Starch cross-linked

Cross-linked starches are obtained by the reaction of starch (R—OH) with bi- or polyfunctional reagents, such as sodium trimetaphosphate, phosphorus oxychloride, epichlorohydrin or mixed anhydrides of acetic and dicarboxylic acids (e. g., adipic acid)  

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Cross-linked starches Cross-linkers Cross-linking... 

Starch derivatives are also used to encapsulate pesticides (qv) in a cross-linked starch—xanthate to improve safety in handling and reduce water leaching losses (51,52). Littie or no pesticide is lost during drying. The encapsulated formulations have excellent shelf life when dry, but when placed in water or soil the pesticide is readily released. 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

Cross-link density, 10 415-416, 417-418 direct measurement of, 10 426 427 Cross-linked copolymers, 7 6 lOt Cross-linked high amylose starch, 13 742 Cross-linked hydrogels, 13 729-730 Cross-linked polymers, internal stresses and, 10 423 424 Cross-linked starches, 4 721 Cross-linked thermoset polymer structure, 10 418... 

Das K, Ray D et al (2010) Preparation and characterization of cross-linked starch/poly(vinyl alcohol) green films with low moisture absorption. Ind Eng Chem Res 49 2176-2185... 

Hung, P. V, Morita, N. (2005). Physicochemical properties of hydroxypropylated and cross-linked starches from A-type and B-type wheat starch granules-Review. Carbohydr. Polym., 59,239-246. 

Koch, V. H., Bommer, H. D., Koppers, J. (1982). Analytical investigations on phosphate cross-linked starches. Starch, 34, 16-21. 

Wurzburg, O. B. (1986b). Cross-linked starches. In O. B. Wurzburg (Ed.), Modified Starches Properties and uses (pp. 41-53). CRC Press, Boca Raton, Florida. 

It should be mentioned that some dyes are not only sorbed on starch by physical interactions They can also cross-link starch. This can happen if a dye has suitable functional groups—for instance, Benzopurpurine, Congo Red, Chrysoidine—and if the pH permits dissociation of reaction sites in these dyes. It is understood that this cross-linking affects the UV absorption spectrum of the dye, and that the variety of starch has no effect on this spectrum.820... 

Specific interactions between starch and proteins were observed as early as the beginning of the twentieth century. Berczeller996 noted that the surface tension of aqueous soap solutions did not decrease with the addition of protein (egg albumin) alone, but it did decrease when starch and protein were added. This effect was observed to increase with time. Sorption of albumin on starch is inhibited by bi- and trivalent ions and at the isoelectric point. Below the isoelectric point, bonding between starch and albumin is ionic in character, whereas nonionic interactions are expected above the isoelectric point.997 The Terayama hypothesis998 predicts the formation of protein complexes with starch, provided that starch exhibits the properties of a polyelectrolyte. Apart from chemically modified anionic starches (such as starch sulfate, starch phosphate, and various cross-linked starch derivatives bearing ionized functions), potato starch is the only variety that behaves as a polyelectrolyte. Its random phosphate ester moieties permit proteins to form complexes with it. Takeuchi et a/.999-1002 demonstrated such a possibility with various proteins and a 4% gel of potato starch. 

There are also patents on compositions of starch with modified esterified, etherified, and cross-linked starch to produce sizes1061 and adhesives.1062-1064... 

The same modeling procedure was applied to 3.5% com SDs and the results used to numerically simulate heat transfer to SDs in a can (Yang, 1997). From recent studies (Yang and Rao, 1998 Liao et al., 1999), the general shape of viscosity versus temperature for native, as opposed to cross-linked, starch dispersions is as shown in Figure 4-20. It is important to note that the values of viscosity of the... 

Antithixotropic Behavior of Cross-Linked Starch Dispersions... 

Tarrega, A., Costell, E., and Rao M. A. 2006. Vane yield stress of native and cross-linked starch dispersions in skim milk effect of starch concentration and X-carrageenan addition. Food Sci. < Tech. Int. 12(3) 253-60. 

In general, other native starch dispersions will be exhibit similar viscosity versus temperature profiles as in Figure 8-7, while cross-linked starch dispersions, due to limited granule rupture, will not exhibit a sharp decrease in viscosity of the segment CD. The t] versus 7 profiles of a 5% CWM STD obtained at values of cu from 1.26 to 31.38rads , 3% strain, andaheatingrateof2.1°C min (Figure 8-8)followed the equation (Tattiyakul and Rao, 2000) ... 

Preparation of cationic starches, done with reagents such as 2-diethylaminoethyl chloride, 2,3-epoxypropyldiethylamine, or by cross-linking starch with epichlorohydrin in the presence of ammonia. The reaction with 2-diethylaminoethyl chloride is done at pH 11 to 12, followed by neutralization with acids. 

Table 7.4.4. Compounds identified in the pyrolysate of starch, cross-linked starch with epichiorohydrin, and in two cationic starches (SEA and SQEA). ...

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