| 摘要 |
In a process for making cross-linked starch acylates a cereal or a "root-type" starch is treated, in any order, with a cross-linking agent comprising at least one polyfunctional etherifying or esterifying agent in an amount from 0.01-10% by weight of dry starch and an acylating agent (1.0-40% by weight of starch) while maintaining the starch in granular form. If the starch is cereal starch, it is reacted with the cross-linking agent until the alkaline fluidity (as defined) is 50 c.c.-90 c.c., and it is acylated with a vinyl ester, or an anhydride of an aliphatic monocarboxylic acid having 1-18 carbon atoms. If the starch is "root-type," the cross-linking reaction is continued until the alkaline fluidity is 30 c.c.-90 c.c., and it is acylated with a vinyl ester of the above monocarboxylic acid. The granular form of the starch is maintained throughout the process. The product has a CIV viscosity at pH 3.5 of at least 700 g.-cm. after 15 minutes, and at least 496 g.-cm. after 40 minutes. Cereal starches are e.g. corn, rice and wheat; root-type starches are e.g. potato, waxy maize, waxy sorghum, cassava. The polyfunctional cross-linking agent may be unsaturated aldehydes e.g. acrolein, crotonaldehyde; dihaloalkanes e.g. ethylene dichloride, 1,2-propylene dibromide, 2,6-hexylene dichloride; dialdehydes e.g. glyoxal, adipaldehyde; methylol compounds e.g. dimethylol urea; epihaloalkanes e.g. epichlorohydrin, 1,2-epoxy-4-chlorobutane, 1,2-epoxy-5-bromopropane, and polybasic acid halides e.g. phosphorus oxychloride and adipyl chloride. Specified acylating agents include vinyl acetate, vinyl hexoate, vinyl stearate, acetic anhydride and propionic anydride. When vinyl esters are used, acetaldehyde formed in situ during the alkaline acylation may be utilized as an additional cross-linking agent during cross-linking with the poly-functional agent. The process may be carried out by suspending granular starch in a polar solvent, e.g. water, alcohols or dioxan, adding an alkaline catalyst and cross-linking agent, and heating at e.g. 100 DEG F. at pH 9-13, until the required alkaline fluidity is attained. After termination of the cross-linking reaction by e.g. adjustment of pH or by addition of sodium bisulphite, the acylating agent is added and acylation carried out at e.g. pH 7.0-12.5 and 65-115 DEG F. Reaction is terminated by adjusting the pH to 6.0, and the cross-linked acylate is isolated by filtration or centrifugation. If acetaldehyde is utilized as an auxiliary cross-linking agent, the acylation is carried out first and the pH adjusted to below 4.0 before the addition of the polyfunctional cross-linking agent. |
