Development, Soil Biodegradation, and Kinetics Evaluation of Starch-Based Bioplastic from Sechium edule and Phaseoulus vulgaris

Plastic pollution is a global concern, posing numerous challenges to the environment and wildlife. Bioplastics (BPs), made primarily from petrochemicals, have emerged as an alternative to conventional plastics. BPs are environmentally-friendly because they are made from biogenic polymers obtained from renewable biomass. In this study, we examined the biodegradability of BPs produced from a combination of starch from Sechium edule (SSE) fruit and the starch of Phaseolus vulgaris (SPV) with a plasticizing agent. The BP with the best physical properties was evaluated for biodegradation under in vitro, over-soil, and soil burial conditions. The BPs formulated with the starch mixtures (SSE-SPV) exhibited hardness values between 455.20 and 1972.00 gf and an elasticity index > 0.86. Under storage conditions of 11.30% and 57.60% relative humidity (RH), the maximum elongation value was achieved with a 6% SSE-SPV concentration, and this property decreased with increasing RH. Under soil burial conditions, a biodegradation percentage of 91.02%, with a 7.6854 mg BP/day degradation rate, was observed. The experimental data of the biodegradation process were fitted to a first-order kinetic model, with biodegradation rate coefficients of 0.1143, 0.0905, and 0.6873 days(- 1) for in vitro, over-soil, and soil burial conditions, respectively. Bacterial presence was observed in the BP samples tested in vitro and soil burial, while fungal presence was noted on the surface of BP tested in over-soil conditions. These results highlighted the potential of the highly biodegradable BP developed in this study as a substitute for single-use or oxo-degradable plastics.