U.S. patent application number 11/427470 was filed with the patent office on 2008-01-03 for covalent bonding of carboxylated cellulose fiber webs.
Invention is credited to Richard A. Jewell, Amar N. Neogi, David W. Park, John A. Westland.
Application Number | 20080000603 11/427470 |
Document ID | / |
Family ID | 38846391 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080000603 |
Kind Code |
A1 |
Neogi; Amar N. ; et
al. |
January 3, 2008 |
Covalent Bonding of Carboxylated Cellulose Fiber Webs
Abstract
Methods are provided for creating covalent bonding of webs by
combining cellulosic fibers having a carboxyl content approximately
greater than 7 meq/100 g with one or more crosslinking agents. In a
first step, a carboxyl group is placed onto a fiber. In an
embodiment, the fiber is then reacted with an oxazoline-functional
polymer which has been combined with a polycarboxylate compound.
Heat is applied to the treated web, and this enables formation of a
cross-linked bridge in the form of a covalent bond. In an
embodiment, the covalent bonding of the carboxylated cellulose pulp
webs utilizes oxazoline-functional polymers and polyacrylic acid.
The oxazoline polymer in combination with polyacrylic acid should
form a network polymer with covalent bonds to the cellulose
carboxyl groups. The non-woven web may be strengthhened by covalent
bonding, thereby improving overall wet/dry strength of the final
product.
Inventors: |
Neogi; Amar N.; (Kenmore,
WA) ; Jewell; Richard A.; (Kalispell, MT) ;
Park; David W.; (Auburn, WA) ; Westland; John A.;
(Auburn, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Family ID: |
38846391 |
Appl. No.: |
11/427470 |
Filed: |
June 29, 2006 |
Current U.S.
Class: |
162/182 ;
162/157.6; 162/9 |
Current CPC
Class: |
D21H 11/20 20130101;
D21C 9/005 20130101 |
Class at
Publication: |
162/182 ; 162/9;
162/157.6 |
International
Class: |
D21F 11/00 20060101
D21F011/00; D21C 9/00 20060101 D21C009/00 |
Claims
1. A method of covalent bonding of a cellulosic web, the method
comprising the steps of: forming a web from highly carboxylated
cellulose fibers; applying a cross-linking agent to the highly
carboxylated cellulose fibers to create a treated web; and curing
the treated web.
2. The method of claim 1 wherein the treated web is cured under
heat.
3. The method of claim 1 wherein the treated web is cured under
pressure.
4. The method of claim 1 wherein a carboxyl content of the fibers
is approximately greater than 7 meq/100 grams.
5. The method of claim 1 wherein the crosslinking agent is a
mixture of oxazoline functionalized polymer and polycarboxylate
compound.
6. The method of claim 1 wherein the crosslinking agent is applied
in an amount ranging from about 8 kg to about 100 kg chemical per
ton of highly carboxylated cellulose fibers.
7. The method of claim 5 wherein the polycarboxylate compound is
applied in an amount ranging from about 8 kg to about 100 kg
chemical per ton of highly carboxylated cellulose fibers.
8. A cellulosic web comprising: a highly carboxylated cellulose
fiber; a functionalized polymer; and a polycarboxylate material;
wherein the functionalized polymer and the polycarboxylate material
form a cross-linking agent and further wherein a covalent bond is
formed between the highly carboxylated cellulose fiber and the
cross-linking agent.
9. The cellulosic web of claim 8 wherein the functionalized polymer
is an oxazoline-containing polymer.
10. The cellulosic web of claim 8 wherein the functionalized
polymer is applied in an amount ranging from about 8 kg to about
100 kg chemical per ton of highly carboxylated cellulose
fibers.
11. The cellulosic web of claim 8 wherein the polycarboxylate
material is applied in an amount ranging from about 8 kg to about
100 kg chemical per ton of highly carboxylated cellulose
fibers.
12. The cellulosic web of claim 8 wherein a carboxyl content of the
highly carboxylated cellulose fibers is approximately greater than
7 meq/100 grams.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to methods for
providing covalent bonds on cellulose fiber webs.
BACKGROUND OF THE INVENTION
[0002] Cellulose fibers are generally held together by hydrogen
bonds. The average energy of a hydrogen bond is 1-5 Kcal. The
strength of a paper product is typically related to the strength of
the hydrogen bonding. Often times when attempts are made to
strengthen the bonding of fibers, other properties are compromised,
such as bulk, stiffness, etc. In some cases, increasing bond
strength can increase the overall cost of the product, which is
undesirable.
[0003] Thus, a need exists for a method for increasing bond
strength between cellulose fibers without compromising properties
of the final product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The embodiments of the present invention are described in
detail below with reference to the following drawings.
[0005] FIG. 1 is a diagram of a system for forming covalent bonds
in an embodiment of the present invention; and
[0006] FIG. 2 is a representation of Epocros polymers in an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0007] The present invention provides a method for creating
covalent bonding of webs by combining cellulosic fibers having a
carboxyl content approximately greater than 7 meq/100 g with one or
more crosslinking agents. In a first step, a carboxyl group is
placed onto a fiber. In an embodiment, the fiber is then reacted
with an oxazoline-functional polymer which has been combined with a
polycarboxylate compound. Heat is applied to the treated web, and
this enables formation of a cross-linked bridge in the form of a
covalent bond. In an embodiment, the covalent bonding of the
carboxylated cellulose pulp webs utilizes oxazoline-functional
polymers and polyacrylic acid. The oxazoline polymer in combination
with polyacrylic acid should form a network polymer with covalent
bonds to the cellulose carboxyl groups. The non-woven web may be
strengthened by covalent bonding, thereby improving overall wet/dry
strength of the final product.
[0008] FIG. 2 illustrates a general class of polymers that have
been functionalized with an oxazoline group.
[0009] Conventional papermaking fiber may be utilized and a furnish
for the same may refer to papermaking fibers made from any species,
including hardwoods and softwoods, and to fibers that may have had
a debonder applied to them but that are not otherwise chemically
treated following the pulping/bleaching process or off-line post
pulping/bleaching & drying process. The cellulose fiber may be
obtained from any source, including cotton, hemp, grasses, cane,
husks, cornstalks or other suitable source. In an embodiment, the
cellulose fiber is chemical wood pulp.
[0010] The oxazoline-functional polymers may be, for example, any
polymer containing an oxazoline containing moiety on the side
chain. In place of oxazoline containing polymers, one can use a
polyfunctional compound capable of reacting to carboxyl groups
(e.g. polyols, polyepoxides, etc.).
[0011] The polycarboxylate compound may be, for example, a polymer
or oligomer containing multiple carboxyl groups.
[0012] The crosslinking agent can include a catalyst to accelerate
the bonding reaction between the crosslinking agent and the
cellulose molecule, but most crosslinking agents do not require a
catalyst. Suitable catalysts include acidic salts which can be
useful when urea-based crosslinking substances are used. Such salts
include ammonium chloride, ammonium sulfate, aluminum chloride,
magnesium chloride, or mixtures of these or other similar
compounds. Alkali metal salts of phosphorus containing acids may
also be used.
[0013] The crosslinking agent typically is applied in an amount
ranging from about 8 kg to about 100 kg chemical per ton of
cellulose fiber. The polycarboxylate compound is applied in an
amount ranging from about 8 kg to about 100 kg chemical per ton of
cellulose fiber.
[0014] The cellulosic fibers may have been treated with a debonding
agent prior to treatment with the crosslinking agent. Debonding
agents tend to minimize interfiber bonds and allow the fibers to
separated from each other more easily. The debonding agent may be
cationic, non-ionic or anionic. Cationic debonding agents appear to
be superior to non-ionic or anionic debonding agents. The debonding
agent typically is added to cellulose fiber stock.
[0015] Suitable cationic debonding agents include quaternary
ammonium salts. These salts typically have one or two lower alkyl
substituents and one or two substituents that are or contain fatty,
relatively long chain hydrocarbon. Non-ionic debonding agents
typically comprise reaction products of fatty-aliphatic alcohols,
fatty-alkyl phenols and fatty-aromatic and aliphatic acids that are
reacted with ethylene oxide, propylene oxide or mixtures of these
two materials.
[0016] Examples of debonding agents may be found in Hervey et al
U.S. Pat. Nos. 3,395,708 and 3,544,862, Emanuelsson et al U.S. Pat.
No. 4,144,122, Forssblad et al U.S. Pat. No. 3,677,886, Osborne III
U.S. Pat. No. 4,351,699, Hellston et al U.S. Pat. No. 4,476,323 and
Laursen U.S. Pat. No. 4,303,471 all of which are in their entirety
incorporated herein by reference. A suitable debonding agent is
Berocell 584 from Berol Chemicals, Incorporated of Metairie, La. It
may be used at a level of 0.25% weight of debonder to weight of
fiber. Again, a debonding agent may not be required.
[0017] In FIG. 1, a conveyor 12 transports a cellulosic mat 14 into
a treatment zone 16 where an applicator 18 applies a crosslinking
agent onto the mat 14. Typically, chemicals are applied optionally
to both sides of the mat. The mat 14 is then conveyed into a dryer
20 followed by a flow through oven 22 to cure the crosslinking
agent.
[0018] The treated pads have low density and good stiffness. The
pads can be cut easily using a sharp knife. The material is
absorbent and strong even when wet.
[0019] The present invention may be better understood by way of the
following examples. It should be understood that, in the following
examples, to produce the desired carboxyl groups in meq/100 g for
experimentation, processes described in U.S. Pat. Nos. 6,379,494;
6,352,348 and 6,919,447 were utilized.
EXAMPLE 1
Ratios on Epocros WS500 and Polyacrylic Acid
[0020] Fluff pulp modified to have a carboxyl content of 21 meq/100
g was used to make a 6 inch airlaid pad at 125 gsm. The
carboxylated pulp can be in either a neutralized form or in a fully
protonated (acid) form. The pads were sprayed with 10 gm of a
solution of oxazoline functionalized polyacrylate (Epocros WS500)
manufactured by Nippon Shokubai and polyacrylic acid
(MW.about.3500) from Rohm&Haas, to yield the required level of
Epocros and polyacrylic acid shown in the table below. The Epocros
level was varied from 3% to 7% based on fiber weight and the
polyacrylic acid from 1% to 5% based on fiber weight. The control
pads contained only polyacrylic acid. The pads were dried and cured
in a convection oven at 120.degree. C. for 10 minutes. The pads
were then tested for wet and dry tensile strength using an Instron
testing device/system with a vertical pull. For the wet tensile,
the pads were sprayed with 10 gm of deionized water, let stand for
10 minutes, then tested.
[0021] From Table 1 it can be seen that there is a substantial
increase in the dry tensile index with higher strength values for
increasing polymer content. The data also show that higher strength
values are obtained from the acid form of the carboxylated pulp.
Similar results are shown in Table 2 for the wet tensile index.
TABLE-US-00001 TABLE 1 Dry tensile Index, Nm/g Percent Epocros
Percent Polyacrylic Acid WS500 1% 3% 5% Tensile Index for acidic
form of pulp Control 0.83 1.20 2.02 3% 1.17 3.62 2.38 5% 1.12 5.70
3.56 7% 1.53 5.08 4.18 Tensile Index for neutralized form of pulp
Control 0.83 1.20 2.02 3% 2.65 3.62 2.29 5% 4.10 3.20 4.40 7% 3.28
3.74 5.15
TABLE-US-00002 TABLE 2 Wet Tensile Index, Nm/g Percent Epocros
Percent Polyacrylic Acid WS500 1% 3% 5% Tensile Index for acidic
form of pulp Control 0.17 0.35 0.49 3% 0.33 1.01 0.65 5% 0.32 1.21
1.18 7% 0.41 1.82 1.24 Tensile Index for neutralized form of pulp
Control 0.17 0.35 0.49 3% 0.39 0.50 0.37 5% 0.89 0.71 0.69 7% 0.54
0.67 0.75
EXAMPLE 2
Effect of Increasing Carboxyl Content in Pulp
[0022] Fluff pulp modified to have a carboxyl content from 3 to 35
meq/100 g was used to make a 6 inch airlaid pad at 125 gsm. The
carboxylated pulp can be in either a neutralized form or in a fully
protonated (acid) form. The pads were sprayed with 10 gm of a
solution of Epocros WS500 and polyacrylic acid (MW.about.3500) from
Rohm&Haas, to yield the required level of Epocros and
polyacrylic acid(PAA) shown in the table below. The Epocros level
was varied from 3% to 7% based on fiber weight and the polyacrylic
acid was held at 3% based on fiber weight. The pads were dried and
cured in a convection oven at 120.degree. C. for 10 minutes. The
pads were then tested for wet and dry tensile strength using an
Instron testing device/system with a vertical pull. For the wet
tensile, the pads were sprayed with 10 gm of deionized water, let
stand for 10 minutes, then tested.
[0023] From Table 3 it can be seen that there is a substantial
increase in the dry tensile index with an increase in the Epocros
content, and there is an optimum carboxyl level. It is also
apparent that the acid form of the carboxylated pulp is more
reactive, yielding higher tensile strengths. Similar results are
shown in Table 4 for the wet tensile index.
TABLE-US-00003 TABLE 3 Dry Tensile Index, Nm/g Percent Epocros -
PAA Carboxyl content of pulp, meq/100 g on pulp 3 12 21 35 Tensile
Index for acid form 3-3 1.13 1.59 3.62 1.62 5.3 1.45 1.60 5.70 2.15
7.3 2.14 1.82 5.08 4.01 Tensile Index for neutralized form 3-3 1.22
1.75 2.93 2.83 5-3 1.45 2.21 3.20 2.87 7-3 2.16 2.97 3.74 3.97
TABLE-US-00004 TABLE 4 Wet Tensile Index, Nm/g Percent Epocros -
PAA Carboxyl content of pulp, meq/100 g on pulp 3 12 21 35 Tensile
Index for acid form 3-3 0.25 0.35 1.01 0.48 5.3 0.30 0.45 1.21 0.54
7.3 0.39 0.49 1.82 0.81 Tensile Index for neutralized form 3-3 0.25
0.34 0.50 0.48 5-3 0.29 0.48 0.71 0.54 7-3 0.38 0.65 0.67 0.87
EXAMPLE 3
Ratios on Epocros WS500 and Polymaleic Acid
[0024] Fluff pulp modified to have a carboxyl content of 21 meq/100
g was used to make a 6 inch airlaid pad at 125 gsm. The
carboxylated pulp can be in either a neutralized form in a fully
protonated (acid) form. The pads were sprayed with 10 gm of a
solution of Epocros WS500 and polymaleic acid (MW.about.3500) from
Rohm&Haas, to yield the required level of Epocros and
polymaleic acid shown in the table below. The Epocros level was
varied from 3% to 7% based on fiber weight and the polymaleic acid
from 1% to 5% based on fiber weight. The control pads contained
only polymaleic acid. The pads were dried and cured in a convection
oven at 120.degree. C. for 10 minutes. The pads were then tested
for wet and dry tensile strength using an Instron testing
device/system with a vertical pull. For the wet tensile, the pads
were sprayed with 10 gm of deionized water, let stand for 10
minutes, then tested.
[0025] From Table 5 it can be seen that there is a substantial
increase in the dry tensile index with higher strength values for
increasing polymer content. The data also show that higher strength
values are obtained from the acid form of the carboxylated pulp.
Similar results are shown in Table 6 for the wet tensile index.
TABLE-US-00005 TABLE 5 Dry tensile Index, Nm/g Percent Epocros
Percent Polyacrylic Acid WS500 1% 3% 5% Tensile Index for acidic
form of pulp Control 0.53 1.20 1.35 3% 0.66 3.65 1.95 5% 1.56 3.9
2.64 7% 2.37 3.67 3.04 Tensile Index for neutralized form of pulp
Control 0.53 1.20 1.35 3% 2.507 1.64 1.84 5% 2.04 2.26 1.75 7% 2.50
2.66 3.19
TABLE-US-00006 TABLE 6 Wet Tensile Index, Nm/g Percent Epocros
Percent Polyacrylic Acid WS500 1% 3% 5% Tensile Index for acidic
form of pulp Control 0.15 0.32 0.40 3% 0.21 0.69 0.49 5% 0.47 1.23
0.74 7% 0.86 1.24 1.13 Tensile Index for neutralized form of pulp
Control 0.15 0.32 0.40 3% 0.32 0.31 0.34 5% 0.48 0.47 0.45 7% 0.62
0.61 0.72
[0026] The Epocros is described as an oxazoline functionalized
polymer. The particular polymer backbone used in the example here
is a polyacrylate co-polymer. Other heating methods beyond those
listed above are contemplated which will accelerate the reaction.
These methods are known by those skilled in the art. The
temperature range for heating may be approximately 60 degrees
Celsius to 150 degrees Celsius. Curing for the process may occur
via heat and/or pressure.
[0027] While the embodiments of the invention have been illustrated
and described, as noted above, many changes can be made without
departing from the spirit and scope of the invention. Accordingly,
the scope of the invention is not limited by the disclosure of the
embodiments. Instead, the invention should be determined entirely
by reference to the claims that follow.
* * * * *