CA1090027A - Water-absorbent starch copolymerizates - Google Patents

Abstract

ABSTRACT OF THE INVENTION Water-absorbent, starch copolymerizates are prepared by copolymeriz-ing an ethylenically unsaturated starch with other ethylenically unsaturated monomers which contain water-attractant groups or precursors or water-attractant groups. The water-absorbent starch copolymerizates may be easily prepared into the desired configuration for a particular end-use or combined with other substrates or carriers. The unpolymerized starch and monomers or precursors thereof may be applied or incorporated into a suitable carrier or substrate (e.g., cellulosio materials such as textiles, papers, etc.) and copolymerized in situ to provide a composite article or unitary construction with the water-absorbent starch copolymerizate permenently bonded or affixed thereto.

Description

i~ 1090()27 . .
BACKGROUND OF THE INVENTION
Within recent years, certain derivatized starches capable of ' absorbing and retaining large amounts of water have been developed. These derivatized starches are frequently referred to as "water-absorbent starches".
In U. S. Patent Nos. 3,935,099 and 3,997,484 (both by Weaver et al.), starch polymers which reportedly absorb more than 1~000 times their own weight are disclosed. Thse water-absorbent starches are generally prepared by grafting polyacrylonitrile to starch molecules and then derivatizing the polyacrylo-nitrile chains to anions. The grafting is accomplished by free-radical 'i' catalysis (e.g.~ceric or irradiation). The starch-grafting process is difficult to control and time consuming. Ihe achievement of a critical .
~^, grafting level is an essential prerequisite for a water-abso~bent, end-product.
; I .. .
A series of derivatization and'neutralization steps are typically used to convert the nitrile group to anions and a water-absorbent starch product.
Ihis contaminates the product with salt. The water absorbency properties ~ .
of these salt-contaminated starches are seriously iimpaired when they are used in aqueous solutions which contain trace amounts of salts and minerals.
It is als'o difficult to achieve uniform and reproducible water-absorbency -` resuits. This apparently arises from difficulties in controlling the '~ 20 reaction. These water-absorbent starch'compositions are also deficient'in '~ certain other properties which are essential and desirable for m~ny end-

2 . .~
' usages (e.g.? lack adhesiveness, prefabrication and shaping, fi~ ~forming, bonding, coating, etc. properties). This generally restricts their usage ' to limited areas of application (e.g., separately contained by a water-25 permeable enclosure or separately added or mixed to another substrate).
In addition, these water-absorbent starches cannot be effectively used at high-solid coating levels or be readily affixed or bonded to a carrier or ' `
substrate or easily provided in a preformed shape.
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, '~0~30.~.~Z'~'United States Patent No. 3,661,815 by Smith also discloses analogous water-absorbent starches which are prepared by saponifying skarch-polyacrylo-nitrile graft derivatives with certain alkali metal bases. ~hese water-absorbent starch gra~ts reportedly absorb more than 50 times their wéight of water. Ihe Smith process and products suffer fron similar deficiencies as mentloned above with respect to Weaver et al.
.. ~ .

I~heinventors desired to more easily and effectively prepare water-` absorbent starch compositions under conditions which provide greater uniformity - and end-product reproducibility. Greater tolerance and compatibility with ; 10 aqueous solutions containing salt and mineral contaminants was also desired.
~ Even more importantly, was the development of a water-absorbent starch which ; j :~
~ could be easily bonded or affixed to a substrate or preformed. Such a water-;- , absorbent starch would considerably expand upon the versatility and usage of water-absorbent starches by the trade.
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.; . . .
OBJECTS
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An ob~ect of the invention is to provide a novel, simple and ~; reproducible method for preparing water-absorbent starch compositions.

... . ~
Another ob~ect is to obtain novel, water-absorbent starch composi-tions which in comparison to existing water-absorbent starches have improved ; 20 versatility, utility and functional properties. ~
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A still further obJect is to provide a novel method for applying or affixing water-absorbent starches to carriers or substrates or preparing preformed products and the products thereof.

rESCRIPIION OF THE INVENTION
According to the present invention there is provided a water-absorbent starch copolymerizate which is capable of absorbing several times its own weight Of water, said starch copolymerizate comprising the copolymerizate ...
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product of ethylenically unsaturated starch molecules and ethylenically un-saturated monomers wlth said ethylenically unsaturated monomers forming a : connective polymeric linkage between said copolymerized starch molecules to provide a non-linear lattice of a plurality of starch chalns linked together by polymeric linkages represented by the ~ormula:
;~ R (~)n R

. (I) --~Starch - Z - C - CH2 - [M]p - CH2 - C - Z - Starch~--H H

, wherein Starch represents a starch chain of D~glucose units, Z represents an .. ~ organo group which links the ~ group to the carbon atom of the starch : H
chain by a sulfur atom or an oxygen atom, R is a member selec.ked from the group consisting of hydrogen and a monovalent organic radical, M represents ` 10 a plurality of copolymerized ethylenically unsaturated monomers with "p"
representing the number of copolymerized monomeric units in said linkage~ (W) is a water attractive group or a hydrophilic moiety such as a member selected from the group of ar~on, cation, non-ion and a~lphoteric, zwitterion.:and amphiphili~.moietiesand mixtures thereof linked to the polymeric linkage and "n" represents the number of (W) ieties contained within the polymeric linkage of said copolymerized monomers.

. .
The water-absorbent starches or their precursors.may be pPepared by - a copolymerization process which comprises copolymerizing:

(a) starch chains containlng appendant, termi~n~al ethylenic unsaturated groups represented by the formula:
'~

(IIj Starch [ Z - C = CH2]a wherein Starch, Z and R are as defined above and "a"

1 represents the degree of substitution of said terminal .' unsaturated groups on said starch chain, and ;!
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(b) ethylenically unsaturated moncmers represented by the formula:

. M ~ )h ~

r.
' ', ' 13~7 wherein M represents an ethylenically unsaturated monomer, ' ~(wr)"represents at least one menber selected from the group ~ consisting of a water-attractant or a precursor thereof, and '~ nl is an integer to provide a cross-linked lattice of a plurality of starch cha~ns linked ~' together by polymeric linkages represented by the formula:
(W )n ' ---~Starch - Z - CHRCH2 - [M]p, - CH2CHRCH2 - Z - Starch3 wherein the Starch, Z, R,(W') and n are as defined above, M
represents a plurality of copolymerized ethylenically unsatu-rated monomers which contain a sufficient number of (W) or (W ) ' 10 precursors within the polymeric linkage~to impart water-absorbency ' to said copolymerized product, and "P" represents the nu~ber of copolymerized ethylenically unsaturated monomers between juxta-positional starch chains. ' - "
, , ' ,:: ' In the copolymerization process, a wide variety of M'-~W ? ~
monomers may be used to prepare the water-absorbènt starch of this invention.
' The value of the n' integer and the particular '~" or '~" precursors which are used in the copolymerization process may vary considerably. ~Some of the monomers will contain "W" or '~r' precursors (e.g., n' has a value of''l-3) while others may be free from the "W" or '~" precursor moieties (e.g., n is 0). Similarly, the copolymerized monomers may belessentially comprised of monomers which contain the "W" or "W" precursors. In the aforementioned ~ormula, M may be comprlsed of an ethylenically unsaturated portion of an organic group of the same chemical composition, or a mixture of different copolymerized monomers in which the M group differs in composition. LIkewise, the "W" or"W " precursors may be of the same or different in type. Ihe amount ., .
of "W" monomer or "W" monomer precursors copolymerized with the'starch is main-~, tained at a level su~ficient to impart water-absorbency to the'copolymerized starch product. I~ '~ " precursors are solely used~ ~hen it is necessary to convert a sufficient number of precursors to the water-attractant form to achieve the desired water-absorbent, starch copo~ymerizate product.

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In comparison to existing water-absorbent starches, the present ; starch copolymerizates are more versatile and useful. They may be preabri-~ cated from water-soluble or water-dispersible, modified or hydrolyzed starches .:' into high-molecular-weight and cross-linked, water-absorbent stæch copoly-merizates. In general, the ethylenically unsaturated starches used herein `'`~ æe most typically provided inawater-soluble form or may be easily converted to such a form. mis renders the present invention p æticulæly applicable ..
:
to prefabricating operations wherein water or aqeuous systems are used to disperse, dissolve or plasticize the stæch. The invention therefore is ideally suited for most prefabricating operations (e.g., coating, molding, ~' casting, extrusion, drying, sheeting, printing, bonding, encapsulating, gelling, impregnating, laminating, plasticizing, etc.) wherein the stæch is initially provided in a form most suitable for prefabrication (e.g., liquid, pliable, moldable, etc.) and then preformed and converted into a solid object.

The starch portion of the ethylenically unsaturated starch chains may be derived from a variety of starch sources, including cereal, leguminous, ~ tuber starches. Illustrative starches include tapioca, corn, high amylose, "~ sweet potato, waxy maize, canna, ærowroot, wheat, sorghum, waxy sorghum, waxy rice, soya, rice, pea, amylose or amylopectin fractions, combinations thereof and the like. The starch amylose content affects the temperature at which a starch will convert to a water-dispersible or starch paste form.
The high amylose starches typically require elevated temperatures and pressures (e.g., extrusion, jet cooking, etc.), for uniform dispersal into ... .
j~ aqueous systems. In contrast, starches of a lower amylose content (e.g., 30% amylose or less) are more easily dispersed or pasted in water (e.g., 50-70C). Prepasted or pregelled starches of an amylose content of less than 30~ normally disperse into water at an ambient temperature (e.g., 23C.).

For many prefabricates, it is advantageous to modify or alter the ,., starch chain to achieve a more functional and versatile starch product. This '' :"
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~V9OOZ7 may be accomplished by derivatizing the starch chains, so that they contain other substituents (e.~., esters or ethers which may contain cationic, anionic, non-ionic, amphoteric, etc. groups). Ihe ethylenically unsaturated --starches may be provided in the pregelled or prepasted form or hydrolyzed (e.g., chemical or enzymatic hydrolysis of granular or non-granular ethy-lenically unsaturated starches) to improve upon their dispersibility into aqueous systems. Ethylenically unsaturated dextrins, maltodextrins and other low viscosity imparting ethylenically unsaturated hydrolyzates (e.g., D.E; 0.2-30), are particularly well suited ~or coating applications. Such ethylenically unsaturated starch hydrolyzates provide a means for achieving a high~solids and low viscosity system which is particularly well suited for aqueous coating and prefabricating applications. Modification, deriva-tization or hydrolysis Or such starches may be accomplished prior or after its derivatization to the ethylenically unsaturated form.

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l~ Ethylenically unsaturated starches which contain hydrophobic substituents may be used but will typically require a dispersant. ~ater-miscible, organo dispersants such as alkanols (e.g., methyl, ethyl, iso-propyl, or butyl-alcohol), polyhydric alcohols (e.g., glycerol, ethylene glycol), ethers, (e.g.j methyl, ethyl or propyl ethers, etc.), ketones (methyl ethyl ketone, ethyl ketone, etc.), as well as conventional anionic, non-ionic and cationic surface active agents or emulsifiers (e.g., see McCutcheon's Detergents and Emulsifiers - North American Edition - 1975) may be used to facilitate their conversion to a more water-dispersible form.
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It is usually advantageous to employ hydrophilic, ethylenically unsaturated starches which will uniformly disperse into water at temperatures above the starch gelation point without the aid of water-miscible organo dispersants or surfactant systems. Hydrophilic starches characterized as yielding a centrifugal starch residue of less than 25% (preferably less than 10%) upon immersion in water (one part ethylenically unsaturated starch/
100 pbw water) for one hour at temperatures above their gelation point and .3~)~i7 centrifugation at 103g's for 10 minutes are most suitably used to coating ~ and preEabricating applications. ~Iydrophilic ethylenically unsaturated - starches containing pendant ethYle ~ ally unsaturated groups with polar moieties or substituents to im~art hydrophilicity to the unsaturated p~rtion of the starch molecule (e.g., hydroxy, carboxy, amide, carbamyl, sulfoamyl, imido, sulfoamuno, thio, thiolamino, oxy, thiocarbonyl, sulfonyl, carbonyl, -' sulfoamido, quaternary ammonium halides, the alkali or ammonium salts) are -" especially useful.
;'` :
~- The water-dispersible, ethylenically unsaturated starches herein r. may be prepared by a variety of starch derivatization processes. Deriva-: .- .
tization processes which may be used to produce appendant, monoethylenically unsaturated groups include reacting alkali metal starch or hydroxyethylated i~ starch salts with an allyl propiolate to provide cæboxylated vinyl starch ether; reacting starch with ethylenically unsatura-ted organic carboxylic anhydrides (e.g., methacrylic anhydride, e~.) or organic allyl halides (e.g., allyl bromides, allyl chloroformates, etc.) or epoxides (e.g., buta-diene monoxides, etc.) to provide ethylenically unsaturated starch esters or ethers. The most ~suitable noethylenic unsaturated starches are the starch esters of alpha, beta ethylenically unsaturated carboxvlic acids ~-, 20 (e.g., acrylate, methacrylate, crotonate, citraconate, itaconate starch ....
; esters as well as alkali salts and a~ides thereof, muxtures thereof and O H
the like); N-allyl carbamate starch esters (e.g., Starch~-O-C-N-C~I2-CH-CH2);
glycidyl methacrylate and glycidyl acrylate starch ethers (e.g., see U. S.

Patent No. 3,448,089); allyl starch ethers (e.g., allyl, iso-propenyl, etc.);

the allyl alkyl starch ethers (e.g., ethyl, propyl, butyl, etc. starch ` ethers) and the allyl alkylene oxide starch ethers; allyloxyalkyl starch ::, ~ ethers (e.g., the allyl oxyethyl, oxypropyl and oxybutyl, etc. starch ethers);
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allyloxy hydroxyalkyl starch (e.g., 3-allyloxy-2-hydroxy-propyl starch, etc.) ; starch acrylamines, etc.; cambinations thereof and the like.
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In a more limited embodiment of the invention, the ethylenicallY
unsaturated starches comprise those starches which will readily and unifornly copolymerize with the bridging comonomers. Ethylenically unsaturated starches which contain polar groups im!mediately ~uxtapositional to the unsaturated group and which activate the copolymerizability of the double bond in the presence of free-radical initiating systems are particularly well suited -~ for this purpose. Such ethylenically unsaturated starches may be represented by Formula III:
R
(III) Starch -~D-Q-E-C=CH2]a wherein starch is a starch chain of DLglucose units, E represents an activat-ing polar group juxtapositional to the ethylenic unsaturation, D ls sulfur or oxygen, Q is an organo group which divalently ~oins the D group to the activating polar group, R represents a monovalent group and "a" represents the D.S. (i.e., the number of appendant ethylenic unsaturated groups per anhydroglucose unit of said starch chain). Typical juxtapositional activat-:.: - O S
" 15 ing polar groups (i.e., E) include carbonyl (-C-), thiocarbonyl (-C-), O O ~ ' " , "
-O~C-, -N-C-, groups and the like. The ethylenically unsaturated portion of the starch chains are most typically comprised of appendant groups which individually have a molecular weight of less than 500 with those having an appendan~ lecular weight of greater than 50 but less than 300 (preferably from 75 to about 150 M.W.) being most typical.

In a more preferred embodiment o~ the invention, the E group con-i R'0 .. .
tains a -N-C- radical, R is a me~ber selected from the group consisting of hydrogen and a mono-organo group which is Joined directly to the nitrogen atom by a monovalent bond.
.~ .
In Formula III, Q may be any divalent organo group which joins the activating radical to the starch chain (e.g.~linked to D and acrylamide _g_ : ~ . . . .: . : .

.. . . ..
: . . .

10900~7 :
nitrogen atoms via carbon linkages). I~he starch oxygen or sulfur atom and activating radical may be directly linked together by a single carbon atom or by an organo group which is comprised of a plurality of carbon atoms.
e -Q- group may be comprised of substituted or unsubstituted, straight or - 5 branched aliphatic groups (e.g., alkylene), substituted or unsubstituted, 5~ arylene group (e.g., naphthlene, phenylene, etc.) as well as divalent -~ organo groups which contain carbon to non-carbon atom linkages (e.g., organo ~ ethers and thioethers, sulfonyl, N-methylene substituted secondary and .
- tertiary amines (such as a -CH2-N(H)-Q- radical). If desired, the Q group-- lO linking chain may also contain other substituents such as carbonyl, carboxy-late, thiocarbonyl, etc. radicals as well as monovalent radicals such as hydroxy, halo (e.g., Br., F., C1 and I), alkyl, aryl, hydroxyalkyl, hydroxy-aryl, alkoxy, aryloxy, carboxyalkyl, carboxyaryl, amine substituents, combinations thereof and the like. Advantageously the divalent Q organo group will contain less than 10 carbon atoms and preferably no more than 7 carbon atoms.

.

In Formula III wherein "E" is an activating group, the R and R
; may be selected from the group consisting of mono-organo and hydrogen sub-stituents. Ihe R and R mono-organo groups may also contain an ester, ether, carboyxlic organo acid, alcohol, hydrocarbyl (e.g., alkyl~ aryl, phenyl, etc.) as well as divalent organo groups containing non-carbon atoms to carbon chain linkages (e.g., such as oxy, sulfonyl, t~io, carbonyl r i~ groups, etc. as mentioned above with respect to Q). Advantageously, R
and R are either H or a substituted or unsubstituted mono-organo group con-taining less than 8 carbon atoms such as a lower alkyl or phenyl group.
` Illustrative substituted mono-organo groups are halo substituted alkyl and ~ phenyl, alkoxy, aryl, phenoxy, phenol and alkanol and correspondingly thiols, 1 alkanoic, phenoic, tolyl, benzoyl, carboxy, sulfoalkyl, sulfo-phenyl, combinations thereof and the like. In the preferred embodiments of this invention, R and R are a member selected from the group consisting of either hydrogen or a 1-5 carbon alkyl (preferably methyl) and "a" has a ` value of at least 0.002.

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-- The most preferred ethylenically unsa-turated starches are the starch acrylamides represented by Formula rv:
'' ~' H R'~ R
(rV) Starch~ D-(Q )n-C-N-C-C-tQH2~a .` ~ ,:
D is a m~mber as defined above (preferably oxy), Ql represents a divalent organo group such as Q is defined above, "a" represents the degree of sub-stitution, R and R' are monovalent groups as defined herein and "n " is a anumber of 0 or 1.
'.
The aforementioned Formula rv starch acrylamides may be prepared by reacting N-methylol acrylamides with starch in the presence of an acid or acid generating catalyst and a polymerization inhibitor as illustrated by the following etherification equation V:
; R'O R
(V) Stæch ¦- OH]a+a(HO-CH2-N-C-C--CH2) ~, (A) (B) - H+
: ~ ~ .
`~ R'O R
StæCh~~~~~CH2~N~C~C=CH2]a+a(H2) (C) (D) wherein "a" of reactants (A) and (B) represent the number of starch hydroxyl groups of (A) etherified with the N-methylol acrylamide reactants (B), R' and ; :.~ . . ..
R æe mono-organo or hydrogen groups such as defined below, and H+ represents an acid or acid generating etherifying catalyst. The above N-methylol acryl-. 15 amide reaction V may also be used to prepare a starch acrylamide reaction ;, :
product (C) wherein Q as illustrated in Formula III contains an alkylene oxy or arylene oxy group by reacting the corresponding hydroxyaryl or hydroxy-alkyl starch ethers (e.g., hydroxypropyl and hydroxyethyl starch ethers) with an N-methylol acrylamide wherein R' and R represent a monovalent group. Sub-stituted acrylamides which contain a reactive N-methylol group linked to the acrylamide nitrogen atoms by intervening divalent Q organo groups and starches containing cationic and anionic or ionic acrylamide substituents may be , . ..
. --11-- :

, ,:
obtained by etherifylng a starch with the appropriate N-methylol acrylamide (e.g., sodium-2-N-methylol ac~ylamido-2-methylpropanesulfonate~ a N-methylol acrylamide quatem ary ammonium halide such as 3-(N-methylol acrylamido)-3-methyl butyl trimethyl ammonium chloride, etc.). Representative R sub-stituents in V above include hydrogen, N-arylol, the N-alkylamines and N-arylamines such as N-methylol-, N-ethyl-; N-isopropyl-; N-n-butyl-;
N-isobutyl-; N-n-dodecY~ N-n-octadecyl-; N-cyclohexyl-; N-phenyl-;
N-(2-hydroxy-1,1-dimethylpropyl)-; N-p-hydroxybenzyl-; N-(3-hydroxybutyl)-;
N-(4-hydroxy-3,5-dimethylbenzyl)-; N-(3-hydroxy-1,1-dimethylbutyl)-;
N-(2-hydroxy-1,1-dimethylethyl)-; N-(2-hydroxyethyl)-; N-(5-hydroxy-1-, .
naphthyl)-; combinations thereof and the like. Illustrative acrylamide . , reactants (B) include N-methylol and N-thiomethyl acrylamides such as N-(hydroxymethyl) acrylamide; N-(hydroxymethyl)-N-[(l-hydroxymethyl) propyl] acrylamide; N-(hydroYymethyl)-2-alkyl acrylamides, (e.g., N-(hydroxy-methyl)-2-(methyl-hepthyl) acrylamide; N-[(l-hydroxymethyl)-l-nonyl]-2-m~thyl acrylamide; N-(l-hydroxymethyl)-2-methyl acrylamide; N-(hydroxymethyl)-2-propyl acrylamide; etc.); N-(mercaptomethyl) acrylamide; N-methylol-N-isopropyl acrylamide; 3-(N-methylol acrylamid~)-3-methyl butyl trimethyl . ammonium chloride (cationic); sodium 2-N-methylol acrylamido-2-methyl pro-pane sulfonate (anionic -CH2:C(H)C(:9)N(cH20H)c[(cH3)2]cH2so3Na )~ combina-tions thereof and the like.

Reaction V may be suitably conducted in the presence of known acid or acid-generating catalysts (e.g., ammonium chloride or phosphate, mono-ammonium acid phosphate, zinc chloride, etc.), preferably at temperatures ... .
between about 70C. to about 95C. until the desired D.S. level is achieved.

Conventional polymerization inhibitors (e.g., hydroquinone, its derivatives, 2,5-di-t-butylquinone, etc.) prevent homopolymerization of the starch acrylamide and acrylamide reactants. qhe starch acrylamides may be prepared ; via solution, slurry, dry, semi-dry or other appropriate condensation processes.

` 30 q!o prepare astarch-acrylamide having a D.S. levelofO.03 or higher, it is ' :' .
.

0()Z~7 lesirable to uniformly disperse the acrylamide, acid or acid-generating catalyst and polymerization inhibltor throughout the starch reactant. Uniform dispersal of the N-methylol-acrylamide reactant, catalyst and polymerization inhibitor throughout the starch may be effectively accomplished by initially ~orming a starch slurry or treating the starch with an absorbable dispersant media (e.g., water) in which the acrylamide, catalyst and polymerization in-hibitor are soluble or placed in mobile form and thereafter imbibing or absorb-ing the dispersant and its solutes into the starch granules.

As more fully explained on page 30, the most appropriate ethylenic unsaturates for optimum water-absorbency will depend upon the starch chain ; type. An ethylenically unsaturated monoglucoside will typically require at -~ least a D.S. of about 2.0 or more, whereas long chain starch chalns (e.g., unhydrolyzed starch) typically require a considerably lower D.S.-level (e.g., 0.0002) to be water-absorbent. Moreover, there exists a direct relationship between the D.S. for any given starch chain and the optimum water-absorbency which may be achieved from the starch copolymerizate there-of. An insufficient or excessive ethylenic unsaturation D.S. level will ~enerally result in a copolymerizate having poor water-absorbency properties.
A D. S. deficiency will fail to provide the necessary multifunctional polymerization sites-for the water-absorbency materials. For a majority o~ starches, however, a starch copolymerizate which is capable of absorbing several times its own weight can be typically obtained by copolymerizing a starch which has an ethylenic unsaturation ranging ~rom ab~out 0.002 D.S.
to about 0.10 D.S. Higher ethylenic unsaturated D.S. levels (e.g., 0.2 or higher) will usually require more carefully controlled copolymerization condi-tions with an appropriate proportion of ethylenically unsaturated monomers and type of monomer. Starch copolymerizates which typically absorb more than 10 times their weight in water are obtained from starches having an ethylenic , unsaturation ranging from about 0.005 D.S. to about 0.05 D.S. For applications ~ 30 requiring a more highly water-absorbant starch (e.g., greater than 100 times :
.

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~1390~Z7 .
the starch dry weight), it is advantageous to use starch substrates which contain appendant ethylenic unsaturation at a level rangingfrom about 0.005 D.S. toabout:0.01 D.S.

Ihe starch copolymerizate water-absorbency properties are directly 5 related to its lattice (i.e., molecular configuration) and its ionic hydro~
philiclty. Ihe characteristics of the starch chain and the polymeric link-ages formed by the interpolymerized ethylenically unsaturated monomers primarily dictate the copolymerizate lattice structure. Failure to achieve proper polymeric lir~age or bridging between starch molecules will adversely , . .
affect the water-absorbency properties of the starch copolymerizate. Ex-~` cessively long polymeric monomer linkages tend to result in an excessively - - open structure which adversely affects the water-absorbency character of the ~ starch copolymerizate lattice. Conversely, excessive cross-linking (e.g., i~ high D.S. ethylenically unsaturated starch) or an insufficient amount of copolymerized monomer (e.g., very short linkages between starch molecules) tend to create a closed lattice and concomitant loss in water-absorbency.
~he net ionic charge of the copolymerizate in con~unction with its water porous lattice contributes to its water absorbtion and retention properties.
¢ Similarly, achievement of the optimum lattice and an insufficient ionic ~` 20 charge impairs its water-absorbency. The combination of a proper lattice -and a sufficient level of ionic charge to attract and absorb water molecules within its porous lattice provides maximum water-absorbency.

- In the water-absorbent starch copolymerizate, the copolymerized ethylenic unsaturated monomers (i.e., -[M]p, of FormLla I) contain a sufficient number of hydrophilic substituents (e.g., ~ (W) of Formula I) to impart water-absorbency to the copolymerized starch product. Illustrative hydrophilic substituents include cationic, anionic, nonionic, ampholytic, zwitterionic, amphoteric moieties, mixtures thereof and the like. As mentioned above, it is unnecessary for each copolymerized monomeric unit to be a water-attractant group. Thus, a significant portion of the polymeric chain units , . .

: .

10~ 27 may be free from ionic substituents with the balance of ~he units providing a sufficient level Of "W" substitution to render the starch copolymerizate water-absorbent. The degree of "W" substitution necessary to achieve a water-absorbent starch copolymerizate will depend upon a multiplicity of 5 factors. Factors such as the ionic charge and type of ionic substituents, proportions of ethylenically unsaturated starch to monomer, hydrophilicity and polarity of the copolymerized monomer units, etc. affect the required '~" substitution level. For most application, it i9 advantageous for the starch copolymerizate to contain either anionic or cationic substituents.

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A variety of conventional, ethylenically unsaturated monomers which either contain thewater-absorbtive substituents or its precursors may be used to prepare the starch copolymerizates herein. The polymeric linkages may be amphiphllic (i.e., contain both polar water-soluble and hydrophobic water-insoluble groups). Anionic monomers include ethylenically unsaturated ; 15 monomers which contain acid groups or acid-salt groups or acid-salt pre-- cursors. Exemplary anionic substituents include carboxylates, oxalates,,~,, benzoates, phosphonates, maleates, malates, phthalates, succinates, sulfate, sulfonates, tartrates, fumarates, mixtures thereof and the like. Illustra-tive ethylenically unsaturated cationic monomers include nitrogen-contain-ing cations such as prim~ry, second~ry and tertiary and quate mary ammoniumcompounds; sulfur containing cations such as sulphonium salts, halides, etc.; phosphorous containing cations such as phosphonium salts; mixtures thereof and the like. Typical nitrogen containing cations include monomers represented by the formula:

M -(NRaRbRC)X
wherein M' represents an ethylenically unsaturated organo group, Ra~ ~ and Rc represents at least one member selected from the group consisting of hydrogen and organo group, and X is an anion (e.g., halide, acetate, CH3S0~, C2H5S04, etc.). Exemplary Ra~ Rb and Rc mono-organo groups include substituted and unsubstituted alkyl, monoheterocyclic (e.g., piperidene, ,0 morpholine, etc.), hydroxyalkyl, aralkyl, cycloalkyl groups as well as ~ 0(32~

;~ cyclic and heterocyclic groups divalently bonded to the nitrogen atom (e.g., - Ra and Rb form a cyclic structure). Ihe preferred nitrogen containing ;,, ethylenically unsaturated cationic monomers are the water-soluble, monomeric salts such as the lower alkyls of 1~5 carbon atoms (e.g., ethyl, methyl, ;-propyl); polyoxyalkylene (e.g., polyoxyethylene and polyoxypropylene3,mixtures thereof and the like; alkoxy (e.g., methoxy, ethoxy,propoxy, etc.);

. .
hydroxyalkyl and polyhydroxyalkyl (e.g., hydroxyethyl, hydroxypropyl, di-hydroxypropyl, dihydroxybutyl); heterocyclic amines (e.g., morpholine);
amines and amides bearing mono-organics; mixtures thereof and the like. Ihe sulfur and phosphorus containing cationic monomers are similar to the afore-. . .
. mentioned except either the phosphorous atom or sulful atom replaces the - nitrogen atom. Ihe preferred phosphorus and sulfur cations are the phos-phonium and sulphonium cationic salts. Water-soluble, "W 11 ethylenically unsaturated monomers which contain an activating group ad~acent to the ethylenic unsaturation (é.g., wherein M contains a CH2=CFLE - radical ~-` with the activating group "E" and the "R" group being as defined above) are .: preferred.
., .

Representative cationic monomers include the N-methylol acrylamide reactants mentioned above, dimethylaminoethyl methacrylate; t-butylamino-ethyl methacrylate; 2-hydroxy-3-methacryloxypropyl trimethyl am,monium chloride; allyl-trimethyl-ammonium chIoride; S-allyl-thiuronium bromide, S-methyl(allyl-thiuronium)methosulphate, diallyl-dibutyl-diammonium chloride, diallyl-dimethyl-a~onium methosulphate, dimethallyl-diethyl-a~monium phosphate, diallyl-dimethyl-ammonium nitrate, S-allyl-(allyl-thiuronium) bromide, N-methyl(4-vinylpyridinium) methosulphate, N-methyl(2-vinyl-pyridinium) methosulphate, allyl-dimethyl-beta-methacryloxyethyl-a~monium methosulphate, beta-methacryloxymethyl-trimethylammonium nitrate; beta-methacryloxyethyl-trimethylammonium p-toluene-sulphonate, delta-acryl-. ,.
oxybutyl-tributylammonium methosulphate3 methallyl-dimethyl-0-vinylphenyl-ammonium-chloride, octyldiethyl-m}vinylphenyl-ammonium phosphate, beta-hydroxyethyl-dipropyl-p-vinylphenyl-ammonium bromide, benzyl-dimethyl-2-,, .

~90~

methyl~5-vinyl-phenyl-ammonium phosphate; 3-hydroxypropyl-diethyl-vLnyl-phenylammonium suLphate; octadecyl-d-Lmethy:L-v`Lnylphenyl-ammonium p-toluene sulphonate, amyl-dimethyl-3-methYl-5-VinYlPhenYl-ammonium thiocyanate, vinyloxyethyl-triethyl-ammonium chloride, N-butyl-5-ethyl-2-vinylpyridinium iodide, N-propyl-2-vinyl-quinolinium methy:L sulphate, N-butyl-5-ethyl-3-vinylpyridinium iodide, N-propyl-2-vinyl-quinolinium methyl suLphate, aLlyl-gan~a-myristamidopropyl-dimethyl-ammoniumchloride, methallyl-gamma-caprylamido-propyl-methyl-ethyl-ammonium bromide; allyl-gamma-capryl-amidopropyl-methylbenzyl-ammonium phosphate, ethalLyl-ga~,ma-myristamido-propyl-methyl-aLpha-naphthyLmethyl-ammonium chloride, allyl-gamma-palmit-amidopropyl-ethyl-hexyl ammonium sulphate; methyaLlyl-gamma-lauramidopropyl-; diamyl-ammonium phosphate, propallyl-ganma-lauramidopropyl-diethyl-ammonium phosphate, methallyl-gamma-caprylamido-propyl-methyl-beta -hydroxyethyl-ammonium bromide~ allyl-gamma-stearamido-propyl-methyl-dihydroxypropyl-- 15 ammonium phosphate, alLyl-gamma-lauramidopropyl-benzyl-beta - hydroxyethyl-ammonium chloride and methaLlyl-gamma-abietamidopropyl-hexyl-gamma'-hydroxy-propyl-ammonium phosph~te, vinyl diethyl-methyl sulphonium iodide, ethylenically unsaturated nitrogen containing cations having the formula CH2=~lQN+tRlR2R3~X- such as disclosed in U. S.Patent No. 3,346,563 by - 20 Shildneck et al. with Q, Rl, R2, R3 and X~ groups being defined as above, mixtures thereof and the like.

Representative anionic monomers include vinyl sùl~onic acid and : vinyl sulfonates (e.g., see U. S. Patent Nos. 3,970,604 by G. Wentworth and 2,859,191 by Turnbull, etc.), allyl sulfosuccinic acid and allyl sulfo-succinates (e.g., see U. S. Patent Nos. 3,219,608 by Ingleby et al.);
sulfo esters of alpha-methylene carboyxlic acids and salts thereof (e.g., see U. S. Patent No. 3,024,221 by LeFevre et al.); sulfo-organic esters of fumaric and maleic acids and salts thereof (e.g., see U. S. Patent No.

3,147,301 by Sheetz); acids and salts of sulfatoalkane acrylates and meth-acrylates (e.g., see U. S. Patent Nos. 3,893,393 by Steckler and 3,711,449 , , ~, . .

` ` 1~9002 ''' by Brendley) acrylamidoalkanesulfonic acid and salts (e.g., see U. S. Patent ~; No. 4,008,293 by Maska et al. and 3,946,139 by Bleyle et al.), vinyl phosphonic acid and vinyl phosphonates; alpha, beta-ethylenically unsaturated carboyxlic acids, their salts (e.g., acrylic acid, methacrylic acid, eth-acrylic acid, propacrylic acid, butacrylic acid, itaconic acid, ~- monoalkyl esters~of-itaconic acid, crotonic acid and crotonates, fumaric acid and fumarates, etc.), mixtures thereof and the like.

. , .
Ihe water-absrobent starches rnay be prepared by initially copoly-merizing the starch with ethylenically IDnsaturated cornonomers which contain reactive sites (e.g., polar or unpolymerized ethylenic unsaturation) which are then derivatized to "W" moieties. For example, the ethylenically un-. .
saturated starches herein rnay be copolymerized with unsaturated precursorsand converted to the anionic form such as by saponification to replace the alkyl estergroup with a metal salt, and known techniques of derivatizing organic compounds to acidic or the neutralized acid-sa~lt form. Preferably the starting monomers contain the hydrophilic structure or one which can ; be directly converted to its '~" form by neutralization. This will avoid the derivatization step as well as the possiblity of contarninating the co-polymerizate with salts and rninerals, and the need to wash and refine to -~ 20 remove such contaminants therefrom.

- The polymeric linkages between copolymerized stàrch chains rnay be comprised of interpolymerized ionic monomeric units and monomeric units free from '~" substituents. The interpolymerized monomeric units free from substituents may be selected fi~om a broad rangeof ethylenically un-saturated monomers. ~ydrophilic and/or hydrophobic comonomers may be used for this purpose. Illustrative interpolymerized comonomers include vinyl ` aromatics (e.g., styrene and styrene derivatives); the alkyl esters of alpha, beta-ethylenically unsaturated acids; the alpha~ beta-ethylenically unsaturated nitriles, alpha, beta-ethylenically unsaturated amides; vinyl halides (e.g., vinyl chloride and bromide)j olefins such as mono- and dl-. -1~
. .

.

oz~

: olefins; vinylidene halide (e.g., vinylidene chloride and bromide), vinyl esters (e.g., vinyl acetate and derivatives); diesters o~ alpha, beta-ethylenically unsaturated dicarboxylic acids (e.g., dimethyl or diethyl ;- itaconate, dimethyl or diethyl maleate, diethyl or dimethyl ~umarate, etc.);
alkyl vinyl ethers such as methyl or ethyl vinyl ether, etc.; alkyl vinyl ` ketones (e.g., methyl vinyl-ketone, etc.), mixtures thereof and the like.
' ' .

Ihe polymeric linkages are advantageously predominantly comprised ~; of polar or water-soluble monomeric units. Illustrative polar or water-`- soluble comonomers free from '~" substituents which may be copolymerized 10 with the '~" monomers and the starch include the hydroxyalkyl esters of alpha, beta-ethylenically unsaturated carboxylic acids such as hydroxyethyl, hydroxyethoxyethyl, hydroxymethyl, 2-3-dihydroxypropyl acrylates and meth-acrylates, di(2,3-dihydroxypropyl) fumarate, di(hydroxyethyl) itaconate, : ethyl hydroxyethylmaleate, hydroxyethyl crotonate, mixtures thereof and the .. ~ .
like; the lower alkyl esters of alpha, beta-ethylenically unsaturated car- :-boxylic acids (e.g., Cl to C2 alkyl ester of mono- and di-carboxylic acid such as methyl and ethyl ester of acrylic, methacrylic, itaconic, fumaric, ~ . .
crotonic, maleic, etc.); N-(3-methylamino) propyl methacrylate; l-butyl-aminoethyl methacrylate; di-methylaminoethyl methacrylate; beta-(5-butyl-,. . .
amino)ethyl ac~ylate; 2-(1,1,3,3-tetra-methylbutylamino) ethyl methacrylate, etc.); alpha, beta-ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, ethacrylonitrile, etc.); alpha, beta-ëthylenically un-saturated amides (e.g., acrylamide and the N-substituted acrylamides such as N-methyl, N-ethyl, N-propyl, N-N-dimethyl and N-N-diethyl, N-butyl, etc.
acrylamides or methacrylamides or ethacrylamides, N-(beta-dimethylamino)-ethyl acrylamide, N-(beta-dimethylamino)ethyl methacrylamide, etc.), vinyl esters (e.g., vinyl acetate, etc.), vinyl alcohol and vinyl ethers (e.g., methyl or ethyl vinyl ether, diethylaminoethyl vinyl ether, diethyl-. , .
aminoethyl vinyl sulfide, 5-aminopentyl vinyl ether, 3 aminopropyl vin~l ether, 2-aminoethyl vinylether, N-methylaminoethyl vinyl ether~; alk~l vinyl .. . .
ketones (e.g., methyl vinyl ketone, etc.~; vinyl pyridine, vinyl pyrrolidone, mixtures thereof and the like.

", --19--~:. ' ' ' ' ' .i, . ~ .

-` lV9(:~2~

The proportions of ethylenically unsaturated starch copolymerized with the ethylenically unsaturated monomers should typically be sufficient to providè a starch copolymerizate which is capable of absorbing at least 10 ~ times it dry wei~ht in water. ~he monomer type and starch type will affect ~, 5 the proportions needed to achieve optimum water-absorbency. In general, the monomer dry weight will usually fall within the range of about 5 tn about 2000 parts by weight for each 100 parts by weight of the ethylenically unsaturated starch. For water-absorbency properties which exceed 50 times the starch copolymerizate weight, about 10 to about 1000 parts by weight copolymerizable monomer for each 100 parts by welght ethylenically unsaturated starch is - typically required. The amount of "W" monomeric units within the polymeric linkage will usually comprise from about 25% to 100% of the copolymerized monomer weight and advantageously at least a major weight of the polymeric - linkage. Water-absorbent copolymers capable of absorbing at least 100 times their dry weight in water are most suitably prepared from about 100 to about 750 parts by weight "W" monomer, and from 0 to about 200 parts by i weight ethylenic monomer free from "W" monomers for each 100 parts by weight ethylenically unsaturated starch.

The water-absorbent starch copolymerizates are advantageously pre-;
20 pared under aqueous polymerization conditions. Homogeneity of the reactants throughout the aqueous phase results in more uniform and reproducible water-absorbent properties. Ethylenically unsaturated starch a~d ethylenically unsaturated monomer systems which provide homogeneous dispersions essentially free from centrifugal residue and/or supernatant (e.g., heated to a tempera-ture above the starch gelation point to gelatinize the s~arch and centri-fuged for 10 mintes at 103g's) as evidenced by less than 10% by weight centri-fuged residue (preferably less than 5%) are Particularly well suited systems for preparing the water-absorbent starch copolymerizates.

''' ' ,.
;. . .

lO900Z7 - In thermal fabrication processes (e.g., molding, calendering, extrusion, etc.), a relatively high monomer and starch to water weight ratio (5:1 to 9:1) is typically used. At the reduced water levels and elevated ;: monomer levels, incompatibility of the ethylenic unsaturated monomer and :.
J
starch system can arise. Elevated fabricatingtemperatures and pressures may be used to improve upon the compatibility of this system. Likewise ` water-miscible solvents in which the ethylenic unsaturated monomers are soluble (e.g., such as glycerol) or emulsifying agents may be effectively utilized to enhance the water-dispersibility of the monomer-starch system into the aqueous phase. In extrusion operations, a sufficient amount of ., .
i water (with or without conventional starch plasticizers) to convert the polymerizable mass to a molten plasticized mass a~ elevated temperatures (e.g., 80-250C.) and pressures is used. The molten mass is then extruded through a die orifice into an atmosphere of reduced pressure and temperature ~` 15 maintained below the boiling point (B.P.) to produce void-free extrudates and above its B.P. to produce puffed extrudates.
:, . ~ :'':

In coating applications~ it is particularly advantageous to utilize a g~latinized or pregelatinized starch. Aqueous coating compositions con-- taining the low viscosity ethylenically unsaturated starch hydrolyzates are - 20 particularly useful when it is desired to coat substrates at dry binder weight levela of at least 40%. Substrates may be uniformly wetted and coated at solids levels ranging from about 50% to 75% by weight with stability .
against syneresis, separation and viscosity changes. Such coatings dry ; easily at nominal evaporation costs. Depolymerization of the starch to ~ :, ~! 25 the appropriate short chain length (e.g., D.E. 0.2-100) for coating applica-:~ tions may be accomplished by conventional saccharification and/or thinning ~ techniques (e.g., acid or enzymatic). The starch chains may be depolymerized , ~, to the appropriate ehain length prior or after the ethylenically unsaturated f derivatives are prepared. Starch chains having a degree of polyermization . j, , .
~ 30 comparable to that achieved by alpha-amylase hydrolysis of starch to a D. E. -~ .
~ ranging from about 0.1 to 32 (advantageously from about 0.25 to about 15 and most ;~
.,,~, . .
., .

lO90~t~ .

pre~erably less than 10) may be effectively used to coat substrates. Ihe reduced starch chain length will not adversely affect starch coating perma-nence provided the ethylenically unsaturated D.S. is sufficiently high enough to provide chains which contain multifunctional unsaturation sites.
' In most coating applications, the water content is typically ad-justed to a ~luidity most suitable to coat the substrate. Ihe starch coating composition viscosity may vary considerably and depends to a large extent upon the type of coating operation e~,ployed (e.g., from about 1 to about 40,000 cps or higher for extrusion coating). Ihe proportions of water, monomer and ethylenic unsaturated starch weight ratios may likewise vary considerably (e.g., about 5 toa~-out 10,000 parts by weight, i.e., pbw, water and about 1 to about 5,000 pbw monomer for each 100 pbw ethylenically unsaturated starch). In coating operations conducted under ambient temperatures, it is advantageous to utilize a homogeneous starch ; 15 coating composition of viscosity greater than about 10 cps but less than 5,000 cps (most typically between about20 cps to 1,000 cps) and containing ~rom about 25 to about 800 pbw water and about 10 to about 2,000 pbw ethylenically unsaturated monomer for each 100 pbw ethylenically unsaturated starch. Water-miscible organo solvents or sur~actants are desirably in-corporated into the coating composition ~or purposes of achieving homogeneity .~ and a uniform monomer dispersion if the starch coating formulation contains a low amount of water and a high monomer concentratlon. ~tarch coating compositions which are adapted for use in high-speed coating operations are typically formulated at a viscosity ranging from about 100 cps to :
` 25 about 300 cps (with or without fugitive organo solvents or surfactants.~ .
at about 30 to about 500 pbw water and about 25 to aboutl~000 pbw (pre-.~ ferably between about 50 to about 500 pbw) ethylenically unsaturated monomer , , ~or each 100 pbw ethylenically unsaturated starch. In ~ormulations for hi~h-speed coating operations, starch coating homogeneity is more easily - ~

.i :

i . : , . ,.. , . :, . ., , , .. , . :

.. ~ , . . ..

109~27 .. .
achieved by using less than 3 weight parts ethylenically unsaturated monomer ~or each 2 weight parts of water and preferably at a weight ratio of less than one part monomer for each water part.

lhe copolymerizates are copolymerized by conventional poly-- 5 merization initiating means. The unpolymerized starch and monomers may be conveniently prefabricated into the desired configuration and then copoly-merized in situ via such conventional polymerization initiating systems.
The starch compositions will undergo copol~erization upon exposure to con-ventional irradiation processes which generate in situ polymerization initia-tors therein (e.g., electron-beam, X-ray, alpha-ray, gamma-ray,-etc.
initiation). Alternatively, free-radical catalysts or free-radical pre-cursors may be uniformly incorporated into the unpolymerized starch composi-tion which will then latently copolymerize upon exposure to appropriate initiating conditions (e.g., photochemical, ultra-violet, heating or microwave techniques, etc.).
,.~ ' ~ .
Conventional free-radical polymerization initiators at levels su~ficient to copolymerize the ethylenic unsaturated starch and monomer (eOg., about 0.2% to about 20% on a starch-monomer weight basis) which may be incorporated into the starch composition include the organic and in-organic peroxides (e.g., hydrogen peroxide, benzoyl peroxide, tertiary butyl hydroperoxide, diisopropyl benzene hydroperoxide, cùmene hydroperoxide, caproyl peroxide, methyl ethyl ketone peroxide, etc.), oxidation-reduc-tion initiator systems (ammonium, potassium or sodium persulfates or hydrogen peroxide with reducing agents such as sodium bisul~ites~ sulfites, sulfoxylate.~ thiosulfates, hydrazine, etc.); azo initiators (e.g., tertiary phatic azo compounds which undergo homolytic dissociation) such as azo di-isobutyronitrile,phenylazotriphenylmethane, l,l'-azodicyclohexane-carbonitrile, l,l-dimethylazoethane; diazoamino compounds (e.g.~ 3,3-di-methyl-l-phenyl-triazene and aryldiazo thioethers) and other free-radical generating catalysts such as certain aromatic ketones (e.g.~ benzoin ' ' ' , ~: ' .

y~ -z~

methyl ether, benzophenone and its derivatives), chlorinated aromatics as well as other free-radical type of polymerization initlators. Free-radical initiator systems which require externally applied energy (e.g., thermally, photochemical, etc.) for free-radical generation may be used to provide a ~ 5 latently copolymerlzed system. Advantageously the free-radical polymeriza-- tion initiators are uniformly dispersed throu~hout the aqueous phase o~ the starch composition at levels ranging from about 0.3% to about 10% (based on polymerizable starch and monomer dry weight).

Polymerization initiation via U.V. and white light sources (e.g., 200-430 nanometer (nm)-range, such as by carbon arc la~lps, Zenon lamps, high pressure mercury lamps) is particularly useful in high-speed coating opera-tions. If desired, conventional photosensitizers (e.g., triethanol amine-- soluble benzophenones, eosin-sulfonates, methylene blue-sulfinate, combina-tions thereof, etc.) by active energy transfer may be incorporated into the starch conposition to facilitate the copolymerization initiation reaction.
The ultra-violet polymerization initiating processes are generally suitable for coatings or films of a thickness of less than about 20 mils (pre~erably less than about lO mils). lhicker starch polymerizate articles or films normally re~uire higher penetrating irradiation devices (e.g., X-ray, electron-beam, gamma generation, etc.) or thermal induction. The ultra-violet copolymerization process is particularly effective for high solids starch coating applications (e.g., about 55% to about 75% dry solids) because it simultaneously dries and copolymerizes the starch coating in a single step.
Water-dispersible, non-fugitive free-radical initiating systems (e.g., catalysts which evaporate or do not leave catalytic residue in the copoly-;~` merizate) such as hydrogen peroxide are preferred.

!
' .
The water-absorbent starch copolymerizates have a wide and divergent field of use. A ma~or advantage of the water-absorbent starches of this ;
~ --2LI_ : ., .
~: ~ . ~: , : ' ' . .
: . .

0Z'7 . , .

invention resides in the ability to apply the unpolymerized product to a substrate or prefabricate it into the desired shape or con~iguration and then convert it to a water-absorbent, starch copolymerizate. Ihe unpoly-merized product can be applied to divergent substratea ranging from natural and man-madeproductsand thereafter polymerized in situ to ~orm an inte-grated product of unitary construction. This advantage is particularly use-ful for applications wherein it is desirable to permanently af~ix or impregnate a natural or synthetic substrate (e.g. films, webbings, fibers, - filaments, etc.) with the water-absorbent starch. Illustrative applica-tions for the water-absorbent starches include hygenic pads, bandages, surgical and catamenial tampons, sanitary napkins, diapers, antiperspirant and deodorant pads, sponges, surgical pads, sorptive dental rolls, dis-infectants, decorative seedling films, etc. If desired, the water-absorbent starch copolymerizates may be admixed with natural and man-made products ~or such divergent uses as cosmetics, water scavengers, paint removers, . , .
solid humectants, pesticides, improving the water-holding capacity of soils, cat~lysts or chemical carrier, binders, etc.
. ~ .

lhe following examples are merely illustrative and should not be ` construed as limiting the scope of the invention.

, . . .
~ 20 EXAMPLE I

; An aqueous acrylamidomethyl starch hydrolyzate ~D.S. O.OO9) was prepared employing the following proportions of reagents.

Parts by weight (pbw) Reagents _ _ __ _ _ ___ 279 STA-TAPE 100 Starchl (250 parts by weight ~, dry starch) 21 N-methylolacrylamide (as 60% aqueous soln.) j 25.8 Ammonium dihydrogen phosphate (acid catalyst) 0.004 Methyl hydroquinone (polymerization inhibitor) 247 water ,:j ; 1 - STA-TAPE lO0 - manufactured by the A. E. Staley Manufacturing Co~pany -A low viscosity, acid-thinned, granular waxy maize starch (100% amylo-pectin) typically characterized as having a Brookfield viscosity of ~- about 500 cps (#2 spindle, 20 rpm, 150C. at a dry solids of 40-45%) and a D.E. of less than 1%.

. :' ' . '' The ingredients were mixed and filtered on a suchner funnel. The starch cake was sucked free of excess aqueous phase and the unwashed cake (with 63 percent retention of non-starch reagents) was air-dried to a ten percent drying loss. The dried reaction premix had the following ratios - 5 of reagents (p~w) - 250 starch; 7.95 N-methylolacrylamide, 0.025 methyl hydroquinone; 29 water. The pcwdered reaction premix was layered onto a stainless steel tray and heated for 2 hours in a forced air oven at 75.5C.
AEter resuspending in distilled water, filtering and washing free of un-reacted reagent impurities, the dried product contained 0.10 percent nitrogen (dry basis), which when corrected for the nitrogen in the STA-TAPE 100 starch (0.022 percent) is equivalent to a D.S. of 0.009. Further information on the preparation of the acrylamidomethyl starches may be found in co-pending U. S.
Patent Application Serial No. 680,549, filed April 27, 1976 by Young et al.
r A portion of the acrylamidomethyl starch (0.77 grams) was homo-geneously dispersed into 8.43 grams water (15 minutes at its boiling point) ~:-and cooled to ambient temperature in a 50 ml. flask. Acry~ic acid (0.48 grams) . -and acrylamide (0.24 grams) were hcmogeneously dispersed into the acrylamido ; starch solution followed by the addition of 0.0169 grams (d.s.b.) ammonium .
~`~ persulfate (2.28% aqueous solution) and 0.0076 gram (d.s.b.) of sodium bi-... .
sulfite (1.04% aqueous solution). Then 0.002 gram (d.s.b.) of ferrous sulfate - (0.28 wt.~ FeSO4.7H2O aqueous solution) was added which caused an exothermic - copolymerization of the ethylenic unsaturates. Within 1 minute the entire reaction medium had gelled (12.1/g) into a copolymerizate which could be ~~ agitated with a magnetic stirrer. To convert the acrylic moieties to the '! 25 anionic salt form, 0.42 gram of solid potassium hydroxide was added. The :.
,~ resultant viscous dispersion (12.53 g total) was then stirred Eor 15 minutes.
The sample contained 15.24 wt.% solids. The gel was then diluted to 5 wt.%
dry solids with 25.64 g distilled water and allowed to stand for 24 hours.

"
:~ .

:: .
~, , 109()~7 Ihereafter the dispersion (36.84 grams) was further diluted with 55.26 g distilled water to provide a 2% gel solids dispersion. The viscosity of the ;; dispersion respectively after standing for six and twenty-three hours (#4 spindle at 20 rpm) was 500 cps and 3500 cps. The solids was again diluted .::
with 90.52 g of distilled water (1% dry solids dispersion) which after 29 hours standing had a 700 cps viscosity t#4 spindle at 20 rpm) and after 58 hours a viscosity o~ 710 cps. The 1% gel dispersion was arnbiently air-dried - (evaporating dish for 11 days). A 0.1526 g sarnple of the resultant gummy resin was transferred and hydrated with 11.85 grams o~ distilled water in a 15 ml. centrifuge tube. ~he sample swelled to the 12 ml. volume. The hydrated sample was centrifuged for 15 minutes at 103 g's. lhe supernatant liquid was decanted into a tared aluminum pan. 11.38 grarns of the swollen gel was transferred to a 50 ml. centrifuge tube and diluted with 11.38 grams - ~ of water and allowed to swell for 17 hours followed by centrifugation ~or : 15 15 minutes at 103g's. me supe~natent (pH 6.6) along with the a~orementioned ~ supernatant was analyzed for water-soluble starch (0.0423 grams.or 27.7% by ;
weight via evaporation).
. ";.
e copolymerizate weight swelling ratio (WSR) was determined by the equation WSR = oIS wherein I, O and S respectively represent the weight 20 of swollen insolubles, 9.63 grams; original sam~le 0.1526 grams and solubles, 0.0423 grams (i-e-, WSR O-S 0.1S26 - 0 0423 . .
EXQMPLE II
~ cationic, water-absorbent starch copolymerizate was prepared by copolymerizing (in 34.6 pbw distilled water) 8.50pbw (0.008 moles) acrylamido-25 methyl starch (d.s. 0.008), 30.9 pbw CH2=C(CH3)-C-OCH(OH)CH2~(CH3)3Cl -;' (0.0199 moles) and 11.1 pbw acrylamide (0.0241 moles). ~he copolymerization , . .
reaction was exothermically initiated with 0.1 pbw ammonium persul~ate (0.13(NH4)2S2O8 + 5 pbw water), 0.07 pbw sodium bisulfite (0.07 pbw NaHSO3 + 5 pbw water) and 0.01 pbw FeSO4.7H20 (0.01 pbw FeSO4.7H2O ~ 4.7 pbw water).
30 Within 90 seconds the copolymerization reaction was completed to yield a water-. .
.
. .

, 1~)9~

: absorben~, hydrated copolymerizate gel. This cationic gel was analyzed in ' accordance with the test procedure of Example I at 25C. The copolymerizate '' contained 73% (by weight) insoluble copolymerizate solids and 27% (by weight) solubles and had a 152 WSR. Ihe insoluble copolymerizate absorbed 152 times 5 its dry weight ~ water at a pH 4.o and 25C.
' EXA~PLE'III t A cationic water-abosrbent starch copolymerizate was prepared~by copolymerizing o.oo8 moles acrylamidomethyl starch (D.S. 0.008 @ 8.45 pbw), 0.0243 moles acrylamide (11.25 pbw) and 0.01673 moles CH2=C(CH3)-C-OCH2CH2~(CH3)3CH3OSO~ (30.82 pbw) with the exothermic initiating system of Example II. me resultant copolymerizate gel (copolymerization completed within 150 seconds after initiation) was admixed with 2000 ml. water and allowed to swell for 8 days at 25C. Ihe decanted supernatent liquid portion thereof contained 20.18% water-solubles. The insoluble copolymerizate (79.82% o~ the total copolymerizable reactants) absorbed 86 times it weight ~:'water at pH 3.6 and 25C.

- EXAMPLE IV ' Employing the polymerizate initiating system of Example II, 10 pbw acrylamidomethyl starch (D.S. 0.008) was copolymerized (about 3 minutes) in 56 pbw distilled water which contained 9 pbw potassium hydroxide with 12 pbw acrylic acid and 12 pbw acrylamide. The anionic copolymerizate gel (tested via the Example III water-absorbency test) absorbed 119 times its dry weight of water. Ihis examplewas repeated again with a 0.056 D.S. starch. Ihe o.o56 D.S. copolymerizate gel only absorbed 27 times its dry weight in water.
The lower water absorbency for the 0.056 D.S. acrylamidomethyl starch co-polymerizate is apparently attributed to its more highly cross-linked structure.

''EXAMPLE ~

IhiseXa~Pleillustrates a water-absorbent copolymerizable starch coating composition which may be copolymerized'in'situ to provide a sub-strate (e.g., textile~ papers, etc.) coated with the water-absorbent, . . . . . . : .
.
.

L~ 3Z7 stareh copolymerizate. The copolymerizable coating composition (pH 6.0) consisted of 10 pbw acrylamidomethyl stareh (0.01 D.S.)2, 47 pbw distilled water, 12 pbw aerylie aeid, 12 pbw aerylamide, 9 pbw potassium hydroxide and 10 pbw aqueous hydrogen peroxide (30%).

Five grams of the eopolymerizable cQmposition was plaeed in an aluminum weighing pan (2" I.D.) and irradiated an ineh away from a 275 watt sun lamp for 1 minute to give a firm gel. Another portion of copolymerizable stareh eomposition was applied with a #40 wire wound rod to a 4" x 12" glass plate and irradiated 6 passes at 20 ft./min. at 1.5" under a ~lanovia 679A
lamp. The copolymerizable starch camposition gelled on the first pass (1/6 see.) and converted to a dry film after the sixth pass through the irradiator - (i.e., one second). The WSR for the resultant stareh copolymerizates were 150.
A 0.056 D.S. acrylamidQmethyl stareh was used instead of the 0.01 D.S. acryl-amidQmethyl starch to provide a eopolymerizate with a WSR of 30.

~ 15 In another test, a 0.014 D.S. acrylamidomethyl stareh was substituted k~, for the 0.01 D.S. aerylamidamethyl starch reaetant and applied to the glass . plates with a #40 wire wound rod (pH 6.2; 25-36 cps viscosity, #1 spindle, at - 20 rpm at 25 C.). After 4 passes through the irradiator, a dry, water-absorbent film coating, 83.51% insoluble eopolymerizate dry solids and a WSR
of 120 was obtained. This test was repeated by immersing three cotton cloth pieees (18" x 6") in the 0.014 D.S. copolymerizable starch coating eQmposi-tions, passing the eoated cotton through the rolls of a Birch Brothers Padder, plaeing the coated eotton pieees on glass plates and then irradiating the three samples for 4, 6 and 8 passes. The dry coating add-on was 46% by weight. The water swelling ratios were 120 for 4 irradiation passes, 86 for 8 passes and slightly more than 100 for the cloth whieh was exposed to 6 passes.
., .

2 - The 0.01 D.S. acrylamidomethyl stareh hydrolyzate contained an average of approximately two acrylamidomethyl groups for eaeh stareh moleeule.

. ' .

-29- ~

.
. ~' ' .
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llll~OOZ~7 Althou~h the a~orerrentioned Examples prirn~rily illustrate the use of relatively high-molecular-weight starch chains, the invention applies to - a broad range of ethylenically unsaturated glucose-containing monomers such as those ranging ~rom a completely hydrolyzed starch (e.g., dextrose) to an unhydrolyzed starch. The glucose-containing monomers which contain multi-` functional ethylenically unsaturated groups provide the necessary structure for the porous lyophilic network. The most appropriate D.S. level for a .
glucose-containing nomer will depend upon the number of glucose units present in its starch chain. To achieve multifunctional copolymerizable groups ~or a rnonosaccharide, disaccharide, trisaccharide or tetrasaccharide rr.onomer would respectively require a D.S. Or 2.0, 1.0, o.66 and 0.5 with the oligosaccharides (e.g., D.P.4+) and higher starch chains requ ~ing a correspondingly lesser D.S. to achieve multifunctionality. In contrast~ the higher lecular weight starches (e.g., unhydrolyzed starches) will typically --- 15 have multifunctional copolynerizable groups at a D.S. o~ 0.0002 or less.
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Since the starch copolymerizates as described herein possess a porous structu-re, their lyophilic properties can be altered via the composi-tion and character of unsaturated starches, monomers and lyophilic groups which are used in their preparation. By replacing the polar, water-attractant groups with ~lon-polar and oil or solvent attractant groups, starch copoly-merizates which may be tailor-made to absorb speclfic solvents, chemicals and~or water-immiscible liquids (e.g., oil) are now possi~le. Similarly, lyophilic and amphophilic starch copolymerizates may be obtained by starch copolymerizates which contain both polar water-soluble and hydrophobic, water-insoluble substituents.
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Since many embodiments of this invention may be made and since manychanges may be made in the embodiments described, the foregoing is interpreted as illustrative and the invention is de~ined by the claims appended hereafter.

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Claims (31)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A water-absorbent starch copolymerizate which is capable of absorbing several times its own weight in water, said starch copolymerizate comprising the copolymerizate product of ethylenically unsaturated starch molecules and ethylenically unsaturated monomers with said ethylenically unsaturated monomers forming a connective polymeric linkage between said copolymerized starch molecules to provide a non-linear lattice of a plurality of starch chains linked together by polymeric linkages represented by the formula:

wherein Starch represents a starch chain of D-glucose units, Z represents an organo group which links the group to the carbon atom of the starch chain by a sulfur atom or an oxygen atom, R is a member selected from the group consisting of hydrogen and a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers with "p"
representing the number of copolymerized monomeric units in said linkage, (W) is a water-attractant group linked to the polymeric linkage and "n"
represents the number of (W) moieties contained within the polymeric linkage of said copolymerized monomers with the number of (W) moieties being sufficient to impart water-absorbency properties to said copolymerizate.

2. The water-absorbent starch copolymerizate according to claim 1 wherein the Z organo group consists essentially ofa group and R' is at least one member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond.

3. The water-absorbent starch composition according to claim 1 wherein the ethylenically unsaturated starch molecules consist essentially of starch molecules and appendant ethylenic unsaturated groups of a molecular weight ranging from greater than 50 to less than 300 and the degree of sub-stitution of said ethylenically unsaturated appendant groups range from about 0.002 to about 0.1.

4. The water-absorbent starch according to claim 3 wherein "W" is at least one member selected from the group consisting of anion, cation, nonion and zwitterion.

5. The composition according to claim 4 wherein the weight of ethylenically unsaturated monomer in said copolymerizate ranges from about 10 to about 1000 parts by weight for each 100 parts by weight of copolymerized ethylenically unsaturated starch and from about 25% to about 100% of the copolymerized ethylenically unsaturated monomer contains the "W" substituent.

6. The water absorbent starch composition according to claim 4 wherein the copolymerized ethylenically unsaturated starch consists essentially of amylopectin hydrolyzate with a degree of substitution of said starch ethylenic unsaturated groups ranging from about 0.005 to about 0.05.

7. The water-absorbent starch according to claim 4 wherein the copolymerized ethylenically unsaturated starch consists essentially of an acrylamide starch having a D.S. ranging from about 0.005 to about 0.05 and a D.E. ranging from about 0.25 to about 15, and the copolymerizate contains 100 parts by weight copolymerized ethylenically unsaturated starch hydrolyzate, from about 100 to about 750 parts copolymerized ethylenically unsaturated monomer which contain "W" groups and from 0 to about 200 parts by weight of copolymerized ethylenically unsaturated monomers devoid of said "W" groups.

8. A method for preparing a water-absorbent starch copolymerizate, comprised of a plurality of starch chains linked together by polymeric link-ages represented by the formula:

wherein Starch represents a starch chain of D-glucose units, Z represents an organo group which links the group to the carbon atom of the starch chain by a sulfur atom or an oxygen atom, R is a member selected from the group consisting of hydrogen and a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers which contain a sufficient number of (W) groups to impart water-absorbency to said copoly-merized product, "p " represents the number of copolymerized ethylenically unsaturated monomers linking together said starch chains, said method compris-ing copolymerizing:
(a) starch chains containing appendant, terminal ethylenic unsaturated groups represented by the formula:

wherein Starch, Z and R are as defined above, and "a"
represents the degree of substitution of said terminal unsaturated groups on said starch chain? and (b) ethylenically unsaturated monomers represented by the formula:
wherein M represents an ethylenically unsaturated monomer, "(W )" represents at least one member selected from the group consisting of a water-attractant group or a precursor of a water-attractant group, and n' is an integer with the proviso that when the copolymerized M'-(W') monomer consists essentially of a precursor of said water-attractant group, a sufficient number of the precursor groups are derivatized to a water-attractant group to impart water-absorbing properties to said starch copolymerizate.

9. me method according to claim 8 wherein (W') is at least one water-attractant group or a precursor of a water-attractant group selected from the group of anion, cation, nonion, and zwitterion, and Z represents an organo group which links the -CRH- group to the starch chain by an oxy moiety.

10. me method according to claim 9 wherein Z comprises an organo group represented by the formula;

and R' is at least one member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond.

11. The method according to claim 10 wherein the appendant ethylenic unsaturated groups of the starch chains consist essentially of groups having a molecular weight ranging from about 75 to about 150 and "a" represents a degree of substitution ranging from about 0.002 to about 0.1.

12. The method according to claim 10 wherein from about 25% to 100%
by weight of ethylenically unsaturated monomers contain the "W" group and the copolymerized weight of ethylenically unsaturated monomer ranges from about 10 to about 1000 parts by weight ethylenically unsaturated monomer for each 100 parts by weight ethylenically unsaturated starch.

13. The method according to claim 12 wherein the ethylenically unsaturated starch consists essentially of amylopectin hydrolyzate and "a"
represents a degree of substitution ranging from about 0.003 to about 0.05.

14. The method according to claim 9 wherein the ethylenically unsaturated starch consists essentially of an acrylamido starch hydrolyzate having a D.S. ranging from about 0.005 to about 0.10 and a D.E. ranging from about 0.25 to about 15, and 100 parts by weight of the ethylenically unsatu-rated starch hydrolyzate is copolymerized with from about 100 to about 750 parts copolymerized ethylenically unsaturated monomers containing the "W"
groups and from 0 to about 200 parts by weight ethylenically unsaturated monomers free from said "W" groups.

15. The method according to claim 14 wherein Z represents an organo group having the formula:

with R' representing either hydrogen or a lower alkyl group of 1 to 3 carbon atoms inclusive, and R represents either hydrogen or methyl.

16. The method according to claim 15 wherein the starch chains con-sist essentially of an amylopectin hydrolyzate and "W" represents at least one member selected from the group consisting of an anion and cation.

17. The method according to claim 8 which includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and ethylenically unsaturated monomers to a substrate and thereafter copolymeriz-ing in situ the applied starch and monomers.

18. The method according to claim 9 which includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and ethylenically unsaturated monomers to a substrate and thereafter copolymeriz-ing in situ the applied starch and monomers.

19. me method according to claim 11 which includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and ethylenically unsaturated monomers to a substrate and thereafter copolymeriz-ing in situ the applied starch and monomers.

20. The method according to claim 14 which includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and ethylenically unsaturated monomers to a substrate and thereafter copolymeriz-ing in situ the applied starch and monomers.

21. The method according to claim 16 which includes the additional steps of applying the unpolymerized ethylenically unsaturated starch and ethylenically unsaturated monomers to a substrate and thereafter copolymeriz-ing in situ the applied starch and monomers.

22. The water-absorbent substrate of a unitary construction comprised of a substrate and the water-absorbent starch copolymerizate of claim 1.

23. In a water-absorbent substrate wherein the substrate is impregnated, coated or combined into a composite structure of unitary construction with a water-absorbent composition, the improvement which comprises the water-absorbent starch copolymerizate of claim 5.

24. The water-absorbent substrate according to claim 23 wherein the water-absorbent starch copolymerizate consists essentially of the copolymerization product of 100 parts by weight of acrylamide starch having a D.S. ranging from about 0.005 to about 0.1 and a D.E. ranging from about 0.25 to about 15, from about 100 to about 750 parts copolymerized ethylenically unsaturated monomer which contain "W" groups and from 0 to about 200 parts by weight of copolymerized ethylenically unsaturated monomers devoid of said "W" groups.

25. A copolymerizable starch_containing composition which can be converted into a water-absorbent starch copolymerizate having a plurality of starch chains linked together by polymeric linkages represented by the formula:

wherein Starch represents a starch chain of D-glucose units, Z represents an organo group which links the group to the carbon atom of the starch chain by a sulfur atom or an oxygen atom, R is a member selected from the group consisting of hydrogen and a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers with "p"
representing the number of copolymerized monomeric units in said linkage, (W) is a water-attractant group linked to the polymeric linkage and "n"
represents the number of (W) moieties contained within the polymeric linkage of said copolymerized monomers with the number of (W) moieties being sufficient to impart water-absorbency properties to said copolymerizate, said copolymerizable composition comprising:
(a) starch chains containing appendant, terminal ethylenic unsaturated groups represented by the formula:

wherein Starch, Z and R are as defined above, and "a"
represents the degree of substitution of said terminal unsaturated groups on said starch chain, and (b) ethylenically unsaturated monomers represented by the formula:
wherein M represents an ethylenically unsaturated monomer, "(W )" represents at least one member selected from the group consisting of a water-attractant group or a precursor of a water-attractant group, and n' is an integer.

26. The copolymerizable composition according to claim 25 wherein "Z" comprises an organo group represented by the formula:

and R' is at least one member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, (W') is at least one water-attractant group or a precursor of a water-attractant group selected from the group of anion, cation, nonion, and zwitter-ion, and the copolymerizable starch composition contains 100 parts by weight of the ethylenically unsaturated starch having a D.S. from about 0.005 to about 0.10, from about 100 to about 750 parts by weight ethylenically unsaturated monomer which contains the "W'" group and from 0 to about 200 parts by weight ethylenically unsaturated monomers which are free of said "W'" groups.

27. The copolymerizate composition according to claim 26 wherein the starch chain consists essentially of an amylopectin hydrolyzate having a D.E. ranging from about 0.25 to about 10 and R represents at least one member selected from the group consisting of hydrogen and methyl.

28. In a method of absorbing water with a water-absorbent substance wherein a water-absorbent substance is placed into a medium which contains water and causing the water-absorbent substance to hydrate and absorb several times its dry weight in water, the improvement which comprises a water-absorbent starch copolymerizate which is capable of absorbing several times its own weight in water with said starch copolymerizate consisting essentially of the copolymerizate product of ethylenically unsaturated starch molecules and ethylenically unsaturated monomers with said ethylenically unsaturated monomers forming a connective polymeric linkage between said copolymerized starch molecules to provide a non-linear lattice of a plurality of starch chains linked together by polymeric linkages represented by the formula:

wherein Starch represents a starch chain of D-glucose units, Z represents an organo group which links the group to the carbon atom of the starch chain by a sulfur atom or an oxygen atom, R is a member selected from the group consisting of hydrogen and a monovalent organic radical, M represents a plurality of copolymerized ethylenically unsaturated monomers with "p"
representing the number of copolymerized monomeric units in said linkage, (W) is a water-attractant group linked to the polymeric linkage and "n"
represents the number of (W) moieties contained within the polymeric linkage of said copolymerized monomers with the number of (W) moieties being sufficient to impart water-absorbency properties to said copolymerizate.

29. The improvement according to claim 28 wherein the Z organo group consists essentially of a group and R' is at least one member selected from the group consisting of hydrogen and a mono-organo group joined directly to the nitrogen atom by a monovalent bond, "W" is at least one member selected from the group consisting of anion, cation, nonion and zwitterion, the weight of copolymerized ethylenically unsaturated monomer in said copolymerizate ranges from about 10 to about 1000 parts by weight for each 100 parts by weight of copolymerized ethylenically unsaturated starch and from about 25% to about 100% of the copolymerized ethylenically unsaturated monomer contains the "W" substituent and "a" represents a degree of substitu-tion ranging from about 0.003 to about 0.1.

30. The improvement according to claim 29 wherein the copolymerized unsaturated starch consists essentially of an acrylamide starch having a D.S.
ranging from about 0.005 to about 0.05 and a D.E. ranging from about 0.25 to about 15, and the copolymerizate contains 100 parts by weight copolymerized ethylenically unsaturated starch hydrolyzate, from about 100 to about 750 parts copolymerized ethylenically unsaturated monomer which contain "W" groups and from 0 to about 200 parts by weight of copolymerized ethylenically unsaturated monomers free of said "W" groups.

31. The improvement according to claim 30 wherein the starch chain consists essentially of an amylopectin hydrolyzate having a D.E. of less than 10 and R represents a methyl group.