biodegradable polymers for use in forming high strength , degradable plastics and methods of forming the polymers are provided . broadly , the methods comprise forming and heating a blended mixture of polylactic acid , a starch , and a linkage group for joining or copolymerizing the polylactic acid and starch . preferred linkage groups comprise an isocyanate moiety , with diphenylmethylene diisocyanate , hexamethylene diisocyanate , and isophorone diisocyanate . the reacted mixture can then be formed into the desired final product which has high tensile strength , modulus of elasticity , percent elongation , and thermal stability .