The effect of the grafting percent on some of the physico-chemical and thermal properties and the decomposition course of novel starch-g-poly(cinnamyl acrylate) copolymers

Abstract

This paper focuses on the chemical modification of potato starch by the cinnamyl acrylate monomer during the graft copolymerization. The maximum of the grafting percent (G) was found to be 49.2% ± 0.3 at the temperature of 65 °C for 120 min in the presence of 1.0 wt% of potassium persulfate at the starch and monomer ratio 1:2.5. The copolymers exhibited excellent resistance to polar solvents and moisture which was independent of their G values. It was due to the presence of poly(cinnamyl acrylate) chains in their structure and their very compact, non-porous structure. The chemical stability of the copolymers was dependent on the G values. The copolymers showed the highest chemical resistance to neutral and acidic environments rather than to the alkaline one. Their thermal stability was ca. 210 °C under the inert and oxidative conditions. The decomposition mechanism of the copolymers was complex and included a lot of multiple simultaneous processes combined with the emission of various volatiles. The interesting fact was that the pyrolysis of starch from the copolymers occurred before that of the grafted polymer. However, the oxidative decomposition of the grafted polymer began at lower temperatures than that of starch from the copolymers.

Keywords: Cinnamyl acrylate; Graft copolymers; Starch.