Industrial Uses of Starch

7/27/2019 Industrial Uses of Starch

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INDUSTRIAL USE OF CORN STARCHIC. R. Russell

Northern Regional Research LaboratoryAgricultural Research ServiceU.S. Department of AgriculturePeoria, I l l inois 61604

lpresented at the 58th annual meeting of th e American Associationof Cereal Chemists, November 4-8, 1973, St. Louis Missouri.

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IntroductionCurrent domestic consumption of corn starch products,including unmodified and modified starches, in industr ia l or nonfoodapplications, amounts to approximately 3 billion pounds per year.About 90% of this volume is accounted for by starch products Qsedas sizing agents and adhesives in making and coating paper andpaperboard; as sizes in tile manufacture of textiles; ffild as adhesivesin producing boxboard, insulation board, paper bags, cardboardcartons, and gummed labels and tapes. Each of these areas ofapplication has been covered in one or more reviel'!s ,litilin the pastfel... years (1-8). The objectives here are to condense and update tilisliterature, to mention a number of o t ~ e r uses, and to discuss someindustrially promising developmental products.

Principal Starch Products Used I n d u s t r i ~Unmodified starch in addition to being useful in variousapplications is an excellent raw material for making many otherindustrial products. I t is relatively inexpensive and can bepartially depolyrnerized and derivatized readily, only relatively1m... levels of modification are needed to alter its propertiessignificantly, and all of the il'lportant industrial processes canbe conducted in the dry state or in aqueous media. Except forenzyme-modified starches, most of which are prepared on-site bythe user and not isolated, and pregelatinized starch, the othermajor industrial grades of modified starch made by a q u e o t ~ processescan be isolated readily by filtration. TIlis is possible becausethe reactions proceed Hell at temperatnres belm... the range wherestarch granules swell, become sticky, ffild start to dissolve.For many industrial applications, starch products areneeded tilat are less viscous, form more stable pastes, and havegreater affinity for natural and synthetic fibers or other substratesthan does unmodified starch. These properties are achieved throughdegradative and substitutive reactions applied singly and in selectedcombinations to s tarch. Starches considered in this reviel'" areeither regular unmodified corn sta rch o r products derived from i tunless othendse noted. The types and amounts of the p rinc ipalstarch products sold for industrial uses are given in Table I.Sales ratiler than consumption figures are given in Tahle Ibecause much of the unmodified starch that is sold is processed inplant by the user to reduce its viscosity to appropriate levels fo rvarious applications. The processes most commonly used are enzymatichydrolysis (9) and steam-jet cooking (10).

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264

Acid-Hodified Starches

TAl3LE I . SALES OF COPJ',) STAROI PrDnucrs FORINDUSTRIAL APPLICATIONS 11'1 1972

4203,n93

1,817340166150Inn100

mllions of PmmdsaStarch ProductUnmodified starchAcid-modified starchOxidized starchDextrinsCationic starcllesPregelatinized starchesAll others includinghydroxyethylstarchTotal

Detailed descriptions of industr ial processes fo r manufacturing acid-modified starches have not been published; hrn'lever, methodsapproximating those used industrially have been described (11).

~ a t a were obtained from starch suppliers. \VaAlmaize and high-amylose starch sales ''lhicll are quitesmall comnared to sales of ordinary corn starchare included in the figures. 'The preparation and propert ies of all the modified starcheslisted in Table I llave been revie'led recently (11-10) and aredescribed only hriefly here to provide background for subsequentsections on industrial utilization.

FlUidity is the inverse of viscosity and is expressed asa number defined as follows: A fluidity number corresponds to thenumber of milliliters of a solut ion of 5 g. of test product, dis-solved in 100 mI. of 0.9% sodium hydroxide, that f l r n \ ~ through a

In essence, acid modification involves heating a fairlyconcentrated slu rry of starch in di lu te hydrochloric or sulfuricacid at 50-55C until the desired degree of conversion is achieved.At this s tage, the react ion is terminated hy neutralization, thenthe product is recovered on a fi l ter, washed 'v ith water, and dried.The course of the reaction is usually follrn1ed by determining thefluidity of samples removed from the reaction at various intervals.


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specially designed funnel in 70 sec. at 25C,. tInder these test condi tions, water has a fluidity of 100 and that of unmodified starchis on the order of 1 (17). Acid-modified starches are often refer redto as fluidity starches and are available in several fluidity gradesranging from 20 to 90. The extent of depolymerization associatedwith various fluidity grades of acid-modified starch is indicatedf r o ~ intrinsic viscosity values of 1.55, 1.05, 0.00, and 0.50 decilitersper gram reported (18) for unmodified corn stardl and 20, 40, and 75fluidity grades, respectively.

Hot pastes of acid-nodified starches are much thinner thanpastes of LUunodified starch at the sane solids content. For thisreason, acid-modified starches as ,.,rell as other partially depo1ym-erized starches are often called thin-boiling starches. The gellinp:pm.,rer, defined as the ratio of cold paste viscosity to hot pasteviscosity (11) is much greater for acid-modified starches than forunmodified starch. The viscosity, film foming, and adhesivecharacteristics make acid-modified starches useful as ,.,ram sizesin textile manufacturing and in cer ta in paper-sizing a p p l i ~ ~ t i o n s .Acid-modified starches also serve as starting material for thepreparation of thin-boiling starch derivatives.Dextrins

Three major t ) ~ e s of d e x t r i n s - - ' ~ l i t e dextrins, yellmvdextrins, and British gums--are commercially availahle.li'hite dextrins are made by heating s ta rch in the presenceof moisture llnder fairly acidic conditions at temperatures rangingfrom 95 to 120C (12). Under these conditions hydrolytic breakdmmis the principal reaction; conseauently, properties of the productsresemble those of acid-modified starches. The white dextrins areused in adhesives and in some types of textile finishes.Yellmv dextrins are made by heating starch at low moisturecontent and moderate acidity at temneratures fron 150 to 190C,. TIleinit ial depolymerization ",hich takes place is follm.,red by rearrangementand repolymerization to give highly branched starches ' ~ l i c h do not

retrograde easily (associate in solution to insoluble aggregates) .The yellm.,r dextrins are the most highly converted, Le. , depolymerized,products among the modified starches. Their degree of polynerization(D.P.) is approximately in tIle range of 20 to 50 (1). Because of tileir1mv D.P., i t is possible to make fairly free f l m . , r i ~ ~ solut ions orpastes "nich contain up to 60% solids. These pastes are very stickyand dry rapidly because of their high solids content. These propertiesmake the yellmv dextrins very useful in adhesive applications ,michconstitute their principal use.

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British gums ar e made hy heating s ta rc h o f very loi'! moisturecontent to 150 to 190C Witil l i t t le or no acid present (1). lmderthese conditions, rearrangement is favored hut some hydrolyticbreakdown occurs. Because of th e high degree of branching in theproducts, their aqueous dispersions are relatively stahle. TheBritish gums are availab le in a \-Tide range of viscosities and varyin color from l ight ta n to dark brO\VJl. Their aqueous dispersion..sare gurrany and spread Hel l, p ropert ies '-Ihich make then useful in avariety of adhesive applications.Oxidized Starch

Sodium hypochlorite is usually used in th e corrnnercial production of thin-bo il ing oxidized starches. Oxidation is conducted by'treating an aqueous alkaline slurry of starch in granule forn withsodium hypochlorite solution containing 5 to 10% available chlorineat temperatures usually in th e ranp:e of 21 to 38C (13). Oncompletion of the oxidation, th e reaction mixture is neutralized'vith acid, bisulfite solut ion or sulfur dioxide is added to dcstrO)'any unspent oxiclant, and the reaction mixture is diluted 'vith ,vater.The product is recovered on a fi l ter , \vashed \vi th ,vater, and dried.lIypoch10rite oxidized starches are availab le in about th e samev i s c o s i ~ ' range as th e acid-converted starches.

Hypochlorite oxidation, in addition to c leaving the starchchains, also introduces a few carboA)'l and carhony1 groups into th estarch molecules. In cOl1U1lercia1 products, the degree of subst itu tion(D.S.) defined as tile average mnnber of substituents pe r anhydrog1ucoseunit ranges from about 0.01 to 0.03 'vith respect to carboxyl groups.The D.S. ,-l ith r espect to carbonyl groups ranges from about 0.005 to0.01 (13). The introduction of these groups inhihits the associat ionof the amylose or linear fraction of starch (1). Consequently, pastesof hypochlorite oxidized starch have much less tendency to gel thando pastes of the parent starch. The oxidized starches gelatinizeand disperse more readily than unmodified starch to give smooth andrelatively stable pastes 'vhich yield tough adherent films on drying.These properties r n a l ~ e the oxidized starches especially useful as surfacesizes and coating adhesives for paper.The comparative viscosity ranges fo r different types ofunmodified starches and partially depolyrnerized s tarches are shO\-.'11in Figure 1 in terms of parts of ''later required to give about thesame hot viscosity for the different starch products (10). Forexample, th e chart shO\vs that 40 fluidity acid-modified starch willrequire about 8.3 parts of ''later to give th e same v i s c o s i ~ ' as75 fluidity acid-MOdified starch in 4 parts of ' 'later.

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24 Potato

22 Amioca

20C l.... TapiocaRawStarchesSagoCorn

~ ~ 14:z:: Wheat

20FluidityStarches 40OxidizedStarches

60 BritishGums

0'---- - - - - - - - - - - - - - - - .....

WhiteDextrins9075

Yellow IDextrinsEach vertical line represents overall range ofavailable converted products

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Fig. 1. Comparative viscosity ranges of different types of starches.Source: Reference 19. Reproduced by pemission of the Corn RefinersAssociation, Inc., fomer1y the Corn Industries Research Foundation.

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Cationic StarchesThe two most widely used types of cationic sta rc hes a re thetertiary aminoalkyl ethers and quaternary ammonium a l l ~ l ethers ofstarch. The fonner ar e prepared by reacting starch in an aqueousalkaline slurry ,'lith either dialkylaminoalkyl chlorides or 2,3epoxypropyl (glycidyl) tert iary amines (14). The quaternary ammonium

derivatives are prepared in similar manner except tilat quaternaryammonium salts of eieler aminoalkyl chlorides or glycidyl amines areused (8). tlost of th e comnercial grades of cat ionic starches haveD.S. in th e range of ahout 0 .02 to 0.05. TIley readily disperse inho t water to give smootil, relatively stable pastes. They are espec ia llyuseful in papennaking application because their positive charge makesthem substantive to the negatively charged pulp fibers. TIley arealso useful as flocculants fo r various types of solids suspended inaqueous systems. In addition to the cationic starches derived fromunmodified s ta rch , thin-boil ing grades derived from acid-modifiedstarches a re al so available commercially.Hydroxyethylated Starches

Hydroxyethylstarch is produced by th e base catalyzed reactionbetlveen starch and ethylene oxide. The D.S. in commercial grades isusually betlveen 0.05 and 0.1 (16). Hydroxyethyls tarch readily disperseson cooking in Hater to give pastes ,'lith good clarity and stabili tytmvard gelling on cooling. Thin-boil ing hydroxyethylstarches derivedfrom acid-modified starches are especially useful as sizing agentsand coating adhesives fo r paper.Pregelatinized Starch

Pregelatinized starch is prepared by drying a concentratedaqueous slurry of starch at high temperature. The most corrnnonlyused equipment for this purpose is th e drum dryer or "hot-roll" (15).During heating the starch granules swell and d is rupt t o give, ,mendry, a product timt is cold-,,rater soluble. Sodium hydroxide is oftenadded to the aqueous slurry to facil i tate gelatinization. Pregelatinizedstarch is made mostly from unmodified starch bu t limited quant it ie s o fmodified starches are also available in pregelatinized fonn. Exceptfo r their cold-water so lub il ity , s l igh tly Imver viscosity, and lesstendency to ge l, propert ies of the pregelatinized s ta rches a resimilar to those of t he paren t starch (15). They ",ere developed fo rusers who do no t Jlave facil i t ies fo r cooking starch.

Applications in Paper and PaperboardStarch and starch products ar e used in making paper andpaperboard as 'vet-end additives, surface sizing agents, and coatingadhesives. These terms are bes t explained by th e brief descriptionof papermaking ,,,,hich follmls.

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FOURDRIHIERWIRE

Paper is made from cellulose fibers obtained mainly fromwood. Basically, papemaking consi st s o f removing th e ,vater from adilute aqueous suspension of fibers th rough a screen to fom a wetfibrous mat which is dried. Paperboard is made in th e same mannerexcept that a more concentrated suspension of fi be rs is used1 Inactual practice, bvo basic types of machine, th e Fourdrinier andcylinder machine, are used in making paper. Essen ti al features o fth e Fourdrinier machine along 1vi th a stock supply system, a sizepress, and a coater are shm,rn in Figure 2. Not a l l machines havea size press and cooter, but machines with a size press are morecOlJillon than those 1'lith a coater. Basic features of the cyl indermachine are the same except fo r the wire section. In this machinea series of vats containing a pulp suspension is used. A 1vire-coveredcylinder partly submerged in each vat picks up a mat of fibers as i trotates. The Net mat is pulled off the top of each cylinder as acontinuous sheet. These wet sheets are brought together to fom asingle sheet made up of as many plies as t he re a re cylinders.Before paper with satisfactoDT strength properties can bemade from pulp, i t must be beaten in either bea te rs o r r ef in er s t obring about fibrillation and hydration. Both of these types ofmachines subject the pulp to vigorous rubbing bebveen b lO hard sur-faces. Beating or refining is generally done at 3 to 5% consistency,

2.rhe mention of firm names or trade products does no t imply that theyare endorsed or recommended by the Department of Agricultureover other firms o r s imil ar products not mentioned.

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Fig. 2. Fourdrinier paper machine ,dth size press, coater, andstock supply system.

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consistency being th e Height percent dry pulp in th e aqueous suspension. Before the pulp is delivered to th e head box and onto th e,,rire (Figure 2), ,vater is added to reduce th e consistency. Dependingon the type of paper or paperboard being made and th e speed of themachine, consistency a t wire ranges from around 0.3 to 0.6%.Generally, but not always, one or more so-called wet-endadditives ar e incorporated in pulp suspension before paper is

made from i t . Wet-end additives include adhesives or bonding agentsto help bind th e fihers firmly together in th e s he et , r os in , allm,f ille r s such as 'cl li te clay, deflocculating agents, wet-strength resins,and dyes. Starch and modified starches ar e th e principal bondingagents used. O ~ l e r bonding agents include cellulose derivatives andnatural gtm1S such as guar gun. Addition of a bonding ap-ent suhstantia lly reduces th e amount of beating and associated pOl-ler needed togive a pulp ~ l a t will make a strong sheet of paper (20). The suspensionof beaten pulp after dilution and addition of any required additivesis r ef er re d t o as t he f ur ni sh . I t is introduced throur,h th e headhoxonto th e moving wire where a continuous wet Heb is famed as,vater drains off under th e influence of gravity and suction. Afterfurther removal of water on th e Het press section, t he s he et is driedby passage over stearn-heated rolls. I f a surface size is to be applied,t he s he et coming off the f i r s t drier section is passed through thesize press Hhere i t is reHetted, generally with a p as te o f modifiedstarch, and then redried. Depending on type of paper being made, aclay o r s im il ar coating rnay be appl ied as discussed under the sectionon coating. The coated sheet is again dried, then pressed and polishedby passage through a series of highly polished s te el r ol ls called acalender s ta c k " h ic h imparts smoothness or gloss to th e paper. Thecalender stack may also be used to apply surface sizes and coatings topaper and paperboard. After leaving th e calender stack, th e paperis Hound into large rolls on th e reel.

Use of Starch Products in PanermakingThe consumption of starch products as wet-end additives, surface sizes, and coating adhesives is given in Table I I. The 1972figures were ohtained by e xt ra po la ti ng t he d at a reported (3) fo r 1968.

fo r extrapolation, an average annual grOl'rth rate of 4.6% was assumed.This assumption seems reasonable because th e production of paper andpaperboard is reported (21) to have increased at an average annualrate of 4. 6g.; since 1968. In 1964 th e figure fo r a ll types o f s ta rc he sused as wet-end additives was 186 million pounds (3) Hhich at ~ l a ttime would correspond to about 156 million pounds of corn starchproducts. In via-, of th e estimated use of 150 million pounds ofcorn starches a t th e wet end in 1964 and th e rise in paper production

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TABLE 11. SALES OF STARO! PRODUcrS FOR VJ\.I{IOUSPURPOSES IN Tll I PAPEi' nmUSTRY

UseWet-end additionSurface sizeCoating ailllesiveTotal

Hillions of Potmdsof All Starch Products- - - - - - - - - ; : 1 )1968a 107296 115650 780376 4401,122 1,335

aSource : Reference 3.bObtained from tile 1968 figures by applying anannual g r r n ~ t h rate of 4.6%.

between 1964 and 1968, the figures in Table II fo r ,'ret-end additivesappear to be much too l r n ~ . I t is doubtful that th e trend tOHardsize-press applicat ion of starches in place of 'vet-end addition toupgrade s tr ength propert ies of paper '\'3.s in ful l enough force between1964 and 1968 to explain tile indicated decline in starch usage atth e ' ve t end. TIle trend trn-,'3.rd size-press application was prormted byth e need to reduce starch losses anel minimize pollution.

Consumption data fo r various types of unmodified and modifiedstarches in papennaking ,-rere reported fo r 1964 (3), but such data fo rlater years do not appear to have been publi shed . Ext rapola tion ofthe 1964 data to ob ta in an estimate of current consumption of cornstarch products is not possihle because corn starch and other starches,including potato and tapioca starches, are a ll lumped toget.1-ter in the1964 figures. Extrapolation is furtiler complicated by th e gainsthat some modified starches have made at th e expense of others duringthe 1964 to 1972 interval. Ilrnl'ever, the principal corn starch productsused in papennaking will be brought out in subsequent discussions.Wet-End Addition

The primary function of starch-based wet-end additives isthat of increas ing the dry strength of paper. Wi th th e exceptionof oxidized starches, use of starch products, particularly cationicstarches, also facil i tates tile incorporation of inorganic f i l lers sucrlas 'vhite clay and diminishes strength losses associated 'd th thepresence of fillers in paper. Unmodified starch and cationic starchesare the principal s tarch products used at th e wet end. Other starchbased wet-end additives include hydroxyethylstarch, starch lightlyoxidized'dth sodium hypochlorite, and dialdehyde starch. Thedialdehyde starch is used to impart wet strength to paper and ' d l lbe discussed later. Except fo r special appl ications , s tarch productsare thoroughly cooked in ,mter, unless they have been pregelatinized,before addition to the aqueous pulp slurries used to make paper.

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The point of addition of starch products at 'vet end denendson t he nature of the product, th e type of paper being made, and thespeed and other operating charac ter ist ics of th e paper machine. Thispoint my be at th e headbox, fan pump, stock chest, beater, or anyother convenient point in th e stock delivery sys tem. The amountadded depends on t he nature of the starch product and the type ofpaper being made. For unmodified starch, th e add it ion level isusually in th e range of 2 to 39" weight percent starch on a dry pulpbasis. The addition level for cationic starches is usually arOlmd0.5% . T!uch lower le vels o f cat ionic s ta rch than t.Ilmodified starchar e needed because th e fomer is much more completely retained thanthe lat ter by th e pulp fibers. In some mills that make heavy gradesof paper and paperboard, unmodified starch or lightly oxidized starchin granule form is added to th e pulp slurry. The starch is retainedby physical entrapment in th e Het paper mat famed on th e ""ire ofth e paper maclline and is gelatinized dur ing drying of th e paper.The lightly oxidized starches gelatinize more readily and ar e moreeffective ~ l a n unmodified starcll in ~ l i s application.Some m ill s a re adding cationic s y n ~ l e t i c p o l ) ~ e r s andunmodified starch at th e same or different points in th e wet-endsystem in place o f cat ioni c s ta rch (22). The cationic polymerfacil i tates th e retention of th e starch as well as fi l lers, i f

present. The extent of this practice is no t l ~ m \ T I bu t competitionfo r i t appears to be in th e making in th e fo m of cationic graftpolymers of starch (23).Although over 40 million pounds pe r year of s y n ~ l e t i c resinsare used as wet-end additives to impart wet strength to paper (3),only one starch product, dialdehyde starch (DAS) , is uo;ed fo r thispurpose. DAS is used mainly in tissue grades of paper, and i tsusage has never exceeded 750,000 pounds per yea r. DAS no t onlyimparts high temporary wet strength to paper, but also improves drystrength properties markedly (24). Paper treated with D.L\S is veryeasy to repulp for recycling in con tr as t to paper treated 'vith' .... e t - s t r e n g ~ l resins. The hir.,h cost of IlAS, engendered largely bysmall scale production (under I million pounds per yea r) , has beenth e l imit ing fac to r in i ts use. The trend tmmrd recycling more and

more paper has revived i nt er es t i n th e use of D.AS because of th eease ,d. th which paper treated ,lith i t can be repu lped . Repulpingof res in- treated paper is difficult and costly, and segregatingsuch paper from o ~ l e r ''i'astepaper is expensive. Therefore, i t isbelieved that th e market fo r DAS could increase markedly i f i t ,vereproduced on a large enough scale to reduce i t s cost sti listantially.Oxidatively crosslinked starch x a n ~ l a t e s (25), starch xanthatecrosslinked with polyethylenimine (26), or 'vith a polyamide-polyamine-

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epichlorohydrin resin (27) all iYJpart high wet strength and drys tr ength to paper. So too does hY!'ochlorite-treated carhamoylethylstarch (28). None of these developr.lents have been industrialized,but the more recent ones (27 ,28) are b e i n ~ actively investigated byindustry .Surface Sizi]1"'&

The end use requirer.lents fo r paper and paperboard dictate' ~ l e t h e r or no t a surface size is applied. Surface sizing is done toimprove the ,vr it ing and printing characteris tics , particularly i n 1 ~holdout, erasability, and strength properties of the sheet. Theprincipal starch products used in surface s iz ing a re e n ~ c m e - c o n v e r t e dstarch, jet-cooked starch, oxidized starch, and hydroA')rethylatedstarches.Acid-r.lodified s L ~ r c h is also used to size special grades ofpaper and paperboard and is usually applied at th e calender stackins tead o f at th e size press. For exar.lples, Kraft paperboard ITlay besized "ith 60-fluidity acid-modified stardl to improve i ts printability,and tmbleached linerboard is often s ized ",ri th 20 to 40 fluidity gradesof the starch to increase scuff resistance (11). In th e lat ter annlication, t he r ap id congealing properties of acic1-r.lodified starch are

desirable because most of the size is retained on the sur face of thesheet , ~ e r e i t is effective as a scuff-resistant film.Several viscosity grades of starches ar e needed to meet therange of surface sizing requireJTIents. In surface sizing, a starchpaste is applied to the sheet, th e excess paste is squeezed ou t byth e size press rolls (Fig. 2), then th e sheet is dried. The sizepress roles may be i n ve rt ic al configuration (one on top of t he o ther )instead of side by side as shmID in Fir ,ure 2. Paste concentrationsvary depending on th e type o f s ta rch product used, th e desired pickupof size by th e sheet, and the type of paper being sized. Usuallypaste concentration falls within the range of 2 to 12% solids (2).In tub sizing, a comparatively slm, process conducted off tile parermachine, solids content may run up to 20%. The pic1.'Up of size by th epaper (weight percent starch in the sheet on a dry basis) varies from

about 1 to 4% depending on the type of paper and i ts intended end use(29) Oxidized starch because of tile anionic character impartedto i t by i ts carboxyl groups acts as a dispersant fo r clay and othermineral f i l lers. Oxidized starch COrles off th e broke (trimr.lings andother wastepaper) tilat is returned to the stock system and adverselyaffects retention of clay and other minerals used in making fi l ledpaper. For this reason, oxidized stardl has been losing favor fo r the

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past several years as a surface-sizing agent and is being replaced byenzyme-converted starch, jet-cooked starch, and some of the morerecently developed derivatives including cationic starcJles (30), starchacetates (31), and cyanoethylated starches (32).Paper Coating

Paper is coated with pigments such as white clays, calciumcarbonate, and titanium dioxide to improve its printability appearance, and brightness and to increase its oracity . The same reasonsfor coating paperboard apply except for improvement in opacity ,Jh.ichis adequate in uncoated boards. In order to apply pigment coatinps topaper an aqueous dispersion containing tile pigment, a dispersinr agentfor the pigment, and an adhesive must be prepared. The pigment-adl-J.esivemix is referred to as a coating color and often contains minor amountsof additives to stabilize the coating color and improve its flow characteristics. These additives include soap which acts as a lubricantand reduces dusting of the d ried coating. Detailed procedures forpreparing coating colors have been published (33). Solids content ofcoating colors, including pigment and binder, range from about 30 to 70%depending on the Height of coating that is to be applied. Starch-basedadhesives are generally used at a level corresponding to about18 Height percent dry starch substance on a dry pigment basis. Enzyme-converted starch, oxidized starch, and dextrins as Hell as hydroxyethylated starches and starch acetates are used as coating adhesives (1).To improve 'vater res is tance of coatings made ,vith starchadhesives, materials such as a latex or urea-formaldehyde resin areused in conjunction with starch (33). !lm.,rever, coatings rnde inthis Hay do not meet all requirements fo r ",'ater resistance and flexibility. Polyvinyl acetate latex, styrene-butadiene latex, and acryliclatex as well as proteins alone or in combination Hith crosslinkingagents are used to meet requirer.1ents ,\nich cannot be met with starchadhesives (3,34).A variety of coaters, including blade, air knife, roll, andbrush coaters, have been developed fo r applying tile coating colorto paper (34). With the blade coater depicted in Figure 2, thecoating color is fed into the V-shaped trough famed betlveen thecoater blade and tile backing roll. Pressure betl1een the blade androll is adjusted t o regulate the amount of coating applied to thepaper as i t passes through the trough of coating color and eMergesbetlveen the blade and roll. To coat both sides of the paper, anothercoater and dryer section like that denicted in Figure 2 is provided.For paperboard, one section generally suffices because most paperboard is coated on one side only.

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In high-speed coating on blade and roll coaters, th e coatingcolor is subjected to very h igh s hear . Therefo re , th e rheologicalbehavior of the coating color is a very important consideration. Thissubject has been reviewed in depth (34); therefore, i t is cOlTnenteJon only briefly here. The coating color should no t thicken up underthe inf luence of high shear. On the other hand, i t should no t thinout too much and allow th e adhesive to strike too deeplY into thesheet leaving the surface coating deficient in adhesive'.

Use of Starch in AdhesivesThe major use fo r stardl-based a&lesives is in so-calledconverting processes applied to paper and paperboarJ. TIlese processesinclude fabrication of corrugated boxboard, paper bags, folding cartons,laminated paperboard, and spiral-1'10und tubes as "lell as off-rochinepigment coating of paper and making of gt.rnU'led labels and tapes. Offmaclline coating refers to coating paper after i t is made in distinctiont o coa ting th e paper as i t is being made on th e paper machine. In1968, 350 million pounds of starch products were used as corrugatingand laminating ailllesives (3 ). App lic ation of tile preViously mentioned4.6% annual grrnolth rate (Table II) to the 350 mill ion f igure brings it

up to 420 mil lion for 1972. The e s t ~ ~ t e d consumption of starch productsin other converting operations in 1969 1v'aS sao million pounds (3).JIrn'lever, this figure is fo r corn starch and a l l other s tarches. Ad jus t ment of t he figu re to a corn starch base brings i t dmffi to around450 million pounds. This figure increases to 513 million fo r 1972i f th e 4.6% annual grrn'lth rate is applied.

Starch products used in ailllesives include unmodified starch,dextrins, hydroxyethylated starches, oxidized starch, waxy maize starch,acid-modified starch, and starch acetates (6,12,13,16,31). Data onth e annual conslunption of individual starch products in adhesivesare not available nor is information on the amount o f s ta rch productsused in anyone adhesive application available.Starch-based adhesives ar e supplied either as dry prn:ders or

ready-to-use liquids depending on th e stabili ty of th e fomulations.Prnoldered adhesives are available i n e ith er co1d-1'later-soluble or hotwater-soluble forms. In addition to starch products, adhesives oftencontain alkali, borax, plasticizers, defoamers, and preservatives(6). Nany different adhesive fonnulations ranging froJT1 fairly sirrrpleto complex have been developed to meet requirements fo r making a ~ ~ d evariety of products. I t is not th e purpose of this revielv to coverall of these many and varied aspects of adhesives, but rather to discussa fel'l selected applications i l lustrative of ti le us e of different typesof starch-based adhesives.

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Corrugated BoardRegular corrugated board consists of one corrugated orfluted mediun and bolO lin ers o r facings. IIOIvever, only one l ineror facer is used sometimes (35). Starch is th e most Hidely usedadhesive employed in g lu ing the linerboard to th e fluted mediun.The adhesive consists of a cooked paste of a so-called carrier

starch, usually unmodified starch, containing sodiun hydroxide andborax in 1ihich is suspended unmodified starch in granule fom. Theconcentration of th e carrier starch in the mix is about 3 1veightpercent and that of th e starch in granule fom about 18%. The pasteof carrier starch serves to keep the starch granules from settl ing.The sodiun hydroxide and borax ar e used to Imler th e gelatinizationtemperature of the granular starcJ1 and to increase tack and a d ~ e s i v estrength. This adhesive is no t stable enough to be sold in liquidfonn. It must be made from th e solid ingredients a t th e plant 1'merei t is being used. In making corrugated board, the adhesive is meteredonto th e peaks or ridges of the fluted mediun, then th e linerboardis applied, follOlved by application of heat and moderate pressure.The s tarch gelat in izes immediately and firmly bonds th e assemhlytogether before i t passes off the corrugating machine to th e storagearea. I f a double-faced board is to be made, th e second l iner isapplied in the same manner.Paper Bags

The type of adhesives used in rna}(ing paper bags variesaccording to th e type of seal and th e kind of bag heing made. Thisis best illustrated by the different starch-based adhesives used inmaking grocery bags and mul tiHall paper sacks.The side-seam adhesive for grocery bags may be made from oxidizedstarch, acid-modified starch, or a dextrin to 1\nich borax, soda ash,and metaqilicate ar e added (36). SoliQq content in ti1e a ~ l e s i v e rangesfrom 20 to 30%. The bottom pastes may be derived from a mixture ofstarch and dex tr in , o r from acid-modified s ta rc h, o r from oxidizedsta rc h to 1\nich caus tic, c lay, soap, tal lOlv, and oti1er minor ingre-dients are added. Solids content in bottom pastes ranges from 15 to

25% depending on the type of starch product and other additives used (36).In tile fabrication of mul tiwall paper sacl's, th e plies ofpaper ar e f i rs t glued togetiler by th e cross-pasting unit 1\nich appliesan intermittent line of glue to each ply. The adhesive used shouldbe tacky and quick setting. ~ l o d i f i e d starches and dextrins to 1..1licha mineral fil ler is often added ar e used as cross-pasting adhesives.Solids in this type of adhesive range from 25 to 33% (6). For sideseam gluing, th e glue may be SlOl'l drying but must have fast ini t ialtack and is usually made from acid-modified starch or 1..11ite dextrins

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(6). Acid-modified starches are used extensively in th e preparationof adhesives for s ea li ng the bottom of rnul tiwall bags. With modernroll-type applicators, solids content of th e adhesive is about 20% (6).Resins such as u r e a - f o r m a l d ~ l y d e a re o fte n added to bottom adhesivesas well as s ide-seam adhesives to provide water resistance (36).GtllTlllID1ed Paper

Envelope seals are probably th e most farnilar example ofgummed paper. Envelope seals are made fron aqueous pastes of highlysoluble dextrins. Solids concentrat ion in these pastes ranges from55 to 65% (36). A nonhumectant type of plasticizer is an importantingredient in th e pastes; i t prevents curl and keeps the adhesivefilm from crazing. If a humectant type of plasticizer were used, theseals would stick together in humid \veather when the envelopes werepackaged.Back seams for envelopes require a different type of adhesive.This adhesive should be slO\ver drying than th e seal adhesive withsome \vet-tack and no color shO\v-through. For this purpose highlysoluble types of \vhite dex tr in s a re u sual ly used along \vith a plasticizer such as urea (36).

Other ApplicationsIn add it ion to the uses just discussed, starch-based adhesivesare used in making spiral-1\Tound tubes, laminated paperboard, andcardboard boxes. They are also employed in gluing paper coveringsto cartons and as packaging seals. Nonpaper-related uses includebonding agents for foundry cores, insulating boards, and accoustical

t i le. In the last t'tvo items together, 155 nillion pounds of starchproducts ",rere used in 1972 according to starch suppliers .Textile Applications

The principal use for starch products in th e textile industryis as a \.;arp size to strengthen \.;arp yarns and improve their resistanceto abrasion during weaving. Starch products ar e a ls o employed inthe finishing of fabrics, in printing, and as components in finishesfor glazing sffiving th read (5) . The las t ttvo appl ications are of aminor nature and will no t be discussed here. The use of s ta rch inprinting pastes was a significant application \vhen large amounts ofwater-dispersible dyes \vere employed, bu t starch \.;as largely replacedby resins \vhen insoluble pigments were introduced as printing agents(1)

The princ ipal s tarch products sold to th e textile industryare listed in Table III. Unmodified starch is used in finishing

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278

~ a t a \1ere obtained from starch suppliers.

TABLE III . SALES OF PRINCIPAL STI\ROIPRODUCTS TO THE TEXTILE nmUSTRY

8317022275

Hillions of POlmdsin 1972a

Unmodified starchAcid-modifiedHigh-amyloseTotal

Starch Product

According to information received from s tarch suppl iers, theamotmt of starch used by th e textile industry has been declining atan annual rate of 5 to 6% for th e past few years. This decline isprobably largely a ref lec tion of further gains by carboxymethylcellulose and polyvinyl alcohol \ihidl were adopted as warp sizingagents several years ago. These polymers have lower 5-day biologicaloxygen demand (BOD) than starch and, therefore, \ \ ~ l e n discharged intostreams or r iv er s do no t d eplete the oxygen in th e water as rapidlyas does starch (1). The replacement of traditional starch productswith new starch derivatives such as the sulfo-succinic acid half esterof stardl (37), \'lhich do no t need to be applied a t as high a level astraditional starch products, also contributes to the decline in th emarket for starch in textile applications. Unforttmately, data onth e volume of th e more effec tive s ta rch products used are no t available.WaI)? Sizing

Warp yarns are sized to enable them to withstand abrasionassociated with th e weaving process. The \\'8.rp yarns are th e yarnsbeb'leen \vhich the shuttle carrying the wef t threads passes duringth e weaving operation. Tlle process of sizing is often called

opera tions, but i t is not a satisfactory vmrp size and is modifiedat the mill to reduce i ts viscosity. The processes commonly used fo rthis purpose are: conversion \-:ith enzyme, steam-jet cooking, andtile subjection of cooked pastes to h i ~ l shear in a specially designedhomogenizer (5). Other starch products used by th e textile industryin addition to those listed in Table III include starch acetates,hydroxyethylated starches, oxidized starch, and dextrins (1,12,13,16,31 ). Informa tion on the amotmts of these starch products currentlyused could not be obtained.


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slashing. Yarns spun from staple fibers such as cot ton are slashedwith pastes \\'hich contain about 9% by weight of a starch product ofappropriate viscosity and about 0.5% of a softening agent (5). Inthe s lashing operation, the strands of yarn a re li ned up side byside and passed through th e size solution follO\'led by passage t..hroughsqueeze rolls to remove excess size. The \ ' let yarn is then dried onsteambheated rolls . With traditional starch-based sizing agent s, t heamount of siz e added to spun yarns is usually 10 to 15% on a dry weightbasis (5).

Materials used to size yarns composed of continuous filamentsnnJSt penetrate the yarn cornpletely (5); therefore, relatively 10\'1-viscosity starches are required. About 3 to 5% of size on a dryweight basis is added to filament yarns (5).After fabric is woven i t is desized by treatment \'lith aqueoussolutions of alkali or enzyme followed by washing with \'later.Ordinary starch products are not satisfactory for sizingsynthetic f ibers or glass fibers. For these applications, highamylose starches as well as synthetic polymers ar e used. The high

amylose starch products include th e unmodified starches with about60% and 70% apparent amylose content as \ 'l el l a s cationic and hydroxy-propyl derivatives of the starches. Information on the amounts ofeach of these starch products used is not available.Textile Finishing

Both unmodified and modified starches are employed in textilefinishing processes to increase th e stiffness of fab ri c, to changethe hand (feel) of the fabric, and to improve appearance by f i l l ingin the interstices of th e weave (5). To increase stiffness andimprove hand, the fabric in the last stages of finishing is passedthrough a dilute paste of starch product, then i t is run throughsqueeze rolls to remove excess paste followed by drying on steam-heated cylinders. In filling operations, a starch paste containingf i l ler such as talc or clay is often used. If permanent propertiessuch as crease res is tance are des ired , synthet ic polymers or mixturesof synthetic polymers and starch ar e employed (7).

~ l i s c e l l a n e o u s ApplicationsMiscellaneous applications f or s ta rc h products include theiruse as flocculating agents, ant icaking agents, mold-release agents,dusting powder, binders fo r pharmaceutical products (tablets andpil ls) , thickening agents, and as rID'! materials in th e productionof chemicals and explosives.

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Developmental ProductsIn addition to th e developmental starch products mentionedin the section on papermaking, a number of other products have beendeveloped which have considerable industrial potential . These areanionic and cationic graft polymers of starch (38 ,39) and starchbased reinforcing agents for rubber (40-42), as ,.,ell as agents ,oJhichenable prn.,dered rubber to be made readily and inexpensively from

latex, the forn in "rhich natural rubber and most synthetic rubbersare f i rs t obtained (43,44).Anionic graft polymers made by t he s apon if icat ion o f s ta rchpolyacrylonitrile graft polymers are exceptionally prn.,erful thickeningagents for aqueous and certain aqueous-organic systems (39). Cationicgraft polymers of s ta rch made by cografting acrylamide and variousaminoacrylates to s ta rch a re very effective flocculating agents forseveral types o f f in el y divided solids suspended in aqueous systems(39,45,46).Incorporation of crosslinked starch xanthate into rubberreinforces the rubber to about th e same degree as do medium gradecarbon blacks (40). The starch product is incorporated into therubber by adding starch xanthate of DS 0.06 to 0.10 to latex ,

follrn'led by addition of an oxidant and acid. The oxidant convertsthe xanthate to the insoluble xanthide (oxidatively crosslinkedxanthate) ''lhich coats th e rubber particles and coprecipitates ,'liththem under th e destabilizing influence of the added acid (40-42).In the early stages of this developmental ''lork, th e coprecipitateof starch xanthide and rubber was obtained as large curds loJhich ''lereconsolidated for subsequent processing and curing. Subsequently,i t ''laS discovered that these large crumbs could be granulated orprn'ldered in a hammer mill without chilling th e crumbs ,'lith liauidnitrogen as is necessary in grinding conventional rubber crumbs (43).In the latest development, prn.,dered rubber has been obtained directlyfrom starch xanthate-latex mixtures by adjusting th e rate of stirringand other variables during the cross linking and coprecipitationstages to give finely divided particles (44). In this process, tilewet particles were ''lashed with alcohol before drying. I t nrn! appearst il at t he alcohol \'lash can be eliminated.

The development of an economical process for making prn'lderedrubber has been a long-sought goal of the rubber industry becauseprn.,dered rubber like prn'ldered plastics can be injection Irolded orextruded ,'lithout prior high-shear milling to give good quality finished products. In add it ion to savings in processing costs, theavailabili ty of prn.,dered nll)ber would considerably reduce th e capitalinvestment needed fo r processing equipment (47).

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Literature Cited1. RUTENBERG, 1\'. n. Hodified starches. I n: Water-s olubl e resins,ed . by R. 1. Davidson and H. Sitt ig, Chap. 2, p. 21. Reinhold:New York (1962).2. NISSEN, E. K. Starch in th e paper industry. In: Starchchemistry and technology, ed. by R. 1. Whistler and E. F.

Paschall, Vol. II , Chap. p. 121. A c a d e ~ i c Press:New York (1967).3. SI'iAi"JSON, J . W. Chemical addit ives : ! lew dimens ions forpapermaking . Amer. Pap . Ind. 39 (Jlarch 1970).4. HJORE, C. A. An economic evaluation of starch use in the texti leindustry. Agr. Econ. Rept. 109, U.S. Dept. Agr., Washington,D.C. (1967).5. CO!'-IPTON, J . , and HARTIN, JiT. H. Starch in the textile indus tn ' .In : Starch chemistry and technology, ed. by R. 1. Whistler'andE. F. Paschall, Vol. II , Chap. \ ~ I , p. 147. AcademicPress: York (1967).6. DUX, E. F. IV. Production and us e of starch adhes i ves . In :Starch chemistry and tecJmology, ed . by R. 1. Whistler andE. F. Paschall, Vol. II , Chap. XXIII , p. 537. AcademicPress: New York (1967).7. JAROWENKO, W. Starch. Encyl. Polym. Sci. Technol. 12: 787(1970).8. WHISTLER, R. 1. Industrial uses of corn starches. In : Corn:Culture, processing, products, ed . by G. E. Inglett , Chap. 10,p. 171. Avi Publishing Co., Inc.: Westport, Connecticut (1970).9. EWING, F. G., and DeGRCXIT, H. S. Evaluatio n of continuousstarch conversion process at Oxford I s Rumford mill. Pap.Trade J . 150(12): 48 (1966).10. GUTIERREZ, W. D. Starch conversion solely by mechanical means.Pulp Pap. Hag. Can. T-581 (November 1967).11. SHILDNECK, P., and SHITI-!, C. E. Production and uses of acidmodified starch. In : Starch chemistry and technology, ed. byR. 1. Whistler and E. F. Paschall, Vol. I I , Chap. IX, p. 217.Academic Press: N ~ o [ York (1967).12. EVANS, R. B. , and WlJRZBURG, O. B. Production and use of starch

dextrins. In : Starch chemistry and technology, ed . by R. 1.1\'histler and E. F. Paschall, Vol. I I , Chap. XI, p. 253. AcademicPress: York (1967).13. SCALLET, B. 1 . , and SOWELL, E. A. Production and us e ofhypochlorite-oxidized starches. In: Starch chemistry andtechnology, ed . by R. L. i\'hist1er and E. F. Paschall, Vol. II ,Chap. X, p. 237. Academic Press: N ~ o [ York (1967).14. PASGfALL, E. F. Production and uses of ca tionic s ta rches. In :Starch chemistry and technology, ed. by R. L. Whistler and E. F.

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Paschall, Vol. II , Chap. XVI, p. 403. Academic Press:New York (1967).15. POWELL, E. L. Production and uses of pregelatinized starch.In: Starch chemistry and technology, ed. by R. 1. Whistlerand E. F. Paschall, Vol. I I , Chap. XXII, p. 523. AcademicPress: New York (1967).16. HJEHMSTAD, E. T. Production and uses of hydroxyethylstarch. In :Starch chemistry and technology, ed. by R. 1. Whistler and E. F.Paschall, Vol. II, Chap. XVII, p. 423. Academic Press:NeI'l York (1967).17. KERR, R. W. Chemistry and industry of starch, 2nd ed., p. 133.Academic Press, Inc.: New York (1950).18. KERR, R. W. Chemistry and industry o f s ta rch, 2nd ed., p. 682.Academic Press, Inc.: Nmv York (1950).19. TIlE CDRN INDUSTRIES RESEARCH FOLlNDATION, INC. Corn starch,3rd ed., p. 21. Corn Industries Research Foundation, Inc:Washington, D.C. (1964).20. SWANSON, J . W. The e ffe ct s o f nat ura l b eat er addit ives onpapermaking fibers. Tappi 33(9): 451 (1950).21. ICIEK, S. E. How to meet th e excess demand. Amer. Pap. Ind.4: 42 (1973).22. ANO:ffi';OUS. Industry finds new use fo r resins. Chem 26 PaperProcessing 5(1): 28 (1969).

23. HEATH, H. D., HOFREITER, B. T., ERNST, A. J . , DOANE, W. M.,HAMERSTRAND, G. E., and SCHULTE, N. I . Cationic and nonionicstarch graft polymers for f i l ler retention. Pulp Pap. Mag.Can., in press.24. HOFREITER, B. T. Dialdehyde starches. In : Wet strength inpaper and paperboard. TAPPI Monograph Series No. 29, ed. byJohn P. Weidner, Chap. 5, p. 50. !lfack Printing Co.: Easton,Pa. (1965).25. HAMERSTRAND, G. E., CARR, M. E., HOFREITER, B. 1 ., and RIST, C. E.Starch xanthides in linerboard: A continuous wet- end process.Tappi 50(8): 98A (1967).26. MAl-JER, G. G., RUSSELL, C. R. , and RIST, C. 13. Crosslinking ofstarch xanthate. 1. Reaction with polyethylenimine. Staerke19(11): 354 (1967).27. CARR, M. E., DOANE, W. M., HAMERSTRAND, G. E., and HOFREITER, B. T.Interpolymer from starch xanthate and polyamide-polyamineepichlorohydrin re sin: Structure and papermaking applications.J . Appl. Polym. Sci. 17: 721 (1973).28. SMITH, H. E., GORDON, S. H. , RUSSELL, C. R. , and RIST, C. E.Wet- and dry-strength agent for paper derived fromcarbamoylethyl starch. Tappi 53(9): 1074 (1970).29. CASEY, J . P. Surface sizing. In : Paper chemistry andtechnology, 2nd ed , Vol. I I , Chap. XIV, p. 1104. IntersciencePublishers, Inc.: New York (1960).

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30. T U T h ~ R , C. W. Cationic starch a t tile mil l o ff er s ecology,marketing advantages. Paperboard P a c l ~ g . 57(7): 24 (1972).31. KP.ua::R, 1. II., and RUTENBERG, W. Production and uses ofstarch aceta tes . In: Starch chemistry and technology, eel.by R. 1. hnistler and E. F. Paschall, Vol. I I , 01ap. XV,p. 369 . Academic Press: New York (1967).32 . POWEPS, R. rT. Surface-sizing of paper ''Iith cyanoethyl acidhydrolyzed starch. U.S. Pat. 3,387,998, June 11 , 1908.33. TEO-lNICAL ASSOCIATION OF TI IE PULP ANn PAPf:R INDUSTRY. Starchand starch products in paper coating. Tappi }!onograph SeriesNo. 17. The l\ssociation, Ne'l'l York (1957).34. CASEY, J . P. Pigment coating. In : Pulp and paper chemistryand technology, 2nd ed., \ ~ l . I I I , Chap. XIX, p. 1551.Interscience Publishers, Inc.: Nel! York (1961).35. CASEY, J . P. Laminating and co rru gatin g. In: Pulp and paperchemistry and technology, 2nd ed. , Vol. III , Chap. XXI,p. 1860. Interscience Publishers, Inc. : Nell' York (1961).36. CAESAR, G. V. Starch and i ts derivatives. In : Handbook ofadhesives, ed . by Irving Skeist, Chap. 12 , p. 170. Reirul0ld:New York (1962).37. CALDWELL, C. G. A reviel'! of industrial starch research. AlsbergSchoch memorial award lecture. Cereal Sci. Today 18(1): 4(1973) .38. FAJ'ITA, G. F. S y n t . ~ e s i s of graft and block copolymers of starch.In : Block and graft copolymerizat ion, ed. by R. J . Ceresa,Vol. 1, Chap. 1, p. 1. John Wiley & Sons: New York (1973).39. FANTA, G. F. Properties and applications o f g ra ft and blockcopolymers o f s ta rch. In : Block and graft copolymerization,ed . by R. J . Ceresa, Vol. 1, Chap. 2, p. 29. John l1iley &Sons: Nel'l York (1973).40 . STEPl-IENS, H. 1 ., HJPYHY, R. J . , and REED, T. F. The u.s e ofstarch as a reinforcing f i l ler fo r rubber. Rubber World 101 (2) :77 (November 1969).41. STEPI-IENS, H. 1 . , ROBERTS, R. 1'1., REED, T. F., and HtJRPIIY, R. J .Starch-elastomer masterbatches prenaration, properties andprocess design. Ind. Eng. Chem. Prod. Res . Develop . 10(1):84 (1971).

42. BUrnANAN, R. A., 1.1'iOLEK, W. F., Kt\TZ, II . C., and RUSSELL, C. R.Starch in rubber. Influence o f s ta rc h type and concomitantvariables in reinforcement of styrene-butadiene rubbers.Staerke 23(10): 350 (October 1971).43. BUGL


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45. FANTA, G. F., BURR, R. C., roANE, W. H., and RUSSELL, C. R.Graft copolymers o f s ta rch with mixtures of acrylamide andth e nitric acid sal t of dimethylamino methacrylate. J .Appl. Polym. Sci. 16: 2835 (1972).46. JONES, D. A. , and EU'QlJIST, 1. F. Starch graft polymers.III . Preparation of graft polymers containing acrylamide,acrylic acid and -methacryloyloxyethyl trimethylammoniumsulfate and evaluation as flocculants fo r b a l ~ i t e ore redmud suspens ions . S taerke 23(3): 83 (1973).47. GOSHEN, T. A., JORGENSEN, A. H. , and WOODS, }!. r;. PO\

Industrial Uses of Starch

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