CA1085118A - Treating flash-extruded polyolefin fibers with mixture of cationic and anionic polymers - Google Patents

Abstract

Abstract of the Disclosure Hydrophilic polyolefin fibers may be prepared, for example, by discharging a heated and pressurized solution of an anionic polyolefin composition containing carboxylic functionality into a zone of reduced temperature and pressure, and then modify-ing the fibers so produced by treatment with an aqueous admix-ture of selected cationic and anionic water-soluble, nitrogen-containing polymers. Blends of the hydrophilic fibers with wood pulp provide paper products having improved physical properties.

Description

~ve Case ~-7-9 This invention relates to a process for the preparation of hydrophilic polyolefin fibers which are readily dispersible in water and which can be blended with wood pulp ibers to pro-vide a pulp which can be made into high quality paper using con-ventional papermaking techniques. More par~:icularly, the inven tion relates to the formation of polyolefin--based fibers contain-ing carboxylic functionality and treatment of these fibers with blends of certain water-soluble, nitrogen-containing polymers, one of which is cationic and the other of which is anionic. The invention also relates to specific blends of the cationic and an-ionic polymers.
In recent yearsl a conside~able amoun~ of effort has been expended in the development of fibrous polyolefin pulps hav-ing hydrophilic properties. One procedure developed for the pur-pose of attaining such hydrophilic properties is that described in U.S. 3,7~3,570 to Yang et al, assigned to Crown Zellerbach Corporation. According to this patent, polyolefin ~ibers having a high surface area are treated with a hydrophilic colloidal polymeric additive composed of a cationic polymer such as mel-amine-formaldehyde and an anionic polymer such as carboxymethyl cellulose. ~nother procedure de~eloped for the preparation of hydrophilic polyolefin pulps has been one involving the spurting of a mixture of the polyolefin and an additive such as a hydro-philic clay or a hy~rophilic polymer, for example, polyvinyl al-cohol. The spurting process used in these preparations is one in which the polyolein and the hydrophilic additive are dis-persed in a liquid which is not a solvent for either component at its normal boiling point, heating ~he resulting dispersion at superatmospheric pressure to dissolve the polymer and any solvent-soluble additive, and then discharging the resulting compositioninto a zone of reduced temperature and pressure, usually atmos-pheric, to form the fibrous product.
A significant deficiency of these hydrophilic polyole-fin pulps has been that, when they have been blended with wood

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pulp, the ~esulting paper products have exhibited considerably le~s strenyth than that of a paper prepared fro~ wood pulp alone. However, some improvement in the strength of paper made from blends of polyolefln pulps and wood pulp has been realized by imparting an anionic character t:o the polyolefin pulp.
For exampl~, in their German application No. 413,922, fil~d March 22, 1974 and published October 17, 1974 as No. 2,413,922, Toray Xrldustriqs, Inc. ha~e dis-closed the preparation of anionic pulps by spurting mixtures of polyolefins ana copolymers of olefinic compounds with maleic anhydride or acrylic or methacrylic acids. Blends of these pulp9 with wood pulp ha~e provided paper ~ith better tensile strength than paper made without the copolymer component.
It is an object of this invention to prepare paper having further improved s~rength properties from blends of polyolefin pulps and wood pulp.
According to one aspect of the invention, there is provided a process for the pxeparation of hydrophilic polyolefin fibers compxising întimately contacting a spurted fibrous polyolefin composition containing carboxylic functionality with a dilute aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said spurted fibrous polyolefin compositlon having an intrinsic viscosity in the polyolefin componen~ of at least 1.0 and an a~ount o~ carboxylic functionality sufficient to provide at least 0.01 milliequivalent of carboxyl groups per gram of said composition, said cationic polymer being the reaction product oP epichlorohydrin and (a) an aminopolyamide deri~ed from a dicarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one secondary or tertiary amine group, or (b~ a polyalkyl-ene polyamine having the formula H2N(C H2 ~lH) ~1, wherein n is an integer 2 through 8 and x is an integer 2 or more, or (c) a poly(diallylamine) or (d~ a polyaminourylene derived from urea and a polyamine having at least three an~ne groups, at least one of which is tertiary, and said anionic polymer being the reaction product of glyoxal and (a) a polyacrylamide containing from abou~ 2 to about 15% acrylic acid units or (b~ a partially hydrolyzed, branc,hed poly-(~-al~ine) containing from about 1 to about 10 mole percent carboxyl groups based on amide repeating units, ~he ratio of said cationic polymer to said anionic polymer being in the F~ 3 -ranye of from about 1:3 to about 1:7 by wsiyht.
~ s an example of the process of this invention, poly-propylene and an ethylene-acrylic acid copolymer are dispersed in a solvent such as methylene chloride, and the dispersion is heated in a closed system to a temperature of a~out 190C. to dissolve the polymer components in the solvent. Under these con-ditions, the pressure generated by the methylene chloride vapors is of the order of 600 p.s.i. After introducing nitrogen to in-crease the vapor pressure of the system to a pressure of about 10 1000 p~S~io I the resulting solution i5 vented to the atmosphere through an orifice, resulting in evaporation of the methylene chloride solvent and formation of the fiber product. The fiber product then is suspended in an aqueous medium formed by blending a dilute aqueous solution of, for example, epichlorohydrin-modified poly(diethylenetriamine-adipic acid) with a dilute aqueous solution of, for example, glyoxal-modified poly~acryl-amide-co-acrylic acid~, and the components of the resulting sus-pension are brought into intimate contact with each other, as by refining in a disc refiner~ The treated fihers may then be isolated and stored in wet cake form, or the suspension contain-ing the fibers mav be used directly in a papermaking process.
Having generally outlined the embodiments of thi.s in-vention, the following examples constikute specific illustrations thereof. All amounts are based on parts by weight.
Exam~le A
A cationic, water-soluble, nitrogen-containing polymer was prepared from diethylenetri~nine, adipic acid and epichloro-hydrin. Diethylenetriamine in the amount of 0.97 mole was added to a reaction vessel equipped with a mechanical stirrer, a ther-mometer and a reflux condenser. There then was gradually addedto the reaction vessel one mole of adipic acid with stirring.
After the acid had dissolved in the amine, the reaction mixture was heated to 170-175~C. and held at that temperature for one and one-half hours, at which time the reaction mixture had become s~
very viscous. The reaction mixture then was cooled to 140C., and sufficient water was added to provide the resulting polyamide solution with a solids content of about 50%. A sample of the polyamide isolated from this solution was found to have a reduced specific viscosity of 0.155 deciliters per gram when measured at a concentration of two percent in a one molar aqueous solution of ammonium chloride. The polyamide solution was diluted to 13.5~
solids and heated to 40C., and epichlorohydrin was slowly added in an amount corresponding to lo 32 moles pe:r mole of secondary amine in the polyamide. The reaction mixtu:re then was heated at a temperature between 70 and 75C. until it a~tained a ~ardner viscosity of E-F. Sufficient water next was added to provide a solids content of about 12.5%, and ~he solution was cooled to 25C. The pH of the solution then was adjusted to 4.7 with con-centrated sulfuric acid. The final product contained 12.5% solids and had a Gardner viscosity of B-C.
Example B
Another representative cationic, water-soluble, nitro-gen-containing polymer was prepared, this time using epichloro-hydrin and a commercially available liquid mixture of polyaminesas the reactants. This mixture contained at least 75% of bis (hexamethylene)triamine and higher homologues, the remainder of the mixture consisting of lower molecular weight amines, nitrilas and lactams. The reaction was carried out in a kettle fitted with a stream jet vacuum system used to exhaust vapors through a condenser instead of permitting them to escape through an open port in the kettle~
The kettle was charged with 704 parts of water and 476 parts of epichlorohydrin, and then 420 parts of the commercial mixture of polyamines was added to the kettle over a period of 35 minutes, the reaction mixture being cooled to prevent the temperature from exceeding 70C. After addition of the amine, six parts of aqueous 20% sodium hydroxide was added t:o ascelerate the reaction and, after a total of 160 minutes at about 70C., the reaction mixture was d1luted with 640 parts of water to re-duce the viscosity to a Gardner value of about C. A total of 44 parts of aqueous 20% sodium hydroxide then was added over a period of 105 minutes. A Gardner viscosity of S was reached after 215 minutes, at which point the reaction was terminated by the addition of 26 parts of concentrated sulfuric acicl dissolved in 1345 parts of water. The resulting solution had a Gardner viscosity of D, and additional sulfuric acid and water were added to adjust the pH to 4 and provide a solids content of 22.5~.
Ex~nple C
A further cationic, water-soluble, nitrogen-containing polymer was prepared, the basic reactants being methyldiallylamine and epichlorohydrinO To 333 parts of methyldiallylamine was slowly added 290-295 parts of concentrated hydrochloric acid to provide a solution having a pH of 3 to A. The solution then was sparged with nitrogen for 20 minutes and the temperature was ad-justed to 50 to 60C. An aqueous 10.7% solution of sodium bi- ~ !
sulfite and an aqueous 10.1% solution of t-butyl hydroperoxide were simultaneously added to the reaction mixture over a period of four to five hours until the resulting polymer, poly(methyl-diallylamine hydrochloride), had a reduced specific viscosity of 0.2 as measured on a one percent solution in aqueous one molar sodium chloride at 25C. The amount of each of the sodium bisul-fite and the t-butyl hydroperoxide used was two mole percent ~-~
based on the polymer repeat units.
To the above polymer solution there then was added 600 parts of aqueous four percent sodium hydroxide, and the tempera- ;~
ture of the resulting solution was adjusted to 35GC. After addi-tion of sufficient water to bring the solids content of the poly mer solution to 22%, there was added 416.3 parts of epichloro-hydrin. The temperature of the reaction mixture was maintained at about 45Co while the Gardner viscosity of the mixture increa-sed from less than A to B+. After the addition of about 304 parts of 36% hydrochloric acid, the reaction mixture was heated .
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to 80C. and maintained at this temperature with continual addi-tion of further amounts of hydrochloric acid until the pH of the reaction mixture had stabilized at 2 for one hour. The reaction mixture then was cooled to 40C., adjusted t:o a pH of 3.5-4.0 with aqueous four percent sodium hydroxide and diluted to 20%
solids.
The resin product from the above process, prior to use in accordance with this invention, must be base activated. This is accomplished by adding 18 parts of water and 12 parts of one molar sodium hydroxide solution to each 10 parts of the 20~ solids solution of the resin. The resulting five percent solids 501u-tion, after aging for 15 minutes, should have a pH of 10 or high-er. Additional sodium hydroxide should be added, if necessary, to obtain this level of pH.
Example D
Another useful cationic, water-soluble, nitrogen-con-taining polymer was prepared from bis(3-aminopropyl)methylamine, urea and epichlorohydrin. Two hundred ten parts of the amine and 87 parts of urea were placed in a reaction vessel, heated to 175C., held at this temperature for one hour and then cooled to 155C. Water was added to the reaction product in the amount of 375 parts, and the resulting so:Lution was cooled to room tempera-ture.
To 271 parts of the above solution was added 321 parts of water, 29 parts of concentratad hydrochloric acid and 89.6 parts of epichlorohydrin. The temperature of the reaction mix-ture was maintained in the range of 39 to 42C. for about 85 minutes while the Gardner viscosity of the mixture increased from A-B to L+. There then was added to the mixture 60 parts of con-centrated hydrochloric acid, and the resulting mixture was heatedfor four hours at a temperature in the range of 60 to 75C., nine more parts of hydrochloric acid being added after about one and one-half hours to keep the pH below 2. The mixture then was cooled to room temperature. The resulting epichlorohydrin-modîf-ied polyaminourylene product contained 27~ solids.
The above product, prior to use in accordance with thisinvention, also must be base activated. Activation i~ accom-plished by adding ten parts of the above product to 10 part~ of one molar sodium hydroxide solution, aging the resulting solution for 15 minutes, and then diluting the solution (13.5% solids) to five percent solids or less for use.
Example E
An anionic, water soluble, nitrogen-containing polymer was prepared from acrylamide, acrylic acid and glyoxal. To a reaction vessel equipped with a mechanical stirrer, a thermo-meter, a reflux condenser and a nitrogen adapter was added 890 parts of water. There then was dissolved in th~ water 98 parts of acrylamide, two parts of acrylic acid and one and one-half parts of aqueous 10% cupric sulfate. The resulting solution was sparged with nitrogen and heatedto 76C., at which point two parts of ammonium persulfate dissolved in six and one-half parts of water was added. The temperature of the reaction mixture in-creased 21.5C. over a period of three minutes following addition 20 of the persulfate. When the temperature returned to 76C., it ~ .
was maintained there for two hours, after which the reaction mix-ture was cooled to room temperature. The resulting solution had a Brookfield viscosity of 54 centipoises at 21C. and contained less than 0.2~ acrylamide based on the polymer content.
To 766.9 parts of t~e above solution t76.7 parts of polymer containing 75.2 parts, or 1.06 mole, of amide repeat units) was added 39.1 parts of aqueous 40% glyoxal (15.64 parts, or 0.255 equivalent based on amide repeat units, of glyoxal).
The pH of the resulting solution was adjusted to 9.25 by the addi~
tion of 111.3 parts of aqueous 2% sodium hydroxide. Within approximately 20 minutes after addition of the sodium hydroxide, the Gardner viscosity of the solution had increased from A to E.
The reaction was then terminated by the addition of 2777 parts of water and about two and six-tenths parts of aqueous 40% sulfuric . ' ., .

acid. The resulting solution had a pEI of 4.4 and contained 2~2 solids.
Exam~le F
Another representative anionic, water-soluble, nitro-gen-containing polymer was prepared using only acrylamide and glyoxal as reactants. In a reaction vessel equipped with a stir-rer, a thermometer and a reflux condenser, there was placed 350 parts of acrylamide, one part of phenyl-~-naphthylamine and 3870 parts of chlorobenzene. This mixture was heated to 80 to 90C.
with vigorous stirring to partially melt and partially dissolve the acrylamide. One part of sodium hydroxide flake then was added to the mixture and, after an induction period, an exothermic reaction occurred and there was separation of polymer on t:he stirrer and on the walls of the reaction vessel. Three more one-part charges of sodium hydroxide flake were added to the reaction mixture at thirty-minute intervals, following which the reaction mixture was heated at about 90C. for one hour. The hot chloro-benzene then was decanted, and the residual solid, a branched, water-soluble poly(~-alanine), was washed three times wikh ace-tone and subsequently dissolved at room temperature in 1000 parts of water. The cloudy solution so obtained, having a pH of about 10.5, was heated at about 75C. for about 30 minutes to effect partial hydrolysis of the amide groups in the poly(~-alanine), and live steam was blown through the solution until the residual chlorobenzene had been removed and the last traces of polymer had dissol~ed. After cooling, the solution was adjusted to a pH of about 5.5 with sulfuric acid. The dissolved polymer contained about two mole percent carboxyl groups, as determined by poten-tiometric titration.
To an aqueous 15% solution of the above polymer was added an aqueous ~0~ solution oE glyoxal in an amount sufficien~
to provide 25 mole percent of glyoxal based on the amide repeat units in the polymer. The pH of the resulting solution was slo~-ly raised to about 9.0 to 9.5 at room temperature by ~he addition 35~
of dilu~e aqueous sodium hydroxide, and the pH was maintained a~
this level until an lncrease in Gardner vlscosity of five to six units had occurred. The solution then was quickly diluted with water to 10% total solids and adjusted to a pH of 5.0 with sul-furic acid.
Example 1 Ninety parts of isotactic polyprop'ylene having an in-trinsic viscosity of 2.1 in decahydronaphthalene at 135C. and 10 parts of an ethylene-acrylic acid copolymer ~Dow, 92:8 ethylene:acrylic acid, melt index 5.3) were charged to a closed autoclave along with 400 parts of methylene chloride as the sol-vent. The contents of the autoclave were stirred and heated to 220C., at which point the vapor pressure in the autoclave was raised to 1000 p.s.i. by the introduction of nitrogen. The re-sulting solution wasspurted from the autoclave into the atmos phere through an orifice having a diameter of one millimeter and a length of one millimeter, resulting in evaporation of the methylene chloride solvent and formation of the desirad fiber product. This fiber product then was disc refined for six min-utes in a Sprout Waldron disc refiner at 0.25~ consistency in an aqueous medium containing 0.1% of a blend of the cationic ~ ~;
polymer of Example A and the anionic polymer of Example E, the weight ratio of the cationic polymer to anionic polymer in the resin blend being 1:5. The refined fiber product, after washing with water, contained 8~5% of attached resin based on nitrogen -analysis.
E ~ ~ -The spurted fiber product of Example 1 was disc refined as in that example except that an aqueous medium containing 0.05%
of the blend of cationic and anionic polymers was used. The re fined fiber product, after washing wi~h water, contained 5.2%

attached resin based on nitrogen analysis.
Example 3 The procedure of Example 1 was duplicated exceE)t for , .

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1 Od8 5~ ~ 8 use of the following con itlons in preparation of the spurted fiber product: ~5 parts oE the polypropylene, five parts of ethylene-acrylic acid copolymer (Dow, 88:12 ethylene:acrylic acid, melt index 7.0), a mixture of 360 part:s of methylene chlor-ide and 40 parts of acetone as the solvent, a temperature of 220C. and a pressure of 1200 p.s.i. The fi.ber product 30 ob-tained, ater disc refining as in Example l, contained 9.0% of deposited resin as determined by nitrogen analysis.
Example 4 The procedure of Example l again was duplicated except for use this time of the following conditions in preparing the spurted fiber product: 90 parts of an isotactic polypropylene having an intrinsic viscosity of 1.3 in decahydronaphthalene at 135C., lO parts of ethylene-acrylic acid copolymer ~Union Carbide, 94:6 ethylene:acrylic acid), 900 parts of methylene chloride as the solvent, a temperature of 200C~, and a pressure of lO00 p.s.i. The fiber product from this spurting process then was disc refined as in Example l, resulting in fibers containing 7.2% of attached resin based on nitrogen analysis.
Example 5 A spurted fiber product was prepared following the pro-csdure of Example l except for use of 80 parts of the polypro-pylene, 20 parts of ~he ethylene-acrylic acid copolymer of Ex-ample 4, 400 parts of methylene chloride, a temperature of 210C.
and a pressure of 1000 p.s.i. The product was disc refined as in ~xample l, giving a fiber product containing 6.7% of deposited resin based on nitrogen analysis.
Examples 6 and 7 Repetition of Example 5 wa5 effected under identical conditions except for use of a 1:7 weight ratio of the cationic polymer of Example A to the anionic polymer of Example E in the resin blend in Example 6 and a 1:3 weight ratio of the polymers in Example 7. The resin pick-up in the fiber p:roduct of Example 6 was 6.5% and was 5.1~ in the fiber product of Example 7.

Example 8 Each of the synthetic pulp9 prepared as described in Examples 1 to 7 was blended with bleached kraft wood pulp t50:50 RBK:WBK, pH 6.5, 500 Canadian S-tandard Freeness) in the ratio of 30% synthetic pulp to 70% wood pulp. Handsheets prepared from the blends were dried and calendered at 500 lbs./linear inch at 60C. The brightness, opac~y, tensile strength and Mullen burst strength of the calendered sheets were determined, and the re- ~
sults are given in ~able 1. In the data given in this table, the ~; :
tensile strength and Mullen burst strength values are expressed as a percentage of the tensile strength and Mullen burst strength of the 100% wood pulp control, all being corrected to a 40 pound ;
per ream basis weight.
Table 1 Mullen rrensile Bursk Example Bri~htness ~ .Stre ~ Str 1 87.3 85.8 90 86 :`
2 87.9 87.2 82 84 . :

3 87.6 87.7 78 78

4 84.4 81.5 71 68 87.2 82.5 78 72 : ::.
6 87.4 81.8 76 76 ::
7 87.5 82.8 79 63 .
It is apparent from the above data that the process of this in-vention will provide paper having from about 70 to about 90% of the tensile strength and from about 60 to about 85% of the Mullen burs~ strength of a paper prepared from 100% wood pulp.
Example 9 The procedure of Example 1 was followed using 200 parts :;
of crystalline polypropylene grafted with three percent by weight of maleic anhydride, 2672 parts of methylene chloride, a tempera-ture of 200C. and a pressure of 1000 p.s.i. The spurted fiber product was disc refined as in Examp]e 1, resulting in fibers containing 2.7% of deposited resin. The refined pulp was blended with wood pulp and handsheets were prepared and evaluated, as in Example 8. The resulting sheets exhibited ~2% brightness, 80 opacity, 67~ tensile strength and 71% Mullen burst strength.
Example 10 The procedure of Example 1 was used to prepare a spurted fiber product from crystalline polyE~ropylene grafted with six percent by weight of acrylic acid. A 3:2 by weight ratio of water:hexane was used as the dispersing medium. The fiber product was disc refined as in Example 1 except to use an aqueous 0.5%
solution of a blend of the cationic polymer of Example A with the anionic polymer of Example F, the weight r~tio of the cationic polymer to the anionic polymer being 1:3. The amount of resin deposited on the fibers was 7.2~. The refined pulp was blended with wood pulp and handsheets were prepared and evaluated, as in Example 8. The resulting sheets showed 87% brightness, 79.3%
opacity and 77~ tensile strength.
Example 11 Ninety parts of high density polyethylene ~DuPont, melt index 5.5-6.5 at 190~C.) was substituted for the polypro-pylene in Example 1 and the admixture with the ethylene-acrylic acid copolymer was spurted from solution in methylene chloride at 200C. and 1000 p.s.i. pressure. The fiber product was disc refined as in Example 1, and the refined pulp was blended with wood pulp and handsheets were prepared and evaluated, as in Example 8. The resulting sheets showed 84% brightness, 30%
opacity, 68% tensile strength and 69~ Mullen burst strength.
Example 12 One hundred and thirty parts of polypropylene having an intrinsic viscosity of 2.2 in decahydronaphthalene at 135Co r 370 parts of methylene chloride, a temperature of 222C. and pressure of 1000 p.s.i. were used in the preparation of a fiber product following the procedure of Example lo Sixty parts of the fiber ~roduct was suspended in 6noo parts oE water, the rcsuLtin(J su~-~13-pension waq agitated, and air containing 0.7 g./cu. ft. of ozone was passed through the suspension at room temperature at a rate of 0.06 cu. ft./min. for a period of 15 minutes. Under these conditions, the ozone pickup by the fiber was 0.53% by weight or the fibers, and the fibers had an acid number corresponding to 0.033 milliequivalent of carboxyl groups per gram of fiber. The wet ozonized fibers were disc refined as in Example 1, and the refined product was found to contain 5.4% of attached resln based on nitrogen analysis. The refined pulp then was blended with wood pulp (50:50 RBK:WBK, 750 Canadian Standard Freeness~, and handsheets were prepared and evaluated as in Example 8. The re-sulting sheets exhibited 87.3% brightness, 87.6% opacity and 84%
tensile strength.
Example 13 . . , The procedure of Example 12 was repeated except for carrying out the ozonization reaction or one hour. The ozone pickup by the fibers was 1~9~, and the fibers had an acid number corresponding to 0.129 milliequivalent of carboxyl groups per gram of fiber. After disc refining, the fibers contained 5.1% of attached resin, and the handsheets prepared according to Example 8 showed 87.2~ brightness, 87.7~ opacity and 89% tensile strength.
Example 14 The procedure of Example 13 was duplicated except for use of high density polyethylene instead of polypropylene and use of pentane as the solvent instead of methylene chloride. The ;
ozone pickup was 1.2~, the acid number was 0.115 milliequivalent per gram, the amount of attached resin was 8.8%, and the hand-sheets exhibited 85% brightness, 87% opacity and 100% tensile strength~
Exam~le 15 Following generally the technique of Example 12, a spurted fiber product was prepared from high density polyethylene grafted with five percent of maleic anhydride, a one percent sus-pension of 60 parts of the fibers in water was prepared, and , .

ozone was passed through the Eiber suspension for one hour at 25C. at a rate of 0.039 g./min. The ozonized fibers were disc refined at 0.125~ consistency in an aqueous medium containing 0.05~ of the resin blend of Example 1. The resin pickup from the refining procedure was 5.4%, and, af-ter blending with wood pulp and forming handsheets as in Example 8, the resulting sheets ex-hibited 37.5% brightness, 85% opacity and 85~ tensile strength.
Example 16 A polypropylene fiber product was prepared using condi-tions comparable to those given in Example 12. A portion of this product was blended with five percent by weight, based on the polypropylene fibers, of wood pulp (50:50 RBK:WBK), and the fiber blend was disc refined until it became water-dispersible. A one percent dispersion of the blend in water was then oæonized by passing ozone through the fiber dispersion at room temperature until the ozonized fibers had an acid number corresponding to 0.07 milliequivalent of carboxyl groups per gram of fiber. Thirty parts of the ozonized pulp was blended with 70 parts of wood pulp, and to portions of the resulting blend in papermaking crocks was added five percent based on total fiber weight of (a) the resin blend of Example 1, (b) a blend of the cationic polymer of Example B with the anionic polymer of Example E, the ratio of cationic:anionic being 1:5 by weight, (c) a blend of the cationic polymer of Example C with the anionic polymer of Example E, the cationic:anionic ratio being 1:5 by weight, and (d) a blend of the cationic polymer of Example D with the anionic polymer of Example E, the ratio of cationic:anionic being 1:5 by weight.
After thorough mixing of the additives with the pulp, handsheets were prepared and evaluated as described in Example 8. The re-sults are given in Table 2.

Table 'rensile Additive ~ y S~r (a) 87. 8 84 ~ 5 67 (b) 87 ~ 1 84 ~ 3 68 (C) 87~6 84~4 7~
(d) 87 ~ 8 84 ~ 2 69 Comparative data obtained from the evaluation of representative ;
prior art processes and polymeric additlves are shown in the following ex~
amples. All amounts again are based on parts by weight.
Comparative Example 17 .
Following the procedure of Example 1, a fiber product was preparedfrom 95 parts of the polypropylene and ive parts o the ethylene-acrylic acid copolymer of that example, and separate portions of the fiber product were disc refined in aqueous medium containing 0.1% of ~a) the resin blend of Example 1, (b) a 1:1 blend of melamine-formaldehyde polymer and carboxymethyl cellulose (D.S. OA4) and (c) a 2:1 blend of the melamine-formaldehyde and carboxymethyl cellulose polymers. Each of the resulting pulps was blended with wood pulp, and handsheets w~re prepared and evaluated, all as described in Example 8~ The results are shown in Table 3.
Table 3 Mullen Tensile Burst Additive Brightness ~ Strength Strength (a) 82~5 87~0 73~5 56~0 (b) 81 ~ 8 86 ~ 7 38 ~ 2 24 ~ 9 ~C) 84 ~ 3 88 ~ 2 44.1 26~ 0 `
These data show that replacement of resin blend (a) by kno~n blends (b) and (c) in the process of this invention does not provide a paper having the desired strength. - ;
Comparative Example 18 A spurted fiber product substantially identical to that of Example 1 was disc refined for six minutes in water in a Sprout Waldron disc refiner at 0.25~ consistency. The refined pulp was blended with bleached kraft wood pulp (50:50 RBK:WBK, 500 Cana-dian Standard Freeness), as in Example 8, and to portions of the resulting mixture in papermaking crocks there was added five per-cent based on total ~iber weigh-t of (a) the resin blend of Ex-ample 7, (b) a blend of the cationic pol~mer of Example B with the anionic polymer of Example E, the wei~ht ratio of the cation-ic polymer to anionic polymer being 1:3, (c) a blend of the 10 cationic polymer of Example C with the anionic polymer of Ex-ample E, the weight ratio of the cationic polymer to anionic polymer being 1:3, and (d) the 2:1 blend of the melamine formal-dehyde and carboxymethyl cellulose polymers of Example 17. Addi- !' tional portions of the pulp mixture were similarly treated with one and one-half percent of (a), (b), (c) and (d) based on total fiber weight. Handsheets were prepared and evaluated as des-cribed in Example 8. The results are yiven in Table 4. . :

Table 4 Mullen :~
Tensile Burst Additive Brightness Opacity Stren~th Strength -(%) (%) (%) (%)

5-0% (a? 82.5 82.4 g7 102 5.0% (b) 81.0 83.8 75 103 5.0% (c) 81.3 80.3 92 86 5.0% (d) 85.6 82.0 .50 52 1.5% (a) 85.1 83.6 67 69 1.5% (b) 84.6 82.9 70 68 1.5% (c) 84.0 81.6 70 95 30 1.5% (d) 86.5 83.1 55 40 It is apparent from the above data that additives (a), (b) and (c) of this invention provide better paper stren~th than known additive (d).

Comparative Examp~e 19 A spurted ~iber product was prepared as in ~xample 1 _ 17 -35~B
- except to omit the ethylene-acrylic acid copolymer and use 100 parts of polypropylene. Separate portions of the fiber product were beaten in a Waring blender in aqueous medium containing 1.0 o~ (a) the resin blend of Example 1, ~b) thle 1:1 blend of the melamine-formaldehyde and carboxymethyl cellulose polymers of Example 17 and (c) the 2:1 blend of the melamine-formaldehyde and carboxymethyl cellulose polymers of Example 17. The result- ~
ing pulps were blended with wood pulp, and handsheets were pre- ~ ~ -pared and evaluated as described in Example 8. Table 5 shows 10 the results obtained. ;~

Table 5 Mullen Tensile Burst -Additive Briqhtness O~acitv Stren~th Strenth ~%) (%) (~) ( ) (a) 87.6 87.5 47.7 37.1 (b) 89.6 87.8 36.2 22.9 (c) 89.2 88.2 36.9 26.3 These data again show the superiority of the additive (a) of this 20 invention over known additives (b) and (c). Moreover, by compar-ison to Example 17, the data with respect to additive (a) show the importance o~ the carboxylic functionality of the anionic ~ ;~
polyolefin composition used in accordance with the process o~
this invention.
Example 20 Eighty parts of the polypropylene of Example 1 and 20 parts of a styrene-maleic anhydride copolymer (75:~5 styrene:
maleic anhydride, molecular weight 19,000) were charged to a closed autoclave along with 250 parts o~ hexane and 250 parts of 30 water. The contents of the autoclave were stirred and heated to - 220C., at which point the vapor pressure in the autoclave was raised to 1000 p.s.i. with nitrogen. The resulting emu:Lsion was spurted from the autoclave into the atmosph~ through an orifice having a diameter of one millimeter and a length o~ one mlllimeter, resulting in formation of a fiber productO

.:

Portions of the fiber produc-t were disc refined for six minutes in a Sprout Waldron disc refiner at 0.25% consistency in (a) water, tb) an aqueous 0.5~ solution oE ~le cationic polymer of Example A, (c) an aqueous 0.5~ solution of glyoxal-modified poly(acrylamide-co-acrylic acid), (d) an aq~leous 0.5~ solution of melamine-formaldehyde polymer, (e) an aqueous 0.5~ solution of cationic starch, and (f) an aqueous ~.5~ solution of a 1:3 blend of the cationic polymer of Example A and the anionic poly-mer of Example F. Each of the resulting pulps was blended with wood pulp, and handsheets were prepared and evaluated, all as described in Example 8. The data so obtained are given in Table 6.

Table 6 ~ullen Refining Tensile Burst Medium Briqhtness Opacity Stren~th Stren~th ( % )-'~ 96 )( % ~
(a) 84.2 81.341 30 (b) 85.2 79.851 48 (c) 85.5 81.~39 32 (d) 81.6 82.548 38 (e) 84.8 79.254 48 (f) 82.1 79.472 71 These data show that individual additives when used in the pro- -cess of this invention are by no means as effective in providing a paper having adequate strength as is a blend of the specific cationic and anionic polymers of this invention, such as the blend used in (f).-The process of this invention is quite simple and at-tractive ~or the reason that it provides synthetic pulps which, 30 when blended with wood pulp, lead to paper productshaving im- `;
proved brightness, opacity, smoothness and printability at low sheet weights compared with conventional filled or unfilled paper. Also advantageous is the fact that the synthetic pulps of this invention do not require the presence of separate water-soluble additives, such as sta.rch, in the ~permaking process, ~:
~ese being rendered unnecessary by the presence of the cationic polymer component incorporatecl in the modified fibers produced by the process of this invention~
In the process of this lnvention, the anionic polyole-fin composition containing carhoxylic functionality may be a polyolefin containing carhoxyl groups which have been introduced into the polymer molecule by grafting the polyolefin with a mon-omer containing carboxylic functionality or by oxidizing the polyolefin with o~ygen or ozone, or the composition may he a polyolefin in admixture with an anionic polymer containing car-boxylic functionality. In any case, the polyolefin may be poly-ethylene, polypropylene, an ethylene-propylene copolymer or a mixture of any of these polvolefin materials.
When the anionic polyolefin composition is an admix-ture of a polyolefin and an anionic polymer containing carboxylic functionality, the latter component may be a polyolefin contain-ing carboxyl groups directly attached to the polymer backbone, a polyolefin grafted with acrylic acid, methacrylic acid, maleic -, anhydride or mixtures thereof, a copolymer of any one of ethylene, propylene, styrene, a-methylstyrene or mixtures thereof with any one of acrylic acid, methacrylic acid, maleic anhydride or mix-tures thereof, as well as mixtures of any of these anionic poly-mer components. Again, wherever specified, the polyolefin may be polyethylene, polypropylene, an ethylene-propylene copolymer or mixtures thereof.
In the foregoing admixtures of polyolefin and anionic polymer containing carboxylic functionality, the ratio of the former to the latter will preferahly be from about 95:5 to about 80:20 by weight, and the amount of available carboxyl in the ani-onic polymer will be from about three to about 30% b~ weight. In general, the anionic polyolefin composition used in the process ;~
of this invention should contain a sufficien~ amount of carbox~
ylic functionality to provide at least O.nl, and preferably at least about 0.04 milliequivalent of car~oxyl groups per gram of the polyolefin pulp. Moreover, the amount of carboxylic functionality may be such as to provi~e up to about one milli-equivalent of carboxyl groups per gxam of khe polyolefin pulp.
A highly c~esixable range is Erom abou-t 0.04 to ahout 0.2 milli-equivalent per gram.
The dispersing medium use~ in the fiber-orming step of the process of this invention contains an organic solvent which is a nonsolvent at i~s normal boiling point for the poly-olefin composition used to form the fibers. It may be the meth-ylene chloride shown in most of the es~amples, or other halogen-ated hydrocarbons such as chloroform, carbon tetrachloride,methyl chloride, ethyl chloride, trichlorofluoromethane and 1,1,2-trichloro-1,2,2-trifluoroethane. Also useful are aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as butane, pentane, hexane, heptane, octane and their isomers; and alicyclic hydrocarbons such as cyclohex-ane. Mixtures of these solvents may be used, and water ~ay be present when it is desired to forrn an emulsion of the polyolefin composition. Moreover, the pressure generated by the solvent vapors may be, and normally will be, augmented ~y a pressurized inert gas such as nitrogen or carhon dioxide.
In carrying out the fiber-forming process, the concen-tration of the polyolefin composition in solution in the solvent normally wiLl be from about 5 to about 40~ by weight, preferably from about 10 to about 20% by weight. The temperature to which the dispersion of the polyolefin composition in the solvent is heated to form a solukion of the composition will be dependent upon the particular solvent used and should be sufficiently high to effect dissolution of the composition. The fiber-forming tem-perature will generally be in the range of from about 100 to about 225C. The pressure on the solution oE the polyolefin com-position may be from about 600 to about 1500 p.s.i., but prefer~
ably is in the range o from about ~00 to about 1200 p.s i. The orifice through which the solution is discharged shoulcl have a diameter of from abou~ 0.5 to about 15 m~., preferably fxom about one to about ive mm., and the ratio of the length of the orifice to its diameter should be from about 0.2 to about ln.
In the fiber~modifying step of the process of this in-vention, the fibers of the fibrous anionic polyolefin composition containing carbo~yli~ functionality are intimately contacted with a dilute a~ueous solution or dispersion of a blend oE certain cationic and anionic nitro~en-containing polymers. The ratio of cationic to anionic polymer in the blend pre,ferably is in the range o from about 1 3 to about 1:7 by weight. The cationic polymer component of the aforementioned blend may generally be classified as the reaction product of epichlorohydrin and a polymer containing secondary or tertiary amine groups, or both.
One representative group of polymers belonging to this defined class may be exemplified by the cationic polymer component used in many of the examples, namely, the reaation product of epi-chlorohydrin and the aminopolyamide derived from diethylenetri amine and adipic acid. Preparation of this product is shown in Example A. However, more generally, this group of cationic poly-mers are the reaction products of epichlorohydrin and an amino-polyamide derived from a dicarboxylic acid and a polyalkylene-polyamine having two primary amine groups and at least one sec- -ondary or tertiary amine group, all as described in U.S.
2,926,116 and U.S. 2,926,154.
Another representative group of polymers belonging to the broadly defined class of cationic polymers is that wherein the polymers are water-soluble reaction products of epichloro-hydrin and a polyalkylene polyamine. The preparation of an ex-emplary product from this group i5 shown in Example B.
Polyalkylene polyamines which can be reacted with epi-chlorohydrin have the formula H2N(CnH2nNH)xH wherein n is aninteger 2 through 8 and x is an integer 2 or more, preferably 2 through 6. Examples of such polyalkylene polyamines are the polyethylene polyamines, polypropylene polyamines and poly-butylene polyamines. Specific examples of these polyalkylene 1 1385~3L8 polyamines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, bis(hexamethylene)triamine and dipropyl-enetriamine. Other polyal~ylene polyamines that can be used include methyl bis(3-aminopropyl)amine; methyl bis(2-aminoethyl)-amine; and 4,7-dimethyltriethylenetetramine. ~ixtures of poly-alkylene polyamines can be used if desired.
The relative proportions of polyalkylene polyamine and epichlorohydrin employed can be varied depending upon the partic-ular polyalkylene polyamine used. In general, it is preferred that the molar ratio of epichlorohydrin to polyalkylene polyamine be in excess of 1:1 and less than 4.5:1. In the preparation of water-soluble resin from epichlorohydrin and tetraethylenepenta-mine, good results are obtained at molar ratios of from about 1.4:1 to 1.94:1. Reaction temperature is preferably in the range of from about 40 to about 60C.
A ~urther group oE cationic polymers useful in accor~
dance with this invention is that in which the polymers are the reaction products of epichlorohydrin and a poly(diallylamine).
The preparation of such a product is shown in Example C. Addi-tional products and the process of preparing them are shown inU.S. 3,700,623.
The final group of cationic polymers used in accor-dance with this invention is that wherein the polymers are the reaction products of epichlorohydrin and a polyaminourylene. `~
The preparation of one of these products is given in Example D.
Related products and their preparation are described in U.S. `~
3,240,664 The anionic polymer component of the aqueous solution or dispersion in which the fibers of the anionic polyolefin com~
position containing carboxylic functionality are modified is illustrated in the examples. One of these is the reaction prod-uct of glyoxal and the polyacrylamide obtained by copolymeriza-tion of acrylamide with acrylic acid. The preparation o an exemplary product is shown in Example E. The amount of acrylic ~51~3 acid units in the copolymer may be from about 2 to ahout 15%.
Comparable products can be prepared by partial hydrolysls of polyacrylamide or a poly(acrylamide-co-alkyl acrylate) such as a copolymer of acrylamide with ethyl acrylate. ~ny of these poly-acrylamides can be prepared by conventional methods for the polymerization of water-soluble monomers and preferably have molecular weights less than about 25,000, for example, in the range o from about 10,000 to about 20,000.
The other anionic, nitrogen-containing polymer shown in the examples is the reaction product of glyoxal and the polymer obtained by partial hydrolysis of a branched, water-soluble poly~-alanine). Preparation of a representative product is shown in Example F. The poly(~-alanine) is prepared by the an-ionic polymeriæation of acrylamide in the presence of a basic catalyst such as sodium hydroxide, and a vinyl or free-radical polymerization inhibitor, such as phenyl-~-naphthylamine, and the polymer will have a molecular weight in the range of from about 500 to about 10,000, preferably from about 2,000 to about 6,000.
Because of the extremely exothexmic nature of the anionic polym-erization, it is preferred to conduct the reaction in a suitable oxganic reaction medium such as toluene or chlorobenzene, inert -to the reaction conditions and capable of dissolvin~ or slurry-ing acxylamide.
The branched poly(~-alanine) produced as described above is a neutral polymer and needs to be anionically modified for the purpose of this invention. Anionic modification of branched poly(~-alanine) can be accomplished by partial hydrolysis of the polymer to convert some of the primary amide groups into anionic carboxyl groups. For example, hydrolysis of poly(~-alanine~ can take place by heating a slightly basic aqueous solution of the polymer having a pH of about 9 to 10 at temperatures of about 50 to about 100C. The amount of anionic groups introduced should be from about one to about ten mole percent, and preferably about two to about five mole percent, based on amide repeatin~ units.

Each of the anionic, nitrogen-containing polymers de-scribed above is modified with glyoxal to provicle the desired an-ionic, water-soluble, nitrogen-containing polymers used in accor-dance with this invention. The reaction with glyoxal is carried out in a dilute neutral or slightly alkaline aqueous solution of the polymer at a temperature of from about 10 to about 50~C., preferably from about 20 to about 30C. The amount of glyoxal used in the reaction mixture may be from about 10 to about 100 mole percent, preferably from about 20 to ahout 30 mole percent, based on amide repeat units in the polymer. The resulting solu-tions possess good stabili-ty.
The process of this invention makes possible the prep aration o improved paper products from blends o wood pulp and polyolefin pulps. The process depends upon the particular com-bination of cationic and anionic nitrogen-containing polymers used in the fiber-modiEying step, and the latter preferably in-volves the use of a refining procedure, such as disc refining.
Moreover, the process depends upon several critical factors, namely, the presence oE at least 80% polyolefin in the poly- ;
olefin-carboxyl-containing anionic pol~mer admixture, when this admixture constitutes the anionic polyolein composition con- ;
taining carboxylic ~unctionality used as the fiber-forming mate-rial~ an intrinsic viscosity of at least 1.0 for the polyolefin, sufficient available carboxyl in the anionic polyolefin composi-tion containing carboxylic functionality and sufficient resin in the aqueous solution or dispersion in which the anionic ibers are modified. However, operation within the limits of these conditions makes it possible to produce a synthetic pulp which, when blended with wood pulp, will provide a paper product having at least 70% of the tensile strength of 100% wood pulp, as well as increased brightness, opacity and smoothness.

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of hydrophilic polyolefin fibers which comprises intimately contacting a spurted fibrous polyolefin composition con-taining carboxylic functionality with a dilute aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said spurted fib-rous polyolefin composition having an intrinsic viscosity, in the polyolefin component, of at least 1.0 and an amount of carboxylic functionality sufficient to provide at least 0.01 milliequivalent of carboxyl groups per gram of said composition, said cationic polymer being the reaction product of epichloro-hydrin and (a) an aminopolyamide derived from a dicarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one second-ary or tertiary amine group, or (b) a polyalkylene polyamine having the formu-la H2N(CnH2nNH)xH, wherein n is an integer 2 through 8 and x is an integer 2 or more, or (c) a poly(diallylamine) or (d) a polyaminourylene derived from urea and a polyamine having at least three amine groups, at least one of which is tertiary, and said anionic polymer being the reaction product of glyoxal and (a) a polyacrylamide containing from about 2 to about 15% acrylic acid units or (b) a partially hydrolyzed, branched poly(.beta.-alanine) containing from about 1 to about 10 mole percent carboxyl groups based on amide repeating units, the ratio of said cationic polymer to said anionic polymer being in the range of from about 1:3 to about 1:7 by weight.

2. The process of claim 1 wherein the spurted fibrous polyolefin com-position containing carboxylic functionality is based on polyethylene.

3. The process of claim 1 wherein the spurted fibrous polyolefin com-position containing carboxylic functionality is based on polypropylene.

4. The process of claim 3 wherein the spurted fibrous polyolefin com-position containing carboxylic functionality is prepared by spurting a mix-ture of polypropylene and an anionic polymer containing carboxylic function-ality.

5. The process of claim 4 wherein the anionic polymer con-taining carboxylic functionality is a copolymer of ethylene and acrylic acid.

6. The process of claim 3 wherein the spurted fibrous polyolefin composition containing carboxylic functionality is prepared by spurting polypropylene and oxidizing the resulting fibers to introduce carboxyl groups into the polypropylene mole-cule.

7. The process of claim 1 wherein the cationic, water-soluble, nitrogen-containing polymer is the reaction product of epichlorohydrin and an aminopolyamide derived from a dibarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one secondary or tertiary amine group.

8. The process of claim 7 wherein the aminopolyamide is derived from adipic acid and diethylenetriamine.

9. The process of claim 8 wherein the anionic, water-soluble, nitrogen-containing polymer is the reaction product of glyoxal and the polyacrylamide obtained by copolymerization of acrylamide with acrylic acid.

10. The process of claim 8 wherein the anionic, water-soluble, nitrogen-containing polymer is the reaction product of glyoxal and the polymer obtained by partial hydrolysis of a branched, water-soluble poly(.beta.-alanine).

11. The hydrophilic polyolefin fibers produced by the process of claim 1.

12. A paper product containing the hydrophilic polyolefin fibers of claim 11.

13. The process of claim 1 wherein the polyolefin compo-sition containing carboxylic functionality is composed of at least 80% polyolefin in admixture with an anionic polymer con-taining carboxylic functionality.