a chemically modified plasticized starch is prepared by reacting starch with an organic dibasic acid or an anhydride of the acid in the presence of a plasticizer using optional free radical initiators , and optionally with the incorporation of nano clays in the reactive extrusion process . the starch is thermoplastic and has a lower viscosity than the traditional thermoplastic starch . the cmps is useful in preparing starch polymer compositions which are at least partially biodegradable .