SYNTHESIS AND PROCESSING OF GRAFT-COPOLYMERS FROM CORNSTARCH AND METHYL ACRYLATE - PHYSICAL AND MECHANICAL-PROPERTIES

Starch-g-poly(methyl acrylate) (S-g-PMA), containing 40-65% PMA, was p repared with ceric ammonium nitrate (CAN) initiation in a 2-gallon rea ctor. CAN initiator was added either in one portion or portionwise. Gr aft copolymers were characterized with respect to % acetone-extractabl e polymer (largely PMA homopolymer), PMA content of the graft copolyme r, and M(w) of PMA grafts. Normal cornstarch as well as waxy and high amylose cornstarches were used in the grafting reaction. Conversions o f monomer to polymer were nearly quantitative. Continuous plastic ribb ons for tensile testing were prepared by extrusion processing. Tensile properties varied with the method used for CAN addition (i. e., singl e portion vs. portionwise) and depended upon the particular starch var iety used in the graft polymerization reaction. Since water acts as a plasticizer for starch, samples extruded at high moisture content exhi bit higher % elongation (%E) values than the same polymers extruded at low moisture. Values for %E also increase with higher percentages of PMA in the graft copolymer.