GB1575951A - Glyoxal poly(beta-alanine) strengthening resins for use in paper - Google Patents

Description

(54) GLYOXAL MODIFIED POLY (BETA ALANINE) STRENGTHENING RESINS FOR USE IN PAPER (71) We, HERCULES INCOR PORATED, 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 novel resins which impart dry strength and temporary wet strength to paper, the process of incorporating them into paper and the paper so treated.

It is known to add certain resins to paper, usually during the paper-making process, to improve wet and/or dry strength of paper.

The type of resin added depends on the properties desired in the final paper product. For tissue, towelling and certain other applications, it is desirable that the strengthening resin added to the paper impart dry and temporary wet strength.

Numerous resins are known in the art that will achieve these results. For example, U.S.

Patents 3,607,622, 3,728,214 and 3,778,215 to Espy and corresponding British Patent 1,269,567 relate to resins which impart both dry strength and temporary wet strength to paper. The resins of Espy are prepared by reacting certain polyamines and aminopolyamides with an acrylamide and then with a polyaldehyde. Also, U.S.

3,556,932 to Coscia et al teaches wet and dry strength resins which are ionic watersoluble vinylamide polymers having glyoxalreactive amide substituents and sufficient CHOHCHO substituents to be thermosetting. The polymers are produced by reacting glyoxal with vinylamide polymers, such as ionic copolymers of acrylamide with monomers which will impart ionic properties to the polymer, e.g., diallyldimethyl ammonium chloride and 2 methyl - 5 - vinyl - pyridine. The vinylamide polymers are produced under conditions which result in addition polymerization of acrylamide through the double bond of the vinyl group. After modification with glyoxal, there is produced a polymer composed of units having the formulae

While these resins do impart dry and temporary wet strength to paper, they have the disadvantage of a relatively short shelf life when stored in aqueous solution at concentrations at which they are generally used during the paper-making process.

In accordance with this invention, it has been found that a water-soluble resin which comprises the reaction product of ( I ) a branched water-soluble poly(p-alanine) which may be modified to introduce anionic or cationic groups and is prepared in an organic reaction medium, and (2) glyoxal is an effective dry strength and temporary wet strength resin for papers. The novel resins of this invention are stable in aqueous solution at relatively high solids concentration and have a long shelf life. The resins of the present invention may be prepared by a) polymerizing acrylamide in the presence of a basic catalyst and a free radical inhibitor in an organic reaction medium to produce branched water soluble poly(P-alanine); b) dissolving the poly(p-alanine) in water to provide an aqueous solution having a solids content of 11 to 400/n by weight; and c) adding glyoxal in the amount of 10 to 100 moleV0, based on the amide repeating units of the poly(p-alanine), thus producing a glyoxal-modified poly(p-alanine).

The poly(p-alanine) used in preparing the novel resins of this invention is a branched, water-soluble, poly(P-alanine) prepared by the anionic polymerization of acrylamide in the presence of a basic catalyst and a vinyl polymerization inhibitor. Anionic polymerization of acrylamide results in a polymer backbone of p-alanine repeating units. The preparation of linear crystalline poly(p-alanine) by the anionic polymerization of acrylamide is described in U.S. Patent No. 2,749,331 to Breslow (see also British Patent 736461). Water-soluble and water-insoluble forms of the polymer are obtained. In later work it was determined that the water-soluble form of poly(p-alanine) can be either a linear crystalline polymer of relatively low molecular weight or a higher molecular weight polymer having a branched structure. Branched, poly(P-alanine) contains repeating units of the formula CH2CH2CONH in the linear segments and repeating units of the formula CH2CH2CON in the segments at which branching occurs.

Primary amide end groups will occur at the end of each branch chain. Hydrolysis of water-soluble branched poly( & alanine) produces p-alanine, NH2CH2CH2COOH, from the linear segments, iminodipropionic acid, HN(CH2CH2COOH)2 from the points of branching and ammonia from the primary amide end groups.

This provides a basis for measuring the degree of branching present in a given sample of poly(/3-alanine). On hydrolysis of the sample the ammonia and/or iminodipropionic acid produced can be measured, thus providing a determination of the degree of branching. The amount of ammonia liberated indicates the number of primary amide groups and since such groups are present only as end groups of the branch chains, an indication of the amount of branching of the poly(i3-alanine) can be determined. Any poly(ss-alanine) containing sufficient branching to be water-soluble is suitable for use in this invention. In general, the branched poly(P-alanine) should contain about one primary amide group for every two to six amide groups present. The molecular weight of branched water-soluble poly(p-alanine) suitable for use in this invention is in the range of five hundred to ten thousand and preferably in the range of two thousand to six thousand.

As stated above, the branched watersoluble poly(p-alanine) is prepared by the anionic polymerization of acrylamide in the presence of a basic catalyst and a vinyl or free-radical polymerization inhibitor.

Because of the extremely exothermic nature of the anionic polymerization, it is preferred to conduct the reaction in a suitable organic reaction medium inert to the' reaction conditions and capable of dissolving or slurrying acrylamide. Suitable media include aromatic and aliphatic compounds, for example, toluene, xylene, tetrahydronaphthalene, chlorobenzene, nitrobenzene and dioxane.

The concentration of the acrylamide monomer in the reaction medium is in the range of 2% to 30/n, and is preferably 8% to 15%.

If desired, an organo-soluble polymeric dispersing agent can be added to the reaction mixture prior to the addition of the basic catalyst. When the dispersing agent is employed, the poly(p-alanine) produced is in powdered or bead form, easily filterable from the reaction medium. Suitable dispersing agents are styrene-butadiene copolymers, polyisoprene, chlorinated polypropylene, chlorinated and maleated polyisoprene, and chlorinated and maleated polyolefins.

Illustrative basic catalysts which can be employed include alkali metals, alkali metal hydroxides, alkaline earth metal hydroxides, quaternary ammonium hydroxides and the alkali metal alkoxides. Examples of suitable basic catalysts are sodium metal, sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium t-butoxide, sodium methoxide, tetramethylammonium hydroxide, potassium t-butoxide, and calcium hydroxide. The amount of catalyst used is in the range of 0.01 to 2.0 mole%, preferably 0.1 to 1.5 mole% based on the monomer.

A free radical inhibitor is added to the reaction mixture to inhibit vinyl polymerization through the double bond of the acrylamide monomer. Examples of free radical inhibitors which can be used are phenyl-P-naphthylamine, hydroquinone, diphenylamine and phenothiazine.

The anionic polymerization reaction is conducted at temperatures in the range of 40"C. to 1400C. and preferably 800C. to 130"C.

In many cases, the anionic polymerization of acrylamide under the above conditions will produce a mixture of water-soluble and water-insoluble poly(ss-alanine). The watersoluble polymer for use in this invention can be readily separated by partially dissolving the polymer product in water and removing the insoluble fraction by conventional methods such as filtration.

Poly(p-alanine) is a neutral polymer. For most, although not all, methods of applying strengthening resins to paper, the resin should be ionic for efficient retention by the pulp. For this reason in preparing the resins of this invention, it is desirable to modify the branched, water-soluble Poly(l3-alanine) before reaction with glyoxal to introduce anionic or cationic groups into the polymer structure. However, if the strengthening resin is to be used in a manner in which the resin does not need to be ionic, for example, surface application to the formed paper sheet, then ionic modification of polyp alanine) prior to reaction with glyoxal is not necessary.

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 9-10 at temperatures of 50"C. to 1000C. The amount of anionic groups introduced should be 1 to 10 mole /O and preferably 2 to 5 mole , based on amide repeating units.

Another method of anionic modification of branched poly(ss-alanine) is by treatment with formaldehyde and then with bisulfite ion.

Cationic modification of branched poly(P-alanine) is accomplished by reacting poly(p-alanine) in aqueous solution with formaldehyde and dimethylamine. This reaction can be carried out by heating an aqueous solution of the three reactants at 70"C. to 800 C. at either a basic pH of 9 to 11 or an acid pH of 2 to 4. This reaction introduces tertiary amine end groups into the polymer. When the pH of the resulting aqueous solution is adjusted to use conditions, i.e., 4.5 to 8.0, the tertiary amine groups are protonated and are thus rendered cationic. The amount of formaldehyde and dimethylamine used is from 2 to 15 mole ,/, based on amide repeating units of the poly(p-alanine). The amount of cationic groups introduced is from 2 to 15 mole% and preferably from 4 to 8 mole%, based on amide repeating units.

The final step in preparing the novel resins of this invention is the reaction of poly(A-alanine) with glyoxal. As stated above, poly(A-alanine) can be modified to introduce anionic or cationic groups, as desired, before reaction with glyoxal.

Reaction of poly(p-alanine) and glyoxal is carried out in aqueous solution. The solids concentration of poly(ss-alanine) in the aqueous solution should be from 11 /" to 40% with 12.5% to 25% being the preferred range. The amount of glyoxal used in this reaction can be from 10 to 100 mole% and is preferably 20 to 30 mole%, based on the amide repeating units of the poly(ss-alanine).

The temperature of the reaction is from 10"C. to 500 C., preferably 200C. to 300 C.

The reaction between the glyoxal and poly(p-alanine) is continued until a viscosity increase of 2 to 10, preferably 4--6 viscosity units on the Gardner-Holdt scale has taken place. The viscosity increase indicates that a certain amount of crosslinking of the poly(p- alanine) has taken place. The amount of crosslinking is insufficient to cause gelation of the poly(p-alanine) solution but is adequate to provide polymeric units of sufficiently high molecular weight to be retained by the cellulose fibers when used as a paper strengthening resin.

The glyoxal modified poly(p-alanine) resins of this invention can be used to impart dry strength and temporary wet strength to paper using any conventional method. Aqueous solutions of the resins may be applied to the formed paper sheet, e.g., by spraying, or tub application. When applied in this manner it is not necessary that the resin be ionic. However, the preferred methods, at the present time, of incorporating these resins into paper involve the addition of dilute aqueous solutions of the resins to an aqueous suspension of paper stock prior to sheet formation. For example, the resin solution can be added to the paper stock in the beater, stock chest, Jordon engine, fan pump, head box or any other suitable point.

Because of the anionic nature of the cellulose fibers, it is desirable to use an ionic resin so that it will be adsorbed on the cellulose fibers. A cationic resin will be adsorbed directly on the cellulose fibers due to the difference in electrostatic charge.

When an anionic resin is used it becomes necessary to add a cationic bridging agent to attach the anionic resin to the anionic cellulose fibers. Thus, when an aqueous solution of glyoxal-modified anionic poly(- alanine) is used in this manner, It Is necessary to add a cationic bridging agent.

Suitable cationic bridging agents include polymeric cationic retention aids such as aminopolyamide-epichlorohydrin resins, polyethylenimine resins, derived from poly(diallylamine) and poly(dialkyl methylamine), cationic starch and other highly cationic polymers, natural or synthetic.

The amount of glyoxal modified poly(P- alanine) added to the paper to impart dry and temporary wet strength is 0.05 to 2% and usually 0.1 to 1% by weight based on weight of the celluslose fibers.

The following examples will serve to illustrate the invention, parts and percentages being by weight unless otherwise indicated.

Example 1 This example illustrates the preparation of a typical glyoxal-modified anionic poly alanine) of this invention and its use as a dry and temporary wet strength resin for paper.

*art A i a 5either wund-bottomed 3-necked 'flask 'equipped with a paddle stirrer, thermometer, and condenser are placed 350 parts dry acrylamide, 1.0 parts phenyl-P- naphthylamine, and 3870 parts chlorobenzene. The mixture is heated to 85--90"C. with vigorous stirring to melt and partially dissolve the acrylamide. Sodium hydroxide flake (1.0 part) is then added.

After an induction period, an exothermic reaction occurs and a polymer separates on the walls of the flask and stirrer. Three more 1.0 part charges of catalyst are added at thirty minute intervals, and the reaction mixture is heated at about 900C. for one additional hour. The hot chlorobenzene is decanted and the resulting solid, brittle polymer is recovered. The polymer is water soluble, branched poly(p-alanine).

Part B A sample of poly(P-alanine) prepared in Part A is dissolved in water containing 2 mole percent sodium hydroxide (based on amide repeat units in the polymer) to provide a solution containing 25% poly(p alanine). The solution is heated at 90- 100"C. for about 30 minutes with steam sparge to remove the ammonia liberated during the hydrolysis reaction. The resulting solution then is cooled and the pH lowered to give a resin containing about 2 mole percent carboxyl groups, as measured by potentiometric titration.

Part C To a 15% aqueous solution of anionic poly(fi-alanine) prepared as in Part B is added 25 mole% (based on amide repeat units) of glyoxal as a 40 /" aqueous solution.

The pH of the resulting solution is maintained at 9-10 at room temperature until a 4-6 unit increase in Gardner viscosity has occurred. Then the solution quickly is diluted with water to 10% total solids and adjusted to pH 5.0 with sulfuric acid. The shelf life of the resulting resin is greater than six months with no loss in efficiency.

Part D The glyoxal modified anionic poly alanine) prepared in Part C is evaluated as dry and wet strength resins in Rayonier bleached kraft pulp. A 3:1 mixture (dry basis) of aqueous solutions of glyoxalmodified anionic poly(ss-alanine) and of a cationic polymer which is the reaction product of epichlorohydrin and the aminopolyamide derived from adipic acid and diethylenetriamine (e.g. commercially available from Hercules Incorporated under the trademark "Kymene 557") is used as the strengthening resin in the following procedure: Rayonier bleached kraft pulp is beated in a cycle beater to a Schopper-Riegler freeness of 750 cc. Portions of this pulp, adjusted to a pH of 6.5 with sulfuric acid, are added to the proportioner of a Noble Wood handsheet forming machine. Samples of the strengthening resin are added to the proportioner in amounts of 0.25%, 0.5% and 1% solids based on pulp solids. The pulp then is formed into handsheets of about 40 pounds per 3,000 square foot basis weight and dried for one minute at a temperature of 100"C. A control handsheet is prepared as above without the addition of a strengthening resin. The resulting handsheets after conditioning at a temperature of 75"F. and 50% relative humidity for over 24 hours are tested for dry strength. The handsheets are also tested for wet strength after soaking in distilled water for 10 seconds and for 2 hours to show the temporary nature of the wet strength.

Results are shown in Table 1.

Example 2 This example illustrates the preparation of a typical glyoxal-modified cationic poly(ss-alanine) of this invention and its use as a dry and wet strength resin for paper.

Part A in an apparatus similar to that described in Part A of Example 1, are placed 20 parts dry acrylamide, 35 parts toluene, and a trace of phenyl-ss-naphthylamine. Sufficient 0.5 M K+ Ot-Bu in t-BuOH is added to the mixture heated under N2 to 9W100 C. to cause polymerization to occur as evidenced by a substantial exotherm and formation of solid polymer. The resulting mixture then is heated at 1000C. for five hours; the toluene is separated and the solid poly(ss-alanine) is dried.

Part B To a 25% aqueous solution of essentially neutral poly(ss-alanine) prepared in Part A is added 7.5 mole% (based on amide repeat units) each of formaldehyde (as an aqueous solution) and dimethylamine hydrochloride. The pH is adjusted to 9.09.5 with aqueous sodium hydroxide, and the solution is heated 20 minutes on a steam bath at 7(w800C. The pH is then readjusted to 6-7. The resulting resin is shown to be cationic by its ability to bias the charge of anionic wood pulp toward electrical neutrality.

Part C To a 20% solution in water of the cationic poly(ss-alanine) prepared in Part B is added 25 mole% glyoxal as a 40% aqueous solution. The pH of the mixture is maintained at 9-10 until a 4-6 unit increase in Gardner viscosity is observed.

The total solids level then is brought to 10% by dilution with water, and the pH is adjusted to 4.5-5.0. The stability of the resulting resin toward gelation is greater than six months.

Part D The glyoxal-modified cationic poly(p- alanine) prepared in Part C of this example is evaluated as a dry and wet strength resin using the procedure described in Example 1.

An aqueous solution of this resin is used as the sole strengthening resin. Results are shown in Table 1.

TABLE 1 Evaluation of Glyoxal Modified Poly(ss-alanine) Resins as Paper Additives Percent Added, Dry Tensile Wet Tensile Strength"' Based on Pulp Strength (Ib/l" width Resin (Dry Basis) (Ib/l" width) 10 sex.121 2 her.131 None 16.8 0.5 0.4 Example 1 0.25 19.9 2.3 1.5 " 0.50 21.8 3.9 1.9 2 1.00 24.1 5.5 3.2 Example 2 0.25 19.5 2.0 0.8 0.50 20.1 2.5 1.3 " 1.00 19.3 3.8 1.4 111Corrected to 40 Ib/ream basis weight '2'Obtained after soaking 10 sec. in water '3'0btained after soaking 2 hr. in water Example 3 This example illustrates the preparation of a typical glyoxal-modified poly(ss-alanine) of this invention and its use as a dry and temporary wet strength resin for paper.

Part A In a round-bottomed 3-necked flask equipped with a paddle stirrer, thermometer, and condenser are placed 200 parts dry acrylamide. 0.44 part phenyl-ss- naphthylamine, and 400 parts dry toluene.

The mixture is heated 30 minutes under an atmosphere of nitrogen at 1000C.with stirring to melt and partially dissolve the acrylamide. Then 4 parts of 1.2 N potassium t-butoxide in t-butanol is added and the mixture is heated at about 90"C. for 18 hours. The hot toluene is decanted and the resulting solid polymer is washed with acetone. The polymer is water-soluble, branched poly(ss-alanine).

Part B A 30 /n aqueous solution of the neutral poly(ss-alanine) prepared as described above is warmed to 40 to 500 C. To this solution is added 50 mole% (based on amide units in the polymer) of glyoxal as a 40% aqueous solution. The pH of the resulting solution is raised to about 9.5 and maintained at room temperature for about 10 minutes during which time there is an increase in Gardner viscosity. Then the solution quickly is diluted with water to 4% total solids and adjusted to pH 5.5 with sulfuric acid.

Part C The glyoxal modified neutral poly alanine) prepared in Part B is evaluated as dry and wet strength resins in hand-sheets prepared from 100% Rayonier bleached kraft pulp (40 Ibs./ream). The handsheets are soaked for 1 minute in a 20% aqueous solution of the glyoxal modified neutral poly(ss-alanine) at a pH of 6.0. The handsheets are then passed through a nip roll and drum dried at 1000C.

Strength data for the thus treated sheets are compared with untreated handsheets as tabulated below.

Tensile Strength (Ibs./in.)* Wet Wet Dry (10 seconds) (2 hours) Untreated handsiieets 19.6 0.9 Treated handsheets 24.3 8.1 2.6 *Tensile strengths are corrected to 40 Ibs./ream basic weight.

WHAT WE CLAIM IS: 1. A water-soluble resin which comprises the reaction product of (1) a branched water-soluble poly(ss-alanine) which may be modified to introduce anionic or cationic groups and is prepared in an organic reaction medium, and (2) glyoxal.

2. A resin according to Claim 1, wherein the branched poly(ss-alanine) is prepared by the anionic polymerisation of acrylamide in the presence of a basic catalyst and a freeradical inhibitor in an organic reaction medium.

3. A resin according to Claim I or 2, wherein the branched, water-soluble poly alanine) is an anionic poly(ss-alanine) produced by partial hydrolysis of an initially prepared branched, water-soluble poly alanine).

4. A resin according to Claim 1 or 2, wherein the branched water-soluble poly alanine) is a cationic poly(ss-alanine) produced by reacting an initially prepared branched water-soluble poly(ss-alanine) with dimethylamine and formaldehyde.

5. A process of preparing a glyoxalmodified poly(ss-alanine) which comprises: (a) polymerizing acrylamide in the presence of a basic catalyst and a free radical inhibitor in an organic reaction medium to produce branched water soluble poly(ss-alanine); (b) dissolving the poly(ss-alanine) in water to provide an aqueous solution having a solids content of 11 to 40 per cent by weight; and (c) adding glyoxal in the amount of 10 to 100 mole per cent, based on the amide repeating units of the poly(ss-alanine) thus producing the glyoxal-modified poly(ss-alanine).

6. A process of producing a glyoxalmodified poly(ss-alanine) substantially as described in the foregoing Examples.

7. The glyoxal-modified poly(ss-alanine) produced by the process of Claim 5 or 6.

8. The process of treating paper with the resin of any of Claims 1 to 4 and 7.

9. The process of treating paper with a mixture of an aqueous solution of the resin of Claim 3 and an aqueous solution of a polyamino-polyamide-epichlorohydrin resin.

10. Paper treated with the resin of any of Claims I to 4 and 7.

11. A blend of cationic and anionic watersoluble nitrogen-containing polymers wherein the cationic polymer is the reaction product of epichlorohydrin and the aminopolyamide derived from adipic acid and diethylenetriamine and wherein the anionic polymer is a resin according to

Claims (1)

1. Claim 3.