GB1577634A

GB1577634A - Preparation of hydrophilic polyolefin fibres for use in papermaking

Info

Publication number: GB1577634A
Application number: GB336377A
Authority: GB
Original assignee: Hercules LLC
Current assignee: Hercules LLC
Priority date: 1976-01-28
Filing date: 1977-01-27
Publication date: 1980-10-29
Also published as: DK36777A; CH618474A5; ATA49477A; DE2703372A1; FR2339686A1; JPS52110923A; DK147079B; FR2339686B1; DK147079C; AT359824B; JPS6031948B2

Description

(54) PREPARATION OF HYDROPHILIC POLYOLEFIN FIBRES FOR USE IN PAPERMAKING (71) We, HERCULES INCORPORATED, a Corporation organised under the laws of the State of Delaware, United States of America, of 910 Market Street, City of Wilmington, State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 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 fibres 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 cationic and the other of which is anionic. The blends of the cationic and anionic polymers are the subject of our Divisional Application 10332/79 (Serial No. 1,577,635).

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. Patent 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 dispersions at superatmospheric pressure to dissolve the polymer and any solvent-soluble additive, and then discharging the resulting composition through an orifice 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 Application No.

413,922, filed March 22, 1974 and published October 17, 1974 as 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 strength properties from blends of polyolefin pulps and wood pulp. According to one aspect of the invention, there is provided a process for the preparation of hydrophilic polyolefin fibers comprising intimately contacting a spurted fibrous polyolefin or composition thereof, containing carboxylic functionality, with an aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said cationic polymer being the reaction product of epichlorohydrin and (a) an aminopolyamide derived from a dicarboxylic acid and a polyalkylene polyamine having two primary amine groups and at least one secondary or tertiary group, or (b) a polyalkylene polyamine having the formula H2N(CnH2nNH)XH, wherein n is an integer from 2 to 8 and x is an integer 2 or more, or (c) a polymer of a 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) an acrylamide copolymer containing from 2 to 15% acrylic acid units or (b) a partially hydrolyzed, branched poly(p-alanine) containing from 1 to 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 1:3 to 1:7 by weight. As is customary for additives in papermaking operations, the aqueous admixture will normally be a dilute one.

As an example of the process of this invention, polypropylene and an ethyleneacrylic 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 generated 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 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(acrylamide-co-acrylic acid), and the components of the resulting suspension are brought into intimate contact with each other, as by refining in a disc refiner. 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. Examples A to F describe the preparation of certain polymers for use therein. All amounts are based on parts by weight.

Example A A cationic, water-soluble, nitrogen-containing polymer was prepared from diethylenetriamine, adipic acid and epichlorohydrin. 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 was then 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 17-1750C. 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 1400C., 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 400 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 75"C. until it attained a Gardner viscosity of E-F. Sufficient water was next added to provide a solids content of about 12.5%, and the solution was cooled to 250C. The pH of the solution then was adjusted to 4.7 with concentrated sulfuric acid. The final product contained 12.5% solids and had a Gardner viscosity of BC.

Example B Another representative cationic, water-soluble, nitrogen-containing polymer was prepared, this time using epichlorohydrin and a commercially available liquid mixture of polyamines as 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, nitriles and lactams. The reaction was carried out in a kettle fitted with a steam 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 commerical 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 700 C. After addition of the amine, six parts of aqueous 20% sodium hydroxide was added to accelerate the reaction and, after a total of 160 minutes at about 70"C., the reaction mixture was diluted with 640 parts of water to reduce the visocity 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 acid dissolved in 1345 parts of water. The resulting solution had a Gardner viscosity of D, and addition sulfuric acid and water were added to adjust the pH to 4 and provide a solids content of 22.5%.

Example C A further cationic, water-soluble, nitrogen-containing polymer was prepared, the basic reactants being poly(methyldiallylamine) and epichlorohydrin. To 333 parts of methyldiallylamine was slowly added 290295 parts of concentrated hydrochloric acid to provide a solution having a pH of 3 to 4. The solution then was sparged with nitrogen for 20 minutes and the temperature was adjusted to 500 to 60"C. An aqueous 10.7% solution of sodium bisulfite 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(methyldiallylamine hydrochloride), had a reduced specific viscosity of 0.2 as measured on a one percent solution in aqueous one molar sodium chloride at 250C.

The amount of each of the sodium bisulfite 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 temperature of the resulting solution was adjusted to 35"C. After addition of sufficient water to bring the solids content of the polymer solution to 22%, there was added 416.3 parts of epichlorohydrin. The temperature of the reaction mixture was maintained at about 45"C. while the Gardner viscosity of the mixture increased from less than A to B+. After the addition of about 304 parts of 36% hydrochloric acid, the reaction mixture was heated to 800 C. and maintained at this temperature with continual addition of further amounts of hydrochloric acid until the pH of the reaction mixture had stabilized at 2 for one hour. The reaction mixture was then cooled to 400 C., adjusted to 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 solution, after aging for 15 minutes, should have a pH of 10 or higher. Additional sodium hydroxide should be added, if necessary, to obtain this level of pH.

Example D Another useful cationic, water-soluble, nitrogen-containing polymer was prepared from bis(3-aminopropyl)methylamine, urea and epichlorohydrin. Two hundred and ten parts of the amine and 87 parts of the urea were placed in a reaction vessel, heated to 1750C., held at this temperature for one hour and then cooled to 1550C. Water was added to the reaction product in the amount of 375 parts, and the resulting solution was cooled to room temperature.

To 271 parts of the above solution was added 321 parts of water, 29 parts of concentrated hydrochloric acid and 89.6 parts of epichlorohydrin. The temperature of the reaction mixture was maintained in the range of 39 to 420C. for about 85 minutes while the Gardner viscosity of the mixture increased from A-B to L+. There was then added to the mixture 60 parts of concentrated hydrochloric acid, and the resulting mixture was heated for four hours at a temperature in the range of 60 to 75"C., 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-modified polyaminourylene product contained 27% solids.

The above product, prior to use in accordance with this invention, also must be base activated. Activation is accomplished by adding ten parts of the above product to 10 parts 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 thermometer, a reflux condenser and a nitrogen adapter there was added 890 parts of water. There was then 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 760 C., at which point two parts of ammonium persulfate dissolved in six and onehalf parts of water was added. The temperature of the reaction mixture increased 21.50C. 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 resulting solution had a Brookfield viscosity of 54 centipoises at 210C. 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 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 pH of 4.4 and contained 2.2% solids.

Example F 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 condenser, there was placed 350 parts of acrylamide, one part of phenyl-A-naphthylamine and 3870 parts of chlorobenzene. This mixture was heated to 80" to 90"C. with vigorous stirring to partially melt and partially dissolved 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 the 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 90"C. for one hour. The hot chlorobenzene then was decanted, and the residual solid, a branched, watersoluble poly(P-alanine), was washed three times with acetone 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 75"C. for about 30 minutes to effect partial hydrolysis of the amide groups in the poly(p-alanine), and live steam was blown through the solution until the residual chlorobenzene had been removed and the last traces of polymer had dissolved. 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 potentiometric titration.

To an aqueous 15% solution of the above polymer was added an aqueous 40% solution of glyoxal in an amount sufficient to provide 25 mole percent of glyoxal based on the amide repeat units in the polymer. The pH of the resulting solution was slowly raised to about 9.0 to 9.5 at room temperature by the addition of dilute aqueous sodium hydroxide, and the pH was maintained at this level until an increase in Gardner viscosity of five to six units had occurred. The solution was then quickly diluted with water to 10% total solids and adjusted to a pH of 5.0 with sulfuric acid.

Example 1 Ninety parts of isotactic polypropylene having an intrinsic viscosity of 2.1 in decahydronaphthalene at 1350C. 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 2200 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 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.

Example 2 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 refined fiber product, after washing with water, contained 5.2% attached resin based on nitrogen analysis.

Example 3 The procedure of Example 1 was duplicated except for use of the following conditions in preparation of the spurted fiber product: 95 parts of the polypropylene, five parts of- ethylene-acrylic acid copolymer (Dow, 88:12 ethylene:acrylic acid, melt index 7.0), a mixture of 360 parts of methylene chloride and 40 parts of acetone as the solvent, a temperature of 220"C. and a pressure of 1200 p.s.i. The fiber product so obtained, after disc refining as in Example 1, contained 9.0% of deposited resin as determined by nitrogen analysis.

Example 4 The procedure of Example 1 was again 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 1350C., 10 parts of ethylene-acrylic acid copolymer (Union Carbide, 94:6 ethylene:acrylic acid), 900 parts of methylene chloride as the solvent, a temperature of 200"C., and a pressure of 1000 p.s.i. The fiber product from this spurting process then was disc refined as in Example 1 resulting in fibers containing 7.2% of attached resin based on nitrogen analysis.

Example 5 A spurted fiber product was prepared following the procedure of Example 1 except for use of 80 parts of the polypropylene, 20 parts of the ethylene-acrylic acid copolymer of Example 4, 400 parts of methylene chloride, a temperature of 210 C.

and a pressure of 1000 p.s.i. The product was disc refined as in Example 1, giving a fiber product containing 6.7 /" of deposited resin based on nitrogen analysis.

Examples 6 and 7 Repetition of Example 5 was 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 1:3 weight ratio of the polymers in Example 7. The resin pick-up in the fiber product of Example 6 was 6.5 /" and 5.1% in the fiber product of Example 7.

Example 8 Each of the synthetic pulps prepared as described in Examples 1 to 7 was blended with bleached kraft wood pulp (50:50 RBK:WBK, pH 6.5, 500 Canadian Standard Freeness) in the ratio of 30% synthetic pulp to 70% wood pulp.

Handsheets prepared from the blends were dried and calendered at 500 Ibs./linear inch at 600 C. The brightness, opacity, tensile strength 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 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 I Mullen Tensile Burst Brightness Opacity Strength Strength Example (%) (%) (%) (%) 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 5 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 invention will provide paper having from about 70 to about 90 /" of the tensile strength and from about 60 to about 85% of the Mullen burst 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 temperature of 200"C. and a pressure of 1000 p.s.i. The spurted fiber product was disc refined as in Example 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 82% 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 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 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 ratio 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 1900C.) was substituted for the polypropylene in Example 1 and the admixture with the ethylene-acrylic acid copolymer was spurted from solution in methylene chloride at 2000 C. 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, 80% 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 135"C., 870 parts of methylene chloride, a temperature of 222"C. and pressure of 1000 p.s.i. were used in the preparation of a fiber product following the procedure of Example 1. Sixty parts of the fiber product was suspended in 6000 parts of water, the resulting suspension was 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 pick-up by the fiber was 0.53 /" by weight of 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 resin 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 resulting sheets exhibited 87.3% brightness, 87.6 /n opacity and 84% tensile strength.

Example 13 The procedure of Example 12 was repeated except for carrying out the ozonization reaction for 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 handsheets exhibited 85% brightness, 87% opacity and 100% tensile strength.

Example 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 suspension of 60 parts of the fibers in water was prepared, and ozone was passed through the fiber suspension for one hour at 250C. 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, after blending with wood pulp and forming handsheets as in Example 8, the resulting sheets exhibited 87.5% brightness, 85 /" opacity and 85% tensile strength.

Example 16 A polypropylene fiber product was prepared using conditions 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 ozonized 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 results are given in Table 2.

TABLE 2 Tensile Brightness Opacity Strength Additive (%) (%) (%) (a) 87.8 84.5 67 (b) 87.1 84.3 68 (c) 87.6 84.4 74 (d) 87.8 84.2 69 Comparative data obtained from the evaluation of repr

Comparison Example 17 Following the procedure of Example 1, a fiber product was prepared from 95 parts of the polypropylene and five parts of 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 (Paramel HE, America Cyanamid) and carboxymethyl cellulose (CMC), D.S. 0.4, Hercules), and (c) a 2:1 blend of the Paramel and CMC polymers. Each of the resulting pulps was blended with wood pulp, and handsheets were prepared and evaluated, all as described in Example 8.

The results are shown in Table 3.

TABLE 3 Mullen Tensile Burst Brightness Opacity Strength Strength Additive (%) (%) (%) (%) (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 known blends (b) and (c) in the process of this invention does not provide a paper having the desired strength.

Comparison 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 Canadian Standard Freeness), as in Example 8, and to portions of the resulting mixture in papermaking crocks there was added five percent based on total fiber weight of (a) the resin blend of Example 7, (b) a blend of the cationic polymer of Example B with the anionic polymer of Example E, the weight ratio of the cationic polymer to anionic polymer being 1:3, (c) a blend of the cationic polymer of Example C with the anionic polymer of Example E, the weight ratio of the cationic polymer to anionic polymer being 1:3, and (d) the 2:1 blend of Paramel and CMC of Example 17. Additional 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 described in Example 8. The results are given in Table 4.

TABLE 4 Mullen Tensile Burst Brightness Opacity Strength Strength Additive (%) (%) (%) (%) 5.0% (a) 82.5 82.4 87 102 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 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 strength than known additive (d).

Comparison Example 19 A spurted fiber product was prepared as in Example 1 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% of (a) the resin blend of Example 1, (b) the 1:1 blend of paramel and CMC of Example 17 and (c) the 2:1 blend of Paramel and CMC of Example 17.

The resulting pulps were blended with wood pulp, and handsheets were prepared and evaluated as described in Example 8. Table 5 shows the results obtained.

TABLE 5 Mullen Tensile Burst Brightness Opacity Strength Strength Additive (%) (%) (%) (%) (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 invention over known additives (b) and (c). Moreover, by comparison with Example 17, the data with respect to additive (a) show the importance of the carboxylic functionality of the anionic polyolefin composition used in accordance with the process of this invention.

Comparison Example 20 Eighty parts of the polypropylene of Example 1 and 20 parts of a styrenemaleic 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.

Portions of the fiber product were disc refined for six minutes in a Sprout Waldron disc refiner at 0.25'1/o consistency in (a) water, (b) an aqueous 0.5D/, solution of the cationic polymer of Example A, (c) an aqueous 0o5% solution of glyoxal-modified poly(acrylamide-co-diallyldimethylammonium chloride) (Parez 631 NC, American Cyanamid), (d) an aqueous 0.5 /O solution of melamineformaldehyde polymer (Paramel HE, America Cyanamid), (e) and aqueous 0.5% solution of cationic starch, and (f) an aqueous 0.5% solution of a 1:3 blend of the cationic polymer of Example A and the anionic polymer 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 Mullen Tensile Burst Refining Brightness Opacity Strength Strength Medium (%) (%) (%) (%) (a) 84.2 81.3 41 30 (b) 85.2 79.8 51 48 (c) 85.5 81.4 39 32 (d) 81.6 82.5 48 38 (e) 84.8 79.2 54 48 (f) 82.1 79.4 72 71 These data show that individual additives when used in the process 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 attractive for the reason that it provides synthetic pulps which, when blended with wood pulp, lead to paper products having improved 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 starch, in the papermaking process, these being rendered unnecessary by the presence of the cationic polymer component incorporated in the modified fibers produced by the process of this invention.

In the process of this invention, the anionic polyolefin or composition thereof 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 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 componnt 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, propylene, styrene, a-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 95:5 to 80:20 by weight, and the amount of available carboxyl in the anionic polymer will preferably be from three to 30% by weight. In general, the anionic polyolefin or composition thereof used in the process of this invention should preferably contain a sufficient amount of carboxylic functionality to provide at least 0.01, and more 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 0.04 to 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 polyolefin or composition thereof used to form the fibers. It may be the methylene chloride shown in most of the Examples, or other halogenated hydrocarbons such as chloroform, carbon tetrachloroide, 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 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 or composition thereof in solution in the solvent normally will be from 5 to 40% by weight, preferably from 10 to 20% by weight. The temperature to which the dispersion of the polyolefin or composition thereof in the solvent is heated to form a solution of the polyolefin or composition thereof will be dependent upon the particular solvent used and should be sufficiently high to effect dissolution of the polyolefin or composition thereof. The fiber-forming temperature will generally be in the range of from 100C to 2250C. The pressure on the solution of the polyolefin or composition thereof may be from 600 to 1500 p.s.i., but preferably is in the range of from 900 to 1200 p.s.i. The orifice through which the solution is discharged should have a diameter of from 0.5 to 15 mm., preferably from one to five mm., and the ratio of the length of the orifice to its diameter should be from 0.2 to 10.

In the fiber-modifying step of the process of this invention, the fibers of the fibrous anionic polyolefin or composition thereof containing carboxylic functionality are intimately contacted with a dilute aqueous solution or dispersion of a blend of certain cationic and anionic nitrogen-containing polymers. The ratio of cationic to anionic polymer in the blend is in the range of from 1:3 to 1:7 by weight. The cationic polymer component of the aforementioned blend may generally be classified as the reaction product of epichlorohydrin and certain types of reactant 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 reaction product of epichlorohydrin and the 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 epichlorohydrin and an aminopolyamide 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. Patent 2,926,116 and U.S. Patent 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 epichlorohydrin and a polyalkylene polyamine. The preparation of an exemplary product from this group is shown in Example B.

Polyalkylene polyamines which can be reacted with epichlorohydrin have the formula H2N(CnH2nNH)XH wherein n is an integer 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 polybutylene polyamines.

Specific examples of these polyalkylene polyamines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, bis(hexamethylene)triamine and dipropylenetriamine. Other polyalkylene polyamines that can be used include methyl bis(3-aminopropyl)amine; methyl bis(2-aminoethyl)amine; and 4,7dimethyltriethylenetetramine. Mixtures of polyalkylene polyamines can be used if desired.

The relative proportions of polyalkylene polyamine and epichlorohydrin employed can be varied depending upon the particular 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 tetraethylenepentamine, good results are obtained at molar ratios of from 1.4:1 to 1.94:1. Reaction temperature is preferably in the range of from 40 to 60"C.

A further group of cationic polymers useful in accordance 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.

Additional products and the process of preparing them are shown in U.S. Patent 3,700,623.

The final group of cationic polymers used in accordance 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. Patent 3,240,664.

The anionic polymer component of the aqueous solution or dispersion in which the fibers of the anionic polyolefin or composition thereof containing carboxylic functionality are modified is 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 E. The amount of acrylic acid units in the copolymer is from 2 to 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 F. The poly( -alanine) is prepared by the anionic polymerization 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 500 to 10,000, preferably from 2,000 to 6,000. Because of the extremely exothermic nature of the anionic polymerization, it is preferred to conduct the reaction in a suitable organic reaction medium such as toluene or chlorobenzene, inert to the reaction conditions and capable of dissolving or slurrying acrylamide.

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 9 to 10 at temperatures of 50 to 1000C. The amount of anionic groups introduced should be from one to ten mole percent, and preferably two to 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 10 to 500 C., preferably from 200 to 300 C. The amount of glyoxal used in the reaction mixture may be from 10 to 100 mole percent, preferably from 20 to 30 mole percent, based on amide repeat units in the polymer.

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 nitrogencontaining polymers used in the fiber-modifying step, and the latter preferably involves the use of a refining procedure, such as disc refining. Moreover, the process depends for optimum performance upon several preferred factors as described in the foregoing, namely, the presence of at least 80% polyolefin in the polyolefin-carboxyl-containing anionic polymer admixture, when this admixture constitutes the 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 or composition thereof 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 tensile strength of 100% wood pulp, as well as increased brightness, opacity and smoothness.

WHAT WE CLAIM IS: 1. A process for the preparation of hydrophilic polyolefin fibers which comprises intimately contacting a spurted (as herein defined) fibrous polyolefin or composition thereof, containing carboxylic functionality, with an aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said cationic polymer being the reaction product of epichlorohydrin and (a) an 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) a polyalkylene polyamine having the formula H2N(CnH2nNH)XH, wherein n is an integer 2 through 8 and x is an integer 2 or more, or (c) a polymer ot' a allylamine or (d) a polyaminourylene derived from urea and a polyamine having at least three amine groups, at least one of which is tertiary, said reaction products of epichlorohydrin and (c) or (d) being base activated prior to use; and said anionic polymer being the reaction product of glyoxal and (a) an acrylamide copolymer containing from 2 to 15 /,, acrylic acid units or (b) a partially hydrolyzed, branched poly( -alanine) containing from 1 to 10 mole percent carboxyl groups based on amine repeating units, the ratio of said cationic polymer to said anionic polymer being the range of from 1:3 to 1:7 by weight.

2. The process of claim 1 wherein the polyolefine of the spurted fibrous polyolefin or composition thereof containing carboxylic functionality comprises polyethylene.

3. The process of claim I wherein the polyolefin of the spurted fibrous polyolefin or composition thereof containing carboxylic functionality comprises 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 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 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, nitrogencontaining polymer is the reaction product of epichlorohydrin and an 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

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 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 10 to 500 C., preferably from 200 to 300 C. The amount of glyoxal used in the reaction mixture may be from 10 to 100 mole percent, preferably from 20 to 30 mole percent, based on amide repeat units in the polymer. 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 nitrogencontaining polymers used in the fiber-modifying step, and the latter preferably involves the use of a refining procedure, such as disc refining. Moreover, the process depends for optimum performance upon several preferred factors as described in the foregoing, namely, the presence of at least 80% polyolefin in the polyolefin-carboxyl-containing anionic polymer admixture, when this admixture constitutes the 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 or composition thereof 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 tensile strength of 100% wood pulp, as well as increased brightness, opacity and smoothness. WHAT WE CLAIM IS:

1. A process for the preparation of hydrophilic polyolefin fibers which comprises intimately contacting a spurted (as herein defined) fibrous polyolefin or composition thereof, containing carboxylic functionality, with an aqueous admixture of water-soluble nitrogen-containing cationic and anionic polymers, said cationic polymer being the reaction product of epichlorohydrin and (a) an 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) a polyalkylene polyamine having the formula H2N(CnH2nNH)XH, wherein n is an integer 2 through 8 and x is an integer 2 or more, or (c) a polymer ot' a allylamine or (d) a polyaminourylene derived from urea and a polyamine having at least three amine groups, at least one of which is tertiary, said reaction products of epichlorohydrin and (c) or (d) being base activated prior to use; and said anionic polymer being the reaction product of glyoxal and (a) an acrylamide copolymer containing from 2 to 15 /,, acrylic acid units or (b) a partially hydrolyzed, branched poly(ss-alanine) containing from 1 to 10 mole percent carboxyl groups based on amine repeating units, the ratio of said cationic polymer to said anionic polymer being the range of from 1:3 to 1:7 by weight.

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, nitrogencontaining polymer is the reaction product of glyoxal and the polymer obtained by partial hydrolysis of a branched, water-soluble poly(ss-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. A process of preparing hydrophilic polyolefin fibres substantially as described with reference to the Examples 1 to 7, 9 to 16, 17(a), 18(a), (b) and (c), and 20(f).