Blends of Sustainable Polymers and Waste Soy Biomass

Sustainable polymers have attracted interest due to their ability to biodegrade under specific conditions in soil, compost, and the marine environment; however, they have comparatively lower mechanical properties, limiting their widespread use. This study explores the effect of incorporating waste soy biomass into sustainable polymers (including biodegradable and biobased) on the thermal and mechanical properties of the resultant blends. The dispersion of the waste soy biomass in the polymer matrix is also investigated in relation to particle size (17 µm vs. 1000 µm). Fine waste soy biomass did not significantly affect the melting temperature of the polymers (polyhydroxyalkanoates, polybutylene adipate terephthalate, polybutylene adipate terephthalate/poly(lactic) acid, and biobased linear low-density polyethylene) used in this study, but their enthalpy of fusion decreased after soy was melt-blended with the polymers. The tensile modulus of the polymers filled with fine waste soy biomass powder (17 µm) was enhanced when melt-blended as compared to unfilled polymers. Additionally, it was found that fine waste soy powder (17 µm) increased the tensile modulus of the polymer blends without significantly affecting processability, while coarse waste soy meal (1000 µm) generally reduced elongation at break due to poor dispersion and stress concentration; however, this effect was less pronounced in PHA blends, where improved compatibility was observed.