Preparation of anti-shrinkage branched poly (butylene succinate-co-butylene terephthalate)/cellulose nanocrystal foam with excellent degradability and thermal insulation

Branched poly (butylene succinate-co-butylene terephthalate) (BPBST) was synthesized by in-situ polycondensation to enhance the foamability of poly (butylene succinate-co-butylene terephthalate) (PBST) and was blended with cellulose nanocrystals (CNC) to address foam shrinkage. The introduction of 2 wt% CNC increased the crystallization temperature of BPBST from 66.6 °C to 87.7 °C, accelerating its crystallization rate and improving both the mechanical properties and complex viscosity of the polymer matrix. Microcellular foams were produced using supercritical CO₂ as a blowing agent, with CNC serving as heterogeneous nucleation sites. The addition of CNC reduced the average cell diameter of the foam and increased the cell density, enhancing the dimensional stability of the foam. BPBST/CNC foam with 1 wt% CNC exhibited a high expansion ratio of 24.7 without shrinkage, along with a low thermal conductivity of 0.0354 W/(m·K), indicating excellent thermal insulation performance. Furthermore, CNC improved the hydrophilicity of the foams and accelerated their degradation. The BPBST/CNC2 foam with an expansion ratio of 17 exhibited a 72.2 % weight loss after 10 d of hydrolysis, showing excellent degradation. This study combines the tunable molecular structure of in-situ copolymerization with the efficiency of melt blending to provide an effective strategy for the production of biodegradable, functionalized foams.