Fibrous compositions

A fibrous product containing (a) a papermaking grade of pulp, (b) a structured particle latex having pH independent cationic groups bound at or near the particle surface and (c) a co-additive. The pulp is represented by unbleached softwood kraft. The latex is represented by a structured-particle latex having (a) a core of a copolymer of styrene and butadiene (b) an encapsulating layer of styrene, butadiene and vinylbenzyl chloride which is reacted with 2-(dimethylamino) ethanol to form quaternary ammonium groups. The co-additive is represented by a hydrolyzed polyacrylamide having a degree of polymerization of 5500. To an aqueous slurry of the pulp are added the latex and an aqueous solution of the co-additive, the resulting suspension is dewatered and dried by heating.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The invention is concerned with latex systems for use in the manufacture of 
paper and with paper products containing a dried composite of (a) 
paper-making pulp, (b) a cationic latex and (c) a water-soluble anionic 
polymer of acrylamide. 
(2) Description of the Prior Art 
The use of latex in the manufacture of paper by wet-end addition, or as a 
beater additive, is well known. Commonly, the latex has been an anionic 
latex but a water-soluble cationic deposition aid has been used therewith. 
Because of the slightly anionic nature of pulp, it has been suggested that 
a low-charge density cationic latex should be used in order to get good 
deposition on the fibers without the use of a deposition aid. 
Combinations of anionic and cationic wet-end additives in which both 
species are water-soluble are known. However, the combination as wet-end 
additives of a cationic latex with a water-soluble anionic polymer is not 
known, particularly latexes having particles with a high density of pH 
independent bound charge at or near the particle surface. 
SUMMARY OF THE INVENTION 
The process and product of this invention includes the combination of a 
paper-making fiber, a cationic latex with a high density of pH independent 
bound charges and a co-additive which is a water-soluble anionic 
acrylamide polymer which is not deactivated by polyvalent metal ions to 
produce a web or sheet, e.g., a paper sheet, with good formation. The 
latex contains a copolymer of a monovinylidene aromatic monomer, an 
aliphatic conjugated diene and optionally other non-ionic monomers 
encapsulated by a thin layer of a water-insoluble organic copolymer having 
bound charges as pH independent cationic groups. The amount of latex 
add-on, solids basis, is from about 5 percent to about 2,000 percent, 
preferably from about 10 percent to about 100 percent, based on the dry 
fiber weight. The co-additive is used in an amount which usually is from 
about 0.15 percent to about 160 percent, by weight, based on the weight of 
the pulp. 
The latex has a bound charge of from about 0.15 milliequivalent to about 
0.6 milliequivalent, preferably from about 0.18 milliequivalent to about 
0.4 milliequivalent, per gram of polymer. The co-additive has a degree of 
polymerization from about 3000, preferably from about 5000, to about 
10,000 and an available charge of from about 0.3 milliequivalent to about 
8 milliequivalents, preferably from about 0.7 milliequivalent to about 4.5 
milliequivalents, per gram of polymer. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The latex binder system to make the product of this invention comprises a 
cationic latex with particles having a high density of bound charges at or 
near the particle surface and a co-additive which is a water-soluble, high 
molecular weight, anionic polymer of an acrylamide having a degree of 
polymerization from about 3000, preferably from about 5000 to about 10,000 
and having an available charge of from about 0.3 milliequivalent to about 
8 milliequivalents, preferably from about 0.7 milliequivalent to about 4.5 
millequivalents, per gram wherein the anionic polymer retains its 
solubility when in the presence of metal ions at a pH in the range of from 
about 4 to about 7. Other constituents of the paper-making composition at 
the wet-end in the process include a paper-making pulp (generally 
cellulosic), water, and optionally pigment and other common additives well 
known in the paper-making art. 
By "bound" as applied to groups or charges is meant that they are not 
desorbable under the conditions of processing. A convenient test is by 
dialysis against deionized water. 
By the term "pH independent groups" as applied to ionic groups is meant 
that the groups are predominantly in ionized form over a wide range in pH, 
e.g., 2-12. Representative of such groups are sulfonium, sulfoxonium, 
isothiouronium, pyridinium and quaternary ammonium groups. 
By the term "non-ionic" as applied to the monomers in this specification is 
meant that the monomers are not ionic per se nor do not become ionic by a 
simple change in pH. For illustration, while a monomer containing an amine 
group is non-ionic at high pH, the addition of a water-soluble acid 
reduces the pH and forms a water-soluble salt; hence, such a monomer is 
not included. The non-ionic nucleophiles, however, are not similarly 
restricted, i.e., "non-ionic" as used with nucleophiles applies to such 
compounds which are non-ionic under conditions of use and tertiary amines, 
for example, are included. 
By "available charge" is meant the amount of charge an ionizable group 
would provide to a polymer when completely ionized. 
Particularly important features of the process for making paper according 
to the present invention are a high level add-on to the pulp of a cationic 
latex having a high bound charge together with a water-soluble, anionic 
co-additive in a synergistic combination. Such a combination especially 
provides high internal bond strength with accompanying good formation. 
The latexes are structured-particle latexes having a non-ionic core of a 
copolymer of a vinylidene aromatic monomer, an aliphatic, conjugated diene 
and optionally small amounts of other monomers encapsulated by a thin 
layer of a water-insoluble organic copolymer having bound charges as pH 
independent cationic groups. 
Latexes prepared by normal emulsion polymerization have high enough 
molecular weight to be useful. Normally the constituent polymer will have 
a degree of polymerization of greater than about 1000. The lower limit can 
be expressed as the start of the plateau region when properties are 
plotted against molecular weight. 
The amount of bound charge in the latex usually is from about 0.15 
milliequivalent to about 0.6 milliequivalent, preferably from about 0.18 
milliequivalent to about 0.4 milliequivalent, per gram of polymer. 
Ordinarily, the particle size will range from about 800 Angstroms to about 
3,000 Angstroms, more particularly from about 1,200 Angstroms to about 
2,000 Angstroms. 
The non-ionic copolymer core of the latexes operable in the practice of 
this invention contains from about 20 percent to about 50 percent of an 
aliphatic, conjugated diene (preferably 1,3-butadiene), from about 20 
percent to about 80 percent of a monovinylidene aromatic compound 
(preferably styrene), from 0 percent to 5 percent of polar, non-ionic 
ethylenically unsaturated monomers and from 0 percent to about 25 percent 
of other ethylenically unsaturated non-ionic monomers which when in the 
form of homopolymers are water insoluble. 
The monovinylidene aromatic compounds are represented by styrene, 
substituted styrenes (e.g., styrene having halogen, alkoxy, cyano or alkyl 
substituents), vinyl naphthalene and the like. Specific examples are 
styrene, .alpha.-methylstyrene, ar-methylstyrene, ar-ethylstyrene, 
.alpha.-ar-dimethylstyrene, ar,ar-dimethylstyrene, ar-t-butylstyrene, 
methoxystyrene, cyanostyrene, acetylstyrene, monochlorostyrene, 
dichlorostyrenes, other halostyrenes and vinylnaphthalene. 
In this specification and claims, by the word "monovinylidene" in the term 
"monovinylidene aromatic" monomer or compound is meant that to an aromatic 
ring in each molecule of the monomer or compound is attached one radical 
of the formula, 
##STR1## 
wherein R is hydrogen or a lower alkyl such as an alkyl having from 1 to 4 
carbon atoms. 
The aliphatic conjugated dienes operable in the practice of this invention 
include butadiene and substituted butadiene and other acyclic compounds 
having at least two sites of ethylenic unsaturation separated from each 
other by a single carbon-to-carbon bond. Specific examples are isoprene, 
chloroprene, 2,3-dimethylbutadiene-1,3, methylpentadiene, and especially 
1,3-butadiene (often abbreviated butadiene). 
The polar, non-ionic, ethylenically unsaturated monomers are represented by 
the acrylamides such as acrylamide and methacrylamide; the 
hydroxyl-containing esters of .alpha.,.beta.-ethylenically unsaturated, 
aliphatic monocarboxylic acids such as .beta.-hydroxyethyl acrylate, 
.beta.-hydroxyethyl methacrylate, .beta.-hydroxypropyl methacrylate, 
4-hydroxybutyl acrylate and 5-hydroxypentyl methacrylate. 
The other ethylenically unsaturated non-ionic monomers which when in the 
form of homopolymers are water-insoluble are represented by the lower 
alkyl acrylate and methacrylate esters such as methyl acrylate, ethyl 
acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate; 
and the unsaturated nitriles such as acrylonitrile and methacrylonitrile. 
In one method for the preparation of latexes useable in the practice of 
this invention, a known starting latex of a non-ionic polymer of a 
monovinylidene aromatic compound and an aliphatic conjugated diene is 
encapsulated with a thin layer of copolymer of an ethylenically 
unsaturated activated-halogen monomer either by adding the 
activated-halogen monomer or a mixture of such monomers to the reaction 
mixture of the starting latex before all of the monomers are converted to 
polymer or by adding the activated-halogen monomer together with one or 
more hydrophobic monomers to a starting latex containing essentially no 
residual monomers, and initiating and continuing polymerization of the 
thus-added monomers to substantially complete conversion. The resulting 
latex, having a particle size (diameter) of from about 800 Angstroms to 
about 3,000 Angstroms consists of the starting latex particle now 
encapsulated with a bound layer having a thickness of from a monomolecular 
layer of the copolymer to about 100 Angstroms. The latex according to the 
foregoing description can then be reacted with a low molecular weight, 
non-ionic, water-stable, nucleophilic compound which can diffuse through 
an aqueous phase, to form particles of polymer having pH independent 
cationic groups, i.e., onium ions, chemically attached at or near the 
particle surface. 
Representative specific nucleophilic compounds are pyridine, quinoline, 
isoquinoline, tetramethyl thiourea, tetraethyl thiourea, 
hydroxyethylmethyl sulfide, hydroxyethylethyl sulfide, dimethyl sulfide, 
diethyl sulfide, di-n-propyl sulfide, methyl-n-propyl sulfide, methylbutyl 
sulfide, dibutyl sulfide, trimethylene sulfide, thiacyclohexane, 
tetrahydrothiophene, N-methylpiperidine, N-ethylpyrrolidine, 
N-hydroxyethylpyrrolidine, trimethylphosphine, triethylphosphine, 
tri-n-butylphosphine, trimethylamine, triethylamine, tri-n-propylamine, 
tri-isobutylamine, hydroxyethyldimethylamine, butyldimethylamine, 
tri-hydroxyethylamine, triphenylphosphorus, and 
N,N,N-dimethylphenethylamine. 
In carrying out the reaction between the nucleophilic compound and the 
particles of latex having activated halogens chemically bound to the 
surface thereof, the latex is stirred gently while the nucleophilic 
compound is added thereto, as the compound per se or in the form of a 
solution. Gentle stirring may continue throughout the ensuing reaction, or 
optionally after dispersion of the compound in the latex, the stirring may 
be discontinued. The reaction is conveniently carried out at ambient 
temperature although temperatures from about 0.degree. C. to about 
80.degree. C. can be used. The reaction occurs spontaneously at a rate 
which depends upon the reactivity of the activated halogen and of the 
nucleophile. It is preferred to carry out the reaction until a predominant 
proportion of the colloidal stability of the product is provided by the 
resulting chemically bound cationic groups. Usually a catalyst is not 
required although with the less reactive materials, a small amount of 
iodide ion may be used to facilitate the reaction. When a desired degree 
of reaction is reached, any excess nucleophile commonly is removed by 
standard methods, e.g., dialysis, vacuum stripping and steam distillation. 
Other pH independent cationic groups can be substituted for cationic groups 
which are chemically bound to the latex particles according to the 
foregoing description by carrying out a further reaction with such 
cationic groups. For example, a cationic structured-particle latex having 
sulfonium groups chemically bound to the structured-particles at or near 
the particle surface can be reacted with hydrogen peroxide at a 
temperature of from about 20.degree. C. to about 80.degree. C., preferably 
at ambient temperature, for a sufficient time to oxidize part or all of 
the sulfonium groups to sulfoxonium groups. Such treatment also reduces 
the odor of the latex. For best results in such oxidation reaction, the 
hydrogen peroxide is used in excess, e.g., from 2 to 10 moles of hydrogen 
peroxide for each mole of sulfonium groups. 
A more complete description of this and related structured-particle latexes 
and method of preparation is found in the copending application of Gibbs 
et al., Ser. No. 569,723 filed Apr. 21, 1975 now U.S. Pat. No. 4,056,501, 
which is incorporated herein by reference. 
The latexes can contain usual additives such as antifoamers, coalescing 
solvents, pigments, and pH adjusting agents. It is preferred that the 
latexes are soap-free but guantities up to about 0.1 milliequivalent per 
gram can be tolerated. 
The latex is added in an amount greater than that required to cause charge 
reversal on the fiber but less than the amount which would exceed the 
capacity of the fiber to hold a mat together during processing. Such an 
amount of latex usually is from about 5 percent to about 2000 percent, 
preferably from about 10 percent to about 100 percent, dry basis 
calculated on the weight of the fiber. 
The co-additive to be used together with the cationic latex in the practice 
of this invention is a water-soluble, high molecular weight anionic 
polymer of an acrylamide having a degree of polymerization from about 
3000, preferably from about 5,000 to about 10,000 having an available 
charge of from about 0.3 millequivalent to about 8 milliequivalents, 
preferably from about 0.7 milliequivalent to about 4.5 milliequivalents, 
per gram wherein the anionic acrylamide polymer retains its 
water-solubility in the presence of polyvalent metal ions at a pH in the 
range of from about 4 to about 7. The acrylamide polymer has non-ionic 
hydrophilic groups and also has an anionic charge because of the presence 
of anions, such as carboxyl groups or sulfate (sulfonate) groups. Various 
known methods can be used to obtain these anionic acrylamide polymers. For 
example, polyacrylamide can be hydrolyzed to various levels. Other methods 
include direct copolymerization of substituted acrylamide monomers such as 
2-acrylamido-2-methylpropane sulfonic acid or with other hydrophilic 
monomers such as the .alpha.,.beta.-ethylenically unsaturated carboxylic 
acids represented by acrylic acid, methacrylic acid, fumaric acid, maleic 
acid and itaconic acid. 
The acrylamide polymer co-additive has a molecular weight high enough to 
flocculate the fines but low enough to avoid poor formation. If the degree 
of polymerization is less than about 3000, flocculation is inadequate and 
drainage is poor. If the degree of polymerization is over about 10,000, 
the flocculation is excellent but paper formation is generally 
unsatisfactory. The optimum charge on the co-additive depends somewhat on 
the hardness of the water used, i.e., the concentration of multivalent 
cations such as Ca.sup.++ in the water. Generally, polymers of low 
available charge content, such as less than about one milliequivalent of 
available charge per gram (meq/g) of polymer, work best in hard water. 
However, in soft water, better results are obtained when the anionic 
acrylamide polymer has greater than one meq./g of the anionic group. 
The minimum amount of co-additive is determined by the amount of latex 
which is added beyond the charge reversal point of the fiber. It is 
preferred to use more than the minimum amount. The operable range for the 
amount of the co-additive is an amount greater than that required to cause 
essentially complete retention of the latex on the fiber but less than the 
amount which would be effective to start redispersion of components of the 
aqueous suspension. Such an amount usually is from about 0.15% to about 
160%, based on the dry weight of the pulp. 
The fiber used in the practice of this invention is a paper-making pulp or 
blend of pulps, i.e., the common grades such as unbleached sulfite pulp, 
bleached sulfite pulp, unbleached sulfate pulp, semibleached sulfate pulp, 
bleached sulfate pulp, and in some instances groundwood. 
The process to prepare the product of this invention preferably is carried 
out as follows: A dilute aqueous suspension of the fiber is formed in the 
normal manner often in a concentration of from about 0.5 percent to about 
6 percent. The latex is added at any convenient concentration, often in 
the concentration as supplied and the resulting mixture is stirred, 
usually for at least two minutes depending somewhat on the equipment 
available. The aqueous suspension usually is then diluted further, often 
with white water from the process. The co-additive is added as an aqueous 
solution at a concentration usually less than about 1 percent solids and 
the mixture is stirred generally for near the minimum time to obtain 
thorough mixing. While the co-additive is usually and preferably the last 
component added at the wet-end of the process, it may be added at any 
time. Optional wet-end additives can be added at a suitable time. 
Webs or sheets are prepared from the resulting suspension on a paper 
machine such as a Fourdrinier machine or a cylinder machine or in a 
laboratory sheet forming apparatus. With such equipment a web or sheet is 
formed by flowing the aqueous suspension over a support such as a screen 
to form a wet web, dewatering the web and completing drying by heating. 
The sheets or webs are fibrous compositions having the fibers distributed 
uniformly through the thickness and preferentially oriented in the plane 
of the sheet or web. The fibers are strongly bonded to a polymer phase 
comprised of a mixture of thermally deformed particles derived from a 
structured-particle latex and an anionic polyacrylamide of the kinds 
described more fully above. The sheets or webs can have any desired 
thickness but usually the thickness is not greater than about 3 
millimeters. 
The product of the invention provides good internal bond strength 
accompanied by good formation of the sheet. The "formation" of a sheet of 
paper refers to the uniformity of distribution of fibers in the sheet. 
Poor formation occurs when the fibers flocculate or clump together causing 
alternating heavy and light spots in the sheet. Besides diminishing the 
aesthetic appeal of the paper, poor formation tends to decrease in-plane 
strength properties such as tensile strength. Poor formation causes uneven 
surfaces which contribute to poor printability. 
Tests referred to in the examples were carried out as follows: 
Canadian Standard Freeness (CSF) 
The values are determined according to TAPPI Standard T 227-M-58 except 
where variations in the procedure are indicated. 
Delamination Resistance 
The internal bond strength of the products is measured by the delamination 
resistance test. In this test, a strip one inch in width of the product to 
be tested is placed between two strips of adhesive tape having sufficient 
adhesiveness that failure will occur in the paper when the two pieces of 
tape are pulled apart. Delamination is started by hand, then continued and 
measured by an Instron Tensile Tester using a jaw separation rate of 12 
inches per minute. The average force resisting delamination over a length 
of about four inches is determined for each of two samples. The average of 
the two samples is recorded in ounces per inch of width, abbreviated 
oz/in. Those values are followed in parenthesis by conversion to metric 
units, i.e., grams per 2.54 centimeters (g/2.54 cm). When a different 
testing tape is used, the new tape is calibrated according to the initial 
tape and values are reported in values according to the initial tape. 
Formation 
A common way to measure formation is to compare visually the sheet to be 
measured with a set of ten standard sheets specifically made with 
decreasing levels of uniformity of fiber distribution (formation) and 
ranked from 1 to 10 with 1 being the best and 10 the worst. Alternatively, 
optical instruments, which are available commercially can be used for 
measuring formation. 
In this specification and claims, all references to degree of 
polymerization (DP) are weight average unless otherwise indicated.

The following examples illustrate ways in which the present invention may 
be carried out, but should not be construed as limiting the invention. All 
parts and percentages are by weight unless otherwise expressly indicated. 
EXAMPLES 1 and 2 
An aqueous dispersion containing 1393 parts of water having a hardness of 
106 ppm (calculated as calcium carbonate) and an alkalinity of 48 ppm 
(calculated as calcium carbonate) and 7 parts (dry basis) of unbleached 
Canadian softwood kraft having a Canadian Standard Freeness (CSF) of 400 
ml. was stirred at such a rate that the kraft was just turning over 
gently. To the moving kraft suspension was added 1.4 parts (dry weight 
basis) of a latex of the kind described below. After stirring at the same 
rate for an additional two minutes, a dilute aqueous solution (0.2% 
solids) of the specified co-additive was added in the amount shown in 
Table I and stirring was continued for an additional 30 seconds. The 
resulting furnish was made into a handsheet (12 inches.times.12 inches) on 
an M/K Systems "Mini-Mill" handsheet machine using water for dilution of 
the description given above. The handsheet was pressed to a solids content 
of from 37 to 38% by placing the sheet and couching blotter between two 
pieces of wool felt and running the resulting sandwich through the press 
at medium speed using a press pressure of 80 psig. The pressed sheet was 
removed from the wool felts, and stripped from the couching blotter, then 
dried in a drier maintained at 220.degree. F. (104.degree. C.). The 
product was just cockle free, and contained about 95 percent solids. 
The latex used in the foregoing experiment was a structured-particle latex 
having 80 percent of (a) a core polymer of 35 percent of butadiene, 65 
percent of styrene and 20 percent of (b) an encapsulating layer of 35 
percent of butadiene, 15 percent of styrene and 50 percent of vinylbenzyl 
chloride which was reacted subsequent to polymerization with 
2-(dimethylamino)ethanol to provide a bound quaternary ammonium charge of 
0.365 milliequivalent per gram of polymer in the latex. 
The co-additive (A) used in the example is a hydrolyzed polyacrylamide 
having 1.94 milliequivalent of available charge per gram and a degree of 
polymerization of 5500. 
For comparison with the above example of the invention, a sheet was 
prepared in the same manner except for co-additive (A) there was 
substituted co-additive (B), a hydrolyzed polyacrylamide having the same 
available charge but having a degree of polymerization of 25,000, i.e., 
outside the range required for this invention. A further comparison (1B) 
was made in the same manner and with the same components except the 
co-additive was omitted. Data are shown in Table I below. 
TABLE I 
__________________________________________________________________________ 
Co-Additive 
Available Trans- 
Forma- 
Example Charge 
Amount 
CSF.sup.(c) 
mission.sup.(d) 
tion 
Delamination Resistance 
No. Kind 
DP.sup.(a) 
meq/g %.sup.(b) 
ml % Rating 
oz/in 
(g/2.54 cm) 
__________________________________________________________________________ 
1 A 5500 
1.94 0.6 505 76 2 22.7 (644) 
2 A 5500 
1.94 1.2 550 87 2 24.1 (683) 
*1A B 25000 
1.94 0.6 673 73 7 25.6 (726) 
*1B None -- 415 23 1 20.9 (593) 
*2B B 25000 
1.94 1.2 723 97 10 32.5 (921) 
__________________________________________________________________________ 
*Not an example of the invention. 
.sup.(a) Degree of polymerization. 
.sup.(b) Based on weight of kraft. 
.sup.(c) At 3.6 g total solids, uncorrected for temperature. 
.sup.(d) 425 Millimicrons, 19 mm cell vs deionized water. 
The turbidity measurements are made on the effluent from the freeness (CSF) 
test and are indicative of the "white water" characteristics which are 
obtained in the paper making process. 
The sheets from Examples 1 and 2 were acceptable in all the properties 
measured. Comparative examples 1A and 2A were deficient in formation and 
therefore are unacceptable. While comparative example 1B indicated good 
formation, the transmission was low indicating poor flocculation onto the 
fibers and additionally the delamination resistance was low. 
EXAMPLES 3-6 
Sheets were prepared as described in Examples 1 and 2 except different 
latexes and a different co-additive in two different amounts were used as 
shown in Table II. The latexes used (Latex C and Latex D) were structured 
particle latexes prepared according to the method disclosed and claimed in 
application Ser. No. 569,723 filed Apr. 21, 1975, now U.S. Pat. No. 
4,056,501. The latex particles contained 70% of a core copolymer 
consisting of 65% of styrene and 35% of butadiene modified with 0.2% of 
dodecanethiol and the core was encapsulated (capped) with 30% of a 
copolymer of 50% of vinylbenzylchloride, 35% of butadiene and 15% of 
styrene which was subsequently reacted with an excess of dimethylsulfide. 
The latter reaction was stopped for Latex C by vacuum distilling the 
excess dimethyl sulfide when the bound charge of sulfonium group was 0.195 
milliequivalent per gram and for Latex D when the bound charge was 0.388 
milliequivalent per gram. 
The co-additive was a hydrolyzed polyacrylamide having an available charge 
of 3.3 milliequivalents per gram as carboxyl groups and having a degree of 
polymerization of 4100. Data are shown in Table II. 
COMATIVE EXAMPLES 3C and 5C 
Sheets were prepared as described for Examples 3 and 5 except no 
co-additive was used. Data are included in Table II. 
TABLE II 
__________________________________________________________________________ 
Co- 
Latex Additive 
Bound 
Example Charge 
Amount 
Formation 
CSF Transmission 
Delamination Resistance 
No. Kind 
meq/g 
%.sup.(a) 
Rating 
ml % oz/in 
(g/2.54 cm) 
__________________________________________________________________________ 
3 C 0.195 
0.3 2 520 74 26.4 (748) 
*3C C 0.195 
none 1 390 16 23.2 (658) 
4 C 0.195 
0.6 2 580 69 26.5 (751) 
5 D 0.388 
0.3 2 500 31 23.5 (666) 
*5C D 0.388 
none 1 420 10 21.5 (610) 
6 D 0.388 
0.6 2 580 87 27.2 (771) 
__________________________________________________________________________ 
*Not an example of the invention. 
.sup.(a) Based on dry weight of fiber. 
Examples 3-6 illustrate the practice of this invention using a different 
kind of cationic bound charge than in Examples 1 and 2 and also illustrate 
the use of widely differing amounts of bound charge.