Note: Descriptions are shown in the official language in which they were submitted.
~1'75~3
- 2 - A.F. Turbak et al 10-1-1
This invention relates to microfibrillated cellulose
and to a process for its preparation.
Processes for opening or beating of pulp fibers to
obtain fibrillation, increased surface area, increased accessi-
bility and fine particle size have long been known. Ball mills
of various types are used for preparing cellulose of several
tens of microns in dimension. Studies have indicated that
such ball milling breaks the chemical bonds of the cellulose
during the sub-dividing process. It is also known to grind
cellulose in water under pressure to produce a microcellulose
with a particle size of less than one micron. In the case of
cellulose derivatives, cold milling of the derivatives in
liquid nitrogen is also disclosed in the prior art. Sonic pul-
verization with a ball mill is also a known method of producing
cellulose in extremely fine particle size. Such finely divided
celluloses have been used as low calorie additives to foods
and as thickeners in pharmaceutical products. They are also
widely used as thickeners, extenders and carriers in the cosmetic
and toiletry industry.
Finely divided celluloses are also produced in the
traditional processes used in manufacturing m~chanical pulps,
fiberboard and paper pulp. Normally, however, these traditional
processes involve the use of additional chemical treatment to
available cellulose pulps, as for example, acid hydrolysis or
merceri~ation, which chemically alter or degrade the prepared
cellulose pulps.
In the paper industry, it is well known that paper
strengths are directly related to the amount of beating or re-
fining which the fibers receive prior to formation. However~
-- 2 --
75~
- 3 - ~.F. Turbak et al 10-1-1
beating and refining as practiced in the paper industry are
relatively inefficient processes since large amounts of energy
are expended to gain relatively minor amounts of fiber opening
and fibrillation.
Special forms of cellulose, such as the microcrystal-
line celluloses, are also known. In microcrystalline cellulose,the amorphous, accessible regions of the cellulose are either
degraded or dissolved away leaving the less accessible crystal-
line regions as fine crystals a few tens of microns in size.
In preparing microcrystalline cellulose, it is necessary to de-
stroy a significant part of the cellulose to produce the finalproduct, and consequently, is is quite expensive. In addition,
most of the desirable amorphous reactive part of the fiber is
removed and destroyed leaving only the microcrystals which are
primarily surface reactive.
It is a principal object of the present invention to
produce a new type of cellulose having properties and charac-
teristics distinguishing it from all previously known celluloses.
It is a further object of the present invention to
produce a finely divided cellulosic material which has vastly
increased surface area, greatly improved absorption character-
istics and vastly improved reactivity and binding capability.
It is an additional object of the present invention
to produce a microfibrillated cellulose without substantial
chemical change or degradation of the cellulose starting mater-
ial.
It is still an additional object of this inventionto provide a procesS for producing a very finely divided cellu-
losic material having a number of unusual properties and uses.
The foregoing and other objects of this invention are
-- 3 --
758
- 4 - A.F. Turbak et al 10-1-1
achieved by passing a liquid suspension of fibrous cellulose
through a small diameter orifice in which the suspension is
subjected to a pressure drop of at least 3000 psi and a high
velocity shearing action followed by a high velocity deceler-
ating impact and repeating the passage of said suspensionthrough the orifice until the cellulose suspension becomes a
substantially stable suspension. The process converts the
cellulose into microfibrillated cellulose without substantial
chemical change.
The microfibrillated cellulose of the invention
has a water retention value of over 280%, a settling volume
after 60 minutes in a 0.5% by weight suspension in water of
greater than 60~ and a rate of degradation increase by hydrolysis
at 60C in one molar hydrochloric acid at least twice as great
as cellulose beaten to a Canadian Standard Freeness value of 50.
The invention will be better understood by refer-
ence to the accompanying drawing in which
Fig. 1 is a schematic cross-sec~ional diagram of
an apparatus suitable for carrying out the present invention;
and
Fig. 2 is a graph showing the rate of degradation
increase ~or acid hydrolysis of microfibrillated cellulose
samples of the invention as compared with the c~rresponding
rate for highly beaten pulp.
~5 Figs. 3,4, & 5 are photomicrographs of untreated
pulp fibers (Fig. 3) and of microfibrillated fibers after 5
passes (Fig. 4) and 20 passes (Fig. 5).
A particularly suitable device for carrying out
the invention is a high pressure homogenizer of a type which
-- 4 --
58
- 5 - A.F. Turbak et al 10-1-1
is commercially available and used to produce emulsions and
dispersions. In such a device, energy is applied to a low
viscosity suspension by a high velocity flow through a re-
stricted area. The heart of such a device is a hom~genizer
valve and valve-seat assembly which is attached to the dis-
charge end of a high pressure pump. A typical valve assembly
is shown in Fig. 1 of the drawing. As shown ~y the arrow,
a liquid suspension enters the valve assembly, the valve
assembly being generally identified by the numeral 1, within
the valve seat 2. At this point the liquid is at high press-
ure and low velocity. As the liquid advances to the small
diameter orifice 3 formed in the close clearance area between
the valve 4 and valve seat 2, there is a very rapid increase
in velocity up to as high as 700 ft/second, depending on the
operating pressur~. The pressure drop is measured from the
entrance to the exit side of orifice 3. As the suspension
emerges from between the valve and the valve seat, it impinges
on an impact ring 5 surrounding the orifice and this results
in a high velocity decelerating impact. Orifice 3 must be
small enough to create the required shearing action but must
be larger than the fiber diameter. This will normally tran-
slate into a diameter of about 1/64" to 1/4". Such homogenizers
and their operation are described at various places in the lit-
erature, as for example in an article entitled "Evaluating Homo-
genizers for Chemical Processing" by L.~. Rees which appearedin Chemical Engineering, May 13, 1974, pages 86-92. Reference
should be made to the foregoing literature for a more complete
description of such devices.
The microfibrillated product of the invention is
compared with untreated pulp in the actual scanning electron
-- 5 --
58
- 6 - A.F. Turbak et al 10-1-1
photomicrographs of Figs. 3,4 and 5, all at a magnification
of 500 times. The pulp in each case was a sulfite pulp
from hemlock wood. In Fig. 3, the untreated pulp fibers are
substantially smooth and of a flattened cylindrical shape,
with kinks or bends. In Fig. 4, the fibers, after five passes
through the homogenizer, have been torn apart into their
component layers and fibrils. In Fig. 5, after twenty passes
through the homogenizer, fiber character is no longer apparent.
Lamellar sheets have been explosively dissected into fibrils.
The microfibrillated cellulosic product of the
invention possesses a number of characteristics which render
it uniquely different from other known cellulosic products.
It is not chemically degraded by the process and its degree
of polymerization remains substantially unchanged. On the
other hand, it has a higher degree of fibrillation and greater
~ accessibility than any previously known cellulosic product. In
addition, in both aqueous and organic solvents, the microfib-
rillated cellulose achieves a "gel-point" after repeated passage
through the fibrillating process. The gel-point is characterized
by a critical point in the process at which the cellulosic
suspension rapidly thickens to a more viscous consistency. The
suspension is thereafter substantially stable even after pro-
longed storage. By substantially stable suspension is meant a
suspension in water which upon di~ution to 0.5% and upon standing
for one hour, maintains at least 60% of its original volume, i.e.
contains no more than 40% of clear liquid. Normally, the present
suspensions will maintain at least 80~ of their original volume;
Such stable suspension or gel-points are well known for starch,
5~3
- 7 - ~.F. Turbak et al 10~
but insofar as known, have never previously been observed for
cellulose. The microfibrillated cellulose of the invention
also has a significantly greater ability to retain water than
the most closely related cellulosic products of the prior
art. Water reten~ion is above 280% by weight of cellulose,
usually above 300% and in many instances ranges considerably
higher. Degradation increase by acid hydrolysis, a recognized
measure of accessibility for cellulose are at least twice as
great as highly beaten cellulosic pulp. Comparisons herein
between the properties of the present celluloses and prior art
cellulose are comparisons with celluloses of the same origin,
i.e. celluloses prepared by substantially similar pulping
techniques~ These foregoing and other characteristics of the
product make it uniquely suitable for a wide variety of ap-
plications, some of which are new, including use with paperproducts and non-woven sheets to improve their strength.
In carrying out the invention, cellulosic pulp
or other unregenerated fibrous cellulose is added to a liquid
to produce a cellulosic suspension. A particularly suitable
source of cellulose is regular, fiber-length pulp, derived from
either hardwood or soft-wood, normally available from a pulping
operation or pre-cut if desired. The pulp may be from any of
the well known digestion techniques including both chemical and
mechanical pulping. Virtually any liquid may be used provided
it is chemically inert in the process and imparts sufficient
fluidity to act as a carrier for the cellulose. In addition to
water, such organic liquids as dimethylsulfoxide, glycerine and
lower alcohols may be used. The proportion of cellulose in the
58
- 8 - A.F. Turbak et al 10-1-1
suspension may vary depending, among other factors, on the
size of the homogenizer or other equipment in which the cell-
ulose is microfibrillated. Larger size or commercial scale
homogenizers may use suspensionscontaining larger proportions
of cellulose. Smaller particle size or shorter fiber length
starting cellulose also permits use of larger concentrations
of cellulose. Normally, the suspension will contain less
than about 10% cellulose by weight and preferably the amount
of cellulose will range from 4-7% by weight in commercial scale
operation.
The foregoing liquid suspension or slurry is in-
troduced in the homogenizer and brought to a pressure of at
least 3000 lbs/sq in. (20,670 kilopascals), preferably 5-8000
psi ~34,450 kPa - 55,120 kPa). The slurry is then repeatedly
passed through the homogenizer until the slurry forms a sub-
stantially stable cellulosic suspension. The temperature of
the slurry rises as the slurry is passed through the homogenizer.
It is believed that an interaction of both high pressure drop
and elevated temperature is necessary to produce the micro-
fibrillated cellulose of the invention. To minimize the numberof passes through the homogenizer, the cellulosic slurry should
be initially heated to a temperature of at least 50C, even
more preferab~y at least 80C, prior to the initial introduction
of the slurry into the homogenizer. At pressures of less than
about 3000 lbs/sq in., no amount of heating or processing will
produce a stable suspension.
The following examples are illustrative of the
practice of the invention. Unless otherwise indicated, all parts
and percentages are by weight.
~8
- 9 - A.F. Turbak et al 10-1-1
Example 1
A 2% cellulose slurry in approximately 3 gallons
of water was prepared using prehydrolyzed kraft pulp which
had been cut to pass through a 0.125 inch screen. The slurry
was divided into four portions, each of which was processed
separately. The starting temperatures of the slurries were
25C (room temperature), 60C, 75C and 85C. The slurries
were passed through a r~anton-Gaulin (trademark) homogenizer
at 8000 lbs/sq. in. (gauge) two or more consecutive times
until a stable suspension or gel-point was reached.
The room temperature slurry required 11 passes
through the homogenizer to produce a stable suspension. ~t
the end of seven passes, the temperature had risen to 70C
and at the end of the eleventh pass, the temperature was 95C.
The slurry whose initial temperature was 85C arrived at the
desired endpoint after 2 passes and the final temperature was
96C.
These experiments indicate that for commercial
production of microfibrillated cellulose, it is more economical
to preheat the system than to utilize repeated passes through
the homogenizer.
Example 2
The entire set of experiments set forth in Example
1 was repeated except that 20% of glycerine, based on total
weight of the slurry, was added to the slurry to determine the
effect of a plasticizer on the process. The glycerine did not
lower the gel-point formation conditions significantly. That
is, it ~7as found the gelling beha~ior again occurred with es-
sentially the same number of passes through the homogenizer at
75il~
- 10 - A.F. Turbak et al 10-1-1
the same initial pressures and temperatures.
~xample 3
~ 11 of the experiments of Example 1 were again re-
peated substituting however an organic carrier, dimethylsul-
foxide, for water. ~o significant change in behaviGr was noted,gelling occurred at the same number of passes at the same ini-
tial pressures and temperatures.
Example 4
A series of experiments was run to compare the
water retention characteristics of microfibrillated cellulose
produced in accordance with the invention with microcrystal-
line cellulose and with highly beaten pulp. The microcrys-
talline cellulose used was a commercially a~ailable grade
sold under the trademark Avicel PH-105. The beaten pulp was
pulp which had been beaten in a standard PFI mill to various
degrees of freeness. (A PFI mill is a machine developed by
Papirindustriens Forsknings Institute-The Norwegian Pulp and
Paper Research Institute. It is known throughout the world
as a PFI mill). Table I records the water retention values of
a series of tests of the foregoing celluloses. The water re-
tention of a cellulose material is a measure of its capacity
to retain water when subjected to centrifugal force under con-
ditions selected to remove most of the surface water. Accord-
ingly, the measurement is primarily that of the water held
within the fiber and reflects the degree of Eiber swelling in
water. The water retention values in Table I represent the
percentage by weight of water based on the weight of the ori-
ginal cellulose. For comparison, Table I also records the
water retention values of the starting prehydrolyzed kraft
-- 10 --
i758
- 11 - A.F. Turbak et al 10-1-1
pulp used to prepare both the microfibrillated pulp and the
beaten pulp. The microfibrillated pulps were prepared at pres-
sures of 8000 psi. The CSF (Canadian Standard Freeness) numbers
are a measure (in ml) of how fast the fibers allow water to
drain from a slurry through a screen. The measurement i~ in
accordance with TAPPI Bulletin ,227 r~-58, dated rlay 1943, re-
vised August 1958. A CSF number of 182 is a very highly beaten
pu}p; a CSF number of 749 is essentially an unbeaten pulp.
~ The water retention tests were conducted by allowing
the sample of the aqueous cellulosic suspension to drain in a
cup with a perforated bottom, centrifuging at 3600 rpm (to give
1000 gravities on the sample)for ten minutes and removing and
weighing the cellulosic sample. The sample was then dried in
an oven at 105C for a minimum of four hours and reweighed.
Water retention values were determined by subtracting the oven
dried weight of the sample from the wet weight after centri-
fuging, dividing by the oven dried weight and multiplying by
100 .
75~3
- 12 - ~.F. Turbak et al 10-1~1
TABLE I
Sample .~o. CelluloseWater Retention
1 Untreated Pulp 57
2 Microcrystalline
Cellulose 112
Beaten Pulp
3 CSF 749 ~ - - 57
4 CSF 500 77
CSF 385 84
6 CSF 182 104
Microfibrillated Pulp
7 Unheated - 8 passes 331
8 Preheated to 75C-4
passes 385
- 12 -
11~1'75~
- 13 - A.F. Turbak et al 10-1-1
E~amPle 5
-
An important distinguishing characteristic of the
finely divided cellulosic product of the invention is its abil-
ity to form a substantially stable suspension. A series of
tests was conducted to determine the settling rate of aqueous
suspensions of microfibrillated cellulose. The microfibril-
lated cellulose was prepared from prehydrolyzed kraft pulp cut
to a screen size of 0.125 inch. A 2% aqueous slurry of the
pulp was passed both at initial room temperature and preheated
through a homogenizer as in Example 1 at 8000 psig for from
one to eight passes. The suspension of microfibrillated cel-
lulose was then diluted to produce a 0.5% dispersion of micro-
fibrillated cellulose in water. The stability of the suspen-
sions was determined by measuring the settled volume as a
percentage of original volume after one hour of standing at
ambient temperature. The untreated cellulosic pulp, prior to
passing through the homogenizer, settled essentially immedi-
ately, i.e. did not form an aqueous suspension. The remaining
results are set forth in Table II.
TABLE II
No. of Passes Final Slurry Settled
Sample Through EIomogenizerTemperature CVolume ~
1 1 50 10 (after only
ten minutes
2 1 (preheated 86 38
to 75C)
3 3 68 42
4 5 77 98
8 100 100
6 4 (preheated 100 100
to 75C)
114~758
- 14 - A.F. Turbak et al 10-1-1
Sample 1 was essentially only slightly fibrillated since it
reached a settled volume of 10% after only ten minutes stand-
ing. Samples 2 and 3 were insufficiently fibrillated as they
reached a settled volume of 42% or less after one hour.
Example 6
In order to compare responses of pulps produced
by different pulping processes, samples of sulfite pulps, kraft
(sulfate) pulps and prehydrolyzed kraft pulps were compared
with respect to water retention values after comparable prep-
aration. All samples were prepared by passing from one toeight times through the homogenizer at initial pressures of
8000 psig and ambient temperatures. Results are set forth in
Table III.
TABLE III
No. of
15Sample No. Type of PulpPassesl~ater Retention
1 Sulfite 0 60
2 Sulfite 5 340
3 Sulfite 8 397
4 Kraft 0 100
Kraft 5 395
6 Prehydrolyzed 0 60
Rraft
7 Prehydrolyzed 5 310
Kraft
8 Prehydrolyzed g 330
Kraft
- 14 -
1'75E~
- 15 - ~.F. Turbak et al 10-1-1
While differences do e~ist, all three pulps appear from Table
III to exhibit marked increases of comparable magnitude in
water retention values after from five to eight passes through
the homogenizer.
Example 7
In order to compare the water retention values of
microfibrillated cellulose with those of pulps beaten to var-
ious degrees of freeness by a standard paper beater, a series
of tests was conducted. A variety of pulps was beaten in a
standard PFI disc refiner to various degrees of CS Freeness
(defined above in Example 4) until the maximum possible amount
of beating was reached. Their water retention values were
measured at the various Freeness levels. The results are set
forth in Table IV.
TABLE IV
CS Water
Sample No. Type of PulpFreeness Retention (%j
1 Sulfite 625 170
2 Sulfite 470 210
3 Sulfite 235 220
4 Sulfite 50 265
Kraft 580 165
6 Kraft 380 185
7 Kraft 215 190
8 Kraft 50 195
9 Prehydrolyzed Kraft 540 165
Prehydrolyzed Kraft 315 195
11 Prehydrolyzed Kraft 100 220
12 Prehydrolyzed Kraft 50 245
- 15 -
75~3
- 16 - A.F. Turbak et al 10-1-1
Table IV illustrates that known methods of beating pulp, even
if taken to abnormal and extreme levels, do not give products
similar to mlcrofibrillated cellulose. ~loreover, the severely
beaten pulps differ from the present microfibrillated cellulose
in another important respect, their chemical reactivity, as
brought out in the following example.
Example 8
A valuable measure of the accessibility of cellulose
is that known as the "cuene residue" test. Cuene, or cupriethy-
lenediamine, at 1 molar concentration, dissolves all celluloses,whether it be cotton or unbeaten pulp, without any residue.
As the cuene concentration is decreased, there is an increasing
proportion of residue remaining, depending on relative insol-
ubility. Dilute cuene tests were made on beaten pulps of
various degrees of freeness (beaten in a PFI mill as in example
7 to corresponding degrees of freeness) and on microfibrillated
cellulose. All of the pulps tested were prehydrolyzed kraft
pulp. The microfibrillated cellulose was passed through the
homogenizer at initial pressures of 8000 psig. ~able V sets
forth the percentage of residue for the various pulps when sub-
jected to the diluted cuene tests at 25C at the cuene concen-
trations shown~
~1~175~3
- 17 - A.F. Turbak et al 10-l-1
TABLE V
% Residue
Cuene Beaten Pulp ~icrofibrillated Pulp
Concentration CS Freeness No. Of Passes
(g/ml) 535 309 89 60 1 5 8
.
12 98.2 98.2 95.5 88.2 79.1 69.1
14 92.7 86.3 79.1 77.3 68.2 41.8 30.0
16 33.6 l9.1 11.8
17 9.1 7.2 ~ 5.4
It will be apparent from the above table that the beaten pulps
have significantly more residue and are far less dissolved as
compared to the microfibrillated cellulose. These data demon-
strate that a major change in accessibility occurs if the pulp
is homogenized in accordance with the invention. Optical
photomicrographs of the various pulp samples of this example
showed an unmistakably more open structure for the homogenized
pulps as compared to the most severely beaten pulps.
The microfibrillated cellulose cf the invention
emerges from the homogenizer as a substantially stable suspen-
sion. The foregoing examples have dealt with the preparation
and testing of such microfibrillated cellulose suspensions.
It has been found that drying of the microfibrillated cellulose
modifies its properties and is moreover relatively costly. It
is accordingly preferred that the microfibrillated cellulose
be used in undried form, as an aqueous or organic suspension.
~owever, it may be desirable in certain instances to use dried
microfibrillated cellulose. The following example illustrates
the preparation of microfibrillated cellulose and the subse-
quent drying and testing of the product so produced.
t~
- 18 - A.F. Turbak et al 10-1-1
Example 9
Moist sulfite pulp(370 grams wet 2 100 grams oven
dried weight), which had not been dried subsequent to pulping,
was dispersed in 10 liters of deionized water using a counter-
rotating mixer. The slurry was passed through a homogenizer at
8000 psig and less than 40~C for .ive, ten and twenty passes.
The resulting slurries were freeze-dried. The reactivity of the
microfibrillated cellulose was determined by measuring the dilute
cuene solubility and comparing the results with that of the
starting pulp and of the starting pulp cut to a screen size of
0.125 inch. The cuene solubility tests were carried out with
0.125N Cuene at 25C with a constant temperature shaker bath.
The following table sets forth the percentage of residue of the
microfibrillated cellulose and of the control samples when sub-
jected to the dilute cuene tests.
TABLE_VI
Sample No. Description of ~ Cellulose
Cellulose Residue
1 Untreated Pulp 71.0
2 Untreated Pulp
(cut to 0.125 Screen Size)52.4
3 Microfibrillated - five passes 33.1
4 Microfibrillated - ten passes 14.9
Microfibrillated - twenty passes 5.7
The "Intrinsic Viscosity" (I.V.) of a long-chain
compound such as cellulose describes a viscosity function
which is proportional to the average degree of polymerization
- 18 -
L75B
- 19 - A.F. Turbak et al 10-1-1
(D.P.) of the long-chain compound. The I.V. of cellulose in
cupriethylene~aminesolution is ~nown as the cuene I.V. It
is obtained from a measurement of the fractional increase in
viscosity of the solvent, due to dissolved cellulose (i.e. the
specific viscosity), at a 0.5% concentration of the solute by
extrapolating the viscosity-concentration function to zero
concentration. The following example compares the cuene I.V.
of a series of pulp samples bothbefore and after homogenization.
Example 10
A 1~ total solids slurry in water of sulfite pulp,
which had not been dried subsequent to pulping, was prepared.
The slurry was homogenized at 8000 psig. at 20 and at 90C
for from 1 to 20 passes. The resulting slurries were then freeze-
dried and their cuene I.V.'s determined. The results are set
forth in Table VII.
20-~ - TABLE VII
Sample Temperature ofNumber Cuene I.V.
No. Homogenization Cof Passes dl/g
1 20 0 8.83
2 20 1 8.81
3 20 5 8.46
4 20 10 8.15
7.55
6 90 0 8.66
7 90 1 8.65
8 90 5 8.30
9 90 10 7.86
7.10
-- 19 --
S8
- 20 - A.F. Turbak et al 10-1-1
Table VII illustrates that, as measured by the cuene I.V., the
cellulose is substantially chemically unchanged as a result of
the homogenization treatment.
The microfibrillated cellulose of the invention can
be further characterized by acid hydrolysis rates of the resultant
material as compared to hydrolysis rates for PFI milled or highly
beaten material. The following examples relate to the relative
rates of acid hydrolysis of microfibrillated cellulose as com-
pared to pulp beaten in PFI mills.
Example 11
Prehydrolyzed kraft pulp was beaten in a standard
PFI mill using water as the beating medium. The beating pro-
ceeded to 10,000 revolutions at which point the CS Freeness was
measured as 50 ml. In the realm of the paper industry this
beating goes far beyond what is required for the formation of
paper and begins to approach the limiting conditions for the
PFI machine.
Prehydrolyzed kraft pulp was passed through a Man-
ton-Gaulin homogenizer using water as a carrier, a pressure drop
of 8000 psig and was homogenized at 100C for 9 passes. Acid
hvdrolysis of these samples was carried out at 60C in 1 M HCl
for 1,2,3, and 5 hours. At the end of this time, the hydrolysis
was stopped and the resultant material was exchanged in acetone
and dried under vacuum at room temperature, over-night. Cuene
IV measurements allow for the calculation of the rate of degra-
dation increase. Degradation increase is directly related to
the number of bonds broken during hydrolysis. The rate of bond
breakage is a measure of cellulose open structure or acces-
- 20 ~
5~
- 21 - A.F. Turbak et al 10-1-1
sibility. The rate of degradation increase for the microfib-
rillated cellulose of this example as compared with that of the
highly beaten pulp is shown by the two solid lines in Fig. 2.
~s there shown it is about 3 1/2times as great for the micro-
fibrillated cellulose.Example 12
Prehydrolyzed kraft pulp was beaten in a PFI mill
using glycerine as the beating medium. Beating was carried out
for 5000 revolutions to a measured CS Freeness of 137 ml. Pre-
hydrolyzed kraft pulp ~as homogenized as described in Example11 but using glycerine as the medium, and the comparative
hydrolysis rates were determined in aqueous acid. The rate of
degradation increase as produced by acid hydrolysis was again
found to be significantly greater, 3.2 X as great for the ho-
mogenized pulp as for the beaten pulp both produced in a glyc-
erine medium. The rate of degradation increase for the two
pulps is shown in the two dashed lines in Fig. 2.
Example 13
Prehydrolyzed kraft pulp was beaten in a PFI mill
using propylene glycol as the beating medium. The beating was
carried out to 10,000 revolutions and a measured CSF of 129 ml.
Prehydrolyzed kraft pulp was also homogenized in propylene
glycol under 8000 psig. pres~ure drop. The relative rates of
hydrolysis are shown in the two broken lines in Fig. 2. Again,
the rate of degradation increase by hydrolysis for the homogen-
ized pulp was 2.1 times as great as that of the highly beaten
pulp .
In all cases therefore, pulps treated by homogen-
ization were quantitatively more open or accessible than the
most thoroughly beaten pulp produced in a PFI mill.
75~
- 22 - A.F. Turbak et al 10-1-1
The chemical and physical accessibility of cellu-
lose may also be measured by reaction with cellulase, an
enzyme that hydrolyzes cellulose to release glucose. Accord-
ingly, tests were carried out to compare the accessibility of
microfibrillated cellulose to the action of cellulase enzyme
with that of a number of other finely divided celluloses. The
tests were carried out wi-th Trichoderma viride enzyme, a cel-
lulase comple~ that is able to convert crystalline, amorphous and
chemically derived celluloses quantitatively to glucose (or
substituted gl~cose from derivatives). Tile system is multi-
enzymatic and contains at least tllree enzyme components, all
of which play essential roles in the overall process.
Example 14
A 1% slurry of sulfite pulp, which had not been
lS dried subsequent to pulping was prepared from 50 grams of
pulp suspended in 5 liters of deionized water. The slurry
was llomogenized at 8000 psig at 20C for 0,5 and 10 passes.
The pulp suspensions were freeze-dried.
Samples of the freeze-dried microfibrillated cel-
lulose were then tested for cellulase reactivity. In addition,for comparative purposes, Avicel microcrystaliine cellulose,
Solka-Floc ball-milled cellulose, PFI milled cellulose and a
control sample of sulfite pulp, prior to homogenization, were
also tested for cellulase reactivty. Sol};a-Floc is a trade-
mark for a finely divided cellulose powder made by ball millingdried pulp. The PFI milled cellulose was milled for 12,500
revolutions to a CSF of 100 which was identical to the CSF of
the 10 pass microfibrillated cellulose.
-- 22 -
758
- 23 - A.F. Turba]~ et al 10-1-1
Samples (0.5000g O.D.) were placed in flasks and
50ml of acetate buffer was added. Then 0.0800g of cellulase
enzyme was added. The flasks were placed in a constant tem~-
erature shaker bath at 37 + 1C. After 70 and 170 hours, the
samples were filtered on sintered glass and the filtrate was
analyzed for free sugars by paper chromatography. Only glucose
was detected. The results of cuene I.V. and cellulase tests
are set forth in Table VIII.
TABLE VIII
10 Cellulose ~umber of Cuene I.V. Glucose Released
Sample Passes (dl!g) by Cellulase
Enzyme (mg/50 ml)
70 hrs. 170 hrs
Control Pulp 0 8.83 37.5 41.0
Microfibrillated 5 8.46 77.0 107
~licrofibrillated 10 8.15 92.5 157
Microcrystalline -- 1.16 15 18.5
Ball-Milled -- 4.08 36 47
PFI Milled -- 8.44 66 91
In spite of the small particle size and lower I.V. of the micro-
crystalline and ball-milled samples, they both were less reactive
than either of the microfibrillated samples, and released less
than 1/3 the glucose generated by 10 pass microfibrillated cel-
lulose. The fibers of the PFI milled sample were similarly not
opened as much as the microfibrillated cellulose even though
they both had identical CSF values and only about 60~ of the
slucose generated by 10 pass microfibrillated pulp was released.
- 23 -
11~1'75~3
- 24 - A.F. Turbak et al 10-1-1
Example 1.'
The microfibrillated cellulose of the invention
can be used to impart significant strength increases to paper
sheet structures. Thus, microfibrillated cellulose was pre-
pared from a 2% aqueous slurry of prehydrolyzed kraft pulpwhich had been cut to 0.125 inch screen size and which had
been passed through a homogenizer 5 times at a pressure of
8000 psi. 20,40 and 60% of the microfibrillated,¢ellulose as
a suspension,sald percentages being based on the total sheet
weight, was added to unbeaten prehydrolyzed kraft pulp and
dispersed for 15 seconds in a blender. The slurry was then
formed into hand sheets according to TAPPI method 7504 for
making 1.25 gram hand sheets. The resulting hand sheets had
the following properties:
TABLE IX
Sample Percent added ~eight of Dry Mullen
No. ~icrofibrillated Cellulose Sheet (g) Burst (kPa)
1 0 1.21 56
(control)
2 20 1.]4 99
3 40 1.02 104
4 60 ' 0.82 64
Example 16
Another set of sheets was prepared using 1/2" cut
rayon to make a non-woven sheet. The addition of 20,40 and
60% aqueous microfibrillated cellulose produced as in Example
15 gave the following results.
- 24 -
~1~17~13
- 25 - A.F. Turbak et al 10-1-1
Sample Percent Added Weight of Dry Mull
No. ~licrofibrillated Cellulose Sheet (g) ELB* Burst(kP
1 0 Insufficient adherence
(control) to hold together
2 20 0.64 53 129
3 40 0.70 60 180
4 60 0.68 57 116
*Elrepho Brightness against a black bac]~ground to show sheet
formation.
These results establish that microfibrillated cellulose is val-
uable as a binder for paper and for non-woven construction. Al-
though it may be used in widely varying amounts, it will normally
be added in amounts ranging from 0.5 to 40% of microfibrillated
cellulose solids based on the weight of the paper product or
non-woven sheet.
The foregoing is a description of illustrative
embodiments of the invention, and it is applicants' intention
in the appended claims to cover all forms which fall within the
scope of the invention.
