about 60 minutes,
applying a pressure of about 2 to about 12 bars, and
treating the wood a temperature ranging from about 20 to about 70 C.
In certain embodiments, the process is green, non-toxic as being carried out
in the
absence of a pesticide or biocide, or as being carried out with an
environmentally safe boron
level in the first or second impregnating solution of no more than 1 % by wt.
In one embodiment, the process is green, non-toxic as being carried out in the
absence of a pesticide or biocide. In one embodiment, the process is green,
non-toxic as
being carried out in the absence of a mold repellant. In one embodiment, the
process is
green, non-toxic as being carried out in the absence of a toxic chemical.
In certain embodiments, the alkali metal (or alkaline earth metal) silicate is
sodium
silicate, potassium silicate, or calcium silicate. Typically, the alkali metal
silicate is sodium
silicate or potassium silicate. In certain embodiments, the weight ratio of
(Si02)/(Na20) of
the sodium silicate in the first and/or second impregnating solution can range
from about 2.0
to about 4.0, from about 2.1 to about 3.5, or from about 2.5 to about 3.5.
In certain embodiments, the concentration of SiO2 in the first impregnating
solution
ranges from about 3 % by wt. to about 15 % by wt. In one embodiment, the
concentration
of SiO2 in the first impregnating solution ranges from about 3 % by wt. to
about 6 % by wt.
The concentration of SiO2 in the second impregnating solution ranges from
about 10 to 15
% by wt.
In certain embodiments, the process further comprises, prior to the treating
step i), a
step of pretreating the wood by drying the wood and/or applying a vacuum to
the wood, to
achieve a moisture content of the wood of less than about 20%.
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In certain embodiments, the conditions sufficient to impregnate the wood in
the
treating step i) comprise two or more of the following conditions:
the concentration of SiO2 in the first impregnating solution ranges from about
3 % by
wt. to about 15 % by wt.;
the weight ratio of (Si02)/(Na20) of the sodium silicate in the first
impregnating
solution ranges from about 2.5 to about 3.5;
applying a pressure of about 4 bars to about 20 bars;
treating the wood at a temperature ranging from about 15 to about 100 C;
and/or
treating the wood for a period of time from about 2 to about 4 hours.
The conditions sufficient to impregnate the wood in the treating step i) may
also
comprise three, four, or all five of the above conditions.
In one embodiment, the conditions sufficient to impregnate the wood in the
treating
step i) comprise the following steps:
the concentration of SiO2 in the first impregnating solution ranges from about
5 A. by
wt. to about 10 (3/0 by wt.;
the weight ratio of (Si02)/(Na20) of the sodium silicate in the first
impregnating
solution ranges from about 2.8 to about 3.2;
applying a pressure of about 10 bars to about 20 bars;
treating the wood at a temperature ranging from about 50 to about 80 C; and
treating the wood for a period of time from about 2 to about 4 hours.
In one embodiment, the conditions sufficient to impregnate the wood in the
treating
step i) comprise the following steps:
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the concentration of SiO2 in the first impregnating solution ranges from about
10 A,
by wt. to about 15 % by wt.;
the weight ratio of (Si02)/(Na20) of the sodium silicate in the first
impregnating
solution ranges from about 2.8 to about 3.2;
applying a pressure of about 10 bars to about 20 bars;
treating the wood at a temperature ranging from about 20 to about 50 C; and
treating the wood for a period of time from about 2 to about 4 hours.
In certain embodiments, the post-treatment step iii) comprises adding gaseous
carbon dioxide to the treated wood, in the absence or presence of water, under
a pressure
ranging from about 2 to about 12 bars, thereby lowering pH of the treated wood
to about 11
or below.
In certain embodiments, the gaseous carbon dioxide is added under a pressure
ranging from about 6 to about 12 bar for a period of time from about 15 to
about 60 minutes,
to lower the pH of the treated wood to about 9 or below. In one embodiment,
the gaseous
carbon dioxide is added under a pressure ranging from about 2.4 to about 7 bar
for a period
of time from about 15 to about 60 minutes, to lower the pH of the treated wood
to about 9 or
below.
In certain embodiments, the post-treatment step iii) comprises heating the
treated
wood at a temperature ranging from about 50 to about 100 C. The heating step
comprises
heating the treated wood with dry air, saturated water vapor, or hot water. In
one
embodiment, the heating step has a duration of about 2 to about 6 days (or
from about 4 to
about 6 days) and comprises varying the rate of increasing the temperature to
the stabilized
drying temperature and the rate of decreasing the temperature to achieve the
desired
moisture level target.
Another aspect of the invention relates to wood (or wood product) modified by
the
processes discussed in all above aspects and all above embodiments relating to
a process
for modifying wood.
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In certain embodiments, the wood is lumber, lumber board, lumber pole,
laminated
lumber, single plate laminate, plywood, particle board, or fiber board. The
lumber may be
any softwood or coniferous species such as southern yellow pine, radiata pine
(pinus
radiata), hemlock, or fir, for example.
In certain embodiments, the modified wood (or wood product) is inert, rot
resistant,
fire resistant, termite resistant, bacteria resistant, and/or fungus
resistant. The modified
wood (or wood product) also has an improved strength as compared to unmodified
wood,
characterized by at least 35% increase in Modulus of Elasticity (MOE) and at
least 4%
increase in Modulus of Rupture (MOR), measured by ASTM D143-14. The modified
wood
also has an improved strength as compared to wood treated by a conventional
phosphate-
based impregnation process, characterized by at least 100% increase in Modulus
of
Elasticity (MOE) and at least 15% increase in Modulus of Rupture (MOR),
measured by
ASTM 0143-14.
The resulting products are inert, namely, neither chemically nor biologically
reactive
and will not decompose, rot resistant, fire resistant, termite resistant,
bacteria resistant,
and/or fungus resistant, and with superior strength properties as compared to
non-
impregnated stabilized lumber, resulting in extended lifetimes. The resulting
products are
also non-toxic and entirely environmentally safe. Lumber for residential and
commercial
construction, railroads (for railway ties) and phone and electric utilities
(for utility poles) and
other applications, may be made in accordance with the disclosed processes. In
some
examples, significant carbon sequestration is provided.
Embodiments of the invention also provide a fire retardant wood (or wood
product)
modified by the process discussed in all above aspects and all above
embodiments relating
to a process for modifying wood.
In certain embodiments, the fire retardant wood (or wood product) modified by
the
process according to this invention satisfies the Class A fire retardant
rating, measured by
ASTM E84 10-minute burn test. In this test, the fire retardant wood modified
by the process
according to this invention does not exceed the 6' flame spread limit (10.5'
total from the
burner as per the ASTM E84 standard which adds 4.5' to the burner position).
The fire
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retardant wood modified by the process according to this invention has an
improvement of
170% as compared to wood treated by a conventional phosphate-based
impregnation
process (against the 6' flame spread limit (10.5' total from the burner as per
the ASTM E84
standard which adds 4.5' to the burner position).
In certain embodiments, the fire retardant wood (or wood product) modified by
the
process according to invention satisfies the Class A fire retardant rating,
measured by ASTM
E2768 30-minute burn test. In this test, the fire retardant wood modified by
the process
according to this invention does not exceed the 6' flame spread limit (10.5'
total from the
burner as per the ASTM E2768 standard which adds 4.5' to the burner position).
The fire
retardant wood modified by the process according to this invention has an
improvement of
350% as compared to wood treated by a conventional phosphate-based
impregnation
process (against the 6' flame spread limit).
In certain embodiments, the modified wood (or wood product) can be used in the
manufacturing all-green fire-retardant high-performance railway ties, which
are another
major infrastructure need.
In certain embodiments, the modified wood (or wood product) has superior
strength
properties, as compared to toxic chemically treated lumber, insect resistance
and rot
resistance, and can be used in various products in constructions including
framing, siding,
structural supports, railings, landscaping, and all areas where dimensional
lumber and
plywood is utilized.
Figure 30 illustrates the comprehensive range of construction
applications for the invention. The resulting product also has a significant
impending use to
work with CLT (cross laminated timber) in a new generation of affordable, low
carbon
sustainable housing construction, an acute and growing necessity in the U.S.
The all green,
high-performance wood reduces carbon impacts, petroleum dependence, exposure
of
waters and wetlands to toxic leaching chemicals, and is also sourced entirely
from
responsibly managed and sustainable American forests.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a flow chart showing an exemplary implementation of the wood
modification process.
Figure 2 shows the effect of silicon dioxide concentration on total silicon
dioxide ( /0)
retained in the impregnated wood sample, after drying the samples at 105 C
for 20 hours
at each concentration.
Figure 3 shows the impregnated wood samples cut into 4 equal parts.
Figure 4 shows the weight increase of the impregnated wood samples.
Figure 5 shows the increase in total silicon dioxide content of the
impregnated wood
after drying the samples at 105 C for 20 hours.
Figure 6a shows the retention of the impregnating solution in weight (%) at
10% and
15% silicon dioxide content in the impregnation solution. Figure 6b shows the
retention of
the impregnating solution at the 20% silicone dioxide content in the
impregnation solution.
Figure 7a shows the retention of the impregnating solution in weight ( /0) at
10% and
15% silicon dioxide content in the impregnation solution, after the wood
samples were dried
at 105 C for 18 hours. Figure 7b shows the retention of the impregnating
solution at the
20% silicone dioxide content in the impregnation solution, after the wood
samples were dried
at 105 C for 18 hours.
Figures 8a and 8b show the mass of silicon dioxide ( /0) along the wood
samples
determined after acid digestion, for 10% sodium silicate (Figure 8a) and 15%
sodium silicate
(Figure 8b).
Figure 9 shows the mass of silicon dioxide ( /0) along the wood samples
determined
after acid digestion, for 20% sodium silicate.
Figures 10a and 10b show the average mass retained in the impregnated wood
samples for 10% and 15% sodium silicate (Figure 10a), and for 20% sodium
silicate (Figure
10b) in the impregnation solution.
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Figure 11 shows the average retained masses of the silicon dioxide inside the
radiata
pine wood samples after impregnation at 15% concentration of silicon dioxide
at 20 C, at
pressures of 0.5 bars, 10 bars, 15 bars, and 20 bars.
Figures 12a and 12b show the average values of the external and internal parts
of
the impregnated wood samples. Figure 12a shows the increase in mass ( /0) of
the wood
samples impregnated with sodium silicate at 10% silicon dioxide and Figure 12b
shows the
increase in increase in mass ( /0) of the wood samples impregnated with sodium
silicate at
15% silicon dioxide.
Figures 13a and 13b show the average silicon dioxide retention values in the
external
and internal parts of the wood samples impregnated with 10% silicon dioxide,
in Figure 13a,
and 15% silicon dioxide, in Figure 13b.
Figure 14 shows the results of the decrease in weight percent of the
impregnated
wood samples with leaching time when the impregnated wood samples were
subjected to
air heated at 50 C, 100 C, and 150 C for 2 hours.
Figure 15 shows the mass percent of silicon dioxide (SiO2) in the impregnated
wood
samples before and after the leaching tests of the samples treated with dry
air at different
temperatures.
Figure 16 shows the percent decrease in the mass of the wood samples
impregnated
with sodium silicate during the leaching experiments, in thermal treatment
with hot water,
when the impregnated wood samples were reacted with water at 50 C, 100 C,
and 150 C
for 2 hours.
Figure 17 shows the mass percent of silicon dioxide (SiO2) retained in the
impregnated wood samples before and after the leaching tests of the samples
treated with
hot water at the different temperatures.
Figure 18 shows the results of the leaching trials of the sodium silicate
impregnated
wood samples treated with saturated water vapor at 50 C, 100 C, and 150 C.
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Figure 19 shows the mass percent of silicon dioxide (S102) retained in the
impregnated wood samples before and after the leaching tests of the samples
treated with
saturated water vapor at different temperatures.
Figure 20 shows the percent of retained mass of sodium silicate impregnated
wood
samples treated with gaseous carbon dioxide at the different pressures during
the leaching
tests, over time.
Figure 21 shows the mass percent of silicon dioxide in the impregnated wood
samples
before and after the leaching tests of the samples treated with gaseous carbon
dioxide at
different pressures.
Figure 22 shows the mass percent of the sodium silicate impregnated wood
samples
retained during the leaching tests, when the impregnated wood samples were
immersed in
water inside an impregnation vessel and then treated with gaseous carbon
dioxide at
different pressures.
Figure 23 shows the mass percent of silicon dioxide (SiO2) retained in the
impregnated wood samples before and after the leaching tests of the samples
immersed in
water inside an impregnation vessel and then treated with gaseous carbon
dioxide at
different pressures.
Figure 24 shows the percent decrease in the mass of the wood samples
impregnated
with sodium silicate prepared at 50 C, 100 C, 150 C of dry air, and 150 C
of water vapor.
Figure 25 compares the mass percent of the sodium silicate impregnated wood
samples retained during the leaching tests for the samples by fixation with
carbon dioxide
gas at 12 bars and for the samples by fixation with carbon dioxide in water at
12 bars.
Figure 26 compares the mass percent of the sodium silicate impregnated wood
samples retained during the leaching tests for the samples by heat treatment
at 100 C of
dry air and for the samples by gaseous carbon dioxide at 12 bars.
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Figure 27 shows the weight gain of the sodium silicate retained in the wood
after the
second impregnation treatment, as compared to the results from a single
impregnation
treatment.
Figure 28 compares the results of the E84 Burn tests for lumber modified by
inventive
double impregnation process vs. conventionally treated lumber.
Figure 29 compares the results of the E2768 Burn tests for lumber modified by
inventive double impregnation process vs. conventionally treated lumber.
Figure 30 is an illustration of construction applications of the product made
according
to the modification process described in the embodiments of this invention.
Figure 31 illustrates the wood sample preparation according to ASTM D143-14.
Figures 32a and 32b show the strength properties (Figure 32a) and relative
strength
properties (Figure 32b) of lumber modified by inventive process vs.
conventionally treated
lumber vs. untreated control.
Figure 33 summarizes the weight loss of samples treated with sodium silicate
and
various other chemical agents. The specimens were subjected to the action of
brown rot
fungi, Serpula lacrymans (standard D1413-07). The X-axis refers to average
weight loss /0,
and the Y-axis refers to the concentration of specific chemical treatment
(from the top to the
bottom: sodium silicate, sodium silicate + bio oil I, sodium silicate + bio
oil II, sodium silicate
+ sodium borate, sodium silicate + copper II, and sodium silicate + copper I,
respectively).
The control corresponds to untreated wood, shown as vertical black line on the
right across
all charts, showing 19.7% average weight loss.
Figures 34a-34e are microphotographs of specimen cross-sections after 16 weeks
of
fungal cultivation with various treatment solutions containing sodium silicate
and other
chemical agents; a) Si02+ Bio Oil I at 20pm; b) Si02+Bio Oil I at 50pm; c)
Pinus taeda
Control at 100pm; d) Si02+ sodium borate at 200pm; and e) SiO2 at 200pm.
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Figure 35 is an image showing operator holding a specimen treated by the
inventive
process, aged 6 months, at a termite field testing area. A 1" x 1" by 18"
stake shows no
evidence of any termite attacks since measurements began.
Figures 36A and 36B show the average thermogram for samples taken from the
surfaces (Figure 36A) and the core (Figure 36B) of the inventors' modified
lumber samples
and conventionally treated lumber samples, as compared to the untreated
control.
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DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Aspects of the invention relate to the infusion of wood (lumber) and other
cellulosic
material with a soluble alkali metal silicate solution, such as a sodium
silicate solution,
optionally under vacuum and/or pressure, and optionally applying post
impregnation
stabilization through the addition of carbon dioxide and/or heat treatment
after infusion to
render the alkali metal silicate solution insoluble, for the purpose of
enhancing the
mechanical properties, rot-resistance, insect resistance, and/or fire-
retardant nature of wood
(lumber) and other cellulosic material.
The Modification Process
Procedures to impregnate cellulosic material, such as forms of southern yellow
pine
(Pinus taeda and Pinus elliotii) species, in the form of dimensional lumber,
plywood, cross
laminated timber (CLT), KD 19 dry planed lumber, as well as railroad cross
ties, utility poles,
utility cross arms and green untreated lumber, for the purpose of improving
some or all of
the wood sourced material's performance characteristics listed above, are
disclosed.
Embodiments of the invention include various wood modification processes with
a
single or double impregnation of an alkali silicate solution, such as sodium
silicate or calcium
silicate.
The U.S.D.A.'s National Forest Service Library defines modified wood as "wood
that
is processed by chemical treatment, compression, or other means, with or
without heat, to
impart permanent properties quite different from those of the original wood."
The aim of
modified wood is to overcome the shortcomings of standard wood. Conventional
wood
treatments usually employ non-sustainable chemicals including EPA registered
preservatives common today. In contrast, the wood modification processes
described in
various aspects of this invention are environmentally friendly and the
modified wood
materials can be safely and easily deposed of at the end of the product
lifecycle.
Various treatment conditions for modifying the wood include, but are not
limited to,
the following aspects.
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lrn preg nation
The "less is more" concept. Alkaline salt impregnations typically use a
relatively high
concentration of sodium silicate (+15 % by wt. as measured as silicon dioxide
content) for
the purpose of enhancing the wood properties. The concentration of SiO2 in the
impregnating solution during the impregnation process can be controlled in a
range from
about 3 % by wt. to about 35 % by wt., from about 3 % by wt. to about 15 % by
wt., from
about 5 % by wt. to about 15 % by wt., from about 5 A by wt. to about 10 %
by wt., or from
about 3 % by wt. to about 6 % by wt. In certain embodiments, the process
utilizes a lower
concentration (3 A, by wt. to 15 % by wt.) to better infuse the lumber and
provide the
fundamental protection properties desired. A lower concentration means a
beneficially lower
viscosity, as a higher viscosity may negatively affect the impregnation
process. Additionally,
at higher concentration and temperature of impregnation, alkali metal (or
alkaline earth
metal) silicate solution tends to form thin silicate films on the wood
samples, commonly
known as efflorescence, which may negatively affect the impregnation process.
The "less
is more" method using the low, specific silicon dioxide concentration levels
allows for both a
superior performance product including the long-term environmental attributes
and, just as
importantly, a much more affordable and competitive price product given the
lower amounts
of sustainable treatment solution utilized in the new production method, as
well as with the
lower amounts of manufacturing cost infrastructure and therefore depreciation
cost (from
the proprietary design, rapid return conversion of existing facilities to all-
green wood plants).
Together these factors are fundamental and ground-breaking and allow for large
scale price-
sensitive construction and infra-structure industries adoption of the all-
green high-
performance modified wood, and thereby significantly higher positive impact of
the products
(and process) on the environment and their ability to realize the invention's
full potential to
improve the planet. In addition, the new all-green high-performance wood can
utilize readily
available sustainable sources of U.S. lumber, further reducing transportation
costs and
negative carbon impact from long-distance sourced imported products.
An impregnation time may be selected to allow the alkali metal (or alkaline
earth
metal) silicate to enter the cell structure of the woody material. The
impregnation time varies
according to the dimensions for the lumber being treated. The reaction time
during the
impregnation process may range from about 20 minutes to about 10 hours, from
about 20
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minutes to about 120 minutes, from about 45 minutes to about 5 hours, from
about 0.5 hour
to about 4 hours, or from about 1.5 hours to about 4 hours. For conventional 2
x 4 lumber
boards, decking and fencing material, and other smaller dimensioned lumber,
for example,
the impregnation time may be from about 45 minutes and 5 hours, depending in
part on the
size of the lumber. For certain large pieces of lumber, the reaction time can
be extended to
about 10 hours.
The temperature in the impregnation of alkali metal (or alkaline earth metal)
silicate
during the impregnation process may range from about 15 C to about 100 C,
from about
C to about 80 C, or from about 50 C to about 80 C. At higher concentration
and
10
temperature of impregnation, alkali metal silicate solution tends to form
thin silicate films on
the wood samples, commonly known as efflorescence, which may have hindered the
impregnation process due to the deposition of silicate particles on the
impregnating face of
the wood sample.
Impregnation of alkali metal (or alkaline earth metal) silicate solution takes
place with
15
the liquid being forced by natural osmosis and applied pressure into the
pores of the
untreated lumber. The pressure applied during the impregnation process may be
about 0.5
bar or higher, for instance, ranging from about 4 to about 20 bar, from about
10 to about 20
bar, or from about 6 bar (-100 psi) to about 18 bar (-250 psi).
Prior to the impregnation process, during raw materials selection and
preparation, the
wood may be pretreated to achieve a moisture content in the range of, for
example, from
about 12% to about 40%, less than about 20%, or from 18 to 20%, so as to
maximize the
efficiency and performance of the impregnation process. The pretreatment step
may include
drying the wood and/or applying a vacuum to the wood to achieve the desirable
moisture
content.
The ratio of SiO2/Na2O in the impregnation of sodium silicate during the
impregnation
process can range from about 2.0 to about 4.0, from about 2.0 to about 3.5,
from about 2.0
to about 3.5, from about 2.5 to about 3.5, or from about 2.8 to about 3.2. The
ratio of
SiO2/Na2O can be an important factor in the impregnation process, in terms of
pH control,
level of impregnation control, and controlling the level of Na2CO3 residual on
the surface of
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the treated lumber, thereby minimizing efflorescence (Na2CO3) on the surface
of the finished
product.
The pH of the impregnation solution in the impregnation process can be
controlled to
range from about 9.0 to about 13.5, about 11 or below, from about 9 to about
11, or about 9
or below, so as to maximize the efficiency and performance of the impregnation
of sodium
silicate process. Increasing the pH of the impregnating solution can result in
agglomeration
and polymerization of the silicon dioxide. One way to lower the pH of the
impregnation
solution is by adjusting the ratio of SiO2/Na2O in the impregnation solution,
as described
herein. Another way to lower the pH is by applying carbon dioxide to the
treated wood, as
described herein.
The Longitudinal vs. Radial impregnation of sodium silicate in wood samples
and
wood production during the impregnation process may be controlled based, at
least in part,
on the dimensions of the wood being impregnated.
The impregnating solution can further comprise an environmentally safe biocide
or
preservative (or an environmentally safe amount of biocide or preservative).
For instance,
the biocide or preservative can optionally, include boron or a boron-
containing compound, a
bactericide, a fungicide, or a combination thereof.
Suitable boron or boron-containing compounds to be added to the impregnation
solution include boron, boric acid, boron oxides, boric acid salts, borates,
borax, or fluoro-
boric acid salts. The addition of Boron-based biocide to the impregnation
solution enhances
resistance to rot and termite resistance performance of the impregnated wood.
Boron is
typically added as boric acid and added to the alkaline salt mixture and
blended into a
homogeneous liquid for use as the impregnation solution. However, boron or
boron-
containing compound, if added, is added in very low concentrations ¨ no more
than 1 % by
wt. to be environmentally safe. It is understood by one skilled in the art
that when the boron
level is above 1 % by wt. it would not be considered as fully environmentally
safe. In one
embodiment, boron or boron-containing compound is added at no more than 0.75 %
by wt.,
or no more than 0.5 % by wt. These levels are considered fully compliant to
remain
consistent with the products' claims as all-green non-toxic to the environment
and humans.
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While boron tends to leach out of the wood in conventional treatment
processes, the
combination of the alkaline salt with the boron and the post impregnation
stabilization
processes of the invention will prevent this. Accordingly, and importantly,
the impregnated
wood is suitable for use in indoor and outdoor environments.
The process may also include stabilization/fixation of Si02 inside the wood
impregnated with sodium silicate solution with one or more of the following
steps.
Carbon dioxide fixation
After the first and/or the second impregnation step(s), CO2 can be applied to
the
treated wood to stabilize or fix the Si02 in the pores of the wood. The CO2
can be added to
the treated wood in the absence or presence of water, under pressure, to lower
the pH of
the host cells of the lumber and cause the SiO2 to precipitate and form a
solid gel like
substance in the pore structure, resulting in a solid matrix that materially
increases strength
properties and also renders the wood more resistant to fire, rot, termite
attack and mold.
Carbon dioxide is typically added in the gaseous form, where the CO2 is
compressed into
the impregnation cylinder at pressures of between about 2 and 12 bars, between
about 6 to
about 12 bars, or between about 2.4 and about 7.0 bars. The residence time for
this gaseous
exposure may be between 15 minutes and 60 minutes, or about 20 to about 45
minutes,
depending on the type of lumber being used.
Previous methods exposing the impregnated wood to CO2 have been conducted at
either an atmospheric pressure for a long period of about 8 hours or conducted
at a high
pressure at 300 to 800 psi for a few minutes. The CO2 fixation discussed
herein used a
much lower pressure at about 2-12 bars (i.e., below 180 psi) for a period of
15 to 60 minutes.
These ranges of pressure and fixation duration can ensure a better control of
pH and a better
result of wood resistance.
Thermal treatment
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After the impregnation step(s), a slow heat treatment can be applied to the
treated
wood to dry and cure SiO2 impregnated in the wood. The heating step may be
carried out
by heating the treated wood with dry air (e.g., in a drying kiln), heating the
treated wood with
hot water, or heating the treated wood with saturated water vapor. For
instance,
impregnated lumber can be passed through a drying kiln for a second time
(first time is for
lumber moisture conditioning prior to impregnation), with a lower (hardwood
regime) range
of temperatures in the drying sequence. The post impregnation thermal
treatment can
typically be at a temperature ranging from about 50 to about 150 C, or from
about 50 to
about 100 C, for a period of time from about 2 to about 6 days, e.g., between
72 hours and
120 hours.
Prior aforementioned patents process has used intensive heating, such as
microwave
heating, to provide sufficient energy. Such process may have created a solid
surface layer;
however, it does not address the internal moisture issues and would result in
total product
structural failure after 40 to 48 months, in cross ties and structural
applications, due to the
surface-only veneer fixation from the microwave treatment.
The heat treatment described herein involves a slower drying at a lower
temperature
and longer duration to allow consistent, homogenous drying of entire cross
section of wood.
Additionally, a heating schedule can include varying the rate of increase and
decrease of
the temperatures, with sharply increasing the temperature to the stabilized
drying
temperature and sharply decrease the temperature to achieve the desired
moisture level
target.
The addition of gaseous carbon dioxide after the impregnation enhances the
wood
modification process, by lowering the pH, through precipitation of the
alkaline salt in the
lumber, thus preventing excessive post impregnation leaching and product
degradation. In
conjunction with a second drying step (the first drying step is prior to
impregnation to
optimally condition the wood), this solidifies the alkali metal silicate in
the pores of the
modified wood.
Second impregnation
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Certain embodiments of this invention relate to a double impregnation process
for
modifying wood. For double impregnation process, after the first impregnation
process (and
related pre-impregnation and post-impregnation treatments), a second, shorter
duration
impregnation process can follow, e.g., before and/or after the carbon dioxide
stabilization/fixation step.
All above descriptions relating to the impregnation step and various reaction
conditions and pre-impregnation and post-impregnation treatments would apply
to the first
impregnation process (and related pre-impregnation and post-impregnation
treatments) in
these embodiments.
The second impregnation step is typically carried out with a second
impregnating
solution comprising an alkali metal (or alkaline earth metal) silicate at a
concentration higher
than the concentration of the first impregnating solution, for a period of
time shorter than the
first impregnation step. For instance, the first impregnating solution can
contain an alkali
metal (or alkaline earth metal) silicate at a concentration of about 5 to
about 10 % by wt.,
and the second impregnating solution can contain an alkali metal (or alkaline
earth metal)
silicate at a concentration of about 10 to about 15 % by wt. For instance, the
second
impregnation step can be carried out for a period of about 10 to about 60
minutes, about 20
to about 60 minutes, or about 20 to about 30 minutes, with an alkali metal (or
alkaline earth
metal) silicate solution having about 10 to about 15 % by wt. SiO2). The
second
impregnation step can be carried out under a pressure of about 2 to about 12
bar (for
instance, from about 6 to about 12 bar) and with an operating temperature of
about 20 to
about 70 C.
The purpose of this second impregnation step is to provide additional surface
protection to the wood, including adding an additional fire protection
barrier. As shown in
Examples below, this optional second impregnation step can enhance the fire-
retardant
properties of the lumber, improve resistance to rot and termite attack, and,
in some
instances, also enhance strength properties. In particular, Example 2
illustrates that the
double impregnation of lumber can result in Class "A" fire retardant
properties ¨ with
significant improvement over conventional phosphate-based fire retardants.
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In accordance with an embodiment of the invention, the parameters and
processing
conditions described above enable both a single and double impregnation
processes
providing both fire retardant and termite repellant protection properties to
the modified
lumber, as well as improved strength and decay resistance, with post
impregnation drying
processes.
An exemplary implementation of the treatment process is shown in Figure 1, as
described below:
1. Mixing of Sodium Silicate with make-up water in a blending tank.
2. Addition of a boron as a biocide to this blending tank¨ (optional).
3. Pumping of the mixture to the heating and agitation vessel ¨ known as the
working
tank.
4. Transport of untreated lumber into impregnation vessel / autoclave.
5. Placing autoclave under vacuum.
6. Addition of liquid mixture from working tank.
7. Application of pressure to the autoclave.
8. Reduction of pressure and placing autoclave under vacuum.
9. If an optional second impregnation step is added that involves addition of
a second,
higher concentration of impregnating solution to the autoclave, it typically
would be
done after step 8. If an optional second impregnation step is not added, step
10
would follow step 8.
10. Addition of gaseous carbon dioxide into autoclave.
11. Removal of treated lumber from autoclave.
12. Addition of heat to treated lumber with a conventional sawmill kiln.
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Alternatively, the optional second impregnation step can be added after step
10. If
an optional second impregnation step is added, there can be an additional step
of adding
gaseous carbon dioxide into autoclave prior to step 9 as well.
Solution Preparation
Water and an aqueous alkali metal silicate, such as sodium silicate (Na2S03),
are fed
into and mixed in a blending tank. Both the sodium silicate and make up water
are pumped
from separate storage tanks. The water is clean potable water.
Sodium silicate is made up of both sodium oxide (Na2O), and silicon dioxide
(SiO2)
which is purchased in a fixed ratio from the chemical supplier. This ratio can
vary from 2.0
to 4Ø However, this ratio can be controlled to range from about 2.0 to about
3.5, or from
about 2.5 to about 3.5.
The concentration of silicon dioxide in the mixture in the blending tank may
be from
about 5% to about 35% (by weight) for example. When impregnation solution is
prepared
for single impregnation, the concentration used typically ranges from 3 % by
wt. to 15 % by
wt., or about 3 % by wt. to about 6 % by wt.
Optional Addition of Biocide
An environmentally safe biocide (or an environmentally safe amount of biocide)
is
optionally added to the blend tank, to provide additional insect, bacterial,
and/or fungal
protection to the end product. The biocide may be boron or boron-containing
compound, for
example. A trace amount (less than about 1% by weight (of the mixture), or
less than about
0.5 % by wt.) may be added.
Pumping to Working tank
The mixture containing SiO2, water (and optionally a biocide) is then pumped
to a
working tank. This tank has an inserted heating element and agitation, which
raises the
temperature of the impregnation solution to the desired autoclave temperature
(between
about 20 C and about 80 C). The agitation ensures a homogeneous mixture and
no
stratification of the various chemicals.
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Lumber Preparation
In one embodiment, lumber is selected for modification. In one example, the
lumber
is radiata pine. In another example, the lumber is southern yellow pine. The
lumber may
be in the form of lumber boards that are defect and knot free, for example.
The lumber may
be in other forms and other types of lumber may be used.
The lumber has been previously dried in a traditional sawmill kiln to a 19%
moisture
content or less (commonly known at KD19, or Kiln Dried 19%). The lumber may be
dried to
a moisture content of from about 12% to about 19%, for example.
The lumber is typically placed on pallets that are strapped and stabilized,
before being
moved into the autoclave.
Application of Vacuum to Autoclave
The strapped and bundled untreated lumber in the autoclave can then be placed
under vacuum conditions for a period of approx. from about 20 minutes ¨ 60
minutes
(depending on lumber charge or other factors). The purpose of the vacuum
application is to
remove any free water in the wood and prepare the pores of the wood for
chemical
impregnation.
The applied vacuum is 22" Hg (or -1.2 bar). This vacuum can be varied by 20%
in
either direction (depending on lumber charge or other factors).
Pumping of Liquid to Autoclave
Once the vacuum is released on the autoclave, the heated and homogenous liquid
from the working tank is pumped into the autoclave. This vessel is filled to
completion and
totally encircles all the lumber.
Impregnation Process
The pressure in the impregnation pressure vessel may then be increased. The
pressure may be increased to a pressure from about 4 bar to about 20 bar, for
example.
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Impregnation of sodium silicate solution takes place with the liquid being
forced by natural
osmosis and applied pressure into the pores of the untreated lumber.
An impregnation time may be selected to allow the sodium silicate to enter the
cell
structure of the woody material. The impregnation time varies according to the
dimensions
for the lumber being treated. For conventional 2 x 4 lumber boards, decking
and fencing
material, and other smaller dimensioned lumber, for example, the impregnation
time may be
set to a time between about 45 minutes and 5 hours, for example, depending in
part on the
size of the lumber. In this example, the impregnation time is set to 1.5
hours. Larger lumber
products, such as railroad ties and utility poles, for example, may be treated
for longer
periods of time of up to 10 hours (depending on lumber charge or other
factors).
When the impregnation completes, the pressure may be reduced. The residual
sodium silicate solution is evacuated back to the working tank, via a liquid
filtration system,
for example, to prevent contamination of the working tank.
The working tank may then be topped by additional make up from the mixing
tank, as
required.
Post Impregnation Vacuum
Once the liquid is drained from the autoclave, a vacuum may be re-applied to
the
vessel. This is for a period of approx. from about 20 minutes ¨ 60 minutes
(depending on
lumber charge or other factors) and at 22" Hg (or -1.2 bar) plus or minus 20%
(depending
on lumber charge or other factors). The purpose of this second vacuum
treatment is to
remove any surplus chemical from the surface of the lumber and prepare this
lumber for the
post-impregnation fixation process.
Carbon Dioxide Stabilization/Fixation
In one embodiment, after evacuation, gaseous carbon dioxide (CO2) is
compressed
into the impregnation vessel under pressure from a carbon dioxide supply tank.
The carbon
dioxide may be maintained at a pressure of from about 2 to about 12 bar, from
about 6 to
about 12 bar, or from about 2 to about 7 bar, for example. The pressure may be
maintained
for a period of from about 15 to about 45 minutes during which the carbon
dioxide fixation
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takes place. This fixation process causes the liquid in the lumber to
precipitate into a gel
solution, thus preventing future leaching and enhancing the various
treatments. The carbon
dioxide can lower the pH of the impregnated wood from about 11 after
impregnation to about
9. This can enable the silica dioxide to better adhere to the cell walls of
the lumber during
impregnation, avoiding leakage out of the lumber.
The carbon dioxide can react with water to form carbonic acid (H2CO3), which
is a
mild acid. The carbonic acid further reacts with the sodium silicate, yielding
silicon dioxide
(SiO2) and sodium carbonate (Na2CO3). Sodium bicarbonate (NaHCO3) may also be
produced but due to the moderately acidic environment the formation of sodium
carbonate
is more likely.
The better adherence of the silicon dioxide to the wood may be due to
polymerization
of the sodium silicate, resulting from a phase change from a liquid to an
amorphous
structure. This solidification process may not be reversible.
The majority of the carbon dioxide in this step is sequestered in the lumber
and the
remaining carbon dioxide, if any, may then be recycled or reused, when safely
evacuated
from the vessel and the pressure reduced to atmospheric pressure. This method
is
consistent with the all-green environmentally friendly process.
Optional Second Impregnation
After the first impregnation steps are completed, the lumber is then exposed,
optionally, to a second impregnation phase, where a higher concentration
impregnating
solution (i.e., higher than the concentration of the impregnating solution in
the first
impregnation step) is pumped into the autoclave and held under pressure for a
time between
20 and 60 minutes, at a pressure of between 2 and 12 bar and at a temperature
of between
20 and 70 C. This higher concentration solution (e.g., between about 10 and
about 15%
by wt. SiO2) can be prepared in a second blending tank and then pumped to one
of the
working tanks, or sequenced through the original blending tank. Deliberate
control of the
time between first and second and systematic elimination of other
environmental impacts on
the lumber between treatments is important to performance output as is the
solution
concentration of each impregnation. Then after the second impregnation steps
are
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completed, the carbon dioxide stabilization/fixation steps are completed. The
carbon dioxide
stabilization/fixation steps may also be done after the first impregnation
step and before the
second impregnation. The carbon dioxide stabilization/fixation steps may also
be done both
after the first impregnation step and before the second impregnation, and
after the second
impregnation step.
Removal of Lumber from Autoclave
The seal on the impregnation vessel can then be broken and the lumber removed.
The stabilization may continue after the carbon dioxide is sequestered and
remaining
portions recycled after its been evacuated. Solidification can continue to
take place over the
next 24 to 48 hours after evacuation. The lumber is therefore left on a drain
table for 24 ¨
48 hours, to allow for completion of solidification, as well as the drainage
of any residual
liquids off the wood to ensure that the lumber is free of any residual
chemicals.
Heat Treatment
Once the lumber has been allowed to stabilize on the drip tray storage system,
it is
moved and placed into a conventional sawmill kiln. This lumber may then be
heated at a
temperature ranging from 50 C to 100 C (depending on environmental
conditions and kiln
design), for a period of 4 days (2 days ¨ 6 days depending on environmental
conditions and
kiln design) with a drying schedule that includes a range of parameters
covering the time
(days), temperatures and rate at which the operator will ramp up to the
stabilized drying
temperatures and ramp down while controlling for the optimal moisture level
target. These
conditions may vary according to the kiln design, lumber treated and the
environmental
conditions, with residence times from 2 days to 6 days and temperatures from
50 C to 100
C.
The residual moisture in the treated and dried lumber is approx. KD19 (kiln
dried
19% moisture) although other % moisture levels can be targeted when needed by
varying
the drying schedule and other kiln setting variables and commercial market
requirements.
Strength Properties
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During the all-green high-performance wood modified process described herein,
the
strength properties of the treated lumber are enhanced.
When compared to untreated or non-modified lumber, these mechanical and
structural performance improvements increase significantly as measured by
industry
standard, for example, by ASTM D143-14, which are The Standard Test Methods
for Small
Clear Specimens of Timber.
In certain embodiments, included in these test methods are the following three
tests,
specifically, standard testing for Modulus of Elasticity (MOE), Modulus of
Rupture (MOR)
and Maximum Tensile Cleavage Load (Tensile). Example 3 below indicates that,
unlike the
traditional fire-retardant treatment processes (typically phosphate-based),
which have been
shown to typically reduce the strength properties of the wood (in terms of
Tensile strength,
MOR and MOE), wood modified according to the modification process described in
the
embodiments of this invention not only have not reduced the strength property
but have
actually stabilized and, in some cases, significantly improved, as compared
against the
untreated SYP control.
The modified wood product is not only stronger than non-sustainably treated
fire
retardant lumber, but also stronger than untreated lumber. For instance, MOE
and MOR
have been shown to be significantly improved ¨ allowing construction sector to
utilize less
lumber for the same output as well as have new flexibility in design and less
constraints to
use FRT wood where strength is no longer viewed as compromised and in fact can
be
increased versus untreated lumber ¨ a unique outcome for the inventors'
process.
Non-sustainable treated FRT wood is by far the primary form of FRT wood
utilized in
U.S. construction applications today, including treated lumber and treated
plywood.
Reduction values quoted here are based on ANSI/AWC NOS! National Design
Specification
for Wood Construction (NDS). In the case of other sustainable modified wood
products, the
inventors believe the embodiments of the invention provides the only FRT wood
using an
alkali metal silicate combined with gaseous carbon dioxide wood modifications
/ treatment
process that results in a product with a Class A rated FRT wood, and where
such green
wood modification process produces wood products that are also termite
resistant
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(subterranean termites), rot resistant (fungal decay), and structurally
superior to comparable
unmodified/untreated wood.
Fire Retardancy
Embodiments of this invention also provided wood (or wood product) treated
specifically for fire retardancy.
There currently is no all-wood, low price, fully environmentally sustainable
Class A
fire retardant industry-approved utility pole. However, the inventors have
demonstrated, for
instance, in Example 2 below, the Class A fire retardant performance of the
wood modified
by the process according to the embodiments of the invention, characterized by
the E84 and
E2768 tests, with successful burn data for both.
In addition to use in utility poles and railroad crossties, the modified wood
product
according to the embodiments of this invention can be used in various other
applications,
such as in construction lumber application, for instance, general dimensional
building and
other infrastructure construction lumber applications that can be low price,
fully
environmentally sustainable, as strong or stronger than untreated lumber,
insect resistant to
building standards, and a Class A fire retardant product or equivalent
international standard.
The All-in-One" Product and Inventory and Cost Reduction
This "all-in one" product, with all the critical high-performance
characteristics, allows
for the significant reduction in the required amount of on-hand inventory held
by lumber
dealers and retailers in the primary points of lumber distribution today, with
estimates in
certain cases (following in-depth interviews with leading lumber distributors
and lumber yard
owners and managers in multiple locations in the U.S., on customary lumber
industry
procurement and inventory stock procedures) resulting in a 50% reduction in
required on-
hand inventory. This is a major break-through product attribute of the all-
green high-
performance lumber product as compared to all its competitors. When the wood
produced
by the all-green modified pressure treatment process described here is
compared to wood
treated by industry standard processes, lumber dealers and lumber retailers
selling standard
products may have to hold up 2 times or 3 times the inventory investment
(versus the
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invention's product) to cover the possible demand for FRT wood that has at
least one other
critical performance attribute, let alone two or three performance attributes,
as is the case
with the new invention.
Until the inventions' all-green high-performance wood, no existing competing
commercialized sustainable wood modification technology, including acetylation
(acetylation
chemically modifies wood with a process where acetic anhydride reacts with the
hydroxyl
groups on large molecules such as lignin and hemicellulose in the plant cell
wall),
furfurylation, (wood impregnated with furfuryl alcohol (C5H602) produced from
a bio-based
liquid) or thermally modified wood (thermal modification uses heat to remove
organic
compounds from the wood cells, so it will not absorb water, expand, contract,
or provide
nourishment for insects or fungi), has achieved a price competitive product
that can compete
directly with the widely used market leading non-sustainable FRT (fire
retardant treated)
wood products. Their pricing is typically 2-3X higher than FRT wood. While
these processes
are producing products exhibiting some of the improved performance such as
better
dimensional stability and decay resistance, none have achieved a Class A fire
rating.
Sustainable Wood Production Facility Modification and Ongoing Process
Optimization
The treatment process described herein may also allow for re-use of an
existing
pressure treating facility (originally designed specifically to be used with
non-sustainable
chemical products) with minimal capital upgrades relative to its full
replacement cost, to allow
for treatment of lumber with alkali metal silicate solutions and pore
impregnation stabilization
using CO2 and thermal treatment. This modification process may include re-
piping and re-
tooling of existing tanks, the addition of agitation and heating coils and
cladding of key
equipment items and the addition of a CO2 gaseous feed system. Such a system
may allow
for a quick upgrade to the new all-green wood system and a very rapid return
on invested
capital.
Al Implementation
Artificial intelligence and machine learning can be integrated into the
facilities design.
Some examples of high-impact use-cases are 1) modernizing and optimizing the
lumber
treatment process as it adapts to the unique profiles of the wood feedstock,
production
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environment, geographic location and weather conditions at the time of
production, 2)
forecasting and macro-variable modelling such as feedstock prices and housing
or
infrastructure product demand, 3) pricing and competitive intelligence, 4)
supply-chain
optimization including lumber and other input chemicals and resources, 5)
renewable energy
sources used in the manufacturing, 6) back office automation, and 7)
predictive
maintenance. Adjusting these variables can have a significant impact on
metrics such as
yield and quality and overall costs. This is consistent with the inventors'
position that the
experiments have identified the important parameters for all of the key
invention materials
and for the processes to modify the wood to achieve the high-performance
characteristics.
These variables can continue to be further improved using large data sets
while applying
the core theories and science developed by the inventors as outlined above and
in the below
examples.
EXAMPLES
The following examples are for illustrative purposes only and are not intended
to limit,
in any way, the scope of the present invention.
Example 1. An exemplary process for modifying wood samples.
Preparation of wood samples.
Radiata pine lumber was purchased from SODIMAC S.A, Chile, in the Concepcion
area. All the selected timbers were physically alike. The timber was cut into
samples of 7.5
mm x 4.5 mm x 2.5 mm and air dried at 50 C for 48 hours in a laboratory kiln.
The samples
were then stored in an air-conditioned room at 65% humidity and 25 C. The
weights of 5
randomly selected samples were constantly monitored until a constant weight
was reached.
The weight of the samples remained approximately constant after 25 hours.
Hence, it can
be safely established that the samples reach equilibrium humidity from about
25 to about 48
hours in the air conditioned room.
Preparation of wood samples for impregnation and the impregnation process.
After the samples were prepared and stored in the air-conditioned room, two
types of
samples were selected for the impregnation process. The first type of samples
had the
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growth rings perpendicular to the impregnation direction ("Radial samples"),
and the second
type of samples had the growth rings parallel to the impregnation direction
("Longitudinal
samples").
The samples were coated with epoxy resin on the four larger faces to prevent
impregnation via those faces, and the samples were cured for 18 hours in the
air-conditioned
room at 25 C. The impregnation faces were not contaminated by epoxy resin or
any other
waxy substances that could hinder the process. An extremely thin slice was cut
from both
of the impregnation faces at the ends of the sample before the impregnation
process to
make sure there was no epoxy in them. Then two radial samples and two
longitudinal
samples were loaded in the impregnation reactor. The samples were positioned
in the
impregnation vessel so that the impregnating faces were not blocked by the
walls or faces
of the other sample. The impregnation reactor was a batch reactor with a
capacity of 800
ml. The lid of the reactor has two openings, one for the entry of vacuum and
the other for
the fluids, nitrogen and sodium silicate solution in our case.
A vacuum was applied for 15 minutes, to remove air inside the reactor and from
the
sample pores. Then, 600 ml of a predetermined concentration of sodium silicate
solution
was injected inside the reactor. Subsequently, the pressure inside the reactor
was raised to
12 bars using gaseous nitrogen, (except for the cases where the effect of
pressure during
the impregnation process was studied). Immediately after the pressure was
raised, the
temperature of the reactor was raised to a desired value and the reactor was
left for a
predetermined time for the impregnation process to occur.
Determination of solid percentage in the sodium silicate solution.
The 38 Baume ("Be") sodium silicate solution was provided by QUIPASUR S.A. in
Chile. To determine the percentage solids present in the sodium silicate
solution, 5 samples
of approximately lg of sodium silicate solution were taken in different watch
glasses. The
glasses were then kept at 105 C for 24 hours in a stove and then cooled down
in a
desiccator for 1 hour. Then weights of the glasses were taken to verify any
change in weight.
The glasses were again placed in the stove at 105 C for two hours. The
average solid
percentage in the sodium silicate solution was found to be 41.81%.
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Quantitative determination of SiO2 in sodium silicate solution.
The silicon dioxide percentage in the original sodium silicate solution that
was used
during the experiments was determined. The specific gravity of sodium silicate
solution
provided by QUIPASUR S.A. is 38 Be and the range of the ratio of SiO2/Na2O was
3.2-3.5.
To determine the amount of SiO2 in this solution, the procedure described in
the instruction
manual
"Determination of sodium silicate in the impregnated wood" was followed. In
accordance with this procedure, about 1g of sodium silicate solution from the
solution
provided by QUIPASUR S.A. was taken in a round bottom flask. Subsequently,
40m1 of
sulfuric acid and 30m1 of nitric acid were added. The sodium silicate solution
tends to
crystallize instantly following contact with an acid solution. A glass rod was
used to crush
the crystal fine apart and the system was subjected to ref lux heating for 45
minutes at 80
C. The round bottom flask was then cooled, and the solution was diluted 10
times its
volume with distilled water. The solution was then filtered. The residue in
the filter was filter-
washed with 500 ml of distilled water. After filtration, residue was dried for
12 hours at 105
C. This was then cooled in a desiccator and weighed. The difference gives the
amount of
silicon dioxide in the sodium silicate solution. This operation was repeated
six times. The
results are shown in Table 1, below. The average amount of silicon dioxide in
sodium silicate
solution provided by QUIPASUR S.A. as determined by the procedure described
above was
32.6 0.21% grams with a standard deviation of 0.51%.
Table 1
No Mass Initial Final Mass
Percentag
of sodium weight weight of SiO2
e (%)
silicate (g) (g) (9)
solution
(g)
1. 1.046 39.243 39.588 0.344
32.9
5 8 1 3
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2. 1.065 50.587 50.931 0.344 32.3
6 6 9 3
3. 1.037 50.192 50.521 0.328 31.7
1 9 5 9
4. 1.093 39.412 39.771 0.359 32.9
1 3 9 6
5. 1.048 53.215 53.561 0.346 33.0
3 1 3 2
6. 1.103 46.155 46.877 0.362 32.9
4 6 0 7
Determination of percentage of residual solid after digestion of wood with
acid
digestion.
Digestion in an acid medium was used to determine the silicon dioxide content
in the
impregnated wood samples. Wood contains inorganic materials that are not
soluble in acid
mixture used during the digestion. The residual inorganic substances may
interfere in the
percentage of silicon dioxide determined using this procedure. The
contribution of the
residual inorganic substances from the wood during the acid digestion of the
impregnated
wood samples with sodium silicate was therefore quantified. To determine the
amount of
solid residue contributed by radiata pine wood after digestion by an acid
solution, the same
procedure as described in the instruction manual "Determination of sodium
silicate in the
impregnated wood" was followed.
Approximately, 1g of dry wood dried at 105 C for 12 hours was taken in a
round
bottom flask. Subsequently, 80 ml of sulfuric acid and 60m1 of nitric acid
were added and
the system was subjected to reflux heating for 45 minutes at 80 C. The round
bottom flask
was then cooled, and the solution was diluted 10 times its volume with
distilled water. The
solution was then filtered whose weight was previously determined. The residue
was filter-
washed with 500 ml of distilled water. After filtration, the residue was dried
for 12 hours at
105 C. This was then cooled down in a desiccator and weighed. The difference
in the
weight gives the amount of solids remained after digestion of the radiata pine
wood. This
operation was repeated six times, the results of which are shown in Table 2,
below:
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Table 2
Mass Initial Final Mass
Percentage
of dry wood weight weight of SiO2
(%)
(g) (g) (g) (g)
1. 1.1470 39.2463
39.2464 0.0001 0.009
2. 1.4284 50.5904
50.5905 0.0001 0.002
3. 1.0621 50.1962
50.1963 0.0001 0.009
4. 1.0817 39.4166
39.4166 0.0000 0.000
5. 1.2825 53.2127
53.2128 0.0002 0.015
6. 1.1143 46.1571
46.1572 0.0001 0.009
The results indicate that the percentage contribution of the solid residue of
the radiata
pine wood after acid digestion is relatively small. Hence, this amount can be
discarded in
the final residue calculation after the digestion of the sodium silicate
impregnated radiata
pine wood.
Effect of the concentration of SiO2 in the impregnating liquor of sodium
silicate.
To explore the effect of the concentration of sodium silicate in the mixture
in the
impregnation of sodium silicate in radiata pine wood, a set of experiments
were conducted
under the following conditions.
Table 3
Temperature ( C) 80
Pressure (bar) 11
Ratio of SiO2/Na2O 3.2
Time (hours) 3
Concentration of Sodium silicate (%) 5, 10, 15, 20,
25, 30
The samples were impregnated according to the procedures described in
instruction
manual "Impregnation of sodium silicate in pine wood" and then weighed and
dried at 105
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C for 20 hours to assure the absence of moisture in the impregnated samples.
The
completely dried samples were then weighed and the increase in the total mass
was
monitored. Figure 2 shows the effect of silicon dioxide concentration on total
silicon dioxide
( /0) retained in the sample, after drying the samples at 105 C for 20 hours
at each
concentration.
As shown in Figure 2, for wood samples impregnated in the direction
longitudinal to
the wood rings, the weight of the impregnated wood samples gradually increases
with
increasing concentrations of silicon dioxide in the impregnation solution
until the
concentration reaches 20%, followed by an abrupt decrease. For wood samples
impregnated in the direction radial to the wood rings, the weight of the
impregnated wood
samples increases from silicon dioxide concentrations of 5% to 10%, followed
by a gradual
decrease. The decreases may be due to reaching a critical viscosity and/or a
critical particle
size of sodium silicate with increase in concentration that may negatively
affect its
impregnation in the radiata pine wood matrix. This experiment supports the
"less is more"
principal of the invention relating to the solution concentration of sodium
silicate and the
importance of using the appropriate solution concentration for given wood
conditions.
Subsequently, the silicon dioxide concentration in the impregnated wood
samples
was determined using gravimetric analysis by acid digestion. The results of
the average
values of the retained silicon dioxide at different lengths along the
impregnation direction
indicates that the retained percentage of 5i02, shown in Figure 3, in the wood
matrix
approximately follows the same trend as that of the increase in mass of the
impregnated
samples shown in Figure 2.
To explore the homogeneity of the impregnation process, the concentration of
SiO2
( /0) within the impregnated samples was determined. For this purpose, the
impregnated
samples were cut into 4 equal parts as shown in Figure 3, and the silicon
dioxide
concentration was determined by acid digestion through gravimetric method.
The results obtained indicated that the least difference in the average
retained values
of silicon dioxide among the external (El and E2) and internal parts (11 and
12) lies in the
SiO2 liquor concentration between 10 and 15%, which suggests that the most
homogenous
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distribution of the impregnating solution occurs somewhere between 10% - 15%
liquor SiO2
concentration.
Effect of reaction time in the impregnation of sodium silicate in radiata pine
wood matrix.
To explore the effect of the reaction time in impregnation of sodium silicate
in radiate
pine wood, a set of experiments was conducted under the following conditions.
Table 4
Temperature ( C) 80
Pressure (bar) 11
Ratio of SiO2/Na2O 3.2
Time (hours) 1, 2, 3, 4
Concentration of Sodium silicate ( /0) 10
The completely dried samples obtained after impregnation and subsequent drying
process at 10 C for 20 hours were weighed and the increase in the total mass
was
monitored. The increase in weight of the impregnated wood samples are shown in
Figure
4. The upper solid line in Figure 4 indicates the increase in mass percent in
the wood for
impregnation with the growth ring in longitudinal direction and the lower line
indicates the
mass increase for impregnation with the growth ring in the radial direction.
This suggests that good results were obtained for samples impregnated in the
radial
and longitudinal directions for time periods in the interval between 2 and 4
hours or more.
In one example, the impregnation time was 3 hours, for example.
Figure 5 shows the increase in total silicon dioxide content of the
impregnated wood
after drying the samples at 105 C for 20 hours. The error bars are the
dispersion (standard
deviation) observed in the silicon oxide along the length of the impregnated
sample. The
average silicon dioxide retained in the impregnated samples was determined
using a wet
gravimetric method with acid digestion. The results indicate that the silicon
dioxide content
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impregnated in the wood samples remains nearly constant within the error bars
after the
impregnation period of 2 hours.
The homogeneity of silicon dioxide impregnation in the impregnated wooden
matrix
was also determined using the same methodology as described above with respect
to Figure
4. The results indicated that there was not much difference in the
concentration of SiO2
along the length of the impregnated samples among those samples impregnated
for 2, 3
and 4 hours, while above 2 hours is preferred.
Effect of Temperature in the Impregnation of Sodium Silicate in Radiata Pine
Wood
Matrix.
Wood samples were impregnated with the growth rings radial to the impregnation
direction under the set of conditions shown in Table 5, below, to determine
the effect of
temperature on impregnation. Other conditions were kept constant. Tests were
performed
at temperatures of 20 C, 60 C, 80 C, and 100 C.
Table 5
Temperature ( C) 20, 60, 80,
100
Pressure (bar) 11
Ratio of SiO2/Na2O 3.2
Time (hours) 3
Concentration of Sodium Silicate (%) 10, 15, 20
The results in Figure 6a show a higher retention of impregnating solution in
weight
(%) with increasing the impregnating temperature at the 10% and 15% silicon
dioxide
content in the impregnation solution. The retention decreased with increasing
the
impregnating temperature at the 20% silicone dioxide content in the
impregnation solution,
as shown in Figure 6b. At higher concentrations and temperatures, it was
observed that the
sodium silicate solution tends to form thin silicate films on the wood
samples, commonly
known as efflorescence. The decrease in retention of impregnating solution at
the 20%
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silicon dioxide content at a higher temperature may, therefore, be due to the
deposition of
silicate particles on the impregnating face of wood samples.
Additional tests were performed at 5% silicon dioxide concentrations, with the
weight
pick up close to the 10% values listed above.
The wood samples were then dried at 105 C for 18 hours. The increase in the
dry
weight of the wood samples that were impregnated with sodium silicate at the
10% and 15%
silicon dioxide content in the impregnation solution at 20 C, 40 C, 60 C,
80 C, 100 C are
shown in Figure 7. Although the retention tendency of impregnating solution in
the wood
samples seems linear with the impregnating temperature, the increase in dry
weight, and
hence the retention of SiO2does not follow a similar tendency. For the 10% and
15% silicon
dioxide mixtures, the increase in dry weight seems to reach a plateau at a
temperature after
50 C and decreases at higher temperatures, as shown in Figure 7a. This may be
due to a
tendency of the wood samples to delignify at higher temperatures and pH
(approx. 11.5 to
12) used in this study. The increase in weight ( /0) of the wood sample at the
20% silicon
dioxide, in contrast, decreases from 20 C to 80 C and then increases at from
80 C to 100
C, as shown in Figure 7b.
The dried wood samples at 105 C for 18 hours were subjected to acid digestion
and
the content of silicon dioxide was determined. Each of the wood samples were
cut into 4
equal pieces including two internal parts and two external parts. The mass of
silicon dioxide
( /0) along the wood samples determined after acid digestion is showed in
Figures 8a and
8b, for 10% sodium silicate in Figure 8a and 15% sodium silicate in Figure 8b.
Although the silicon dioxide content was not homogenous in all the
impregnations,
the silicon dioxide content and the standard deviation of the silicon dioxide
content along the
wood sample were calculated.
Figures 8a and 8b show that the silicon dioxide content in the wood samples
follow
the same tendency as that of the increase in dry weight shown in Figures 7a
and 7b,
however, there exists greater inhomogeneity of silicon dioxide inside the
wooden matrix
which decreases with increase in temperature.
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The 20% silicon dioxide solution, however, shows the opposite tendency, as
shown
in Figure 9, which shows the weight percent of silicon dioxide retained in the
impregnated
wood samples at different temperatures and at the 20% silicon dioxide
concentration of the
impregnating solution. The impregnation may be hindered due to the deposition
of silicate
particles on the impregnating face of the wood sample.
The average mass retained in the impregnated wood samples for the 10%, 15%,
and
20% sodium silicate content in the impregnation solution are shown in Figures
10a and 10b.
Figure 10a shows that for the lower concentrations of silicon dioxide in the
impregnating
solution (10% and 15%), the average mass of silicon dioxide retained in the
impregnated
wood remains approximately constant at temperatures above 50 C, while that for
the 20%
solution decreases with temperature, as shown in Figure 10b. These experiments
confirm
the importance of controlling the temperature settings for the sodium silicate
solution
depending on the sodium silicate concentration being used and the specific
ranges need to
achieve the modified wood performance results.
Effect of pressure in the impregnation of sodium silicate in radiate pine wood
matrix.
To illustrate the effect of pressure in the impregnation of sodium silicate
inside the
radiata pine wood, wood samples were impregnated with growth rings radial to
the
impregnation direction, at different external pressures. All the other
experimental conditions
were kept constant. The experiments were conducted under the set of conditions
shown in
Table 6:
Table 6
Temperature ( C) 20
Pressure (bar) 0.5, 10, 15,
20
Ratio of SiO2/Na2O 3.2
Time (hours) 3
Concentration of Sodium silicate ( 70) 15
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Figure 11 shows the average retained masses of the silicon dioxide inside the
radiata
pine wood samples after impregnation at 15% concentration of silicon dioxide
at 20 C, and
pressures of 0.5 bars, 10 bars, 15 bars, and 20 bars. The error bars indicate
the
inhomogeneity of silicon dioxide mass percentage inside the wooden matrix.
The results indicate that the retained mass of silicon dioxide increases
linearly until
bars, after which it levels out and becomes pressure independent. This may be
due to
the existence of a threshold pressure beyond which the pores in the wood exert
minimum
resistance to the fluid flow inside the wood sample and hence, approximately
the same
amount of silicon dioxide gets deposited. The most silicon dioxide was
retained in the
10 interval between about 10 bars and about 20 bars. In one example, 15
bars is used.
Effect of the ratio of SiO2/Na2O in the impregnation of sodium silicate in
radiata pine
wood matrix.
The effect of the weight ratio of silicon dioxide to sodium oxide (Na2O) was
also
determined. The ratio of Na2O and SiO2 in the impregnating solutions were
adjusted
according to the instruction manual "Preparation of impregnating solution of
sodium silicate."
All the experimental conditions but the ratio of SiO2/Na2O and the
concentration of the
impregnating solution was kept constant. The experiments were conducted under
the set of
conditions shown in Table 7:
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Table 7
Temperature ( C) 20
Pressure (bar) 12
Ratio of SiO2/Na2O 2.85, 2.55,
2.25, 1.95
Time (hours) 3
Concentration of Sodium silicate ( /c.) 10, 15
The impregnated samples were kiln dried at 105 C for 20 hours and the
increase in
mass of the dried impregnated samples was noted. The results indicate that the
change in
mass percent of the samples decreases with a decrease in the ratio SiO2/Na2O.
Without
limiting the invention, this may be due to an increase in the pH of the
impregnating solution
due to the increased amount of sodium oxide, resulting in agglomeration and
polymerization
of the silicon dioxide.
The stove dried wood samples at 105 C for 20 hours were then subjected to
acid
digestion, as described above, and content of silicon dioxide was determined.
Each of the
wood samples were cut into 4 equal pieces and the external parts were named: E
(El and
E2) while the internal two parts were named as 1 (11 and 12). The average
values of the
external and internal parts of the samples are shown in Figures 12a and 12b.
Figure 12a
shows the increase in mass ( 70) of the wood samples impregnated with sodium
silicate at
10% silicon dioxide and Figure 12b shows the increase in increase in mass (%)
of the wood
samples impregnated with sodium silicate at 15% silicon dioxide. The red solid
lines indicate
the tendency of the mass percent to decrease with decreasing ratios of
SiO2/Na2O.
Figures 13a and 13b show the average silicon dioxide retention values in the
external
and internal parts of the wood samples impregnated with the 10% silicon
dioxide, in Figure
13a, and the 15% silicon dioxide, in Figure 13b. Figures 13a and 13b indicate
that the
impregnation of the liquor was not homogenous in all the wood samples and
shows high
dispersions among the internal and external segments. However, it seems that
the
impregnation process is affected by the change in the ratio of SiO2/Na2O for
both
concentrations of the impregnation solution (10% and 15% of SiO2). The
aforementioned
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experiments confirm the importance of controlling the pressure settings for
the solution
impregnation while also selecting the appropriate ratio of SiO2/Na2O being
used.
Fixation of SiO2 inside the wood samples impregnated with sodium silicate
solution.
Multiple strategies were followed to study the fixing of silicon dioxide
inside the
impregnated wood samples via thermal and chemical methods (lowing pH). The
durability
of the wood when exposed to humid conditions is closely linked to the water
solubility of the
chemicals used. Sodium silicate is highly soluble in water, making it less
attractive for
outdoor applications with high humidity.
In a thermal treatment, bonded water is disassociated from the silicate salt
and the
number of bridging oxygen atoms are reduced, shifting the equilibrium of the
silicon dioxide
towards a less soluble form in water. Three different processes for the
thermal treatment
were studied: 1) thermal treatment with water vapor, 2) thermal treatment with
hot air, and
3) thermal treatment with hot water. In 1) thermal treatment with water vapor,
the samples
impregnated with sodium silicate salt at 10% concentration were treated with
saturated water
vapor at three different temperatures, 50 C, 100 C, and 150 C for 2 hours, and
the samples
were digested to determine the silicon dioxide content. In 2) thermal
treatment with hot air,
the impregnated samples were subjected to air heated at 50 C, 100 C, and 150 C
for 2
hours and further analyses were carried out. In 3) thermal treatment with hot
water, the
impregnated samples were reacted with water at 50 C, 100 C, and 150 C for 2
hours and
further analyses were conducted to determine the silica content in the treated
samples.
Two different pH treatments were also studied: 1) gaseous carbon dioxide (CO2)
where the treated samples were subjected to three different pressure of carbon
dioxide (3
bars, 6 bars, and 12 bars), and 2) water acidified with carbon dioxide, where
the treated
samples were submerged in water inside a reactor and the pressure of the
reactor was
raised to desired values for two hours at 3 bars, 6 bars, and 12 bars.
For all the treatments mentioned above, wood samples were impregnated with
sodium silicate at:
= Pressure (bars): 12
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= Impregnation time
3
(hours):
= Concentration of
10%
S102:
= Ratio (SiO2/Na2O): 2.85
= Temperature: 50 C
Seventy-two samples were prepared in a 10-liter reactor conditioned for this
purpose.
The temperature in the reactor was controlled by saturated vapor that
circulated through an
external jacket around the reactor. The samples obtained from the impregnation
of sodium
silicate into the wood matrix were subjected to the thermal and pH treatments
described
above.
The treated samples were then subjected to acid digestion to determine the
silica
content.
To evaluate the fixing of SiO2 inside the sodium silicate impregnated wood
samples,
leachability of sodium silicate was determined and silicon dioxide content was
determined
using acid digestion method before and after each leaching cycle.
Thermal treatments
1. Samples treated with hot air
The impregnated samples were subjected to air heated at 50 C, 100 C, and 150 C
for 2 hours and analyzed. The results of the decrease in weight percent of the
samples with
leaching time is shown in Figure 14.
In Figure 14, the percent retention in mass decreases with increasing time.
More
mass was retained at 100 C than at 50 C, suggesting that mass retention is
better at higher
temperatures. At 150 C, however, less mass was retained.
It was observed that the samples released colored substances during the
leaching
process, which could have been due to the leaching of lignins and/or
hennicelluloses, along
with silicon dioxide and sodium hydroxide, resulting in the higher loss of
mass. It can
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therefore be concluded that at the lower temperatures (50 C and 100 C), the
loss of lignin
and hemicelluloses is not significant.
To determine the amount of sodium silicate leached during the experiments, the
silicon dioxide content in the samples was determined using acid digestion
method before
and after the leaching trials, as discussed above. The mass percent of silicon
dioxide (SiO2)
in the impregnated wood samples before (blue bars) and after (orange bars) the
leaching
tests of the samples treated with dry air at different temperatures is shown
in Figure 15. The
mass percentages of SiO2 did not vary significantly. This also indicates that
the loss in the
mass of the samples observed during the leaching process is not due to silicon
dioxide, but
may be due to the loss of lignin, hemicelluloses, and sodium hydroxide (NaOH),
which are
formed as the result of reaction between water and sodium oxide (Na2O) present
in sodium
silicate.
2. Samples treated with hot water
In thermal treatment with hot water, the impregnated samples were reacted with
water
at 50 C, 100 C, and 150 C for 2 hours and further analyses was conducted to
determine
the silica content in the treated samples. The percent decrease in the mass of
the wood
samples impregnated with sodium silicate during the leaching experiments is
shown in
Figure 16.
Initially, the percent of the retained mass decreased at substantially the
same rate
until 10 hours, where it diverged. Less mass was lost at 150 C than at 50 C
and 100 C.
The most mass was lost at 50 C. This may be due to the fact that most of the
extractables
from the samples were already extracted during the hot water treatment process
and just a
fraction of the remaining extractables were leached out during the leaching
process,
resulting in a gradual decrease in mass of the samples with time. The percent
mass retained
was higher at 50 C, 100 C, and 150 C than in the hot air heat treatment
results shown in
Figure 14.
The mass percent of silicon dioxide (SiO2) retained in the impregnated wood
samples
before (blue bars) and after (orange bars) the leaching tests of the samples
treated with hot
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water at the different temperatures are shown in Figure 17. The change in the
mass percent
of SiO2 in the impregnated samples was similar in all the cases.
The pH of the leachate after each leaching cycle was monitored. The pH of the
leachate during the early cycle was very high (of the same order of magnitude
as sodium
silicate solution), and gradually decreases with the increase in leaching
time.
3. Samples treated with water vapor
The results of the leaching trials of the sodium silicate impregnated samples
treated
with saturated water vapor at 50 C, 100 C, and 150 C are shown in Figure 18.
The loss in
mass of the impregnated wood samples was least in the wood samples treated
with water
vapor at 100 C and higher at 150 C. The tendency of the loss in mass of the
samples in
Figure 18 is similar to those observed in Figure 14.
The change in the mass percent of silicon dioxide in the impregnated samples
before
(blue bars) and after (orange bars) the leaching tests of the samples treated
with saturated
water vapor at different temperatures is shown below in Figure 19. The masses
before and
after leaching at the different temperatures was substantially the same.
pH change treated samples by gaseous CO2 under pressure
1. Samples treated by gaseous CO2 under pressure without water
In these trials, the impregnated samples were treated with gaseous carbon
dioxide
under pressure at 3 bars, 6 bars, and 12 bars. Figure 20 shows the percent of
retained
mass of sodium silicate impregnated wood samples treated with gaseous carbon
dioxide at
the different pressures during the leaching tests, over time. The leaching
tests involved
placing heat treated samples of size 2 x 2 x 2 cm into 330 ml of distilled
water in a 600 ml
beaker, which was stirred for 8 hours. Then the samples were dried at 60 C for
16 hours.
Four leaching cycles were performed for each of the samples.
As shown in Figure 20, increasing the treatment pressure decreases the mass
loss
from the samples during the leaching tests. This indicates that more carbon
dioxide gas
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impregnates the wood samples and reacts with the sodium silicate solution
already inside
the wood, as the treatment pressure is increased.
As discussed above, the carbon dioxide lowers the pH of the impregnated wood
from
about 11 after impregnation to about 9 after CO2 treatment. This is due to
reaction of the
carbon dioxide with water to form carbonic acid (H2CO3), which is a mild acid.
The carbonic
acid further reacts with sodium silicate (Na2S03), yielding silicon dioxide
(SiO2) and sodium
carbonate (Na2CO3). Sodium bicarbonate (NaHCO3) may also be produced but due
to the
moderately acidic environment created by the distilled water, which has a pH
of 5.1, the
formation of sodium carbonate is more likely. These reactions may enable the
sodium
silicate to better adhere to the cell walls of the lumber during impregnation,
avoiding leakage
of the sodium silicate out of the lumber.
As indicated in the above trials, the change in mass of the samples is not due
to the
leached silicon dioxide, but may be due to the loss of lignin at high
temperature and the loss
of sodium compounds. In this case, the loss in mass of the samples during the
leaching
process may be due to the loss of unreacted sodium hydroxide and sodium
carbonate, which
has low solubility in water at room temperature.
The silicon dioxide content of the leached and unleached samples were also
determined. Figure 21 shows the mass percent of silicon dioxide in the
impregnated wood
before (blue bars) and after (orange bars) the leaching tests of the samples
treated with
gaseous carbon dioxide at different pressures.
Figure 21 is consistent with the results in the trials with leaching of heat
treated
samples, that there are essentially no changes in the silicon dioxide content
of the
impregnated wood samples due to leaching.
2. Samples treated with water in a CO2 environment under pressure.
Impregnated wood samples were immersed in water inside an impregnation vessel
and then treated with gaseous carbon dioxide at different pressures. The
results obtained in
these trials are summarized in Figure 22, which shows the percent of the mass
of the sodium
silicate impregnated wood samples retained during the leaching tests.
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There does not appear to be much differences in mass change when the
impregnated
samples are immersed in water at 6 bars and 12 bars. This may be due to the
formation of
equivalent amount of sodium carbonate and/or a similar rate of leaching of the
sodium
carbonate along with sodium hydroxide. The change in mass of the samples
treated with
water under 3 bars of pressure was much more than at 6 bars and at 12 bars,
which may
be due to the lack of formation of sodium carbonate and sodium hydroxide,
which are readily
soluble in water and may have been readily leached out.
The silicon dioxide content of the leached and unleached samples was also
determined. The results are shown in Figure 23, indicating that the silicon
dioxide content
was substantially the same before and after leaching.
Comparison of fixation strategies
A comparison among the treatment strategies to fix sodium silicate inside the
wood
samples is presented.
The heat treated samples were subjected to acid digestion. The results for the
samples dry air heat treated samples at 50 C, 100 C, 150 C and water vapor
heat treated
samples at 150 C are compared to determine the effect of heat treatment in the
silicon
dioxide content. The results are shown in Table 8, below:
Table 8
Treatment method SiO2 content (%)
Dry air at 50 C 15.447
Dry air at 100 C 15.2954
Dry air at 150 C 15.2116
Water vapor at 150 C 15.2711
The leaching experiments were conducted according to the method described
above.
Figure 24 shows the percent decrease in the mass of the wood samples
impregnated with
sodium silicate prepared at 50 C, 1 00 C, 150 C of dry air, and 150 C of
water vapor. The
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percent reduction in weight of the wood samples after each drying process of
16 hours is
shown in Figure 24.
Figure 24 shows a decrease in the mass of the impregnated samples with
increasing
time for all heat treatment strategies. The greatest mass retained was
provided by 100 C
dry air, followed by 50 C dry air, 150 C vapor, and 150 C dry air. The
leaching test results
show that heat treatment with dry air at 100 C yields better results than the
samples treated
at 50 C with dry air. This may be due to higher removal of water at higher air
temperature
and hence higher precipitation of silicate due to the lack of bridging oxygen.
It was observed that the samples released colored substances during the
leaching
process. The colored substances released during leaching of these samples may
be lignins
along with sodium silicate, indicating slight delignification. The decrease in
overall mass of
the samples may not, therefore, represent the loss of sodium silicate during
the leaching
process. The samples treated at higher temperature (150 C) by both dry air and
water vapor
lost more mass and were slightly delignified.
A general comparison among the heat treatments and pH change treatments of the
impregnated samples before leaching is presented in Figure 25 and Figure 26,
respectively,
where only the treatment process in which least loss of samples mass during
the leaching
process was noted has been presented.
Figure 25 compares the mass of the leached samples for fixation with carbon
dioxide
gas at 12 bars and for fixation with carbon dioxide in water at 12 bars.
After 10 hours, more mass was retained when the fixation treatment was gaseous
carbon dioxide at 12 bars.
Figure 26 compares heat treatment at 100 C of dry air and gaseous carbon
dioxide
at 12 bars.
More mass was retained with a pH change treatment with gaseous carbon dioxide
at
12 bars than with a heat treatment of 100 C dry air. This tendency would
further increase
at higher pressures. Due to the pH of the water (pH-5.1) that was used for
initial,
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impregnation treatment and the leaching process, it is likely that the silicon
dioxide was
already polymerized and precipitated due to lower pH of water.
These results from the above experiments conclusively indicate that the
inventors'
unique use of CO2 under pressure as the primary fixation method for silicon
dioxide (SiO2)
is highly effective in eliminating the probable leaching issues customary for
many of the
chemicals impregnated into lumber using forms of the pressure treated wood
modification
processes.
The three thermal treatment experiments outlined below in detail concluded the
following important findings, namely, while the hot air and hot water
treatments were partially
efficacious, the use under pressure of gaseous CO2 for fixation by the
inventors was far
superior as outlined in the gaseous CO2 experiment section below, pH Treated
Samples.
Example 2. A double impregnation process for further improving wood
protection performance
In this example, the wood sample preparation, impregnation process, and the
fixation
by pH change treatment by gaseous CO2 under pressure as described above in
Example 1
have been carried out as the first stage.
The process in the second stage described below involves the use of a second,
shorter duration of impregnation, after the CO2 fixation step in the first
stage. In this second
stage, a higher concentration of sodium silicate solution (i.e., a sodium
silicate concentration
higher than the sodium silicate concentration of the impregnation solution in
the first stage,
e.g., 10 to 15% Si02) was applied to the wood in the autoclave under a
pressure of about 2
to 12 bar and a temperature of about 20 to 70 C, for a period of about 20 to
30 minutes.
The purpose of this second impregnation is to provide additional surface
protection to the
wood, including adding an additional fire protection barrier.
This second impregnation shows a weight pick up averaging 104%, as compared to
98% in a single-stage impregnation process, as shown in Table 9 below, as well
as in Figure
27. This additional 6% weight pick up is considered important for additional
lumber
protection properties.
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Table 9. Specimen weight gains after the impregnation treatment, comparing the
results from the first stage impregnation (initial) and after the second stage
impregnation
(subsequent)
Calculation: Weight 2 -Weight 1 Weight 4 -Weight 3
Weight 4 - Weight 1
Specimen # % Weight Gain -Initial % Weight Gain -Subsequent
%Weight Gain -Total
1 53% 10% 52%
2 107% 14% 125%
3 99% 20% 127%
4 96% 20% 123%
104% 5% 112%
6 44% 21% 110%
7 97% 9% 112%
8 109% 6% 111%
9 127% 7% 136%
104% 9% 111%
11 95% 8% 109%
12 122% 7% 124%
13 67% 6% 58%
14 46% 6% 39%
105% 4% 103%
16 157% 4% 98%
17 131% 5% 136%
18 60% 8% 55%
19 113% 5% 115%
108% 2% 110%
21 110% 2% 112%
Average 98% 9%
104%
Where: Weight 1 is Pre-initial impregnation weight
Weight 2 is Post-initial impregnation weight
Weight 3 is Pre-subsequent impregnation weight
Weight 4 is Post-subsequent impregnation
weight
5 The concept of weight pick-up indicates the first protection barrier
in preparing
pressure-treated lumber - the more chemical retained after impregnation, the
better chance
the wood has to resist fire, termite attack, rot and decay. The impregnation
is combined with
the second protection barrier ¨ fixing or stabilizing the chemicals
impregnated in the wood,
to prevent leaching out of the impregnated chemicals and the associated lumber
degradation
10 with time. The wood-modification process illustrated in the examples
balance the first and
second protection barriers, the comprehensive chemical retention and long-term
chemical
stability, both of which being achieved without strength degradation. This is
a unique and
important mix of critical wood protection outcomes achieved comprehensively in
the wood
when using an all-sustainable chemical modification process.
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The results in Table 9 and Figure 27 indicate that the double impregnation
provides
a better barrier for attack by fire. The fixation by CO2, followed by the
second impregnation
treatment, provides an additional layer of protection to make the wood less
prone to burning,
as shown in Table 10 below.
In this case, the E84 10-minute burn test was applied to both conventionally
treated
lumber (a phosphate-based treatment solution) and the wood treated by the
inventive double
impregnation process as described above, and the corresponding flame spread
was
measured. These tests were performed at an accredited ASTM Fire Testing
Laboratory,
using a 24' long Steiner Tunnel and applying the standard burn techniques for
the E84 test.
The samples used were 2 x 4 x 8 untreated lumber: 2" x 4", eight ft long #2
untreated
lumber, which was kiln dried to approx. 19% (KD19). This lumber was run
through the
double impregnation process as described above and then dried in a
conventional sawmill
kiln using optimal drying schedules. These products were then isolated,
wrapped and
shipped to the ASTM testing facility, where they were burned within one week
of
manufacture.
The maximum flame front is a measure of the amount of advancement of the flame
down the tunnel, as propagated by a methane burner, and measures the ability
of the wood
to resist flame spread. The stated limit of 6.0 ft from the measuring point
(and 10.5' from the
burner) is the industry standard for wood burning to not exceed, to obtain the
Class "A" fire
retardant rating.
Two tests were carried out ¨ one for a 10-minute burn (ASTM E84) and one for a
thirty minute burn (ASTM E2768). ASTM E-84: Standard Test Method for Surface
Burning
Characteristics of Building Materials. ASTM E2768: Standard Test Method for
Extended
Duration Surface Burning Characteristics of Building Materials (30 Minute
Tunnel Test).
These are part of the ASTM E119 or UL 263 that meet the global standards for
fire retardant
rating.
The results of the first test are shown in Table 10 as well as in Figure 28.
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Table 10. E84 Burn tests for wood modified by inventive double impregnation
process vs. conventionally treated wood.
Time Max Flame Front
Actual Actual Flame Front
of burn Allowable for Class A Fire
Flame Front for for Conventionally Treated
(minutes) Retardant Inventive Lumber
Product (ft)
(ft) (ft)
1 6 0
0
2 6 0.2
0.8
3 6 2.0
2.2
4 6 2.0
2.8
6 2.0 3.8
6 6 2.2
4.0
7 6 2.2
4.2
8 6 2.2
4.3
9 6 2.2
4.4
6 2.2 4.4
It can be seen clearly here that the modified lumber by the inventive double
5 impregnation process resulted in a lower flame spread down the tunnel, as
compared to the
lumber made with a conventionally treated process, by a factor of 170% (as
compared to
the 6' flame spread limit). Lower flame spread corresponds directly with flame
retardancy
and safety.
The more stringent test for measuring the burn characteristics of lumber is
using the
10 E2768 test ¨ with the same Steiner tunnel, but for a period of thirty
minutes. The results of
this test are shown in Table 11 below as well as in Figure 29.
Table 11. E2768 Burn tests for wood modified by inventive double impregnation
process vs. conventionally treated wood.
Time Max Flame Front Actual
Actual Flame
of burn Allowable for Class A
Flame Front for Front for Conventional
(minutes) Fire Retardant Invention Lumber Treated
Lumber (ft)
(ft) (ft)
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1 6 0 0
2 6 0.2
0.8
3 6 2
2.2
4 6 2
2.8
6 2 3.8
6 6 2.2
4.0
7 6 2.2
4.2
8 6 2.2
4.3
9 6 2.2
4.4
6 2.2 4.4
11 6 2.2
4.5
12 6 2.2
4.5
13 6 2.2
4.5
14 6 2.2
4.5
6 2.2 4.5
16 6 2.2
4.5
17 6 2.2
4.5
18 6 2.2
4.5
19 6 2.2
4.5
6 2.2 4.5
21 6 2.2
4.5
22 6 2.2
4.5
23 6 2.2
4.5
24 6 2.2
4.5
6 2.2 4.5
26 6 2.2
5.3
27 6 2.2
5.3
28 6 2.2
6.3
29 6 2.2
7.5
6 2.2 8.5
This data shows, once again, the superior performance of the modified lumber
by the
inventive double impregnation process over the thirty minute time test as
compared to the
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conventionally treated product and the ability of the lumber modified by the
inventive double
impregnation process to meet or exceed the stated Class "A" fire retardant
standard. In this
case the improvement is 350%, as compared to the 6' limit over the 30-minute
test.
Example 3. Relative Strength Properties
The change in the relative strength properties of the wood is important,
particularly in
the context of FRT wood which until now has been regarded as requiring a
compromise on
strength in order to achieve required safety for fire risk. Traditional fire-
retardant treatment
processes (typically phosphate based) have been shown to reduce the strength
properties
of the wood (in terms of Tensile strength, MOR and MOE). However, as shown in
Table 12
and Table 13 below, for wood samples made according to the modification
process
described in the embodiments of this invention (Inventors' Impregnation), the
strength
properties have not been reduced but actually stabilized and in some cases,
significantly
improved, as compared against the untreated SYP control.
Sample lumber dimensions were cut 1 inch in width by dimensional thickness
(which
was approximately 1.5 inches). The span used for testing was 28 inches. The
test speed
was 0.5 inch per minute and was run on an MTS electromechanical universal test
frame with
a 2,000-pound loadcell. The strength properties were measured by ASTM D143-14,
which
are The Standard Test Methods for Small Clear Specimens of Timber. See Figure
31.
Table 12. Strength Properties of Lumber Comparison
Data for Strength Properties of Lumber
MOR (ksi) MOE (psi)
Tensile (lbf)
SYP Control 12,280 2,094
2,117
Inventors' Impregnation 12,787 2,866
1,925
Cony. Phosphate Treated lumber 10,881 1,350
2,194
The relative improvements of these strength properties, as measured against
the
SYP control (untreated) sample and the typical conventional phosphate treated
wood are
shown in Table 13 below.
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Table 13. Inventors' impregnation as compared to SYP control and conventional
FRT
wood
Inventors' Impregnation as Compared to: (% Improvement)
MOR MOE Load at
Break
SYP Control 4.1% 36.8%
(9.0%)
Cony. Phosphate Treated lumber 17.5% 112.4%
(12.2%)
The above data show the significant improvement of the strength properties. In
particular, the MOE of the wood sample modified by the inventors' impregnation
process
has improved over 112% relative to conventional FRT wood, and over 30%
relative to
untreated SYP control wood. These results indicate a ground breaking paradigm
shift in the
FRT wood landscape and would allow for fundamental review of the use of the
inventors'
all-green superior strength fire retardant lumber product in numerous
applications as
described herein, both in terms of substituting conventional non-sustainable
FRT wood as
well as making use of FRT wood for additional fire safety where previously
strength
degradation was an accepted compromise and often also a major hurdle to both
design and
cost challenges.
The data are also summarized in Figures 32a and 32b. Improvements to lumber
samples modified by the process according to the embodiments in this invention
in MOE,
and MOR properties averaged +36.9% (MOE) and +4.0% (MOR), respectively, as
compared
to the untreated SYP control lumber samples, with the Tensile being
statistically similar.
As compared to non-sustainable treated lumber (conventional phosphate treated
lumber), these performance improvements show a significant improvement in the
MOE
(+112%) and MOR (+18%). This factor is significant in the lumber construction
industry with
the added strength and flexibility improvements directly impacting cost and
design flexibility
and usage.
Using non-sustainable treated/modified Southern Yellow Pine utilized in
wall/floor
environments and trusses in roof framing, using current industry leading
processes and
formulations that are NOT sustainable and testing these samples using industry
standard
testing as defined by, for instance, ASTM D5664 (ASTM D5664 is Standard Test
Method for
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Evaluating the Effects of Fire-Retardant Treatments and Elevated Temperatures
on
Strength Properties of Fire-Retardant Treated Lumber) and ASTM D6841 (ASTM
D6841 is
Standard Practice for Calculating Design Value Treatment Adjustment Factors
for Fire-
Retardant-Treated Lumber), the adjustment factors for MOR and MOE are known to
be
approximately 0.80 to about 0.95 as compared to the Southern Yellow Pine (SYP)
untreated
control. In comparison, the ranges for the inventor's modified lumber,
according to the
modification processes described in the embodiments of this invention, are
expected to be
approximately from 1.05 to greater than 1.40, as compared to the Southern
Yellow Pine
(SYP) untreated control (as derived from the testing data utilized to prepare
samples shown
in Figure 31 and Figures 32a and 32b). This result is unprecedented and
further is counter
to other non-sustainable modified wood products and their manufacturing /
treatment
processes, especially those used for preparing fire-retardant-treated (FRT)
wood, where
mechanical strength properties are generally reduced during the impregnation
process.
In addition, as shown in the widely referenced analysis of conventional FRT
wood
treatments, there is a significant deterioration in the strength properties of
fire retardant
lumber and other non-sustainable chemical preservative treated wood products
over time
after exposure to natural elements including temperatures, microbial and ultra-
violet rays.
Therefore, starting with a significantly higher range of strength parameters
such as MOE
and MOR in a FRT product as seen in the all-green high performance wood when
used in
construction environments exposed to degradation elements is a major paradigm
shift to the
current FRT lumber landscape and the design and material usage and cost
reduction
implications for architects and builders could be significant given these
results. See
Winandy and Rowell, "Chemistry of Wood Strength" Handbook of wood chemistry
and wood
components, pages 303-347 (CRC Press, Roca Raton, Florida, 2005).
Example 4. Rot and Decay Resistance
The all-green wood made with a sodium silicate impregnation solution according
to
the modification process described in the embodiments of this invention
provides an
effective barrier to rot and termites, while also retaining the fire and
strength benefits from
the modification process. To support these findings, certain tests were
carried out in a
leading lumber research and development and testing facility in Chile and
Uruguay using
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the appropriate species. The results show that the modification process
described in the
embodiments of this invention with sodium silicate impregnation solution
effectively protects
wood from degradation from fungi, although a combination of sodium silicate
and sodium
borate provided the best resistance profiles for rot and decay. However, when
combined
with sodium silicate in the impregnation solution, an environmentally safe
level of boron of
no more than 0.5 % by wt. would be more than sufficient to resist fungal
attack.
Samples of wood were prepared according to the modification process described
in
the embodiments of this invention with sodium silicate, along with other types
of chemical
agents, and tested according to ASTM D1413-07 "Standard Test Method for Wood
Preservatives by Laboratory Soil-Block Cultures".
Additionally, in order to provide broader results and provide control
measures,
samples were also evaluated according to European Standard EN 113 "Wood
preservatives
- Test method for determining the protective effectiveness against wood
destroying
basidiomycetes - Determination of the toxic values". All tests were conducted
at the
Tacuarembo headquarters of the University of the Republic in Uruguay with
samples of
pinus radiata and pinus taeda.
Rot Tests Results According to Standard D1413-07
Figure 33 shows a summary of the results of resistance to degradation from
exposure to the dry rot fungi, Serpula lacrymans, under standardized
conditions. A
summary of the observations is listed below:
= Sodium Silicate: Sodium silicate treated wood showed a weight loss of
7.3%,
which was substantially less than the untreated control sample showing a
weight
loss of 19.7%. This confirms that impregnation according to the modification
process described in the embodiments of this invention with only sodium
silicate
effectively protects wood from degradation from dry rot fungi, Serpula
lacrymans.
= Sodium Silicate Bio Oil I and Sodium Silicate Bio Oil II: Different
proportions
of Bio Oil I (aqueous phase of pyrolytic pine bark liquid) and Bio Oil ll
(oily phase
of pyrolytic pine bark liquid) were added to a sodium silicate solution
containing
5.49% SiO2. The results obtained with both agents were similar; no
improvements
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to the resistance of fungus were noted. In fact, a small increase in
degradation
was noted.
= Sodium Silicate + Sodium Borate: Differing proportions of sodium borate
were
added to a sodium silicate solution containing 5.49% SiO2. This combination
provided the best results of observed weight loss. Between 0.6% and 7% (with
an average of 3.4%) weight loss was observed. This shows a trend of increased
resistance to fungal attack by increasing boron concentration. Importantly,
the
Inventors concluded that an environmentally safe level of Boron, under 0.5%,
was
more than sufficient when being used with Sodium Silicate to resist fungal
attack.
=
Sodium Silicate + copper ll salts: Differing proportions of copper sulfate
were
added to a sodium silicate solution containing 5.49% SiO2. While copper 0 and
copper 1 are known to be effective preservatives, copper ll was tested as it
is
more water soluble and consequently was hypothesized that wood impregnation
should be more effective. Results show that wood mass losses were slightly
lower
than when impregnating only with sodium silicate (6.7% average loss vs 7.3%
average loss, respectively). Both results show improvements over the untreated
control samples showing an average weight loss of 19.7%.
= Sodium Silicate + copper I salts: Only two tests were conducted with
cuprous
oxide; this compound is not soluble in water and notoriously difficult to
achieve
efficient penetration. Results were not shown to be promising as evidenced by
larger weight loss in these specimens.
Rot tests according to standard EN 113
Table 14 illustrates the testing results of the samples subjected to white and
brown
rot fungi (Trametes versicolor and Gloeophyllum separium, respectively) in
accordance with
the European standard EN113 test.
In addition to the control specimens of Pinus taeda and Pinus radiata three
groups of
testing samples made according to the modified processes described in the
embodiments
of this invention were impregnated with a sodium silicate solution containing
5.49% SiO2
with no other additives, a sodium silicate solution containing 5.49% SiO2 +
0.6% Bio Oil I
(aqueous phase of pyrolytic pine bark liquid), and a sodium silicate solution
containing
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5.49% Si02+ 0.4% sodium borate, respectively. The results are listed in Table
14 and Table
15 below.
Table 14. Weight loss and moisture content of samples subjected to the decay
of brown and white rot fungi according to the 16-week EN 113 testing standard.
White rot Brown rot
Controls
(Trametes versicolor)
(Gloeophyllum separium)
Moisture Weight Moisture
Weight
Treated Specimens
(%) loss ( /0) (%)
loss (%)
Pinus taeda ¨ control 21.6 16.81 19.4
26.18
Pinus radiata ¨ control 22.9 19.98 29.7
30.37
Sodium Silicate 64.0 4.01 61.9
4.91
(5.49% SiO2)
Sodium Silicate 58.2 9.49 61.2
6.63
(5.49% SiO2)
+ Bio Oil 1(0.6%)
Sodium Silicate 60.1 5.92 62.7
4.12
(5.49% SiO2)
+ Sodium Borate
(0.4%)
Table 15. Relative % weight loss improvement of treated specimens compared
against untreated control specimens.
White Rot Brown Rot
(Trametes versicolor) (Gloeophyllum separium)
Weight Loss Improvement Weight Loss Improvement
Controls & Treated Specimens as compared to:
as compared to:
Pinus taeda - control
P. taeda P. radiata P. taeda P. radiata
Pinus radiata - control
Sodium Silicate (5.49% 5i02) 319% 398% 433%
519%
Sodium Silicate (5.49% SiO2) + Bio Oil 1(0.6%) 77% 111% 295%
358%
Sodium Silicate (5.49% SiO2) + Sodium Borate (0.4%) 184% 238% 535%
637%
Table 14 illustrates the obvious benefits the Inventors' lumber modification
treatment
provides against white and brown rot decay. In the case of white rot (
Trametes versicolor),
the inventive modification process with sodium silicate impregnation solutions
showed
weight losses of 4.01% (with no other additives), 9.49% (with Bio Oil l), and
5.92% (with
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sodium borate), as compared to the controls of Pinus taeda and Pinus radiata
showing
weight losses of 16.81% and 19.98%, respectively. In the case of brown rot
(Gloeophyllum
separium), the inventive modification process with sodium silicate
impregnation solutions
showed weight losses of 4.91% (with no other additives), 6.63% (with Bio Oil
I), and 4.12%
(with sodium borate), as compared to the controls of Pinus taeda and Pinus
radiata showing
weight losses of 26.18% and 30.37%, respectively.
Table 15 illustrates the increased benefits in the context of the two
controls. Large
triple digit improvements in improved weight loss can be seen with a range of
77% to 637%,
depending on treatment solution and the comparison control variable.
Figures 34a-34e show the specimens treated with sodium silicate treatment
solutions
slowed fungal decay and limited damage to cell walls. Figure 34a and 34b show
month 1
and month 2, respectively, of specimens treated with the inventors' process
(5.49% Si02+
0.6% Bio Oil I) exposed to G. separium where a slowing of cellular wall damage
is displayed
despite an increased virulence of this fungus and an increased affinity of
brown dry rot by
conifer woods.
In comparison, Figure 34c shows a cross-section of a control sample taken from
the
middle of the specimen and illustrates deterioration of the cellular walls and
prolific
advancement of the fungus.
Figure 34d displays specimens treated with a sodium silicate solution
containing
5.49% SiO2-l- a 0.4% concentration of sodium borate. Figure 34e displays a
specimen
treated with a sodium silicate solution containing 5.49% SiO2 with no
additional additives.
Both specimens display an advanced ability to slow fungal advancement and
cellular wall
deterioration.
Example 5. Termite Resistance
Termites, although essential recyclers of carbon in tropical ecosystems, are
serious
structural pests in urban environments. Traditional termite management was
based largely
on the use of biocides, which did not require an intimate knowledge of the
organism. Legal
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and socioeconomic pressures have forced many of the most effective (but
equally
environmentally damaging) toxicants out of the marketplace.
The original environmentally-persistent (persistent organic pollutant, POPs)
termiticides (organochlorines) were effective and provided multiple decades of
protection
and were usually applied before construction. These were then replaced with
less effective
soil termiticides and insecticides used as barriers with approaches that
ranged from killing
large portions of the termite population to killing some portion of the
population around the
treatment boundary, causing a secondary repellency from necrophobia. These
were
required to be applied more frequently than the organochlorines. Additional
approaches
were added that included physical barriers, biological controls, physical
control, and a range
of baiting technologies. Most of these have had mixed results and continue to
negatively
impact the environment. In addition, construction lumber is pressure treated
with various
non-sustainable chemicals as a further method of termite control and with the
long-term
consequences of the chemicals eventually leaching back into the environment
and losing
their efficacy and thereby requiring additional treatments at the sites. See
Woodrow and
Grace, "Termite Control from the Perspective of the Termite: a 2151 Century
Approach," ACS
Symposium Series, Vol. 982, American Chemical Society (April 2, 2008), which
is
incorporated herein by reference in its entirety.
The inventors have focused their termite control strategy on the combination
of a
sustainable chemical in the wood that accomplishes both stable termite
resistance without
termite elimination and without long-term detrimental leaching of toxic
chemicals into the
environment. The inventors have been able to achieve both critical outcomes
according to
the modification process described in the embodiments of this invention,
thereby creating a
natural barrier product inside the cellulose structure of the wood itself such
that the termites
then do not want to forage on it. This combination is what makes the
inventors' modified
lumber approach uniquely effective against termites.
The following experiments have been conducted to evaluate the efficacy of the
inventive process against termites in the field.
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A termite testing field was created consisting of SYP stakes. These are 18 of
2" x 4"
x 18", (half modified using the inventive processes and half untreated), and
18 of 1" x 1" x
18", (half modified using the inventive process and half untreated), which is
the lumber
industry practice sized standard stake method. These samples were planted in a
controlled
field in Appling, GA and are monitored on a monthly basis. As of this date,
the 2" x "4 stakes
were in the ground for approximately 12 months, and the 1" x 1" stakes, for
approximately 6
months. To date, there has been no termite attacks on either of the 2 x 4 or 1
x 1 modified
stake samples. As shown in Figure 35, a specimen treated by the inventive
process, aged
6 months, at a termite field testing area (a 1" x 1" by 18" stake) shows no
evidence of any
termite attacks since measurements began.
No other methods were applied to deter termite colonies from the field area.
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Example 6. TGA test
TGA (thermographic analysis) test was used in this example to thermally
destruct
eight wood samples made according to the modification process described in the
embodiments of this invention and four conventionally treated lumber samples.
Samples of
the 2 x 4 modified lumber (according to the modification process according to
the
embodiments of the invention) were sent to a reputable University Laboratory
in North
Carolina, where TGA tests were performed on the lumber, as compared to a
control
(untreated) SYP sample, as well as a conventionally (phosphate-based) treated
lumber.
The data is presented in Table 16 and Figures 36A and 36B.
Table 16. Thermograms for Inventor's modified lumber and conventionally
treated
lumber
Sample Residual Mass after Residual
Mass after
Nitrogen Atmosphere (c)/0) Air Atmosphere (
/0)
Control 20.0 0.4
Invention Surface 37.1 11.4
Invention Core 35.9 10.1
Conventional 34.9 5.4
Surface
Conventional Core 18.7 2.2
Figures 36A and 36B show the average thermogram for samples taken from the
surfaces and also the core of the Inventor's modified lumber samples and
conventionally
treated lumber samples. For the outermost surface (Figure 36A), the Inventors'
modified
lumber samples had slightly higher levels of residual char (37.1% vs. 34.9%)
than the
conventionally treated samples, indicating slightly better fire performance.
Both treatments
performed better than the untreated control. The residual char levels for the
samples taken
from the core (Figure 36B) were significantly different, with the Inventors'
modified lumber
sample performing much better than the conventionally treated sample (with
35.9% vs.
18.7% char residue). The core of the Inventors' modified lumber samples all
performed
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better than the control, whereas the conventionally treated sample had a
similar
performance as the control.
These results show that the Inventor's modifications for lumber samples taken
from
the surface and core increased the residual char, which is an early indicator
of fire
resistance. These results also show that the conventionally treated samples
taken from the
core and exposed to either nitrogen or air atmosphere at 700 C more easily
degraded than
the Inventors' core samples. Therefore, the results illustrate that the
modification process
provided an impregnation that penetrated into the 2x4 samples better than the
conventional
treatment.
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