Poly(L-lactic acid) (PLLA) is commercially successful bio-based plastic, where end-of-life materials can undergo industrial composting. To create a circular economy, a desirable alternative to composting is chemical recycling to monomer (CRM), where direct depolymerisation to L-lactide can be achieved. CRM of PLLA is typically impeded by thermal decomposition and side reactions, due to the high ceiling temperate (T_c) of PLLA in bulk (>600 °C), which preclude implementation on a large scale, and has led to the development of catalytic strategies, under vacuum or high dilution in high boiling point solvents conditions.. In this study, a commercially available Sn(II) catalyst and low boiling point solvents, at a range of temperatures and concentrations, were explored for the CRM of PLLA in a continuous flow process. The solvent THF was found to produce the best results, where up to 92% conversion of lactide could be achieved, with 92-97% selectivity for L-lactide formation at temperatures 150-170 °C. Further, inline monitoring of monomer and polymer concentrations in flow were used to determine the depolymerisation rate coefficient k_depo and the activation energy of k_depo was determined to be 129.4 kJ mol^–1.

中文翻译：

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聚丙交酯在连续流动条件下的解聚


聚 L-乳酸 （PLLA） 是商业上成功的生物基塑料，报废材料可以进行工业堆肥。为了创造循环经济，堆肥的理想替代方案是化学回收为单体 （CRM），其中可以实现直接解聚为 L-丙交酯。由于PLLA的散装最高温度（TC）（%3E600°C）较高，PLLA 的CRM通常受到热分解和副反应的阻碍，这排除了大规模实施，并导致了催化策略的发展，在真空或高稀释度高沸点溶剂条件下。在本研究中，在一系列温度和浓度下，探索了市售的 Sn（II） 催化剂和低沸点溶剂在连续流工艺中用于 PLLA 的 CRM。发现溶剂 THF 产生最佳结果，其中丙交酯转化率高达 92%，在 150-170 °C 的温度下对 L-丙交酯形成的选择性为 92-97%。 此外，使用流动中单体和聚合物浓度的在线监测来确定解聚速率系数 k_depo，并确定 k_depo 的活化能为 129.4 kJ ^mol-1。