EP0000628A1

EP0000628A1 - Process of preparing hydrophilic polyolefin fibers, the fibers so produced, and paper containing said fibers.

Info

Publication number: EP0000628A1
Application number: EP78300120A
Authority: EP
Inventors: Terence William Rave
Original assignee: Hercules LLC
Current assignee: Hercules LLC
Priority date: 1977-07-27
Filing date: 1978-07-05
Publication date: 1979-02-07
Also published as: NO782561L; FI782163A; FI63453B; AT367123B; AU3836778A; DK335378A; BR7804818A; CA1113208A; IT7826126A0; JPS6139435B2; ES472054A1; ATA542978A; JPS5427095A; IT1097438B; FI63453C; US4154647A; AU521439B2

Abstract

Hydrophilic polyolefin fibers are prepared by treating an anionic fibrous polyolefin composition containing carboxylic functionality with an aqueous admixture of selected cationic and anionic water-soluble, nitrogen-containing polymers. The anionic polyolefin composition may, for example, be a pololefin containing carboxyl groups which have been introduced into the polymer molecule by grafting the polyolefin with a monomer-containing carboxylic functionality or by oxidizing the polyolefin with oxygen or ozone or the composition may be a polyolefin in admixture with an anionic polymer containing carboxylic functionality.

Blends of the hydrophilic fibers with wood pulp provide paper products having improved physical properties.

Description

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 fibers to provide a pulp which can be made into high quality paper using conventional papermaking techniques. More particularly, the invention relates to the formation of polyolefin-based fibers containing carboxylic functionality and treatment of these fibers with blends of certain water-soluble, nitrogen-containing polymers, one of which is cat-ionic and the other of which is anionic.
In recent years, a considerable amount of effort has been expended in the development of fibrous polyolefin pulps having hydrophilic properties. One procedure developed for the purpose of attaining such hydrophilic properties is that described in U.S. 3,743,570 to Yang et al, assigned to Crown Zellerbach Corporation. According to this patent, polyolefin fibers having a high surface area are treated with a hydrophilic colloidal polymeric additive composed of a cationic polymer such as melamine-formaldehyde and an anionic polymer such as carboxymethyl cellulose. Another procedure developed 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 hydrophilic clay or a hydrophilic polymer, for example, polyvinyl alcohol. The spurting process used in these preparations is one in which the polyolefin and the hydrophilic additive are dispersed in a liquid which is not a solvent for either component at its normal boiling point, heating the resulting dispersion at superatmospheric pressure to dissolve the polymer and any solvent-soluble additive, and then discharging the resulting composition into a zone of reduced temperature and pressure, usually atmospheric, to form the fibrous product.
A significant deficiency of these hydrophilic polyolefin pulps has been that, when they have been blended with wood pulp, the resulting paper products have exhibited considerably less strength than that of a paper prepared from wood pulp alone. However, some improvement in the strength of paper made from blends of polyolefin pulps and wood pulp has been realized by imparting an anionic character to the polyolefin pulp. For example, in their German patent No. 2,413,922, Toray Industries, Inc. have disclosed the preparation of anionic pulps by spurting mixtures of polyolefins and copolymers of olefinic compounds with maleic anhydride or acrylic or methacrylic acids. Blends of these pulps with wood pulp have provided paper with-better tensile strength than paper made without the copolymer component.
It is an object of this invention to prepare paper having further improved dry-strength properties from blends of polyolefin pulps and wood pulps. According to one aspect of the invention, there is provided a process for the preparation of hydrophilic polyolefin fibers comprising stirring a suspension of the fibers of a spurted fibrous polyolefin composition containing carboxylic functionality in a dilute aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said cationic polymer being (a) the reaction product of ammonia or a lower alkyl amine and an epichlorohydrin-modified aminopolyamide derived from a dicarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one secondary or tertiary amine group, or (b) the reaction product of epichlorohydrin and a condensate of cyanamide or dicyandiamide with a polyalkylene polyamine having the formula H₂N(C_nH_2nNH)_xH, where n is an integer 2 through 8 and x is an integer 2 or more, or (c) a poly-(diallyldialkylammonium chloride) or (d) a poly(acrylate or methacrylate alkyl ester containing quaternary ammonium groups), 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 parinthf hydrolyzed, branched poly(β-alanine) containine sor 1 to about 10 mole percent carboxyl groups based on smide repeating units, the ratio of said cationic potymer to a anionic polymer in said admixture of polymers baing in the range of from about 3:1 to about 1:5 by weight and the amount of said admixture of said polymers deposited on the fibers of said fibrous composition being from about one to about 15% by weight based on said fibrous composition. It is a significant feature of the process of this invention that the cationic nitrogen-containing polymer used in the fiber-modifying step of the process is one which imparts no substantial amount of wet strength to the paper product and thus permits the reworking of broke to take place readily.
As an example of the process of this invention, polypropylene 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 about 190°C. to dissolve the polymer components in the solvent. Under these conditions, the pressure generahed by the methylene chloride vapors is of the order of 600 p.s.i. After introducing nitrogen to increase the vapor pressure of the system to a pressure of about 1000 p.s.i., the resulting solution is 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 biend- ing a dilute aqueous solution of, for example, the reaction product of ammonia with epichlorohydrin-modified poly-(diethylenetriamine-adipic acid) with a dilute aqueous sola- tion of, for example, glyoxal-modified poly(acrylamide-co- acrylic acid), and the components of the resulting suspension are brought into intimate contact with each other by stirring. The treated fibers may then be isolated and stored in wet cake form, or the suspension containing the fibers may be used directly in a papermaking process
Having generally outlined the embodiments of this invention, the following examples constitute specific illustrations thereof. All amounts are based on parts by weight.

Example A

A cationic, water-soluble, nitrogen-containing polymer was prepared from diethylenetriamine, adipic acid, epichlorohydrin and ammonia. Diethylenetriamine in the amount of 0.97 mole was added to a reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. There then was gradually added to 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 very viscous. The reaction mixture then was cooled to 140°C., 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 40°C., and epichlorohydrin was slowly added in an amount corresponding to 1.32 moles per mole of secondary amine in'the polyamide. The reaction mixture then was heated at a temperature between 70° and 75⁰C. until it attained a Gardner viscosity of E-F. Sufficient water next was added to provide a solids content of about 12.5%, and the solution was cooled to 25°C. The pH of the solution then was adjusted to 4.7 with concentrated sulfuric acid. The resulting solution contained 12.5% solids and had a Gardner viscosity of B-C, and 80 parts of this solution was diluted to 10% solids with 20 parts of water. After adding sufficient sodium hydroxide to adjust the pH of the solution to 7, the solution was combined with 18.7 parts of concentrated (28%) aqueous ammonia and heated under reflux at 80-85°C. for two hours. The resulting solution contained 10.1_% solids.

Example B

Another representative cationic, water-soluble,

Example D

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 thermometer, a reflux condenser and a nitrogen adapter was added 890 parts of water. There then was dissolved in the 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 heated to 76°C., 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 increased 21.5°C. over a period of three minutes following addition of the persulfate. When the temperature returned to 76°C., it was maintained there for two hours, after which the reaction mixture was cooled to room temperature. The reselting solution had a Brookfield viscosity of 54 centipoises at 21°C. and contained less than 0.2% acrylamide based on the polymer content.
To 766.9 parts of the above solution (76.7 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 addition of 111.3 parts of aqueous 2% sodium hydroxide. Within approximately 20 minutes after addition of sodium hydroxide, the Gardner viscosity of the solution had increased from A to E. The reaccion 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 pH of 4.4 and contained 2.2% solids.

Example E

Another representative anionic, water-soluble, nitrogen-containing polymer was prepared using only acrylamide and glyoxal as reactants. In a reaction vessel. equipped with a stirrer, a thermometer and a reflux cordens- er, there was placed 350 parts of acrylamide, one part of phenyl-β-naphthylamine and 3870 parts of chlorobenzene.
by potentiometric titration.
the autoclave was raised to 850 p.s.i. by the introduction of nitrogen. The resulting solution was spurted from the autoclave into the atmosphere through an orifice having a diameter of one millimeter and a length of one millimeter, resulting in evaporation of the pentane solvent and formation of the desired fiber product.
The spurted fiber product was blended with six percent by weight, based on the polypropylene fibers, of bleached kraft wood pulp (50:50, RBK:WBK, 500 Canadian Standard Freeness), and the fiber blend was disc refined until it became water-dispersible. One hundred ten parts of the fiber blend was suspended in 7090 parts of water, the resulting suspension was agitated, and a gas mixture containing three percent ozone in oxygen was passed through the suspension at room temperature at. a rate of three and one-half cubic feet per minute for five hours. The ozonized pulp fibers had an acid number corresponding to 0.06 milliequivalent of carboxyl groups per gram of fiber.
Thirty parts of the ozonized pulp was blended with 70 parts of bleached kraft wood pulp, and to portions of the resulting blend in papermaking crocks was added five percent, based on the refined pulp content of the blend, of (a) a blend of Kymene® 557 (cationic polymer formed by reaction of epichlorohydrin with the aminopolyamide derived from adipic acid and diethylenetriamine) with an anionic polymer prepared according to Example D, the ratio of cationic:anionic being 1:5 by weight, (b) a blend of a cationic polymer prepared according to Example A with an anionic polymer prepared according to Example D, the cationic:anionic ratio being 1:5 by weight, (c) a blend of a cationic polymer prepared according to Example B with an anionic polymer prepared according to Example D, the cationic:anionic ratio being 1:5 by weight, and (d) a blend of a cationic polymer prepared according to Example C with an anionic polymer prepared according to Example D, the ratio of cationic:anionic being 1:5 by weight.
After thorough mixing of the additives with the pulp, handsheets were prepared, dried and calendered at 500 lbs./ linear inch at 60°C. The opacity, brightness and Mullen burst strength of the calendered sheets were determined, and the results are given in Table 1. In the data given in this table, the Mullen burst strength values are expressed as a percentage of the Mullen burst strength of the 100% wood puly control, all being corrected to a 40 pound per ream basis weight.
Broke reworking studies made at a pH of 10 and a temperature of 150^oF. showed that the papers made using additives (b), (c) and (d) were completely repulped after 10, 5 and 5 minutes, respectively, whereas the paper using additive (a) re- required 20 minutes for complete repulping. These studies were carried out in a standard TAPPI disintegrator, as described in TAPPI Method T 205 os-71, operating at 2800 r.p.m. and using one-inch squares of paper at a consistency of 1.33%.

Example 2

The procedure of Example 1 was following using as the additives (a) a blend of Kymen® 557 with an anionic polymer prepared according to Example E, the ratio of cationic: anionic being 1:3 by weight, and (b) a blend of a cationic polymer prepared according to Example B with an anionic polymer prepared according to Example E, the ratio of cationic:anionic being 1:3 by weight. The data obtained from evaluating the resulting handsheets are given in Table 2.
Broke reworkability studies carried out as in Example 1 showed that the paper made using additive (b) was completely repulped after 10 minutes, whereas the paper made using additive (a) required 30 minutes for complete repulping.

Example 3

The procedure of Example 1 was repeated except for use of 1:3 by weight ratios of cationic:anionic polymers in the blends. The results obtained are shown in Table 3.
The brightness and opacity of the handsheets were essentially the same as those of Example 1.

Example 4

The procedure of Example 1 was repeated except for use of 1:1 ratios by weight of cationic:anionic polymers in the blends. The results obtained are shown in Table 4.
The brightness and opacity of the handsheets were substantially the same as those of Example 1.
Results comparable to those shown in Examples 1 to 4 were obtained when the ozonized pulp fibers of Example 1 were replaced with spurted fibrous anionic polyolefin compositions containing carboxylic functionality prepared in accordance with the following examples.

Example 5

Ninety parts of isotactic polypropylene having an intrinsic viscosity of 2.1 in decahydronaphthalene at 135°C. 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 solvent. The contents of the autoclave were stirred and heated to 220°C., at which point the vapor pressure in the autoclave was raised to 1000 p.s.i. by the introduction of nitrogen. The resulting solution was spurted from the autoclave into the atmosphere 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 desired fiber product. This fiber product then was disc refined for six minutes in a Sprout Waldron disc refiner at 1.5% consistency in water.

Example 6

The procedure of Example 5 was followed using 200 parts of crystalline polypropylene grafted with three percent by weight of maleic anhydride, 2672 parts of methylene chloride, a temperature of 200°C, and a pressure of 1000 p.s.i. The srurted fiber product was disc refined as in Example 5.

Example 7

The procedure of Example 5 was used to prepare a spurted fiber product from crystalline polypropylene 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 5.

Example 8

Ninety parts of high density polyethylene (DuPont, melt index 5.5-6..5 at 190⁰C.) was substituted for the polypropylene in Example 5 and the admixture with the ethylene-acrylic acid copolymer was spurted from solution in methylene chloride at 200°C. and 1000 p.s.i. pressure. The fiber product was disc refined as in Example 5.

Example 9

Eighty parts of the polypropylene of Example 5 and 20 parts of a styrene-maleic anhydride copolymer (Arco, 75:25 styrene:maleic anhydride, molecular weight 19,000) were charged to a closed autoclave along with 250 parts of hexane and 250 parts of water. The contents of the autoclave were stirred and heated to 220°C., at which point the vapor pressure in the autoclave was raised to 1000 p.s.i. with nitrogen. The resulting emulsion was spurted from the autoclave into the atmosphere through an orifice having a diameter of one millimeter and a length of one millimeter, resulting in formation of a fiber product. The fiber product was disc refined as in Example 5.
In the process of this invention, the anionic polyolefin composition containing carboxylic functionality may be a polyolefin containing carboxyl groups which have been introduced into the polymer molecule by grafting the polyolefin with a monomer-containing carboxylic functionality or by oxidizing the polyolefin with oxygen or ozone, or the composition may be a polyolefin in admixture with an anionic polymer containing carboxylic functionality. In any case, the polyolefin may be polyethylene, polypropylene, an ethylene-propylene copolymer or a mixture of any of these polyolefin materials.
When the anionic polyolefin composition is an admixture of a polyolefin and an anionic polymer containing carboxylic functionality, the latter component may be a polyolefin containing 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, pcopylene, styrene, alpha-methylstyrene or mixtures thereof with any one of acrylic acid, methacrylic acid, maleic anhydride or mixtures thereof, as well as mixtures of any of these anionic polymer 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 preferably be from about 95:5 to about 80:20 by weight, and the amount of available carboxyl in the anionic polymer will be from about three to about 30% by weight. In general, the anionic polyolefin composition used in the process of this invention should contain a sufficient amount of carboxylic functionality to provide at least 0.01, and preferably at least about 0.04 milliequivalent of carboxyl groups per gram of the polyolefin pulp. Moreover, the amount of carboxylic functionality may be such as to provide up to about one milliequivalent of carboxyl groups per gram of the polyolefin pulp. A highly desirable range is from about 0.04 to about 0.2 milliequivalent per gram.
The dispersing medium used in the fiber-forming step of the process of this invention contains an organic solvent which is a nonsolvent at its normal boiling point for the polyol.efin composition used to form the fibers. It may be the methylene chloride shown in some of the examples, or other halogenated hydrocarbons such as chloroform, carbon tetrachloride, methyl chloride, ethyl chloride, trichlorofluoromethane and 1,1,2-trichloro-1,2,2-trifluorethane. 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 cyclohexane. Mixtures of these solvents may be used, and water may be present when it is desired to form an emulsion of the polyolefin composition. Moreover, the pressure generated by the solvent vapors may be, and normally will be, augmented by a pressurized inert gas such as nitrogen or carbon dioxide.
In carrying out the fiber-forming process, the concentration 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 solution 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 temperature will generally be in the range of from about 100° to about 225°C. The pressure on the solution of the polyolefin composition may be from about 600 to about 1500 p.s.i., but preferably is in the range of from about 900 to about 1200 p.s.i. The orifice through which the solution is discharged should have a diameter of from about 0.5 to about 15 mm., preferably from about one to about five mm., and the ratio of the length of the orifice to its diameter should be from about 0.2 to about 10.
In the fiber-modifying step of the process of this invention, the fibers of the fibrous anionic polyolefin composition containing carboxylic functionality are suspended in a dilute aqueous admixture of certain cationic and anionic nitrogen-containing polymers and the suspension is stirred, resulting in the deposition on the fibers of from about one to about 1.5% by weight of the admixture, based on the weight of the fibrous composition. The ratio of the cationic to the anionic polymer in the admixture of these polymers preferably is in the range of from about 3:1 to about 1:5 by weight, more preferably from about 1:1 to about 1:3 by weight. A preferred type of cationic polymer component of the aforementioned admixture is one which is derived from a polymer containing secondary or tertiary amine groups, or both. One representative group of polymers belonging to this type may be exemplified by a cationic polymer component used in many of the examples, namely, the reaction product of ammonia with the epichlorohydrin-modified aminopolyamide derived from diethylenetriamine and adipic acid. Preparation of this product is shown in Example A. However, more generally, this group of cationic polymers are the reaction products of ammonia or lower alkyl amines with epichlorohydrin-modified aminopolyamides derived from a dicarboxylic acid and a polyalkylenepolyamine having two primary amine groups and at least one secondary or tertiary amine group, all as described in U.S. 3,951,921.
Another representative group of polymers belonging to the preferred type of cationic polymers is that wherein the polymers are the water-soluble reaction products of.epi-_. chlorohydrin and the condensates of a polyalkylene polyamine with cyanamide or dicyandiamide. The preparation of an exemplary product from this group 'is shown in Example B. Additional products and the process of preparing them are 'disclosed in U.S. 3,403,113.
Another group of preferred cationic polymers useful in accordance with this invention is that in which the polymers are poly(diallyldialkylammonium chloride)s. These are linear polymers having units of the formula:
where R is hydrogen or lower alkyl and R' is alkyl or a substituted alkyl group. Polymers having units of the above formula are obtained by polymerizing quaternary ammonium chloride salt monomers in which the quaternary ammonium cation is represented by the formula:
in which R and R' are as indicated above, in the presence of a free radical catalyst.
In both of the above formulae, each R can be the same or different, and, as stated, can be hydrogen or lower alkyl. The alkyl groups may contain from 1 to 4 carbons and are preferably methyl, ethyl, isopropyl or n-butyl. R' of the formulae represents alkyl or substituted alkyl groups. The R' alkyl groups may contain from 1 to 18 carbon atoms, preferably from 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, hexyl, octyl, decyl, dodecyl, tetradecyl, and octadecyl. R' may also be a substituted alkyl group. Suitable substituents include, in general. any group which will not interfere with polymerization through a vinyl double bond. Typically, the substitutents may be carboxytate, cyano, ether or amido. Preparation of the aforementioned diallyldialkylammonium chloride polymers is shown in U.S. 3,288,770.
A final group of effective cationic polymers useful in accordance with this inventicn is that in which the polymers are homopolymers, or certain copolymers, of acrylate and methacrylate alkyl esters containing quaternary ammonium groups. The preparation of an exemplary product from this group of cationic polymers is shown in Example C. As disclosed in U.S. 3,686,109, the alkylene group in these compounds preferably contains two to four carbon atoms, as in, for example, methacryloyloxyethyldimethylbenzylammonium chloride and acryloyloxy-n-butyl-diethylmethylammonium methyl sulfate. Other representative monomers are acryloyloxyethyl- trimethylammonium methyl sulfate, methacryloxyethyltrimethyl- ammonium methyl sulfate, methacryloyloxyethyldiethylmethyl- ammonium methyl sulfate and methacryloyloxyethyldiethyl- methylammonium chloride. These monomers all contain quaternary ammonium groups having three alkyl substitutents, each of which contains one or two carbon atoms.
Any of the foregoing monomers may be copolymerized with an acrylamide having the formula
wherein _R ¹, _R ² and _R ³may each be hydrogen or a lower alkyl group having one to four carbon atoms. Representative compounds of the abbve formula are acrylamide, methacrylamide and N-isopropylacrylamide, with acrylamide being preferred. The acrylamide monomers may be used in amounts up to about 75 mole percent when copolymerized with the acrylate and methacrylate esters containing quaternary ammonium groups. Processes for carrying out the polymerizations here involved are well known in the art.
The polymers which are useful as the anionic polymer component of the aqueous solution or dispersion in which the fibers of the fibrous anionic polyolefin composition containing carboxylic functionality are modified also have been illustrated in the examples. One of these is the reaction product of glyoxal and the polyacrylamide obtained by copolymerization of acrylamide with acrylic acid. The preparation of an exemplary product is shown in Example D. The amount of acrylic acid units in the copolymer may be from about two to about 15%. Comparable products can be prepared by partial hydrolysis of polyacrylamide or a poly(acrylamide- co-alkyl acrylate) such as a copolymer of acrylamide with ethyl acrylate. Any of these polyacrylamides 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 of 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(P-alanine). Preparation of a representative product is shown in Example E. Additional information on the preparation of this product is given in U.S. 4,035,229.
As shown by the above patent, the branched poly(β-alanine) initially produced is a neutral polymer. This polymer needs to be anionically modified for the purpose of this invention, and the patent shows that anionic modification of branched poly(P-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(P-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 100°C. 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 repeating units.
Each of the anionic, nitrogen-containing polymers described above is modified with glyoxal to provide the desired anionic, water-soluble, nitrogen-containing polymers used in accordance 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 30°C. The concentration of the polymer in the solution may be from about five to about 40% by weight, but preferably is from about seven to about 20%. The amount of glyoxal used in the reaction mixture may be from about 10 to about 100 mole percent, preferably from about 20 to about 30 mole percent, based on amide repeat units in the polymer. The reaction is allowed to continue until a viscosity increase of from about two to about ten, preferably from about four to about six, units on the Gardner scale has taken place. This increase in viscosity is indicative that some crosslinking of the polymer has desirably taken place, but this amount of crosslinking is insufficient to cause gelation. The reaction then is terminated, usually by dilution of the reaction mixture with water and addition of sulfuric acid to lower the pH to about 4.5-5.0. The resulting solutions possess good stability.
The process of _'this invention makes possible the preparation of improved paper products from blends of wood pulp and polyolefin pulps. The process depends upon the particular combination of cationic and anionic nitrogen-containing polymers used in the fiber-modifying step, and the particular cationic polymers used provide the additional advantage of facile broke reworking. Moreover, the process depends upon several critical factors, namely, the presence of at least 80% polyolefin in the polyolefin-carboxyl-containing anionic polyolefin composition containing carboxylic functionality used as the fiber-forming material, an intrinsic viscosity of at least 1.0 for the polyolefin, sufficient available carboxyl in the anionic polyolefin composition containing carboxylic functionality and sufficient resin in the aqueous solution or dispersion in which the anionic fibers 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 Mullen burst strength of 100% wood pulp, as well as improved brightness, opacity, smoothness and printability at low sheet weights compared with conventional filled or unfilled paper.

Claims

1. A process for the preparation of hydrophilic polyolefin fibers which comprises stirring a suspension of the fibers of a spurted fibrous polyolefin composition containing carboxylic functionality in a dilute aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said cationic polymer being (a) the reaction product of ammonia or a lower alkyl amine and an epichlorohydrin-modified aminopolyamide derived from a dicarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one secondary or tertiary amine group, or (b) the reaction product of epichlorohydrin and a condensate of cyanamide or dicyandiamide with a polyalkylene polyamine having the formula H2N{CnH2nNH)xH, where n is an integer 2 through 8 and x is an integer 2 or more, or (c) a poly-(diallyldialkylammonium chloride) or (d) a poly(acrylate or methacrylate alkyl ester containing quaternary ammonium groups), 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(.0-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 in said admixture of polymers being in the range of from about 3:1 to about 1:5 by weight and the amount of said admixture of said polymers deposited on the fibers of said fibrous composition being from about one to about 15% by weight based on said fibrous composition.

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

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

4. The process of claim 3 wherein the spurted fibrous polyolefin composition containing carboxylic functionality is prepared by spurting a mixture of polypropylene and an anionic polymer containing carboxylic functionality.

5. The process of claim 4 wherein the anionic polymer containing 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 molecule.

7. The process of claim 1 wherein the cationic, water-soluble, nitrogen-containing polymer is the reaction product of ammonia or a lower alkyl amine and an epichlorohydrin-modified aminopolyamide derived from a dicarboxylic 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(P-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.