Acetylated cassava starch-based microcellular foams prepared by supercritical CO₂ processing: Structure, foaming behavior and biodegradability

Abstract

Acetylated cassava starch-based microcellular foams were prepared using supercritical carbon dioxide (ScCO₂) processing to investigate the combined effects of the degree of substitution (DS) and saturation pressure on the foam morphology, physical properties, and degradation behavior during soil burial. Thermoplastic starch prepared from acetylated cassava starch with measured DS values of 1.39 and 1.69 containing 30 wt% triacetin was saturated with ScCO₂ at 70 °C and pressures ranging from 105 to 205 bar, followed by rapid depressurization. The foam morphology and physical properties were influenced by both DS and saturation pressure. Increasing the saturation pressure reduced the average cell size and increased the cell density, whereas a higher DS produced more homogeneous cellular structures with lower crystallinities. At 180 bar, the foam prepared from DS 1.69 exhibited an average cell size of 4.62 μm and cell density of approximately 10⁹ cells·cm⁻³ . Variations in cellular morphology were accompanied by corresponding changes in bulk density, compressive strength, water uptake, wettability, and weight loss after 30 d of soil burial. Compared with the foam prepared from DS 1.39, the foam prepared from DS 1.69 exhibited lower water uptake, higher surface hydrophobicity, and lower weight loss during the soil burial test. The results demonstrate that differences in the degree of substitution and saturation pressure led to distinct cellular structures, resulting in corresponding differences in the physical properties of the acetylated starch-based microcellular foams