synopsisAcrylonitrile grafts readily to granular corn starch in aqueous slurry when initiated by hydrogen peroxide plus activator. Prime evidence for grafting lies in the ease of separating PAN from starch in high yield when the initiator is arobisisobutyronitde rather than peroxide. Grafting efficiencies are determined by extraction with appropriate solvents: dimethylformamide for homo-PAN, and Looiling water for ungrafted starch. Grafting efficiencies of PAN range from 78 to 95%, M,, values for grafted PAN are 4,000 to 90,O00, and frequency of attachment of side chains range from 300 to 1100 glucose units per chain. Increasing the monomer level, a t fixed initiator concentration, tends to result in longer rather than more frequent side chains. AN behaves much as has been previously found for MMA, but the somewhat more efficient grafting at more frequent intervals and the more nearly uniform distribution of polymer in the starch granule suggest that AN penetrates the starch granule more readily than MMA. INTRODUCTIONThe grafting of poly(methy1 methacrylate) (PMMA) to granular corn or its unsaturated esters3 by way of free-radical initiation has been described in previous papers from this laboratory. Means of separating ungrafted homopolymer of methyl methacrylate from the graft haye been studied in detaiL4 This paper reports results of similar techniques used to prepare and characterize grafts of PAN (polyacrylonitrile) to granular corn starch.Grafting of PAN to starch has already b&n carried out, but under conditions widely dzerent from those here reported. Walrath et a1.6 prepared grafts to wheat starch by mutual or preirradiation from a ' W o source. Kimura and co-workers grafted by initiation with ceric salt in solutions of potato amylose6 or by use of reprecipitated starch peroxidized with ozone.' Fanta et a1.8 studied the effects of reaction conditions on composition of product obtained by initiation with ceric nitrate in dilute solutions of wheat starch. EXPERIMENTAL MaterialsUnmodified and hypochlorite-oxidized starches were A. E. Staley production materials. The unmodified starch was defatted prior to use as free of nonvolatiles and readily polymerjzable, was used as received. All other reactants were reagent grade or equivalent. PolymerizationThe procedure was the same as previously described for methyl methacrylate.' On addition of the peroxide to the mixture containing all other reactants, the temperature rose from its initial 30°C. to a peak within the next 15 min. Total reaction time was 60-90 min. The product was filtered, washed with water, and dried in air a t room temperature. Conversion of monomer to polymer was 95% or higher in each instance, except for those runs initiated with AIBN (azobisisobutyronitrile). Characterization of RESULTS AND DISCUSSION Qualitative Description of ProductsThe products are recovered in the form of fine white powders, similar in appearance to the original starch. Even the appearance of individual particles is changed hardly a t all by the polymerization, as shown...

Graft copolymers were prepared by the radical‐initiated polymerization of methyl methacrylate in aqueous slurries of granular corn starch. High conversions of monomer were realized, giving products which were readily recovered by filtration. The products were free‐flowing, white powders, which by microscopic examination looked much like granular starch. Grafting was demonstrated by extracting the granular products with ethylene dichloride, which in most instances removed only a minor part of the poly(methyl methacrylate). When azoisobutyronitrile was used for initiation, a high conversion of monomer resulted, but about 90% of the polymer was extractable with ethylene dichloride. Further evidence for grafting was obtained by extraction of predissolved product, prepared by dissolving the granular product in dimethyl sulfoxide, to destroy the structure of the starch granules, and precipitating with alcohol. The fractions soluble in ethylene dichloride contained significant amounts of carbohydrate. Similar treatment of product prepared with azoisobutyronitrile initiation or of physical blends of starch and poly(methyl methacrylate) gave much more efficient separation of starch from PMMA. Failure to obtain grafting with AIBN initiation suggests that grafting occurs mainly as a result of attack on starch by radicals generated by the reaction of hydrogen peroxide or organic hydroperoxide with ferrous iron. Acid hydrolysis of the products removed the starch. The PMMA so recovered typically had viscosity‐average molecular weights of the order of 106, which suggests the grafts contained very long branch chains of PMMA attached at very infrequent intervals.

PMMA content of graft copolymers with granular starch can be determined by acid hydrolysis with sufficient precision to allow reasonable estimates of efficiency and frequency of grafting. Preparation of the graft copolymer by initiation of methyl methacrylate with hydrogen peroxide and activators results in products containing long PMMA side chains attached to the starch at very infrequent intervals, but the length and frequency of attachment can be varied considerably by changes in the ratios of reactants. The highest frequency achieved was with PMMA of number‐average molecular weight of about 30,000, attached at a frequency of one chain per 230–250 glucose units in the starch. Under the more favorable conditions, oxidized starch yielded product of significantly more frequent grafting than did unmodified starch. Gradual addition of monomer, initiator, and activator to the starch slurry gave slightly higher frequency of grafting than did complete addition of all reactants at the start of the polymerization.

Irrigation-induced erosion and subsequent sediment loss is a serious agricultural and environmental problem. Recent recognition of this problem has stimulated the development and evaluation of erosion and sediment-loss-control technology. Research results indicate that the application of the technology available today can reduce sediment loss by 70-100%. Important practices include irrigation-water management, sediment-retention basins, buried-pipe tailwater-control systems, vegetative filter strips, tailwater-recovery systems, keeping crop residues on the soil surface and in furrows, and implementing conservation tillage practices.

ABSTRACT:The environment of a weather station site is important in estimating consumptive use by irrigated crops. Consumptive use may be overestimated when air temperature and vapor pressure data from a weather station with an arid local environment are used without modification. To document the effect of weather station aridity on consumptive use estimates, three sites in irrigated areas and two sites in nonirrigated, arid rangeland in southern Idaho were instrumented with weather stations during 1981. Air temperatures were higher and vapor pressures were lower at the arid sites. Use of air temperatures and dewpoint estimates from arid sites caused an overestimation of ET, by 17% (210 mm) over the irrigation season. Results indicate the importance of weather site evaluation and adjustment of siting effects and weather before consumptive use estimates are made. A procedure is outlined for adjusting historical temperature data to reflect an irrigated condition.