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Rigid and film bioplastics degradation under suboptimal composting conditions: A kinetic study
Summary
This study examined how well bioplastics — including PLA and starch-based film bags — degrade in home composting conditions that may not reach optimal temperatures, finding that film bioplastics degraded completely within 60 days but rigid PLA items would require 2-3 years at suboptimal conditions. These results highlight the gap between biodegradable plastic claims and real-world composting performance.
The present research investigates the degradation rate of bioplastics under various composting conditions, including suboptimal ones. Lab-scale tests were carried out setting three variables: temperature (37°C-58°C), humidity (30%-60%) and duration of the thermophilic and the maturation phases (15-60 days). The composting tests were carried out following modified guideline ISO 20200:2015 and lasted for 60 days. Bioplastics in the synthetic waste matrix consisted of Mater-Bi® film biobags and PLA rigid teaspoons. A kinetic study was performed, resulting in faster degradation rates for film bioplastics (first-order kinetics with k = 0.0850-0.1663 d-1) than for rigid (0.0018-0.0136 d-1). Moreover, film bioplastics reached a complete degradation within the 60 days of the test. Concerning the rigid products, 90% degradation would be achieved in 2-3 years for mesophilic conditions. Finally, in the undersieve of 0.5 mm some microplastics were identified with the ImageJ software, mainly relatable to rigid (PLA) bioplastics. Overall, the results disclosed that the combination of mesophilic temperatures and absence of moistening slowed down both the degradation and the disintegration process of bioplastics.