Tailoring Crystalline Morphology via Entropy-Driven Miscibility: Toward Ultratough, Biodegradable, and Durable Polyhydroxybutyrate

The excessive use and disposal of plastic products have become a severe threat to the environment, animal welfare, and human health. Naturally synthesized, marine-degradable polyhydroxybutyrate (PHB) represents a viable green substitute for conventional plastics. However, the inherent brittleness of PHB remains a major challenge due to undesirable large spherulites and secondary crystallization. Herein, we report PHB-based (up to 70 wt %) ductile and flexible materials by facile physical blending with edible poly­(vinyl acetate) (PVAc). Theoretical and experimental analyses show that entropy rather than enthalpy drives the high miscibility between two polymers. Entropic mixing turns fragile PHB spherulitic crystals (>70 μm) into myriads of ultrafine domains (500%), toughness (∼62 MJ m–3), flexibility, and shape recovery under repeated bending (180°) or twisting (360°). Under controlled composting conditions, the food-safe bioblends exhibit ∼2.4 times weight loss of virgin PHB. The proposed strategy proves applicable to other crystalline/amorphous polymeric mixtures. This discovery sheds new light on the rational design of green plastics for future sustainable electronics, agriculture, and biomedicine.