Institut de Chimie de Clermont Ferrand (ICCF), UMR 6296 Université Clermont Auvergne, CNRS, Sigma Clermont, ICCF, F-63000 Clermont-Ferrand, France.
Faculty of Technology, Department of Environmental Engineering, Tomas Bata University in Zlin,762 72 Zlín, Czech Republic.
Molecules. 2018 Oct 18;23(10):2682. doi: 10.3390/molecules23102682.
This study is devoted to the degradation pathway (bio, photo degradation and photo/bio) of Poly(Lactic acid) PLA polymers by means of melt viscoelasticity. A comparison was made between three PLA polymers with different microstructures (L, D stereoisomers). Biodegradability was determined during composting by burying the polymer films in compost at 58 °C. Melt viscoelasticity was used to assess the molecular evolution of the materials during the composting process. Viscoelastic data were plotted in the complex plane. We used this methodology to check the kinetics of the molecular weight decrease during the initial stages of the degradation, through the evolution of Newtonian viscosity. After a few days in compost, the Newtonian viscosity decreased sharply, meaning that macromolecular chain scissions began at the beginning of the experiments. However, a double molar mass distribution was also observed on Cole⁻Cole plots, indicating that there is also a chain recombination mechanism competing with the chain scission mechanism. PLA hydrolysis was observed by infra-red spectroscopy, where acid characteristic peaks appeared and became more intense during experiments, confirming hydrolytic activity during the first step of biodegradation. During UV ageing, polymer materials undergo a deep molecular evolution. After photo-degradation, lower viscosities were measured during biodegradation, but no significant differences in composting were found.
本研究致力于通过熔体粘弹性研究聚乳酸（PLA）聚合物的降解途径（生物、光降解和光/生物）。比较了三种具有不同微观结构（L、D 立体异构体）的 PLA 聚合物。通过将聚合物薄膜埋在 58°C 的堆肥中进行生物降解性测试。熔体粘弹性用于评估材料在堆肥过程中的分子演变。粘弹性数据绘制成复平面。我们使用这种方法通过牛顿粘度的演变来检查降解初始阶段分子量降低的动力学。在堆肥中几天后，牛顿粘度急剧下降，这意味着在实验开始时大分子链开始断裂。然而，Cole⁻Cole 图上也观察到双摩尔质量分布，这表明存在与链断裂机制竞争的链重组机制。通过红外光谱观察到 PLA 水解，实验过程中出现并变得更强的酸特征峰，证实了在生物降解的第一步中存在水解活性。在紫外线老化过程中，聚合物材料经历了深刻的分子演变。光降解后，在生物降解过程中测量到较低的粘度，但在堆肥中没有发现显著差异。
