Kazakhstan combines a large agricultural-residue base with an expanding grain-processing sector, creating a credible platform for biodegradable polymers if feedstock availability is matched to polymer chemistry, pretreatment intensity, and realistic end-of-life routes. This critical review integrates Kazakhstan-specific production data with the chemistry of starch, cellulose, hemicelluloses, lignin, and rice-husk silica and evaluates the conversion pathways most relevant to domestic implementation. Collectible dry residues from wheat, barley, maize, and rice are estimated at about 15.1 Mt yr⁻¹, while potato and cereal starch streams provide directly processable carbohydrates. Near-term options are thermoplastic starch (TPS), cellulose/nanocellulose reinforcement, lignin-containing functional composites, and hybrid materials using rice-husk-derived silica. PLA and PHA offer higher-value routes but require fermentation, purification, polymerization or recovery, and dedicated end-of-life infrastructure. The review emphasizes molecular limitations—hydrogen-bonded polysaccharide networks, retrogradation, interfacial polarity mismatch, lignocellulosic recalcitrance, filler agglomeration, and environment-dependent biodegradation—and links them to processing and performance tests. A staged strategy is proposed: compound and reinforce existing starch streams first, build regional fractionation and standardized intermediate platforms next, and develop PLA/PHA fermentation only after low-cost carbon streams, product markets, and life-cycle advantages are demonstrated.