IRRADIATION-MODIFICATION OF STARCH-CONTAINING THERMOPLASTIC BLENDS .1. MODIFICATION OF PROPERTIES AND MICROSTRUCTURE

Irradiation-modification of the blends of various starches with a synt hetic polymer [poly (ethylene-co-vinyl alcohol)] was carried out using an electron beam. The effect of irradiation on neat starches was stud ies using gel permeation chromatography. Changes in the thermal and me chanical properties of the blends, as well as in their microstructures , were also evaluated. The data indicate, consistent with other report s in literature, that starch molecules fragment under the effect of io nizing radiation, while the EVOH is relatively unaffected. These subst antial (mainly physical) modifications to the starch molecules manifes t themselves in changes in the thermal behavior of the blends. Further more, the mechanical properties of filaments obtained from molten irra diated pellets were quite different from those of control filaments, a t least for some starches. Micrographic examination of some blends ind icated a correspondence between a modification in the microstructure o f the filaments and a change in their mechanical properties. It seems likely that the enhanced mobility of the fragmented starch molecules i n the melt is responsible for these changes in the microstructure and concomitantly, the mechanical properties of the blend. Such an irradia tion-based physical modification of starch may be of use in tailoring the properties of commercial blends of starches with synthetic thermop lastics. (C) 1996 John Wiley & Sons, Inc.