U.S. patent application number 10/409762 was filed with the patent office on 2004-10-14 for method of making pulp having high hemicellulose content.
Invention is credited to Bourree, Grant R., Herring, William J., Jack, David B..
Application Number | 20040200589 10/409762 |
Document ID | / |
Family ID | 33130647 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040200589 |
Kind Code |
A1 |
Herring, William J. ; et
al. |
October 14, 2004 |
Method of making pulp having high hemicellulose content
Abstract
Bleached, Kraft chemical pulp having increased hemicellulose
content compared to conventional Kraft chemical pulps. In one
embodiment, the pulp has a hemicellulose content greater than about
17 weight percent as measured by the 18% caustic solubility test.
In another aspect, a method for making wood cellulose pulp having
increased hemicellulose content compared to conventional Kraft
chemical pulps. In the method, a lignocellulosic material is pulped
in caustic sulfide to provide a first brownstock, which is treated
with oxygen to provide a second brownstock, which is then bleached
to provide the pulp product.
Inventors: |
Herring, William J.; (Kent,
WA) ; Jack, David B.; (Federal Way, WA) ;
Bourree, Grant R.; (Grande Prairie, CA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY
INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Family ID: |
33130647 |
Appl. No.: |
10/409762 |
Filed: |
April 8, 2003 |
Current U.S.
Class: |
162/82 ; 162/65;
162/72; 162/88; 162/89 |
Current CPC
Class: |
D21H 11/10 20130101;
D21C 3/02 20130101; D21H 27/10 20130101; D21C 9/147 20130101; D21C
3/222 20130101; D21C 9/14 20130101; D21C 9/16 20130101 |
Class at
Publication: |
162/082 ;
162/072; 162/065; 162/088; 162/089 |
International
Class: |
D21C 003/20; D21C
009/14; D21C 009/147 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for making a chemical pulp, comprising: (a) pulping a
lignocellulosic material in caustic sulfide to provide a first
brownstock, wherein the caustic sulfide comprises polysulfide and
anthraquinone; (b) treating the first brownstock with oxygen to
provide a second brownstock; and (c) bleaching the second
brownstock to provide a bleached pulp.
2. The method of claim 1, wherein the polysulfide is present in an
amount from about 4 to about 9 g/L in the white liquor.
3. The method of claim 1, wherein the anthraquinone is present in
an amount from about 0.03 to about 0.1 percent by weight based on
the weight of lignocellulosic material.
4. The method of claim 1, wherein the kappa number after pulping is
in the range from about 20 to about 65.
5. The method of claim 1, wherein the kappa number after pulping is
in the range from about 36 to about 43.
6. The method of claim 1, wherein treating the first brownstock
with oxygen comprises treating with oxygen at a pressure between
about 80 and about 120 psi and at a temperature from about 90 to
about 130.degree. C.
7. The method of claim 1, wherein the kappa number after treating
with oxygen is in the range from about 8 to about 35.
8. The method of claim 1, wherein bleaching comprises bleaching
without elemental chlorine.
9. The method of claim 1, wherein bleaching comprises bleaching
with chlorine dioxide.
10. The method of claim 1, wherein bleaching comprises at least two
chlorine dioxide bleaching stages.
11. The method of claim 1, wherein bleaching comprises an alkali
extraction stage.
12. The method of claim 1, wherein bleaching comprises bleaching
without chlorine.
13. The method of claim 1, wherein bleached pulp has a
hemicellulose content greater than about 17 weight percent as
measured by the 18% caustic solubility test (TAPPI T-235
CM-00).
14. A method for making a chemical pulp, comprising: (a) pulping a
lignocellulosic material in caustic sulfide to provide a first
brownstock, wherein the kappa number after pulping is in the range
from about 20 to about 65; (b) treating the first brownstock with
oxygen to provide a second brownstock; and (c) bleaching the second
brownstock to provide a bleached pulp.
15. A method for making a chemical pulp, comprising: (a) pulping a
lignocellulosic material in caustic sulfide to provide a first
brownstock; (b) treating the first brownstock with oxygen to
provide a second brownstock; and (c) bleaching the second
brownstock to provide a bleached pulp, wherein bleached pulp has a
hemicellulose content greater than about 17 weight percent as
measured by the 18% caustic solubility test (TAPPI T-235 CM-00).
Description
FIELD OF THE INVENTION
[0001] The present invention relates to cellulose pulp and, more
particularly, to chemical pulp having increased hemicellulose
content.
BACKGROUND OF THE INVENTION
[0002] Pulp refers to cellulose fibers that have been liberated
from wood or other lignocellulosic materials through physical
and/or chemical processes. Pulp manufactured for papermaking
applications is generally dispersed in water as a slurry and then
reformed into a web or sheet.
[0003] Pulping methods include chemical, mechanical, and
chemi-mechanical processes. While mechanical pulping methods rely
on physical action and thermal energy to liberate fibers, chemical
pulping methods rely on the effect of chemicals to separate fibers
from raw materials. Generally, the more chemicals used in a pulping
process, the lower the pulp yield and lignin content because
chemical action degrades the wood and solubilizes wood components
including lignin and hemicellulose. While mechanical pulp yields
are typically greater than about 90 percent, chemical pulp yields
are considerably lower, more often in the range from about 40 to
about 65 percent.
[0004] Although chemical pulping methods result in lower pulp
yields, these methods provide individual pulp fibers that are
uncut, which is in contrast to fibers produced from mechanical
pulping methods. Furthermore, pulp fibers produced by chemical
pulping methods provide paper products having increased strength
because lignin, which interferes with interfiber hydrogen bonding,
is largely removed during the process. Of the chemical pulping
processes, the Kraft process produces generally stronger pulps
compared with the other major chemical pulping method, the sulfite
process.
[0005] Chemical pulping of wood and other lignocellulosic materials
results in delignification of the raw material. Delignification is
the process of breaking down of lignin and rendering the breakdown
products soluble in the cooking liquor (alkali), such that the
lignin can be removed from the cellulose. A pulp's lignin content
can be measured by kappa number. The higher the measured kappa
number, the greater a pulp's lignin content. The kappa number is
often used to monitor delignification during and after pulping
processes. A similar test is the permanganate number.
[0006] Pulps produced by the Kraft pulping process have a light to
dark brown color and, as a consequence, are bleached to increase
the pulp's brightness.
[0007] Accordingly, there exists a need for a Kraft pulp that
offers the advantage of strength associated with conventional Kraft
pulps, while at the same time has improved yield and increased
hemicellulose content compared to conventional Kraft chemical
pulps. The present invention seeks to fulfill these needs and
provides further related advantages.
SUMMARY OF THE INVENTION
[0008] In one aspect of the invention, a Kraft chemical pulp having
increased hemicellulose content is provided. The Kraft chemical
pulp is a wood pulp having increased hemicellulose content compared
to conventional Kraft chemical pulps. In one embodiment, the pulp
has a hemicellulose content greater than about 17 weight percent as
measured by the 18% caustic solubility test. The pulp can be
incorporated into sheets having initial (unrefined) tensile
strengths significantly greater than sheets incorporating
conventional Kraft chemical pulp fibers. The pulp is more readily
refined than conventional chemical pulps and achieves
strength/drainage properties at significantly less refining energy.
The pulp can be produced in higher yield than other Kraft chemical
pulps.
[0009] In another aspect, the invention provides a method for
making cellulose pulp having increased hemicellulose content. In
the method, a lignocellulosic material is pulped with a liquor,
which includes sodium hydroxide (NaOH), sodium sulfide (Na.sub.2S),
anthraquinone, and some residual sodium carbonate
(Na.sub.2CO.sub.3) from the causticizing process, to provide a
first brownstock. The first brownstock is treated with oxygen to
provide a second brownstock, which is then bleached to provide the
pulp product. The caustic sulfide includes polysulfide and
anthraquinone. Chlorine dioxide is used in the bleaching.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0011] FIG. 1 is a flow diagram illustrating of a representative
method for producing the pulp of the invention; and
[0012] FIG. 2 is a graph comparing percent yield as a function of
kappa number for pulps made by the method of the invention (A) and
for pulps made by conventional cooking (B), digester yields for the
methods are also illustrated (C and D, respectively).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] In one aspect, the present invention provides a wood
cellulose pulp having increased hemicellulose content. The Kraft
chemical pulp of the invention is a wood pulp having increased
hemicellulose content compared to conventional Kraft chemical
pulps. Because hemicellulose imparts flexibility to a fiber, the
pulp fibers of the invention are more flexible in papermaking
systems and exhibit greater interfiber bonding compared to
conventional Kraft chemical pulps. The increased flexibility and
interfiber bonding of the fibers renders sheets or webs that
incorporate these fibers stronger than sheets or webs incorporating
conventional Kraft chemical pulp fibers. The pulp of the invention
provides sheets having initial (unrefined) tensile strengths
significantly greater than sheets incorporating conventional Kraft
chemical pulp fibers.
[0014] As a result of the pulp fiber's flexibility and increased
hydrogen bonding potential, the amount of refining required to
achieve a particular sheet strength (tensile strength) or
advantageous drainage property (Canadian Standard Freeness, CSF) is
greatly reduced. Thus, the pulp of the invention can be refined to
a predetermined point more readily than a conventional Kraft
chemical pulp making the pulp of the invention more attractive from
a refining energy requirement basis. The pulp of the invention is
more readily refined than conventional Kraft chemical pulps and
achieves strength/drainage properties at significantly less
refining energy.
[0015] Because the pulp of the invention has increased
hemicellulose content compared to other Kraft chemical pulps, the
pulp is produced in higher yield than other Kraft chemical
pulps.
[0016] The pulp of the invention is a fully bleached pulp suitable
for paper grade market pulp.
[0017] Hemicellulose Content. As noted above, the pulp of the
invention advantageously has an increased hemicellulose content
compared to conventional chemical pulps. In one embodiment, the
pulp of the invention has a hemicellulose content greater than
about 17 percent as measured by the 18% caustic solubility test
described below. The hemicellulose content of the pulp of the
invention is about 2 percent greater than conventional chemical
pulps. Other conventionally produced softwood Kraft pulps have a
hemicellulose content less than about 16 percent as measured by the
18% caustic solubility test.
[0018] The hemicellulose content of pulp can be measured by several
methods. One empirical method is the 18% caustic solubility method
(TAPPI T-235 CM-00). In this method, a weighed quantity of pulp
(1.5 g) is soaked in 18 percent by weight aqueous sodium hydroxide
(100 mL) for 1 hour. During the soak, the pulp fibers swell and the
pulp's hemicellulose dissolves into solution. The pulp is then
filtered, and 10 mL of the filtrate is mixed with 10 mL of
potassium dichromate and 30 mL sulfuric acid. This solution is
titrated with ferrous ammonium sulfate. The percent alkali
solubility is then calculated using the amounts of the various
solutions and the amount of pulp. The method is usually an
underestimate of hemicellulose content because not all of the
hemicellulose is dissolved and removed from the pulp during this
procedure. Hemicellulose content for a pulp may also be determined
by sugar analysis of completely digested pulp. Such a determination
would generally provide a higher hemicellulose content value than
the 18% caustic solubility method.
[0019] Sheet Tensile Strength. The pulp of the invention has an
unrefined sheet tensile strength significantly greater than other
Kraft chemical pulps. Conventional chemical pulps provide sheets
having initial tensile breaking lengths from about 2.5 to about 4.0
km as measured by the TAPPI T 220. The pulp of the invention
provides sheets having initial tensile strengths of from about 4.5
to about 5.5. In one embodiment, the pulp provides a sheet having
an initial tensile strength of about 5, which is at least a 20
percent increase compared to conventional Kraft chemical pulps.
[0020] Yield. Due at least in part to the pulp's increased
hemicellulose content, the pulp of the invention is produced in
greater yield than other conventional Kraft chemical pulps. The
yield provided by the method of the invention is at least about 3.0
to about 3.5 percent greater than for conventional Kraft pulps.
FIG. 2 is a graph that compares percent yield as a function of
kappa number for pulps made by the method of the invention (e.g.,
cooked with polysulfide and anthraquinone and treated with oxygen)
(Curve A in FIG. 2; from about 47 to about 51 percent) and for
pulps made by conventional cooking followed by oxygen treatment
(Curve B in FIG. 2; from about 45 to about 47 percent). Digester
yields for these processes are also illustrated (Curves C and D,
respectively, in FIG. 2). Yields are based on the weight of
oven-dried chips introduced to the digester. For the pulps made by
the method of the invention, the digester kappa was 33, 38, and 43.
For the pulps made by conventional methods, the digester kappa was
34, 38, and 44.
[0021] Brightness and Lignin Content. The pulp of the invention is
a fully bleached pulp (i.e., brightness greater than 89% ISO).
There are two principal types of measurements to determine the
completeness of the pulping or bleaching process: the degree of
delignification and the brightness of the pulp.
[0022] There are many methods of measuring the degree of
delignification of the pulp. Most are variations of the
permanganate test. The normal permanganate test provides a
permanganate or K number that is the number of milliliters of 0.1 N
potassium permanganate solution consumed by one gram of oven dry
pulp under specified conditions (see TAPPI Standard Test T-214).
The kappa number is similar to the permanganate number, but is
measured under carefully controlled conditions and corrected to be
the equivalent of a 50 percent consumption of the permanganate
solution in contact with the sample. The test gives the degree of
delignification of pulps through a wider range of delignification
than does the permanganate number. The kappa test measures the
consumption of permanganate ion by lignin. The kappa number is the
number of milliliters of 0.1 M potassium permanganate consumed by
one gram of pulp in 0.5 N sulfuric acid after a 10 minute reaction
time at 25.degree. C. under conditions such that one-half of the
permanganate remains unreacted (see TAPPI Standard Test T-236). The
kappa number for the pulp of the invention is described below in
reference to the pulping process.
[0023] There are also a number of methods of measuring pulp
brightness. Brightness is a measure of reflectivity and its value
is expressed as a percent of some scale. Brightness can be measured
by TAPPI Method T 525 OM-92.
[0024] The brightness of the product pulp of the invention is in
the range from about 75 to about 95% ISO. In one embodiment, the
pulp's brightness is from about 88 to about 92% ISO. In another
embodiment, the pulp has a brightness of about 90% ISO.
Pulping/Bleaching Methods
[0025] In another aspect of the invention, a method for making a
cellulose pulp having increased hemicellulose content pulp is
provided. The method includes the steps of Kraft chemical pulping,
oxygen delignification, and bleaching. The combination of steps in
the method provides for delignification while maintaining
hemicellulose content to improve yield and provide a chemical pulp
having the advantageous characteristics noted above.
[0026] A flow diagram illustrating a method for producing the pulp
of the invention is illustrated in FIG. 1. Referring to FIG. 1,
wood chip supply 10 provides wood chips to digester 20. Liquor is
provided to the digester from white liquor supply 70 through
polysulfide/anthraquinone processor 80. The
polysulfide/anthraquinone processor provides liquor containing
polysulfide and anthraquinone to the digester. White liquor and
brownstock from the digester are provided to oxygen reactors 30.
The oxygen treated pulp from the oxygen reactors is then provided
to bleach stages 40. The bleached pulp from the bleaching stage is
then provide to pulp machine 50. At the pulp machine, the pulp is
deposited onto a foraminous support (e.g., Fourdrinier), water is
withdrawn, the wet pulp pressed, and then dried to provided the
pulp product.
[0027] Chemical Pulping. Pulping is the process in which wood chips
or other wood particulate matter is converted to fibrous form.
Chemical pulping requires cooking of the chips in solution with a
chemical, and includes partial removal of the coloring matter such
as lignin associated with the wood. The pulp of the invention can
be prepared by the Kraft process as described herein. In general,
the pulping process useful in making the pulp of the invention is a
full chemical pulping method using sodium hydroxide and sodium
sulfide at a pH greater than about 12, at a temperature from about
160 to about 180.degree. C. for about 0.5 to about 5 hours.
[0028] The cooking liquor useful in the pulping process of the
invention includes polysulfide. Polysulfide has the formula
NaS(S).sub.nSNa, where n=4-6. The polysulfide is used in the
process to mitigate alkaline peeling (i.e., to improve the quality
of the cellulose and increase pulp yield by reducing the occurrence
of destructive chemical reactions referred to as "peeling"). In one
embodiment, in the practice of the method, a polysulfide system
provides the digester with between about 4 to about 9 g/L
polysulfide (as sulfur). In another embodiment, a polysulfide
system provides the digester with between about 5.0 to about 6.5
g/L polysulfide at about 25 to 37 percent sulfidity.
[0029] In addition to polysulfide, the pulping process of the
invention also includes anthraquinone to mitigate alkaline peeling.
Anthraquinone is added to the polysulfide in the polysulfide system
(see polysulfide/anthraquinone processor 80 in FIG. 1).
Anthraquinone is a pulping additive useful to increase
delignification, decrease carbohydrate degradation, and improve
pulp yield. Anthraquinone achieves these advantageous properties
through a chemical cycle that leads to the lignin reduction and the
oxidation of cellulose's reducing endgroup aldehyde to a carboxylic
acid. Anthraquinone is typically used in an amount up to about 0.10
percent by weight based on the total weight of wood. In one
embodiment, anthraquinone is used from about 0.03 to about 0.07
percent by weight based on the total weight of wood. Modified
anthraquinones, such as 1,4-dihydro-9,10,-dihydroxyanthracene (DDA,
or soluble anthraquinone, SAQ), can also be used.
[0030] Lignin content is typically measured during chemical pulping
to monitor the degree of cooking (i.e., delignification) or to
measure residual lignin before bleaching and between bleaching
stages to monitor the process. As noted above, lignin can be
measured indirectly by measuring the amount of oxidant consumed by
lignin in the sample.
[0031] After digesting, the pulp has a kappa number in the range
from about 20 to about 65. In one embodiment, the kappa number
after digesting is about 34 to 45. In one embodiment, the kappa
number after digesting is about 36 to 43. In a further embodiment,
the kappa number after digesting is about 38.
[0032] The products from the pulping or digesting are black liquor
and brownstock. Black liquor is the waste liquor from the pulping
process and contains the original cooking inorganic elements and
the degraded, dissolved wood substances. Black liquor contains
lignin and lignin byproducts and is separated from the brownstock
and directed to a recovery system that separates the lignin and
byproducts from the residue cooking chemicals, which can be
recycled back to the digester. After separating from black liquor,
the pulp produced from the digestion is washed to provide
brownstock. Screening may occur before or after oxygen
delignification. In the process of the invention, brownstock is
introduced into the oxygen delignification system.
[0033] Oxygen Delignification. The oxygen delignification system
useful in producing the pulp of the invention achieves from about
40 to about 50 percent delignification.
[0034] Oxygen delignification is the delignification of pulp using
oxygen under pressure in aqueous alkali. Pressures typically range
from about 550 to about 700 kpa (about 80 to about 120 psi). The
alkali is typically sodium hydroxide present in about 3 to about 5
percent by weight based on the weight of pulp. Delignification can
be carried out at temperatures from about 90 to about 130.degree.
C. for a period of time from about 20 to about 60 minutes. The
oxygen stage can be carried out in a single vessel or in a
two-vessel system. The oxygen delignification step may include the
use of magnesium ion in an amount from about 0.05 to about 0.25
percent by weight based on the weight of pulp to mitigate extensive
carbohydrate degradation.
[0035] After oxygen delignification, the pulp has a kappa number in
the range from about 8 to about 35. In one embodiment, the kappa
number after oxygen delignification is about 18 to 22.
[0036] Further details of oxygen delignification are described in
U.S. Pat. No. 4,172,006, Method for Delignifying Wood Chips With
Oxygen By Adding Cooking Liquor Under Pressure; U.S. Pat. No.
4,295,925, Treating Pulp With Oxygen; U.S. Pat. No. 4,295,926,
Method and Apparatus for Treating Pulp With Oxygen; and U.S. Pat.
No. 4,298,426, Method and Apparatus for Treating Pulp With Oxygen
in a Multi-Stage Bleaching Sequence; each incorporated herein by
reference in its entirety.
[0037] The pulp produced by the oxygen delignification step is
introduced to the bleaching stage.
[0038] Bleaching. Bleaching is the treatment of pulp fibers with
chemical agents to increase their brightness. Brightness is a term
used to describe the whiteness of pulp or paper on a relative
scale. Bleaching of chemical pulps is achieved by lignin and color
removal.
[0039] Chemical pulp bleaching can be accomplished using various
chlorine- and/or oxygen-containing compounds (e.g., chlorine
dioxide) in combination with alkali (e.g., sodium hydroxide)
extractions in several stages. Bleaching of chemical pulps tend to
involve the use of chemicals that are more specific to lignin
removal than to carbohydrate degradation. Each stage includes a
bleaching step and a washing step to provide progressively bleached
pulp. Each stage includes a pump and a mixer to mix the pulp with a
bleaching chemical, a retention tower to allow time sufficient for
the pulp and bleaching chemical to react, and a washer to remove
the bleaching chemical and solubilized pulp components from the
bleached pulp. The bleaching chemical and solubilized pulp
components are typically washed from the pulp with either fresh
"mill water" or filtrate from another bleach stage in a counter
current wash flow to save the use of fresh water. The wash water
may be alkaline or acid depending on the stage being washed.
[0040] In one embodiment of the method, the bleaching process is an
Elemental Chlorine Free (ECF) bleaching process. In the process,
chlorine dioxide is the bleaching agent and aqueous sodium
hydroxide is the alkali extractant. In one embodiment, the
bleaching method includes three stages. Examples of representative
stages include: D(Eop)D; D(Eo)D; DED; D(EP)D; D(Eop)P; D(Eo)P;
D(EP)P; D(Eop)DED; D(Eo)DED; D(EP)DED; D(EP)D(EP)D; or
D(PaP)(Eop)DEDP, among others. For these stages, D refers to
chlorine dioxide bleaching, E refers to extraction, Eo refers to
extraction including oxygen, P refers to bleaching with hydrogen
peroxide, Eop refers to alkaline extraction including oxygen and
peroxide, and PaP refers to Papricycle.
[0041] In one embodiment of the method, the bleaching sequence
includes the following: (1) chlorine dioxide treatment, (2) sodium
hydroxide treatment with oxygen and peroxide, (3) chlorine dioxide
treatment, (4) sodium hydroxide treatment, and (5) chlorine dioxide
treatment.
[0042] In another embodiment of the method, the bleaching process
is a Total Chlorine Free (TCF) bleaching process (i.e., a process
that does not include chlorine).
[0043] There are many other bleaching sequences that can be used in
the method of the invention. Listings of these sequences may be
found in the standard texts. Other stages include bleaching with
chlorine, chlorine dioxide, hydrogen peroxide, or a hypochlorite.
These stages are interspersed with alkali extraction and/or
washing.
[0044] After bleaching, the pulp is directed to a headbox in which
the bleached pulp is slurried, deposited onto a forming wire (e.g.,
fourdrinier forming wire), and dried to provide a web of bleached
pulp.
[0045] Further details of pulping and bleaching devices, processes,
and procedures are described in U.S. Pat. No. 4,172,006, Method for
Delignifying Wood Chips With Oxygen By Adding Cooking Liquor Under
Pressure; U.S. Pat. No. 4,295,925, Treating Pulp With Oxygen; U.S.
Pat. No. 4,295,926, Method and Apparatus for Treating Pulp With
Oxygen; and U.S. Pat. No. 4,298,426, Method and Apparatus for
Treating Pulp With Oxygen in a Multi-Stage Bleaching Sequence.
Pulp Products
[0046] The pulp of the invention can be advantageously incorporated
into absorbent products such as tissue and towel products. Tissue
and towel products typically include a combination of fibers.
[0047] A representative tissue product can include from about 10 to
about 40 percent by weight of the pulp of the invention. The tissue
can further include other pulp, for example, bleached northern or
southern softwood Kraft pulp, bleached northern or southern
hardwood Kraft pulp, and chemi-thermomechanical pulp (CTMP), among
others.
[0048] A representative towel product can include from about 30 to
about 75 percent by weight of the pulp of the invention. The towel
can further include other pulp, for example, bleached northern or
southern softwood Kraft pulp and chemi-thermomechanical pulp
(CTMP), among others.
[0049] The pulp of the invention can also be used in making
saturating base paper in which the base paper that includes the
pulp of the invention is saturated with a material such as, for
example, melamine or latex.
[0050] The pulp of the invention can also be advantageously
incorporated into flexible packaging paper grades and other
technical grade papers.
[0051] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *