Described herein are methods for rendering biodegradable a plastic material that is not itself biodegradable, by blending the plastic material with a carbohydrate-based polymeric material that is formed from a) one or more starches and a plasticizer (e.g., glycerin), b) an additive known in the art as an OXO material and/or an additive that interacts with microbes that contribute to biodegradation of the non-biodegradable material. The carbohydrate-based polymeric material is less crystalline than the non-biodegradable materials, e.g., being substantially amorphous, and having a crystallinity of no more than 20%. When tested under conditions causing biodegradation, the blend biodegrades to an extent greater than the content of the carbohydrate-based polymer.