Embedded CTAB enables depolymerization of PLA composite films under mild, household-compatible alkaline conditions

Polylactic acid (PLA) is considered a promising biodegradable material; however, its complete degradation is typically limited to industrial composting systems, making household-level end-of-life management challenging. In this study, we developed a simple and efficient PLA depolymerization method suitable for dilute alkaline conditions. Optimized depolymerization was achieved by immersing PLA films incorporating 10 wt% cetyltrimethylammonium bromide (CTAB) in a 1% aqueous solution of sodium hydroxide. The use of a microwave oven significantly accelerated degradation from 6 h to 2 min. Early-stage molecular-weight evolution during depolymerization was characterized using gel permeation chromatography (GPC) together with differential scanning calorimetry (DSC). The primary degradation products were identified as lactic acid and sodium lactate by nuclear magnetic resonance (NMR) spectroscopy. After depolymerization, residual CTAB was effectively adsorbed by activated carbon (AC). Furthermore, biochemical oxygen demand (BOD) tests at 25 and 50 °C further indicated a faster initial oxygen uptake rate than that of cellulose for the AC-treated depolymerization products, which is consistent with the ready microbial assimilation of lactic acid-based monomers. This study serves as a proof-of-concept demonstration that PLA–CTAB composite films enable rapid depolymerization under accessible dilute alkaline conditions, with posttreatment activated carbon adsorption providing a framework for the responsible management of residual CTAB.