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 one or more starches, and a plasticizer (e.g., glycerin). The carbohydrate-based polymeric material is less crystalline than the starting starch materials, e.g., being substantially amorphous, and having a crystallinity of no more than 20%. Third party testing shows blends of such materials render the entire blend biodegradable, believed to be due to the low crystalline substantially amorphous carbohydrate-based polymeric material breaking the hygroscopic barrier associated with the non-biodegradable plastic material, so that when blended together, both the plastic material and the carbohydrate-based polymeric material are biodegradable.