Note: Descriptions are shown in the official language in which they were submitted.
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Method for Makinfl Dimensionall,X Stable Comaosite Products from
Lignceilulosic Material
Background of the Invention
The present invention relates to a process of making highly dimensionally
stabie composite
products from lignocellulosic material without the addition of synthetic resin
binders and products
produced therefrom where the final product is similar to conventionat high
density products made
with high resin content
The technologies of manufa.cturing wood-based composite products have not
changed
significantfy since their original inception about 80 years ago (Masonite wet
process for
manufacturing thin hardboard). Essentially, the processes involve reducing
wood into fibres,
particies, chips, strands etc, adding synthetic, resins and then consolidating
them under heat and
pressure to produce a composite product. Their physical properties, and
therefore their end
applications, are determined in large part, by the quantity and nature of the
synthetic resins used
to bind them. Urea- and phenol-formaidehyde are the most common resin binders
in use. UF
resin yields wood composite products for interior use, while PF, which is more
expensive, is
usually used in composite products intended for exterior use. Incremental
improvemerrts have
been made by modifications to resins, methods of application, methods of
producing feedstock,
chemical additives for modil"ication of feedstock, orientation of feedstock
and pressing methods.
However, the use of synthetic resins derived from petrochemicals remains as
the main method of
bonding.
One notable exception to the conventlonal processes of manufacturing is the
Masonite process
for thin hardboard, which differs from the conventional dry processes in that
lignin, a component
of wood, is used as a binder- No additional synthetic resins are added.
However, the Masonite
process is "wet," in that significant quantities of water are required to wash
out water solubles,
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which interfere with the bonding process, from the fibre feedstock. The
washing process also
results in about 30% loss of raw material. Furthermore, the resulting product
is limited in
thickness to less than 6 mm and possesses screen marks on the backside. For
these reasons,
only a few wet process hardboard mills remain in operation today around the
world.
One major drawback of conventional lignocellulosic composite products is their
dimensional
stability, measured by thickness swelling and linear expansion. Wood is
hygroscopic in nature. It
will absorb moisture and in a humid environment, it will swell. Conversely,
wood will lose moisture
and shrink in a dry environment. The fluctuation of humidity around the wood
results in
dimensional changes in accordance with the changes of the surrounding humidity
while direct
contact with water causes great dimensional changes. This dimensional change
is undesirable,
particularly in the case of lignocellulosic composite products, such as
particleboard, fibreboard,
oriented strand board and high pressure laminate, because these composite
products are
compressed into a higher density than their original form in order to develop
interfacial adhesive
bonding. Dimensional changes not only weaken the glue bond holding the
products together, but
also result in physical changes which compromise the integrity of the
application for which the
product is used; i.e. warping, cupping, buckling, bowing, splitting and
cracking.
Significant improvement of the dimensional stability of composite products
produced by
conventional methods is very expensive, requiring additional quantities of
resin, longer pressing
times, higher temperature, tempering (addition of oil to hardboard) or
chemical modification of
fibre before pressing into the final product. Generally speaking, a highly
dimensionally stable
composite product from lignocellulosic material made with conventional methods
is not
commercially viable, except for certain specialized and limited applications.
One such product is high density composite. This product can be distinguished
from lower density
composites by its appearance, in which the visibility of fibres or particles
is virtually eliminated, as
the product takes on a plastic like appearance and texture, and improved
physical properties,
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demonstrating lower thickness swelling than their lower density counterparts.
Generally speaking,
this type of product is achieved by using very high quantities of synthetic
resins (generally, in the
range of 30 - 60 %) mixed with lignocellulosic materials, which are then
consolidated under heat
and high pressure to produce a very dense, and tough, water resistant product,
with a density of
around 1300 - 1500 kg/m3. However, the costs of production are extremely high
due to the high
resin content, and the use of Kraft paper impregnated with phenolic resin as a
feedstock,
resulting in limited use of these products.
One method of producing a high density composite with a thickness of 7.0 mm
involves the
assembly of 44 layers of resin impregnated Kraft paper (consisting of I
overlay paper
impregnated with melamine resin, 1 decor paper impregnated with melamine
resin, 41 Kraft
papers impregnated with phenol resin and I balance paper impregnated with
melamine or phenol
resin). When consolidated under heat and pressure, the resulting product
retains a uniform,
plastic like appearance. However, the laminated material has the disadvantage
of low
dimensional stability under varying climatic conditions. In particular, the
plate expands or shrinks
significantly more in the transverse direction than the longitudinal direction
as a result of the
orientation of fibres in the Kraft paper feedstock.
An improvement of the paper layering method of producing high density
composite product is
taught in the US patent 4,503,115, entitled "Plate shaped moulded article and
process for its
preparation and use." In that patent, lignocellulose fibres are pressed
together with thermosetting
synthetic resins in the proportion 15 to 45% by weight to dry fibre, to a
density between 900 to
1600 Kg/m3. The use of the fibre has the advantage of reducing costs, as the
fibre is cheaper
than Kraft paper, and improving the linear expansion properties, as the
elimination of paper also
eliminates the problem of differing dimensional variations resulting from the
fibre orientation of the
Kraft paper. However, the raw material costs of this method remain high, due
to the high content
of expensive resins, resulting in limited applications of the product.
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A product that requires a high degree of dimensional stability, and
particularly low levels of linear
expansion, is laminate flooring. Laminate flooring is produced according to
two general methods.
The less expensive method of more recent development is the direct pressure
lamination process
(DPL) which involves pressing an abrasive resistant paper and melamine
impregnated decorative
paper on top of a fibre or particle coreboard with a melamine impregnated
balance paper on the
bottom of the coreboard. This laminate flooring is very popular. A second
method to manufacture
laminate flooring is by high pressure laminate (HPL). In the HPL process an
abrasive resistant
paper and melamine impregnated decorative paper and several sheets of phenol
impregnated
Kraft paper are assembled and pressed to a density of approximately 1,400
Kg/m3, for a
relatively long time at a relatively high temperature. The resulting high
pressure laminate is
sanded on one side to improve its glue ability to the core board. The balance
laminate is
produced in a similar manner, being assembled with melamine and/or urea
impregnated papers
on the top and bottom with several sheets of phenol impregnated Kraft paper in
the middle. The
balance laminate is also sanded on one side to provide a suitable surface for
gluing. The method
to produce laminate flooring according to the HPL method is to assemble on the
top a decorative
HPL laminate (typically between 0.6 - 0.8 mm), in the middle, a core board of
high density
fiberboard or high density chipboard (density between 800 and 900 Kg/m3), and
on the bottom, a
balance laminate (typically between 0.6 - 0.8 mm). Laminate flooring by the
HPL method is widely
considered to be of better quality than the DPL method; however, because of
the higher costs
associated with the HPL method it is not as popular as the DPL method.
According to a European
consumer report, the best HDF core board has a thickness swelling of 7%.
In US patent 5,017,319, EP 0,492,016, Canadian Patent 1,338,321 and EP
0,161,766, there is
disclosed another process for making thermosetting resin adhesive and
composite products from
lignocellulosic material without the addition of synthetic resin. This process
involves first using
high pressure steam to decompose and hydrolyze the hemicellulose fraction,
which accounts for
20-30% by weight of the lignocellulose, into low molecular weight water
solubles. These water
soluble materials are then utilized as a thermosetting adhesive to bond "in
situ" the other
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components; i.e. the cellulose and lignin fractions of the lignocellulosic
material under heat and
pressure in a moulding operation to produce a reconstituted composite product.
Since
hemicellulose is one of the components of wood that is most hygroscopic and
therefore most
responsible for dimensional change in natural wood, its destruction renders
the reconstituted
product less hygroscopic and enhances dimensional stability. Furthermore,
these patents also
teach a secondary thermo-hydrolysis targeting and converting the cellulose
fraction into water
soluble resin material for the production of reconstituted composite products.
In addition, the low molecular weight water solubles derived from
hemicellulose decomposition
are able to permeate cell wall tissues and fill voids in the cellulose fibres,
acting as a bulking
agent. During the hot pressing operation, these water solubles polymerize,
thermoset, and
become water insoluble, thus eliminating or reducing water absorption. This
bulking effect also
enhances the dimensional stability of the reconstituted composite product.
Thus, the water
solubles, derived from hemicellulose decomposition, act as both a bonding and
bulking agent to
produce a moulded composite product with good mechanical strength and
dimensional stability.
The lignin fraction, comprising 20 - 25 % by weight of the lignocellulosic
material, although
decomposed and hydrolyzed by the high pressure steam into low molecular weight
lignin and
lignin decomposition products, which are water insoluble, is left in the
hydrolyzed lignocellulosic
material as a filler,. The cellulose fibre (accounting for 45 - 50 % of
lignocellulose), which is not
affected by the first steam treatment and which retains its physical integrity
and is used as the
backbone of the reconstituted composite product. The water soluble material
functions as an
adhesive, bonding "in situ" cellulose fibre and lignin together to yield a
reconstituted composite
product. The novelty of this process lies in the use of hemicellulose
decomposition products as a
binder, to improve physical properties of the composite products thus
produced. The elimination
of synthetic resin binders represents a significant breakthrough and
improvement over
conventional methods of manufacturing composite lignocellulosic products.
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SUMMARY OF THE INVENTION
We have now discovered that the low molecular weight iignin and lignin
decomposition products,
which are encrusted on the ceitulose fibres and which are not water-soluble,
can be used to
function as a bonding agent under high pressure moulding In the manuFaoture of
high density
composite products. It Is belleved that, under high pressure and heat during
the moulding
operation, the lignins beoome plasticized, melt and flow, in conjunction with
the water solubles
from hemicellulose hydrolysis andlor cellulose hydrolysis to develop an
adhesive bond, thus
further strengthening the physical properties. In addition, the densification
of the product under
high pressure, combined with the bulking effect of the hydrolyzed
hemiceliukme, eliminates
virtually all remaining voids in the material, further enhancing the product's
water resistance.
Another posslbility is that as the lignin decomposition products have
undergone an
autocondensation in which the function groups of the side chain, the phenolic
hydroxyl groups
and the reactive carbon atoms of the aromatiC rings are involved to form
bonding. The resulting
composites, produced without the addition of any synthetic resins, are
superior, partlcularly in
dimensional stability to those high density products manufactured according to
conventional
methods using large amounts of synthetic resins. In terms of economics, the
produCtion costs for
the high density composite product is estimated to be 50 - 60 % lower than
that for conventionaily
produced high density cornposites, 1=urther cost savings can be realized from
use of non-wood,
alternative feedstocks, such as agricultural residues.
In accordance with one embodiment of the present Invention there Is provided a
method of
making a dimensionally stable composite product from lignooellulosic materiai
comprising:
a) bringing the lignocellulosic material in dfvided form into oontact with
high pressure
steam at a temperature high enough to decompose and hydrolyze hemicellulose
and
lignin contained in said lignocellulosic material without carbonization
thereof;
b) maintaining the lignocellulosic material in contact with high pressure
steam for a time
sufficient only for the decomposition and hydrolysis of hemicellubse into
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hexose sugars, sugar poiymers, furfural products, dehydrated carbohydrate,
organic
acids of lignin into and low molecular weight lignins and other lignin
decomposition
products, with negligible degradation of celluiose;
c) drying the hydrolyzed lignocellulosic material;
d) forming the iignoceliulosic material in comminuted form, e. g. as fiber or
particies, into
a mat or web;
e) compressing the said mat or web at a temperature and a pressure for a
sufficient time
to polymerise, cross-link, and thermoset the water-soluble resin nraterial and
iignin
decomposition products into an adhesive which forms a bond 'in situ' yielding
a
reeonstituted composite product_
In the method according to the Invention the hydrolyzed lignocellulosic
material may be
comminuted into fiber or particie form (e.g. before or after drying) or
rendered Into such fprm by
explosive discharge from a vessel in which the lignocellulosic materiai has
been subject to step a)
and b)_
in acxordanee with the present invention there is provided a method of making
a dimensionally
stable composite product from lignoceliuiosic material, comprising:
a) bringing the iignoceiiuiosic materiaf in divided form into contact with
high pressure
steam at a temperature high enough to decompose and hydroiyze hemicellulose
and
lignin contained in said lignocellulosic materiai without carbonization
thereof;
b) maintaining the iignoceiiuiosic material in contact with high pressure
steam for a time
sufficient only for the decomposition and hydrolysis of hemicellulose into low
molecular weight, water~soiubie resin material including (or comprising)
pentose and
hexose sugars, sugar polymers, furrural products, dehydrated carbohydrate and
organic acids of lignin Into and low molecular weight lignins and other lignin
decomposition products, with negligible degradation of cellulose;
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c) drying the hydrolyzed lignocellulosic material;
d) forming a residue of the lignocellulosic material, in comminuted form, e.g.
as fiber or
particles, together with low molecular weight, water-soluble resin material
including (or
comprising) pentose and hexose sugars, sugar polymers, furfural products,
dehydrated carbohydrate and organic acids derived from decomposition and
hydrolysis of one or more of hemicellulose and cellulose, into a mat or web;
and
e) compressing the said mat or web at a temperature and a pressure for a
sufficient time
to polymerise, cross-link, and thermoset the water-soluble resin material into
an
adhesive which forms a bond "in situ" yielding a rigid reconstituted composite
product,
the.low molecular weight lignins and other lignin decomposition products
formed in
step b) also contributing to forming the bond.
The pH of the residue may be adjusted before the thermosetting in step e).
In a first preferred aspect of the invention, water-soluble resin material in
steps d) and e) is at
least in part the water-soluble resin material produced in step b) and the mat
or web also includes
low molecular weight lignins and other lignin decomposition products formed in
step b), such
lignin decomposition products also contributing to forming the bond in step
e). In this aspect of
the invention it is not normally necessary to adjust the pH.
In a second preferred aspect of the invention the method further comprises,
subsequent to step
b) and prior to step c)
i) separating the water-soluble resin material derived from hemicellulose from
the
lignocellulosic material and concentrating the separated water-soluble resin
material,
by evaporation, into a thermosetting resin material suitable for use as a
thermosetting
waterproof resin adhesive;
ii) bringing the previously hydrolyzed lignocellulosic material, from which
the water
soluble resin material derived from hemicellulose has been removed, in contact
with
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high pressure steam for a second time and for a time sufficient for the
hydrolysis and
decomposition of a major (or minor portion) of the cellulose into water
soluble resin
material including hexose and pentose sugars, sugar polymers, furfural,
dehydrated
carbohydrates, organic acids and other decomposition products; and
iii) drying the residue of the hydrolyzed lignocellulose (the residue
comprising mainly the
water-soluble material from the cellulose hydrolysis, low molecular weight
lignins and
other lignin decomposition products and residue of cellulose fibre);
and wherein in steps d) and e) the water soluble resin material is that
produced in step ii), the mat
or web also including low molecular weight lignins and other lignin
decomposition products
formed in step b) and which also contribute to forming the bond.
An acid or acid catalyst may be used prior to step ii) to adjust the pH of the
previously hydrolysed
lignocellulosic material from which the water-soluble resin material derived
from hemicellulose
has been removed.
This invention thus relates to a process for making dimensionally stable
reconstituted composite
products from lignocellulosic material. By treating lignocellulose with high
pressure steam to
decompose and hydrolyse the hemicellulose and/or cellulose and lignin
fractions of the
lignocellulose and using those decomposition products as both a bonding and
bulking agent, it
converts, under heat and pressure in a moulding operation, the treated
lignocellulose into
moulded composite products such as panel boards and moulded articles, which
are preferably
stiff or rigid and are preferably of high density and fully thermoset. The
composite products thus
produced possess good physical and mechanical properties. Specifically, the
dimensional
stability in terms of the thickness swelling and linear expansion of panel
boards such as
fibreboards and particleboard can be minimized to very low levels when the
panel boards are
made in high density. The adhesive bond developed from thermosetting of the
decomposition
products of hemicellulose, cellulose and lignin is strong and stable, and
resistant to boiling water
and acid hydrolysis, and is free of formaldehyde emissions. Thus the
reconstituted panel boards
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and moulded products are suitable for exterior and particularly for indoor
applications. The
absence of free formaldehyde emissions makes the product very suitable for
interior applications.
The manufacturing cost for the reconstituted products is significantly lower
in comparison to the
conventional process because expensive synthetic resin is not used.
Example 1.
This example demonstrates the pre-treatment of thermo-hydrolysis by high
pressure steam of
lignocellulose, followed by hot pressing and densification of the hydrolyzed
lignocellulose into a
moulded product.
Fresh spruce and hard maple planar shavings of about equal parts, containing
approximately 22
% moisture content were loosely loaded and packed into a pressure vessel.
After sealing the
vessel, high pressure steam of 447 psi (240 C) was introduced. The steam
pressure was
maintained at 447 psi for 90 seconds after which the outlet valve of the
pressure vessel was
instantaneously opened with an explosive discharge. The treated lignocellulose
was collected in a
bin through a cyclone that separated the material and steam. The hydrolyzed
planar shavings
were reduced into shredded fibers and fine particles, dark brown in colour
with high moisture
content. The water soluble resin material from hemicellulose hydrolysis
contained about 18 %
sugars and a pH of 3.7. Similarly, the lignin fraction was also decomposed
into lignin
decomposition products of low molecular weight, which was water insoluble, and
was encrusted
on the surface of the cellulose fiber and particles. This hydrolyzed
lignocellulose was dried to low
moisture content of about 3 %. The dried material was formed into a mat of
predetermined size
and weight that was then compression moulded into a single layer, homogeneous
plate of 8 mm
thickness. One mould temperature of 200 C was used with a press time of 20
minutes, which
included a cooling time of 5 minutes. The pressing pressure ranged from 300 to
1050 psi,
depending on the density of the panelboard pressed. A total of 5 plates (400 X
400 X 8 mm), of
different densities were made and tested. Mechanical and physical properties
were tested in
accordance with ASTM D-1037. Additional tests for wet M.O.R. after 2 hour boil
were performed
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in accordance with CAN0188.0M78 - National standard for exterior grade wood
based panel
board. The plates were tested for free formaldehyde emissions and the result
was 0.1 mg/m2h,
according to the gas analysis method (norm PN-D-97013:1999). This level of
formaldehyde
emissions classifies the product with an EO rating which is the most stringent
formaldehyde
emissions standard for the composite panel industry. This low level of free
formaldehyde
emissions will achieve the newly proposed European standard for "F-zero" or
"formaldehyde free
bonded" boards. Test results are listed in Table 1. Figure 1 clearly
demonstrates the bonding
capability of lignin in high density panelboards in which the internal bond
strength exhibits an
exponential increase. It is also very interesting to note that the colour of
the higher density
panelboards was dark brown and their plastic like texture were very similar to
commercial high
pressure laminate made with Kraft paper and phenolic resin. Lignins are
believed to be the
natural binder in lignocellulose and are chemically, phenolics in nature;
therefore, it is possible,
that when low molecular weight lignins and other lignin decompositon products
are thermoset,
under heat and pressure, they develop an adhesive bond resembling the bond
derived from a
phenol-formaldehyde resin.
Table 1. Physical and mechanical properties of 8 mm spruce:maple plates
Board Density MOR MOR MOE Internal Swell 24 hr L.E. (%)
No. Kg/m3 (MPa) (MPa) (MPa) Bond cold water
Dry Boil 2 hr (MPa) soak (%)
A 760 13.5 3.2 1400 0.35 15.6 0.24
B 920 26.7 12.6 3050 0.87 7.8 0.20
C 1060 45.3 21.7 4930 1.36 3.6 0.17
D 1210 60.2 32.3 7120 2.16 2.7 0.17
E 1380 82.6 44.3 9540 > 3.0 < 1.0 0.16
Example 2.
This example demonstrates the use of higher pressing temperature and/or longer
pressing time
to enhance the dimensional stability, particularly the thickness swelling of
lignocellulose panel
boards. Fresh maple chips containing about 57 % moisture content was treated
with high
pressure steam (198 C) for about 8 minutes. The treated maple chips were fed
through a disc
refiner under a steam pressure of 6 bars to process the treated maple chips
into fibers. The wet
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fibers were dried by hot air to a moisture content of 3 - 5 %. The dry fibers
were felted into a mat
400 X 400 mm. A total of 8 mats were made in an identical manner. These 8 mats
were hot
pressed at a platen temperature ranging from 160 - 220 degrees Celsius and
pressed for a time
ranging from 2- 4 minutes. Target thickness was 8.0 mm and target density was
1,050 Kg/m3.
Test results are listed in Table 2. It is evident that mechanical properties
were not significantly
affected by the higher press temperature and long press times. However, the
dimensional
stability, i.e., thickness swelling and linear expansion of the maple fiber
boards are significantly
reduced by the higher press temperature and longer press times.
Table 2. Physical and mechanical properties of 8 mm maple fiberboards
Press Press Density M.O.R. M.O.E. Internal 24 hr cold 2 hr boil L.E.
Temp. Time (Kg/m3) (MPa) (MPa) Bond water water (%)
de C) min (MPa) swell % swell %
160 2 1030 48.6 5460 1.7 9.6 20.2 0.19
160 4 1050 52.2 5840 1.9 7.4 16.6 0.18
180 2 1040 48.6 5570 1.9 8.5 15.2 0.19
180 4 1070 53.6 6020 2.1 8.0 10.7 0.17
200 2 1060 54.3 6330 2.4 6.3 13.5 0.17
200 4 1070 54.8 6480 2.6 5.5 10.2 0.16
220 2 1050 54.6 6350 2.6 4.2 10.8 0.15
220 4 1070 55.2 6320 2.7 2.7 9.2 0.14
Example 3.
This example illustrates the flexibility of the inventive process for making
preformed semi-rigid,
partially cured sheets in the thickness range of 6 to 12 mm to a density
between 550 to 900
Kg/m3 for future processing into high density composite plates. The preformed
sheets of
fibreboard can be effectively and economically produced on a continuous press.
The semi-rigid
sheets are easily handled in a subsequent operation to yield a final composite
product, or readily
packed for shipping or storage, in contrast to the soft and fragile mats used
in conventional
processes.
Mixed beech and pine wood chips at a ratio of 65:35, by volume, were
continuously loaded into a
digester (chip cooker) at a commercial medium density fiberboard plant. The
chips were cooked
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under a steam pressure of 12 bar (190 C) for about 10 minutes and then
extruded continuously
through a pressurized refiner with counter-rotating disc plates that
comminuted the steam treated
wood chips into fibers and fiber bundles. The fibers were dried in a flash
tube dryer to a moisture
content of 5 %. The dried fibers were conveyed to a forming station and felted
into a continuous
fiber mat, which was pre-pressed to remove excess air, and pressed in a
continuous press under
heat (180 C maximum temperature) and pressure to transform the soft mat into a
semi rigid and
rigid panel of a pre-determined thickness and density. Thickness ranged from 6
to 12 mm, and
density ranged from 520 to 900 Kg/m3. The consolidation of the preformed
sheets was due to the
adhesive bond developed by the water soluble resin material which was derived
from the
hemicellulose hydrolysis during the steam treatment of the wood chips. These
preformed sheets
were cut to size for secondary processing into final composite products and
packed for shipping
or storage.
Example 4.
This example shows the densification of preformed sheets into high density
composite
panelboards. The pre-formed rigid MDF sheet, 10 mm thick, 700 kg/m3 density,
containing less
than 2% moisture content was, in a second operation, compressed into high
density fiberboard.
Two of the pre-formed MDF sheets were placed in a single daylight press. They
were pressed
under a specific pressure of 1,100 psi and a platen temperature of 165 Celsius
for 25 minutes. At
the end of the heating period the platen temperature was lowered to about 70
Celsius in about 3
minutes. At this time the pressure was reduced to 0 and the press was opened.
The average
density of this high density 10 mm fiber board was 1,370 Kg/m3. Bending
strength (MOR) was
87.5 MPa, MOE: 9,740 MPa, Internal Bond: > 3.5 MPa, thickness swelling after
24 hour soaking:
1- 2 %, and after 2 hour boiling: 4 - 6 %, linear expansion in the length of
0.17 % and linear
expansion in the width of 0.16 %.
Example 5.
This example demonstrates the manufacture of high density laminate flooring
board from
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preformed MDF sheets at a commercial manufacturing facility. Pre-formed
sheets, 6 mm in
thickness, with a density of 680 Kg/m3 were assembled in the following manner.
From the top the
stratification of the assembly was 1) a melamine impregnated overlay
protective paper 2) a
melamine impregnated decorative paper 3) two preformed MDF sheets panels, 4) a
melamine
impregnated balance paper. The total assembly was placed between two stainless
steel caul
plates and placed in the press for densification. The same pressing conditions
were used as in
Example 4 with the exception that the press heating time was 35 minutes, in
order to improve the
dimensional stability of the final product. The panels after pressing and
cooling were cut to a size
of a 195 X 1305 mm and profiled with a tongue and groove for laminate
flooring. This 5.9 mm
thick laminated flooring board had a density of 1,410 Kg/m3, bending strength
(MOR): 102 MPa,
MOE: 12,470 MP, Internal bond > 3.5 MPa, surface strength > 3.5 MPa, 24 hour
cold water
soaking (center): 0.0 %, edge swelling: 2.8 %, linear expansion in the length
of 0.15 % and linear
expansion in the width of 0.14 %. The extended press time under heat further
reduced the
thickness swelling. The best laminate flooring board on the market today
claims a core board
center swell of 7.0 % after 24 hour cold water soaking.
Example 6.
This example demonstrates a method to make laminated flooring board with
superior mechanical
strength and dimensional stability, i.e., virtually no thickness swelling
after 24 hours immersion in
cold water.
The raw material preparation and production of the preformed MDF sheets was
identical to
example 2 however, the preformed MDF sheet had a thickness of 12 mm and a
density of 800
Kg/m3. The preformed MDF sheet was assembled with melamine resin impregnated
papers.
From the top the stratification of the assembly was 1) a melamine impregnated
overlay protective
paper 2) a melamine impregnated decorative papers 3) a preformed MDF sheet or
panel as
coreboard, 4) a bottom melamine impregnated paper. A stainless steel caul
plate with wood grain
etched structure was placed on top of the assembly, and a glossy smooth caul
plate was placed
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on the bottom of the assembly. The entire assembly was carried into a single
opening press and
pressed under a specific pressure of 1,100 psi or 800 N/cm2 with a platen
temperature of 165
deg C. The heating time was 20 minutes at 165 degrees Celsius, and then the
platen temperature
was reduced to 65 degrees Celsius in about 3 minutes. The pressure was reduced
to 0 and the
press was opened. The consolidated panel of 6.9 mm, and 1410 kg/m3 density,
was cut into to a
size of a 195 X 1305 mm and profiled with an interlocking tongue and groove as
laminated
flooring board.
The mechanical and physical properties of the 6.9 mm laminated flooring board
were tested in
accordance with EN 13329, DIN EN 311, 319, 310, DIN EN 438-2.18 and ISO 2813.
Test results
are listed in Table 3.
Table 3. Physical and mechanical properties of 6.9 mm laminated flooring board
Test Standard Unit Result
Thickness EN 13329 Mm 6.9
Surface tightness Werkstandard PV 054 Grade 5
Hardness Werkstandard PV 010 Grade 1
Resistance against cigarette DIN EN 438-2.18 Grade 5
Impact resistance (small ball) EN 13329 N 12
Impact resistance (big ball EN 13329 mm 1900
Abrasion resistance EN 13329 Umdr. 4000
Edge swelling EN 13329 % 1.89
Edge swelling after redry EN 13329 % 0.06
Linear expansion length EN 13329 % 0.15
Linear expansion width EN 13329 % 0.14
Linear contraction length EN 13329 % - 0.04
Linear contraction width EN 13329 % - 0.06
Surface Soundness DIN EN 311 N/mm2 >4
Internal Bond DIN EN 311 N/mm2 >4
Modulus of Rupture DIN EN 311 N/mm2 91.35
Modulus of Elasticity DIN EN 311 N/mm2 12000
Gloss (60 deg) ISO 2813 19.8
Example 7.
This example demonstrates the advantages of using preformed low density
fiberboard (LDF)
sheets for the production of three-dimensional doorskins in a separate
operation. The preformed
sheets were produced at a commercial fiberboard plant as described in Example
3. The
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preformed sheets of LDF were 6.3 mm thick with a density of 550 Kg/m3 and had
a moisture
content of 2 - 3 %. The LDF sheets were packed at the MDF plant and shipped to
the doorskin
factory for densification into three dimensional doorskins. The semi-rigid
preformed sheets were
first sprayed with water at a rate of 30 gr/m2 on both sides of the preformed
sheet. After water
spraying, the preformed sheets were positioned directly in the moulding press
for densification
and thermosetting to produce a rigid doorskin. The moulding temperature was
185 C,
densification pressure of 500 psi (54.5 Kg/cm2) and a press time of 75
seconds. The moulded
doorskin was 3.2 mm thick with a density of 1040 Kg/m3. MOR: 47 MPa, MOE 6.5
GPa, IB 1.58
MPa, thickness swelling after 24 cold water soak 14.3 %. The surface of the
doorskin was tight
and smooth. The moulded doorskin did not show any stress marks or weak spots
along the
contour or deep profile area indicating the good mouldability and flow
property of the preformed
sheets when pressed in the mould under heat and pressure. Here again, the
presence of the
decomposed lignin acting as lubricant in the preformed LDF sheet improved and
promote the
mouldability of the preformed sheet.
Example 8.
This example illustrates the use of agricultural by-products of rice husks and
sugar cane bagasse
for the production of high density panelboard.
Rice husks with a moisture content of 8 - 9 % and fresh sugar cane bagasse
containing 40 - 45 %
M.C. were mixed in equal portion based on the oven dry weight and treated with
high pressure
steam of 475 psi (240 C) for 60 seconds. The treated mixture was instantly
expelled from the
treating vessel with an explosive discharge which rendered the lignocellulosic
material in fine
powdery particles. The treated material was dried to about 2 % moisture
content and formed into
a mat of 400 X 400 mm. The mat was compression moulded under a pressure of
1200 psi (83
Kg/cm2), a platen temperature of 165 C, a moulding time of 25 minutes
(including a cooling time
of 5 minutes), into a high density plate of 8 mm thickness with a density of
1460 Kg/m3. This
moulded plate was very hard with a MOR: 52.2 MPa, MOE: 6.3 GPa, IB: >3.5 MPa,
Hardness: >
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40 KN, thickness swelling <1.0 % and a linear expansion of 0.18 %, and 0.19
respectively with
regard to direction of the plate thus indicating the isotropic nature of the
plate. The linear
expansion was measure on a sample first oven dried for two hours and measured
again after
immersion in cold water for 24 hours. This is a quick test method according to
the norm
CAN3.0188.3-M82, Exterior Bond Mat Formed Wood Particleboard, which measures
the linear
expansion from changes in relative humidity from 50 % to 90
Example 9.
This example illustrates the conversion of the cellulose fraction into water
soluble resin material
for the production of reconstituted composite products.
Mixed beech and pine wood chips, which had been steam treated at 12 bar
pressure for 10
minutes, as described in Example 3, (i.e., hydrolyzed lignocellulosic
material) were eluted once
with hot water to extract a major portion of the water soluble resin material.
Subsequently the
chips were sprayed with a solution of dilute sulfuric acid that contained
about 0.8 % sulphuric
acid, by weight, to the chips. The acid treated chips were steam treated for a
second time at 15
bar pressure for 12 minutes to convert a major portion of the cellulose into
water soluble resin
material. At the end of the steam treatment, the steam pressure was suddenly
released and the
hydrolyzed chips were expelled from the treating vessel with an explosive
discharge that reduced
the wood chips into fine particulates. The hydrolyzed material was wet, grey
in colour and had a
consistency similar to pot soil. The material consisted of lignin
decomposition products, water
soluble resin material, and residue of cellulose fiber. Prior to drying the
material, a solution of
sodium hydroxide was added to the wet hydrolyzed material to adjust the pH to
about 3.5. After
drying the hydrolyzed material had a moisture content of 3 - 5 %, and was
ready as a feed stock
for the production of reconstituted composite product. A laminate flooring
board with a thickness
of 6.9 mm was fabricated following the same procedure as described in Example
6. The physical
properties of this laminated flooring board was very comparable to that of
laminated flooring
boards that were produced from beech and pine wood chips which were thermo
hydrolyzed only
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once. Interestingly, an edge swelling after 24 hours cold water soaking of 1.3
% versus 1.9 %,
indicates an improved dimensional stability that could result from the
cellulose hydrolysis and the
high content of lignin decomposition products in this laminate flooring board.
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