CA1096540A - GLYOXAL MODIFIED POLY(.beta.-ALANINE) STRENGTHENING RESINS FOR USE IN PAPER - Google Patents

Abstract

Rave Case 4-8 GLYOXAL MODIFIED POLY(.beta.-ALANINE) STRENGTHENING RESINS FOR USE IN PAPER

Abstract of the Disclosure Novel resins, useful as strengthening resins for imparting dry and temporary wet strength to paper, are disclosed.
The resins are prepared by reacting branched water-soluble poly(.beta.-alanine) with glyoxal.

Description

: ~ ~ g ~ S 40 Rave Case -8 This invention relates to novel resins which impar~ dry strength and temporary wet strength to paper, the process o in-corporating them into paper and the paper so treated.
It is known to add certain resins to paper, usually dur-ing the paper-making process, to improve wet and/or dry strength of paper. The type of resin added depends on thP properties de-sired in the final paper product. For tissue, towelling and cer-tain 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 relate to resins which impar~ both dry strength and temporary wet strength to paper. The resins of Espy are prepared by rPacting certain polyamines and aminopolyamides with anacrylamide and then with a polyaldehyde. Also, U.S.
3,556,932 to Coscia et al teaches wet and dry strength resins which are ionic water-soluble vinylamide polymers having glyoxal-i reactive amide substituents and sufficient - CHOHCHO substitu-ents 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 hav-ing the formulae - CH2 _ fH _ CH~-fH
C = O and C - O

NH2 NHCHOHCHo 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.

-2-~6s~0 In accordance with one aspect this invention provides a water soluble resin which comprises the reaction product of a branched water-soluble poly(beta-alanine) having a molecular weight in the range of about 500 to about 10,000 with from about 10 to about 100 mole %~ based on the amide repeat-ing units of the poly(beta-alanine) of glyoxal, said poly(beta-alanine having been prepared by the anionic polymerization of acrylamide in a suitable or-~anic reaction medium inert to the reaction conditions in the presence of a basic catalyst and a free-radical inhibitor.
It has been found that glyoxal modified poly(beta-alanine) resins are effective dry strength and temporary wet strength resins for papers. The novel resins of this invention are stable in aqueous solution at relatively high solids concentration and have a long shelf life.
In another aspect, the present invention relates to a process for preparing the resins defined above which comprises:
a) anionically polymerizing acrylamide in the presence of a basic catalyst and a free-radical inhibitor in a suitable organic reaction medium inert to the r~action conditions to produce branched water-soluble poly(beta-alanine) having a lecul æ weight in the range of about 500 ~o about 10,000;
b) dissolving the poly(beta-alanine~ in water to provide an aqueous solution having a solids content of about 11 to about 40~; and c) adding glyoxal in the amount of about 10 to about 100 mole ~, based on the amide repeating units of the poly(beta-alanine) and continuing the reaction at a te~perature from about 10 C. to about 50 C. until a vis-cosity increase of about 2 to about 10 uni~s on the Gardner-~Ioldt scale has t~ken place, thus producing a glyoxal-modified poly(beta-alanine~.
The poly(beta-alanine) used in preparing the novel resins o~ this invention is a branched, water-soluble, poly(beta-alanine) prepared by the anionic polymerization of acrylamide in the presence of a basic catalyst and a vinyl polymerization inhibitor. ~nionic polymerization of acryla~ide re-sults in a polymer backbone of beta-alanine repeating units. The preparation of linear crystalline poly(beta-alanine) by ~he anionic pol~merization o~
ac~ylamide is described in United States Patent No. 2,749,331 to Breslow.

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Water-soluble and water-insoluble forms of the polymer are obtained. In later ~Jork it was determined that the water-sol~le form of poly(beta-alanine) can be either a linear crystalline polymer of relatively low molecular weight or a higher molecular weight polymer having a branched structure. ~ranched, polytbeta-alanine) contains repeating units of the formula ~v~C~2C~2CO~
in the linear segments and repeating units of the formula ~C~12CH2CO~ in the segments at ~hich branching occurs. Primary amide end groups will occur at the end of each - 3a -branch chain. Hydrolysis of water-soluble branched poly(~-ala-nine) produces ~-alanine, NH2CH2CH2COO~, from the linear segment~, iminodipropionic acid, HN~CH2CH2COOH)2 from the points of brar.ch-ing 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(~-alanine). On hy-drolysis 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 pres-ent only as end groups of the branch chains, an indication of the amount of branching of the poly(~-alanine) can be determined.
Any poly(~~alanine) containing sufficient branching to be water-soluble is suitable for use in this invention. In general, the branched poly(~-alanine) should contain about one primary amide group for every two to six amide groups present. The molecular weight of branched water soluble poly(~-alanine) suitable for use in this invention is in the range of about five hundred to about ten thousand and preferably in the range of about two thousand to about six thousand.
As stated above, the branched water-soluble poly(~-alanine) is prepared by the anionic polymerization o acrylamide in the presenceof a basic catalyst and a vinyl or ~ree-radical polymerization inhibitor. Because of the extremely exothermic nature of the anionic polymerization, it i5 preferred to conduct the reaction in a suitable organic reaction medium inert to the reaction csnditions and capable of dissolving or slurrying acryl-- amide. Suitable media include aromatic and aliphatic compounds, ~or example, toluene, xylene, tetrahydronaphthalene, chloroben-zene, nitrobenzene and dioxane.
The concentration of the acrylamide monomer in the reaction medium is in the range of about 2% to about 30%, and is preferably about 8~ to about 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 i5 employed, the poly(~-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 chlori-nated and maleated polyolefins.
Illustrative basic catalysts which can be employed in-clude alkali metals, alkali metal hydroxides, alkaline earth met-al hydroxides, quaternary ammonium hydroxides and the alkalimetal alkoxides. Examples of suitable basic catalysts are sodium metal, sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium t-butoxide, sodium methoxide, tetramethylammonium hydrox-ide, potassium t-butoxide, and calcium hydroxide. The amount of catalyst used is in the range of about 0.01 to about 2.0 mole %, preferably about 0.1 to about 1.5 mole % based on the monomer A free radical inhibitor is added to the reaction mix-ture to inhibit vinyl polymerization through the double bond of ^=
the acrylamide monomer. Examples of free radical inhibitors which can be used are phenyl-~-naphthylamine, hydroquinone, diphenyl-amine and phenothiazine.
The anionic polymerization reaction is conducted at temperatures in the range of about 40C. to about 140C. and preferably about 80C. to about 130C.
In many cases, the anionic polymerization of acrylamide under the above conditions will produce a mixture of water-solu-ble and water~insoluble poly(~-alanine). The water-soluble poly-mer for use in this invention can be readily separated by parti-ally dissolving the polymer product in water and removing the in-soluble fraction by conventional methods such as filtration, etc.
Poly(~-alanine) is a neutral polymer. For most, al-though 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 ~b~
desirable to modify the branched, water-soluble poly(~-alanineJ
before reaction with glyoxal to introduce anionic o~ cationic groups into the polymer structure. However, if the strsngthening 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 poly(~-alanine) prior to reaction with glyoxal is not necessary.
Anionic modification of branched poly(~-alanine) can be accomplished by partial hydrolysis of the polymer to convert some of the primary amide groups into anionic carboxyl groups. For example, hydrolysis of poly(~-alanine) can take place by heating a slightly basic aqueous solution of the polymer having a pH of about 9-10 at temperatures of about 50C. to about 100C. The amount of anionic groups introduced should be about 1 to about 10 mole % and preferably about 2 to about 5 mole %, based on amide repeating units.
Another method of anionic modification of branched poly(~-alanine) is by treatment with formaldehyde and then with bisulfite ion.
Cationic modification of branched poly(~-alanine) is accomplished by reacting poly(~-alanine) in aqueous solution with formaldehyde and dimethylamine. This reaction can be carried out by heating an aqueous solution of the three reactants at about 70C. to about 80C at either a basic pH of about 9 to about 11 or an acid pH of about 2 to about 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~, about 4.5 to about 8.0, the tertiary amine groups are protonated and are thus rendered cationic. The amount of formaldehyde and dimethylamine used is from about 2 to about 15 mole ~, based on amide repeating units of the poly(~-alanine). The amount of cat-ionic groups introduced is from about 2 ~ about 15 mole % and preferably from abou-t 4 to about 8 mole %, based on amide repeat-ing units.

~ 'he ~inal step in preparing the novel r~sin~ of this invention i~ the reaction of poly(~-alanine) with glyoxal. As stated above, poly(~-alanine~ can be modified to introduce anionic or cationic groups, as desired, before reaction with glyoxal.
Reaction of poly(~~alanine) and glyoxal is carried out in aqueou~
solution. The solids concentration of poly(~-alanine) in the aqueous solution should be above about 10~ and can be from about 11% to about 40~ with about 12.5% to about ~5% being the preferred range. The amount of glyoxal used in this reaction can be from about 10 to about lOQ mole % and is preferably about 20 to about 30 mole ~, based on the amide repeating units of the poly(~-ala-nine). The temperature of the reaction i5 from about 10C. to about 50C., preferably about 20C. to about 30C.
The reaction between the glyoxal and poly(~-alanine) is continued until a viscosity increase of about 2 to about 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(~-alanine) has taken place.
The amount of crosslinking is insufficient to cause gelation of the poly(~-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 ylyoxal modified poly(~-alanine) resins of this invention can be used to impar~ dry strength and temporary wet strength to paper using any conventional method. Aqueous solu-tions of the resins may be applied to the formed paper sheet, e.g., by spraying, or tub application, etc. 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 solu-tions of the resins to an aqueous solution 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 en~ine, fan pump, head box or any other suitable point. Because of the anion-c nature of the cellulose fibers, it is desirable tG Uge an i5nicresin~so that it will be adsor~ed on the cellulose fibers. P.
cationic resin ~ill 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 in-clude polymeric cationic retention aids such as aminopolyamide--epichlorohydrin resinst polyethylen~mine, resins derived from polytdiallylamine) and poly(dialkylmethylamine), cationic starch and other highly cationic polymers, natural or synthetic.
The amount of glyoxal modified poly(~-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 cellu-lose fibers.
- The following examples will serve to illustrate the in-vention, parts and percentages being by weight unless otherwise ~- 20 indicated.
~ Exam~le 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.
Part A In a 5-liter round-bottomed 3-necked flask equipped with a paddle stirrer, thermometer, and condenser are placed 350 parts dry acrylamide, 1.0 par-ts phenyl-~-naphthylamine, and 3870 parts chlorobenzena. The mixture is heated to 85 - 90C. with vigorous stirring to melt and partially dissolve the acrylamide. Sodium hydroxide ~lake (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 minu-te intervals, and the reaction mixture is heated at about 90C. for one additional hour. The hot chlorobenzene is decanted and the resulking solid, brittle polymer is recovered. The polymer is water-soluble, bran~hed poly(~-alanine).
Part B A sample o~ poly(~-alanine) prepared in Part A is dissol-ved in water containing 2 mole percent sodium hydroxide (based on amide repeat units in the polymer) to provide a solution contain-ing 25% poly(~-alanine). The solution is heated at 90-lOO~C. for about 30 minutes with steam sparge to remove the ammonia libera-ted 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 titra-tion.
Part C To a 15~ aqueous solution of anionic poly(~-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 re-sulting 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 effic-lency .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) o~ aqueous solu-tions of glyoxal-modified anionic poly(~-alanine) and an amino-polyamide -- epichlorohydrin resin (commercially available ~rom Hercules Incorporated under the trademark "Kymene 557") is used as the strengthening resin in the following procedure:
Rayonier bleached kraft pulp is beaten in a cycle beat-er to a Schopper-Riegler freeness of 750cc. 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. Sam-ples of the strengthening resin are added -to the proportioner in amounts of 0.25%, 0.5% and 1% solids based on pulp solids. The 36~
pulp then is formed into handsheets of about ~0 pounds per ~,000 square foot basis weight and dried for one minute at a tempera-ture of 100C. A control handsheet is prepared as above without the addition of a strengthening resin. The resulting handsheets after conditioning at a temperature of 75F. and 50% relative humidity for over 24 hours are tested for dry strength. The hand-sheets are also tested Eor 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(~-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-~-naphthylamine. Sufficient 0.5 M K+
Ot-Bu in t-BuOH is added to the mixture heated under N2 to 90-100C. to cause polymerization to occur as evidenced by a sub-stantial exotherm and formation of solid polymer. The resulting mixture then is heated at 100C. for five hours; the toluene is ~; separated and the solid poly(~-alanine) is dried.
.
Part B To a 25~ aqueous solution of essentially neutral poly (~-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 9.0-9.5 with aqueous sodium hydroxide, and the solution is heated 20 minutes on a steam bath at 70-80C. 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 wa~er of the cationic poly(~-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 un-til a

4-6 unit increase in Gardner viscosity is observed. The total solids level then is brought to 10% by dilution with water, and ~10--the pH i5 adjusted to 4~5-5Ø The stability of the resulting resin tcward gelation is greater than six months.
Part D The glyoxal-modified cationic poly(~-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.

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Example 3 This example illustrates the preparation of a ~ypical glyoxal-modified poly(~-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 drv acryl-amide, 0.44 part phenyl-~-naphthylamine, and 400p~rts dry tol-uene. The mixture is heated 30 minutes under an atmosphere of nitrogen at 100C. 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 mix~ure heated at about 90C. for 18 - hours. The hot toluene is decanted and the resulting solid poly-mer is washed with acetone. The polymer is water-soluble, bran-ched poly~-alanine).
Part B A 30% aqueous solution of the neutral poly(~-alanine) prepared as described above is warmed to 40 to 50C. 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 lQ 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 handsheets prepared from 100% Rayonier bleached kraft pulp (40 lbs./ream).
The handsheets are soaked for 1 minute in a 20% aqueous solution of the glyoxal~modified neutral poly(~-alanine) at a pH of 6Ø
The handsheets are then passed throuyh a nip roll anddrum dried at 100C.
Strength data for the thus treated sheets are compared with untreated handsheets as tabulated below.

~6~U
Tensile Strenqth (lbs./in.)*
~y_ Wët ~~0 se~conds~ Wet~ (2 hours) :. Untreated handsheets 19.6 0.9 Treated handsheets 24.3 8.1 2.6 *Tensile strengths are corrected to 40 lbs./ream basic weight.

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Claims (5)

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

1. A water-soluble resin which comprises the reaction product of a branched water-soluble poly(beta-alanine) having a molecular weight in the range of about 500 to about 10,000 with from about 10 to about 100 mole %, based on the amide repeating units of the poly(beta-alanine) of glyoxal, said poly(beta-alanine) having been prepared by the anionic polymerization of acrylamide in a suitable organic reaction medium inert to the reaction condi-tions in the presence of a basic catalyst and a free-radical inhibitor.

2. The resin of claim 1 wherein the basic catalyst is sodium hydroxide.

3. The resin of claim 1 wherein the basic catalyst is sodium t-butoxide.

4. The resin of claim 1, 2 or 3 wherein the free-radical inhibitor is phenyl-beta-naphthylamine.

5. The process of preparing a glyoxal-modified poly(beta-alanine) which comprises:
a) anionically polymerizing acrylamide in the presence of a basic catalyst and a free-radical inhibitor in a suitable organic reaction medium inert to the reaction conditions to produce branched water-soluble poly(beta-alanine) having a molecular weight in the range of about 500 to about 10,000;
b) dissolving the poly(beta-alanine) in water to provide an aqueous solution having a solids content of about 11 to about 40%; and c) adding glyoxal in the amount of about 10 to about 100 mole %, based on the amide repeating units of the poly(beta-alanine) and continuing the reaction at a temperature from about 10°C. to about 50°C. until a viscos-ity increase of about 2 to about 10 units on the Gardner-Holdt scale has taken place, thus producing a glyoxal-modified poly(beta-alanine).