A new starch-vegetable oil graft copolymer, wherein the vegetable oil has been reacted onto the starch backbone using thermal or free radical initiators has been produced in a twin-screw co-rotating extruder. The starch-vegetable oil graft copolymer can further be reinforced with biofiber in the presence of an optional modifier such as maleic anhydride by reactive extrusion processing to form composites suitable to be injection molded into biodegradable articles.