Abstract
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.
Highlights
Nowadays, the impact of domestic wastes on the environment is the focus of many researchers.During service life, it is well known that polymer materials age, mainly if they are exposed to UV light
Various stereoisomer of PLA were studied during photo-ageing, and biodegradation in Compression molded films were exposed to UV radiations and buried in compost to evaluate the compost
Compression molded films were exposed to UV radiations and buried in compost to photo-ageing impact onto the biodegradation properties in the case of PLA
Summary
The impact of domestic wastes on the environment is the focus of many researchers. It is well known that polymer materials age, mainly if they are exposed to UV light. The consequence is a decrease of the material properties leading to failure and waste production. The questions of the ecological treatment of these wastes have motivated many studies on biodegradable polymers [1,2,3]. Poly(lactic acid) is a good candidate to respond to this problem, because it is compostable [4,5,6] and bio-based [7]. PLA show properties comparable to other polymers like polyethylene or polystyrene [8]
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