GB2075537A - Derivatized and Thinned Starches - Google Patents

Abstract

This invention relates to derivatized and thinned starches which have a degree of substitution in the range from about 0.05 to about 0.4 and an intrinsic viscosity in the range from about 0.12 to about 0.28 deciliters per gram. The starches have the unique property of yielding stable, aqueous dispersions of high solids content (greater than 25% by weight) when graft copolymerized with one or more vinyl monomers. The starch graft copolymers exhibit superior tensile strength and abrasion resistance.

Description

SPECIFICATION Derivatized and Thinned Starches This invention relates to derivatized and thinned starches which, when polymerized with vinyl monomers, produce graft copolymers having good tensile strength and abrasion resistance. Moreover, these starches, when graft copolymerized with vinyl monomers, have the unique property of producing aqueous dispersions which are stable and exhibit no substantial change in viscosity over extended periods of time, even when the dispersions have a high content of solids, that is, of the graft copolymer.

The production of derivatized starches and the production of thinned starches is known as is their use to produce aqueous dispersions when graft polymerized with vinyl monomers. It is also known that the resultant polymeric dispersions are useful as paper coatings, adhesives, and sizes for hydrophobic fibers.

Mino petal, U.S. 2,922,768 disclose the use of a ceric salt along with poiymeric alcohols capable of being oxidized by the ceric salt to produce graft copolymers; starch, partial ethers of starch such as cyanoethylated starch and partial esters of starch such as acetylated starch are included in the polymeric alcohols described. Brockway, (J. Polymer Sci.: Part A, Vol. 2, p. 3721, 1964) discloses the use of hypochlorite oxidized starches. Brockway, et al U.S. 3,095,391, use granular, unpasted amylaceous materials such as native starch and modified starch to produce graft copolymers.The modified granular, unpasted starches disclosed in U.S. 3,095,391 include: oxidized granular starch, acid modified granular starch prepared by heating an acidified aqueous suspension below the pasting temperature, hydroxyethyl ethers of starch, and granular starch modified by reaction with vinyl acetate in water.

Brockway, et al, U.S. 3,061,471, discloses use of a "thin boiling starch" to avoid unduly viscous emulsions (dispersions) of graft copolymers. Brockway describes a "thin boiling starch" (Col. 2) as "those starch products, whether modifications of native starch or derivatives, which when gelatinized in water, produce pastes that are less viscous, cohesive and tacky and tend less to gel than the native starches. Such modified starches and starch derivatives including, for example, the hypochloriteoxidized, the acid-modified, the ethers (e.g., hydroxyethyl and carboxymethyl ethers), the acetates, the enzyme-converted and so on." The use of a number of vinyl monomers with modified and unmodified starches both granular and gelantinized (pasted) as starting materials to prepare starch graft co-polymers is known. U.S.

3,061,472 to Brockway discloses thin-boiling starches such as hypochlorite-oxidized and acid modified starches, starch ethers, starch acetates and enzyme-converted starches polymerized with an acrylic ester of an alkanol. The products have utility in sizing hydrophobic fibers. U.S. 3,095,391 to Brockway et al. teaches the use of granular unpasted starch, granular hypochlorite-oxidized starch, acid modified granular starch prepared by heating an acidified aqueous suspension of granular starch below the pasting temperature, granular starch reacted with ethylene oxide, and granular starch reacted with vinyl acetate as suitable materials for polymerization with vinyl monomers including vinyl acetate, ethyl acrylate, styrene, methacrylic acid, the butyl esters of acrylic and methacrylic acids, methyl methacrylate, acrylonitrile, acrylamide, 4-vinyl pyridine and diethylaminoethyl methacrylate. The products have utility as adhesives, flocculants and sizes.

The graft copolymerization reactions are usually carried out in aqueous media with the resulting compositions being obtained as aqueous dispersions or latices. Since the valuable and useful portion of such a latex is the graft copolymer portion of the dispersion, it is desirable that the compositions be prepared at the highest practicable solids level. Furthermore, if the latices are to have any useful life they must be stable. That is, the dispersions should not separate into two or more phases or undergo any excessive increase in viscosity within the periods required for commercial usage.Such problems when producing polymer compositions from the previously known starches have been noted in U.S: 3,984,361 where gelatinized cationic starches polymerized with a vinyl monomer to form aqueous dispersions are stabilized by sonification and in U.S. 4,029,61 6 where aqueous dispersions of pullulan polymerized with an ethylenic compound are distinguished from those based on starch by exhibiting stability and not undergoing gelation or "aging".

The production of graft copolymers of starch and vinyl monomers initiated by inducing free radicals on a starch is well known. Reviews have been published by J. C. Arthur, Jr. (Advances in Macromolecular Chemistry, Vol. 2, Academic Press, London 8 New York, pp. 1-87, 1970) and by G.

F. Fanta (Block and Graft Copolymers, Vol. 1, John Wiley Sons, London & New York, pp. 1-45, 1973).

A number of chemical activators are known. U.S. Patent 3,138,564 to Borunsky discloses graft polymerization of 1,3 butadiene and acrylonitrile to starch using ozone and Fe(ll). British patent 869,501 discloses the production of starch graft polymers utilizing polymerization initiators such as hydrogen peroxide, organic peroxides, hydroperoxides and dilute solutions of ceric ions. Yields may be improved by the use of an activator for these initiators such as mild reducing agents, e.g., ferrous ammonium sulfate, sodium formaldehyde sulphoxylate and the like. C.E. Brockway (Am. Chem. Soc.

Div. Org. Coatings Plast. Chem., pp. 502-508, 1967) and U.S. Patents 3,061,471 to Brockway et al.

and 3,061,472 to Brockway disclose the use of hydrogen peroxide to graft polymerize various vinyl monomers onto starch. Additionally, C. E. Brockway(J. Polymer Sc!.: Part A, Vol.2, pp. 3721-3731, 1 964) discloses use of hydrogen peroxide to graft polymerize methyl methacrylate to starch. For the most part these initiators are nonspecific and induce homopolymerization of single monomers and copolymerization of monomer mixtures as well as the desired graft polymerization of monomer and monomer mixtures to the starch. This produces products which tend to separate on storage.

Such problems can be minimized or avoided by the use of a Cerium(lV) initiator. Although some homopolymerization has been reported using Cerium (IV) by Fanta, et al. (J. Appl. Polymer Sci., Viol.10, pp. 91 9-937, 1966) the most important pathway for Cerium (IV) initiation of free radicals as outlined by Fanta (Block and Graft Copolymers, Vol. 1, p. 3, Ed. R. J. Ceresa, John Wiley & Sons, London 8 New York, 1 973) would be expected to give graft copolymers to the exclusion of any homo- or copolymers.

Extensive use has been made of this system to graft vinyl monomers to starch.

The starches of this invention are both derivatized and thinned. The starches are derivatized to a degree of substitution in the range from about 0.05 to about 0.4 and they are thinned to an intrinsic viscosity in the range from about 0.12 to about 0.28 deciliters per gram (dl/g). The invention also encompasses methods for the preparation of the derivatized and thinned starches.

These derivatized and thinned starches, when polymerized with a vinyl monomer or monomers under the influence of a free radical-initiator which acts to produce graft copolymers to the substantial exclusion of the production of homo- or copolymers of the vinyl monomer(s), yieid dispersions which do not have the problems of phase separation, undue increase in viscosity upon storage, and gelation inherent in those produced from the previously known starches. Moreover, these starches provide starch graft copolymers with good tensile strength and abrasion resistance.

The derivatized and thinned starches of this invention are useful starting materials for the production of starch graft copolymers with good tensile strength and abrasive resistance. Moreover, the physical and chemical properties of the derivatized and thinned starches permit the production of stable dispersions at high solids content, i.e., greater than 25% solids. These dispersions are stable (show no undue increase in viscosity or gelation) over extended periods of time. They are useful as sizings for textile fibers pandas coatings and adhesives for paper products. Additionally, these novel derivatized and thinned starches have the usual uses of such starches, for example as industrial adhesives, and corrugating adhesives. Use as paint thickeners and the like are also possible.

The novel starches of this invention are both derivatized and thinned. For optimum results in the preparation of the stable, aqueous starch graft copolymer dispersions, which these starches yield, the starches should be free of substances which interfere with the graft polymerization reaction or adversely affect the final dispersion. The derivatization step may introduce reagents, salts or byproducts which have such effects. Such substances can readily be removed by washing the derivatized starch provided that the starch remains in granular form. Minor degrees of solubility can be tolerated in the granular starch since these are readily repressed by the addition of a water miscible organic liquid, such as ethyl alcohol, to the wash water.

The starch can be thinned by chemical means such as acid hydrolysis, followed by derivatization while keeping the starch in granular form. Likewise, the starch may first be derivatized and the granular product thereafter gelatinized and thinned. A combination of acid and enzyme thinning may also be employed. When derivatization is the first step it is preferred that thinning be accomplished by enzymatic means. This sequence is the preferred method of preparation of the starches.

The starches applicable to the production of the derivatized and thinned starches of this invention are those such as corn starch, wheat starch, potato starch and the like. Corn starch is preferred.

The preparation of starch derivatives is well known. However, we have found that to produce starch derivatives with the properties which lead to stable dispersions upon graft polymerization with vinyl monomers it is necessary to control the degree of substitution. The type of substituent also has an effect on the stability of the dispersions. Likewise, it is necessary to control the degree of thinnirig of the starches if optimum physical properties, such as tensile strength and abrasion resistance, of the copolymers are to be achieved.

At the same degree of substitution bulky and charged substituents on the starch tend to provide relatively more stable dispersions than small or uncharged substituents. Any substituent which does not interfere with polymerization and which provides starch derivatives exhibiting stable viscosities at solids levels of about 30% to 45% by weight after thinning is a suitable substituent. These include anionic, cationic and non-ionic substituents. The preferred substituents are of the cationic and nonionic types. Carbamylethyl, alkyl, benzyl and benzalkyl starch derivatives are exemplary of the nonionic derivatives. The dialkylaminoalkyl substituent exemplifies the cationic derivatives.

The preferred starch derivatives are those with hydroxyalkyl, cyanoalkyl, dialkylaminoethyl, and acyl substituents. The most preferred are the hydroxyethyl, cyanoethyl, diethylaminoethyl, carbamylethyl and acetyl derivatives.

The degree of substitution chosen will affect the rate of change in viscosity of the dispersion produced by graft polymerization. With higher degrees of substitution dispersions which do not double in viscosity in 30 months can be prepared. However, most industrial applications do not require such extremely stable latices. The practical considerations are that the final dispersions should not become so viscous that they are difficult to handle or must be thinned, for processing, to a solids level too low for the intended use. The initial viscosity of the polymeric dispersion will depend upon the initial viscosity of the starch dispersion and this viscosity is related to the solids content of the starch dispersion. Increasing solids content increases the initial viscosity of the polymeric dispersion.

Consequently, if a low solids content is adequate for the intended use the polymeric dispersion may be prepared at low solids content and consequent low initial viscosity thereby permitting greater increases in viscosity without becoming unduly viscous.

The degree of substitution of a derivatized starch is not proportionally related to the properties which impart improved viscosity stability to the polymeric dispersions. At low degrees of substitution (about 0.02) there is little effect on viscosity stability of the dispersion obtained by graft copolymerization of the derivatized starches with vinyl monomers. However, dependent upon the type of substituent, a dramatic and unexpected improvement in the stability of the final starch graft copolymer latex appears at degrees of substitution of the starch of from about 0.05 to 0.1 as graphically illustrated in Figure 1. With a bulky and/or charged substituent such as the diethylaminoethyl radical, degrees of substitution above about 0.05 rapidly increase the stability. With the carbamylethyl radical a similar increase is seen at degrees of substitution above about 0.1.At degrees of substitution between 0.08 and 0.09 the cyanoethyl and acetyl derivatives show the same remarkable improvement in the stability of the final dispersion.

The starch derivatives of this invention have a degree of substitution of at least about 0.05. The maximum degree of substitution is limited only by practical considerations. It is desirable that the starch derivative be free of unreacted reagent, salts arid by-products if it is to be polymerized. This is most economically done by washing the derivative and this is facilitated if the starch remains in the granular form and is not solubilized by excessive derivatization. Since higher degrees of substitution usually increase the solubility of the derivatives the degree of substitution selected should be consistent with removal of the reagent, salts and by-products.

The preferred range of degree of substitution is from about 0.05 to about 0.4 and the range from about 0.06 to about 0.2 is especially preferred.

The starch derivatives useful in the practice of this invention are those that can be gelatinized and thinned. The formation of colored products may be prevented by avoiding excessive temperatures during those processes. Thinning may be accomplished by known means such as acid hydrolysis or enzyme treatment. Thinning by enzymatic means such as of alpha-amylase is preferred.

The degree of thinning of the starch, as determined by the intrinsic viscosity, is an important aspect of this invention. Excessive thinning adversely affects the properties of the starch which impart optimum tensile strength and abrasion resistance to copolymers obtained from the starch. For example, free films of a graft copolymer prepared from a cyanoethyl starch with a degree of substitution of 0.161 thinned to intrinsic viscosities (dl/g) of about 0.10, 0.14, 0.1 8 and 0.27 and polymerized with ethyl acrylate demonstrate that relatively small changes in intrinsic viscosity can have a substantial effect on the physical properties of the graft copolymer. A free film cast from the copolymer obtained from the starch thinned to an intrinsic viscosity of about 0.10 dl/g had a tensile strength of about 1,470 g/mm2.However, when the same starch was thinned to an intrinsic viscosity of about 0.14 dl/g a film from a copolymer prepared from that starch had a tensile strength greater than 2,000 g/mm2. The tensile strength showed no marked increase above this value as the intrinsic viscosity increased but slowly diminished to about 1,950 g/mm2 at an intrinsic viscosity of about 0.18 and to about 1,870 g/mm2 at an intrinsic viscosity of about 0.27 dl/g.

Similar changes in abrasion resistance appeared when the copolymers were applied to a 50%/50% cotton-polyester blend yarn and the cycles to 11 breaks were measured on a Walker (T.M.) Abrader. With the copolymer prepared from the starch thinned to an intrinsic viscosity of about 0.10 only about 820 cycles were required for 11 breaks. However, when the copolymer was prepared from the starch thinned to about 0.14 dl/g the number of cycles required for 11 breaks rose above 1,100.

The number of cycles for 11 breaks remained greater than 1,100 when the starch was thinned to an intrinsic viscosity of about 0.18 and used for a copolymer and fell to about 1,000 when the starch was thinned to an intrinsic viscosity of about 0.27 and used for a copolymer.

The range of intrinsic viscosity of the thinned starches is from about 0.12 to about 0.28 dl/g. For optimum tensile properties of the graft copolymers the range of intrinsic viscosities from about 0.13 to about 0.21 dl/g is preferred.

Any monomer polymerizable onto the derivatized and thinned starch through a free radical initiated reaction may be used to produce starch graft copolymers. In general these are vinyl monomers such as vinyl halides, vinyl esters, vinyl ethers, alkylvinyl ketones, N-vinyl carbazole, N-vinyl pyrrolidone, vinyl pyridene, styrene, alkyl styrenes, acrylic acid, alkyl acrylates, methacrylic acid, alkyl methacrylates, acrylamide, substituted acrylamides, vinyiidene halides, itaconic acid, 1-3 butadiene and the like. Among these, acrylonitrile, methyl methacrylate, vinyl acetate, 2-ethylhexyl acrylate, and the lower alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate are preferred when a single monomer is used to form the graft copolymer.

The especially preferred single monomers used to produce the starch graft copolymers are methyl acrylate, ethyl acrylate and methyl methacrylate.

As is well known, combinations of two or more monomers can be polymerized together to form copolymers or block copolymers and such combinations can also be used to produce starch graft copolymers with the derivatized and thinned starches. When two or more monomers are polymerized with the starches the preferred monomers are dimethylaminoethyl methacrylate, ethyl acrylate, butyl acrylate, methyl methacrylate and methacrylic acid.

Any polymerization initiator that acts to initiate free radical polymerization on the derivatized and thinned starches to the substantial exclusion of initiation of homo- or copolymerization of the monomer or mixture of monomers utilized to form a starch graft copolymer is a suitable initiator.

Ceric ammonium nitrate is an example of such an initiator. This initiator may be used in amounts from about 0.5% to 8% by weight of the derivatized and thinned starch. Amounts below about 0.5% do not provide adequate initiation of the graft polymerization and are apt to result in sizeable amounts of unreacted monomer. Initiator levels from about 1.4% to 4% by weight of the starch are preferred.

The combination of hydrogen peroxide and acetate ion also is a useful initiator. Sodium acetate or glacial acetic acid may be used to supply the acetate ion. This initiator may be used at a pH in the range from about 2 to about 9 and at initiating temperatures of about 400 to 900 C. The mole ratio of acetic acid to hydrogen peroxide is about 2 and the amount of peroxide from about 0.5% to 2.0% based on the weight of the starch.

The amounts of monomer or monomers added will vary according to the properties desired in the final dispersion. The dispersions made from the derivatized and thinned starches may have a solids content of as high as 40% by weight or more, dry basis. The starch-monomer ratio may be 100/25 by weight or less, dry basis and preferably is 100/40 or less. The lower limit of this ratio is a matter of choice depending upon economic considerations and the intended viscosity of the final dispersion. As increasing amounts of monomer are incorporated in the dispersions the economic advantages of using the derivatized and thinned starch as a significant portion of the final copolymer are diminished.

The initial polymerization conditions should provide sufficient monomer to support the polymerization once it is initiated. This is readily accomplished in a conventional batch process where the monomer or monomers are added in a single increment. However, any mode of addition which will adequately utilize the initially generated free radicals without causing undue problems in temperature control will suffice, that is, the monomer or monomers may be added as a single increment, incrementaliy over the time of polymerization or continuously so long as the required conditions for polymerization are achieved. When mixtures of monomers are used they may be added as such to produce the conventional type of copolymer chain grafted onto the starch or may be added sequentially, individually or as discrete mixtures, to produce block copolymers grafted onto the starch.

The temperature at which the polymerization is carried out will depend upon the monomer system and catalyst used. Heating or cooling or a combination thereof may be required to achieve or maintain the desired polymerization temperature. Temperatures in the range from 0 to 1 000C may be utilized depending upon the catalyst and monomer system. Temperatures in the range from 250 to 800C are preferred. However, if a catalyst produces or requires a low pH prolonged exposure to such acidic conditions may result in excessive hydrolysis of the starch and adversely affect the properties of the final polymer.

Surfactants may be used to stabilize the dispersions during the polymerization or they may be added after the reaction is complete. When present during the polymerization the surfactant chosen should not interfere with the initiator system or otherwise adversely affect the polymerization reaction.

Triton X-200 and Triton X-405 (Rohm and Haas Co.) are examples of surfactants that do not interfere with the polymerization reaction when the initiator is a cerium compound.

The following examples are illustrative of the invention and not intended to limit the scope of the invention or the ambit of the claims.

Furthermore, unless otherwise designated, the term "solids" and "percent solids" as used herein refers to total dry substance including the starch and, where appropriate, any monomer(s) utilized to produce the starch graft copolymer dispersion. Viscosities given in centipoise (cps), unless otherwise indicated, have been determined at 240C using a model H.A.T. Brookfield viscometer and the appropriate spindle. Expressions and procedures used in the specifications and claims follow: Activity of SolubleAlphaAmylase. The activity of soluble alpha amylase preparations was determined by a modification of Standard Test Method, AATCC 103, 1965 "Bacterial Alpha Amylase Enzymes Used in Desizing Assay of,' published in the 1967 Edition of Technical Manual of the American Association of Textile Chemists and Colorists. Volume 43, pp. B-1 74 and B-175. The method was modified as follows: the buffer solution for the starch substrate was prepared by dissolving 25.3 g of c.p. sodium hydroxide and 340 g of c.p. potassium dihydrogen phosphate in water and diluting the solution to 2 liters; 125 ml of the buffer solution was added to the cooled, pasted starch substrate before the substrate was brought to the 500 ml volume; the pH of the starch substrate was determined and, if necessary, adjusted to 6.20+0.05; and a 0.025 molar calcium chloride solution, prepared by dissolving 11.1 g of anhydrous c.p. calcium chloride in water and bringing the volume to 4 liters, was used for enzyme sample dilutions. Results were converted to liquifons where one Bacterial Amylase Unit equals 2.85 liquifons.

Intrinsic Viscosity Intrinsic viscosity measurements were made on a number of 32% starch pastes previously liquified and thinned to Brookfield viscosities ranging from 40 cps to 30,800 cps. Measures of Reduced Viscosity were first obtained at five dilutions (0.5 g/l 00 ml, 1.0 g/l 00 ml, 1.5 g/l 00 my, 2.0 g/l 00 ml and 2.5 g/1 00 ml) of each sample according to the procedures of Myers and Smith "Methods in Carbohydrate Chemistry", Volume IV, page 124-127, edited by R. L. Whistler, Academic Press, New York, 1 964. Intrinsic viscosity values were then derived by-extrapolating the reduced viscosity values obtained at the five dilutions to zero concentration.

The following formulas were used to calculate the reduced viscosity values. In these formulas t,=flow time in the Cannon-Ubbelohde viscometerfor pure solvent (1.00 M NaOH Solution), t=flow time in the Cannon-Ubbelohde viscometer for the diluted starch solution made 1.00 M with respect to NaOH and C=concentration of the diluted starch in grams per 100 ml.

t-to Specific viscosity=nsp= to nsp Reduced viSCOSitY=nred= C Kjeldahl Nitrogen Analysis Kjeldahl analyses for nitrogen were done using the standard Analytical Method of the Corn Refiners Association, Number B-48.

Carboxyl Analysis Analyses for carboxyl groups were made using the standard Analytical Method of the Corn Refiners Association, Number C-22.

Acetyl Analysis Carboxyl groups were determined using the standard Analytical Method of the Corn Refiners Association, Number C-2.

Degree of Substitution The degree of substitution (D or S) was determined using the following formulas: a) Nitrogen-containing substituents (162) (% Nitrogen) D ofS= (100) (14)-(A) (% Nitrogen) A=Molecular weight of the nitrogen-containing radical minus one Cyanoethyl, A=53 Carbamylethyl, A=71 Diethylaminoethyl, A=99 b) Acetyl-containing substituents (162) (% Acetyl) DofS= (100) (43)-(42) (% Acetyl) c) Carboxyl-containing substituents (162) (% Carboxyl) DofS= (100) (45)-(44) (% Carboxyl) Example I This Example illustrates the effect of degree of substitution of the starch on viscosity stability of cyano-ethyl, acetyl, diethylaminoethyl, and carbamylethyl starch derivatives.

A. Preparation of Cyanoethyl Corn Starch Derivatives To 10 liters of corn starch slurry (40.87% dry substance starch by weight) were added 10% an hydros sodium sulfate (% based on the dry substance starch) and 590 ml of caustic salt solution (a solution of sodium hydroxide and sodium chloride having 1.65 equivalents of titratable caustic per liter and a density of 270 Baume' at 200C). The slurry alkalinity (ml of 0.1 N HCI required to neutralize 30 ml of slurry) was 24.0. To each of six 2-quart jars was added 1 597 ml of the slurry (equivalent to 728 g of dry substance starch per jar). The jars, equipped with stirrers and parts for addition of reagents, were placed in a water bath (in a hood) set for 450 C. The appropriate quantity of acrylonitrile was added to each jar as presented in the table below.After 1 6 hours of reaction time the mixtures were adjusted to pH 6.3, filtered and washed twice and dried at 1800 F. Each sample was analyzed for Kjeldahl nitrogen and from the nitrogen value (less 0.04%) the degree of substitutions of cyanoethyl groups was calculated.

A-l A-2 A-3 A-4 A-5 A-6 Acrylonitrile Used (% based 1.0 2.5 3.0 3.5 4.0 6.0 on dry substance starch) Nitrogen Analysis (%N) 0.259 0.585 0.674 0.709 0.844 1.324 Calculated Degree of 0.030 0.069 0.080 0.084 0.101 0.161 Substitution The cyanoethyl corn starch derivatives were enzyme thinned and graft polymerized and the viscosity stability of the resulting products was determined.

B. Preparation of Acetyl Corn Starch Derivatives The method of C. E. Smith and J. V. Tuschhoff, U.S. Patent 3,081,296 utilizing vinyl acetate in aqueous media was used to prepare acetate derivatives of corn starch of differing degrees of substitution.

Dried, powdered corn starch (approximately 4369 g dry basis) was added with stirring to water to give 9000 ml of a 23.00 Baume' starch slurry (40.8% dry substance). The pH of the mixture was adjusted to 7.0 and 1 500 ml of slurry were placed into each of six 2-quart jars (equivalent to 728 g dry substance starch each). The 2-quart jars, equipped with stirrers and ports for addition of reagents, were placed in a constant temperature water bath. With the bath temperature at 270C, the appropriate quantity of sodium carbonate was added followed by the appropriate quantity of vinyl acetate (see below). After a reaction time of 45 minutes, each slurry was adjusted to pH 6.4 using dilute hydrochloric acid.Each product slurry was filtered through paper, washed twice with additional water and then dried in a forced air oven at approximately 1800 F. Analyses for acetyl content by standard methods, were obtained to determine the degree of acetyl substitution for each product.

B-l B-2 B-3 B-4 B-5 B-6 Quantity of Sodium 0.63 1.44 1.92 2.64 3.33 4.29 Carbonate Used (% based on dry substance starch) Quantity of Vinyl 2.10 4.80 6.40 8.80 11.11 14.3 Acetate Added (% based on dry substance starch) Acetyl Content (%) 0.83 1.77 2.66 3.26 3.88 4.85 Calculated Degree of 0.032 0.068 0.103 0.127 0.152 0.192 Substitution The starch acetate derivatives were then enzyme thinned and graft polymerized and the viscosity stability of the resulting products was determined.

C. Preparation of Diethylaminoethyl Corn Starch Derivatives To each of four, 2-quart jars contained in a water bath and equipped with stirrers was added 1 500 ml of suspension containing 728 g of powdered corn starch. To each suspension was added 1 58 g sodium sulfate, the appropriate quantity of diethyiaminoethyl chloride reagent (see below) and the pH was adjusted to approximately 7.0. To each suspension was then added the appropriate quantity (see below) of a caustic-salt solution (a solution containing 6.60 g of sodium hydroxide and 25.6 g of sodium chloride per 100 ml). The reaction mixtures were stirred for 7 hours at 50--55 OC, cooled and filtered on a Buchnerfunnel. Methanol was added in cases where filtration was inhibited by swelled starch particles.The DEAE starch derivatives were washed twice with water or water/methanol (35/65) solution and dried. Nitrogen contents (Kjeldahl Method) were obtained to calculate degree of derivatization.

C-i C-2 C-3 C-4 Diethylaminoethyl 3.19 6.37 12.74 21.23 chloride used (% based on Starch) Caustic-Salt Solution 164 328 655 1091 used (ml/l 500 ml of starch suspension) Nitrogen Content 0.299 0.437 0.549 1.04 (% dry basis) Calculated Degree of 0.035 0.052 0.066 0.130 Substitution The DEAE-starch derivatives were enzyme thinned and graft polymerized and the viscosity stability of the resulting products was determined.

D. Preparation of Carmamylethyl Corn Starch Derivatives Acrylamide was reacted with granular starch in alkaline slurry employing the method of E. F.

Paschall, U.S. Patent 2,928,827. To 7500 ml of corn starch slurry containing\3622 g dry substance starch was added 790 g of anhydrous sodium sulfate and 815 ml of caustic-salt solution (a solution containing 6.60 q of sodium hydroxide and 25.6 g of sodium chloride per 100 ml). The alkaline slurry was divided into four equal portions and placed in four 2-quart jars, contained in a water bath and equipped with stirrers and thermometers. The appropriate quantity (see below) of acrylamide was added to each jar and the mixtures were allowed to react at 520C for 1 8 hrs. The resulting starch siurries were adjusted to pH 4.0 then filtered using a Buchner funnel. The filtered products were then washed twice each with water, filtered and dried.The resulting starch derivatives were analyzed for nitrogen (Kjeldahl Analysis) and carboxyl content (carboxyl groups are created by partial hydrolysis of carbamylethyl groups to form carboxyethyl groups) to calculate the degree of derivatization.

D- 1 D-2 D-3 D4 Acrylamide Used (% 1.32 3.07 3.95 7.89 of dry substance starch) Nitrogen Analysis 0.162 0.345 0.431 0.769 (% dry basis) Carboxyl Analysis 0.146 0.224 0.287 0.485 (% dry basis) Calculated Degree of 0.019 0.041 0.051 0.093 Substitution, Carbamylethyl groups Calculated Degree of 0.004 0.008 0.010 0.018 Substitution, Carboxyethyl Groups Calculated Total 0.023 0.049 0.061 0.111 Degree of Substitution These starch derivatives were enzyme thinned and graft polymerized and the viscosity stability o the resulting products was determined.

E. Enzyme Thinning and Graft Polymerization The following procedure was used to prepare graft co-polymers of each of the samples in A through D of this example.

Into a 2-liter resin kettle equipped with an agitator, a thermometer, a reflux condenser, and a nitrogen gas dispersion tube were placed 650 g deionized water then 350 g (dry basis) derivatized starch, to give a 35% starch slurry. The pH was adjusted to 7.5-7.8, followed by the addition of 4350 liquefons of alpha-amylase activity derived from B. subtilis. The slurry was heated to 780 over a fortyfive minute period and held at 780C until the viscosity of the gelatinized starch was approximately 200 cps (240C Brookfield, No. 2 Spindle, 20 rpm). The enzyme was inactivated by heating to 960C and the liquefied starch cooled to approximately 600. At a temperature not greater than 600 C, a nitrogen sparge was started and 12.5 g Triton X-200 surfactant was added, followed by the addition of 278.5 g ethyl acrylate.At a temperature of 48-520C, 6.13 g ceric ammonium nitrate dissolved in 1 5 g of deionized water was added. After the exothermic reaction subsided (approximately 200C temperature increase) the reaction temperature was maintained at 750C for three hours. Then 0.5 g each of ammonium persulfate and sodium metabisulfite was added to the reaction mixture to reduce the level of unreacted monomer. The mixture was maintained at 750C for an additional one hour period, cooled to room temperature and the pH adjusted to 8.5 with 28 percent ammonium hydroxide. The final preparations had a solids content of approximately 45.0%.

The following table summarizes the date obtained on viscosity stability of the samples.

Table 1 Days to 100% Increase in Viscosity Substituent: DEAE* Acetyl Cyanoethyl Carbamylethyl DofS 0.023 1-2 0.030 < 1 0.032 2-3 0.035 < 1 0.049 1-2 0.052 1-2 0.061 5-6 0.066 60 0.068 15-16 0.069 7-8 0.081 16-17 0.101 < 60 0.103 < 60 0.111 57-58 0.130 ** 0.152 ** 0.161 ** 0.192 ** *Diethylaminoethyl **No significant change in viscosity at 60 days. These data are depicted in the graph, Figure 1.

Example II This Example shows the relation of the intrinsic viscosity of the thinned starches to tensile strength and abrasion resistance of graft copolymers made from the thinned starch.

Four samples of a cyanoethyl-substituted corn starch prepared as in Example I, A-6 (D. of S.

0.161) were enzyme thinned, according to the procedure of Example I, E, to differing viscosities. Each of these four samples was graft polymerized following the procedure of I, E.

Free films of the graft copolymers were cast on Mylar (T.M.). The films were dried, cut in strips 1/2" wide and then stored at approximately 65% relative humidity (R.H.) and 700F for about 5 days.

The average thickness of the films was determined and the tensile strength of the films was measured using an Instron-TM Universal Testing Instrument. The tensile strength related to each of the intrinsic viscosities of the derivatized and thinned starch appears in Table 2, below.

The four graft copolymers were affixed as sizes to a 50% cotton/50% polyester yarn and conditioned at 65% R.H. and 700F for about 2 days. The abrasion resistance of these samples was then determined with a Walker Abrader according to the method of Stallings and Worth, "Textile Industries", March, 1 950. This method consists of abrading 36 sets of yarns and recording the number of cycles to obtain the first 11 breaks. The results appear in Table 2.

Table 2 Intrinsic Tensile Abrasion Resistance Viscosity dl/g Strength g/mm2 (cycles to 1 1 to break 0.1 1470 825 0.14 2030 1150 0.185 1950 1120 0.273 1870 1020 The terms and expressions used herein are descriptive and are not to be interpreted as limiting the invention or excluding any equivalent materials or procedures since it is recognized that modifications or substitutions of the features described may be made within the scope of the claimed invention.

Claims (14)

Claims

1. A derivatized and thinned starch capable of yielding stable, aqueous dispersions of high solids content when graft copolymerized with a vinyl monomer, said starch having a degree of substitution in the range from about 0.05 to 0.4, and an intrinsic viscosity in the range from about 0.12 to 0.28 dl/g.

2. A derivatized and thinned starch according to Claim 1 wherein the degree of substitution is in the range from about 0.06 to about 0.2.

3. A derivatized and thinned starch according to Claim 1 or Claim 2 wherein the intrinsic viscosity is in the range from about 0.13 to about 0.21.

4. A derivatized and thinned starch according to any of Claims 1-3 wherein the substituent is a non-ionic substituent.

5. A derivatized and thinned starch according to any of Claims 1-3 wherein the substituent is a cationic substituent.

6. A derivatized and thinned starch according to any of Claims 1-3 wherein the substituent is selected from the group consisting of hydroxyethyl, cyanoethyl, diethylaminoethyl, carbamylethyl and acetyl.

7. Process for producing a derivatized and thinned starch capable of yielding stable, aqueous dispersions of high solids content when graft copolymerized with a vinyl monomer which comprises derivatizing said starch to a degree of substitution in the range from about 0.05 to about 0.4 and thinning said starch to an intrinsic viscosity of from about 0.1 2 to about 0.28 dl/g while maintaining the starch in granular form after the derivatization step.

8. Process as in Claim 7 wherein the degree of substitution is in the range from about 0.6 to about 0.2.

9. Process as in Claim 7 or Claim 8 wherein the starch is thinned to an intrinsic viscosity in the range from about 0.13 to about 0.21.

1 0. Process as in any of Claims 7-9 wherein the starch is first derivatized and thereafter thinned by enzymatic means.

11. Process according to Claim 10 wherein the substituent is a non-ionic substituent.

12. Process according to Claim 10 wherein the substituent is a cationic substituent.

1 3. Process according to Claim 10 wherein the substituent is selected from the group consisting of acetyl, hydroxyethyl, cyanoethyl, carbamylethyl and diethylaminoethyl.

14. An industrial adhesive prepared from a derivatized and thinned starch as in any Claims 1 - 6.

1 5. A derivatized and thinned starch as claimed in Claim 1 and substantially as hereinbefore described with reference to any of the Examples.

1 6. Process for producing a derivatized and thinned starch as claimed in Claim 7 and substantially as hereinbefore described with reference to any of the Examples.