Grain starches, chemically or genetically modified grain starches, tuber starches, and some from other botanical sources were treated at room temperature in media containing a constant amount of water and sodiumhydroxide. Appearances and viscosities of the mixtures were noted during a 7‐day quiescent period. The point of complete gelatinization of the starch was deducible from the viscosity changes, as well as from visual observations. Although there were some noticeable differences between the starches, an NaOH to starch ratio of 3.5 to 3.8 meq/g should assure complete gelatinization within several hours or less. This alkali: starch ratio is compared to previous ratios expressed in the literature. A slight dependency of the ratio upon the starch concentration is indicated. The birefringence endpoint temperature ranges of the starches were determined, and other implications from the experiments with the 21 materials are discussed.
SynopsisStarch xanthate with degrees of substitution (D.S.) ranging from 0.12 to 0.56 reacted with vinyl monomers (acrolein, acrylamide, acrylic acid, acrylonitrile, methyl acrylate, or styrene) and hydrogen peroxide to form aqueous gels of starch-polyvinyl monomer graft copolymer. The same reactions conducted in a rubber latex medium resulted in a self-acidifying, self-heating, and self-foaming coagulation to give a foam rubber. Such products were formed from several synthetic latices (NBR, SBR, polyisoprene, and polychloroprene types) and natural rubber latex; noted for each were the effects of the D.S., of monomer and peroxide concentrations, and of starch:elastomer ratios. The dried foams were evaluated by standard strength tests. Foam rubber of acceptable extensibility and enhanced tensile strength (up to 110 psi) was obtained with 0.12-0.15 D.S. xanthate and with proper balance of vinyl monomer, peroxide, and starchelastomer ratio. Resilience was fair to good, but compression set was rather poor compared to most foam rubbers of general use.
Flours from 12 different species of grain, pod seed, and tuber plants were gelatinized with aqueous sodium hydroxide at room temperature. Changes in physical appearances and viscosity patterns were noted over a 7‐day quiescent period in graded‐strength alkali solutions in sealed jars. The alkali strength, 0.07–0.85‐N, was sufficient to peptize proteins and hemicelluloses. Color development was strong and rapid and several flours evolved notable amounts of ammonia and perhaps amines. No two flours produced the same viscosity development patterns as time progressed. From the observed visual and viscosity changes, it was apparent that alkali gelatinization of the flours generally was complete within several hours at levels of 2.82‐3.52 meq NaOH/g flour. Some discussion centers on differences between flours, between some species of flours and the starches obtained from those species, and the possible role of other flour constituents on the gelatinization behavior.
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