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Influence of time and room temperature on mechanical and thermal degradation of PLA

Poly(lactic) acid, PLA, is a compostable thermoplastic which degrades fast under composting conditions of microorganisms, high humidity and temperatures. However, PLA degrades slowly below its glass transition temperature and in low humidity, hence, when used as short-shelf life product containers and not disposed to composting systems, PLA may cause environmental pollution. Therefore, when not disposed to proper waste management systems, the effect of long incubation time at room temperature on mechanical and thermal properties of PLA is the main concern of this study. To determine the effect of room temperature on semi-crystalline PLA degradation at a low humidity percentage, PLA films (PLA2) were kept at room temperature for 5 years at 40±10% humidity. Some PLA films (PLA3) were pre-treated at 55°C under dry conditions for 1 year and then kept at room temperature for 4 years. Influence of incubation time and temperature on PLA degradation was evaluated by mechanical, thermal analyses and by Fourier-Transformation Infrared Spectroscopy Analysis (FTIR) and compared with the initial PLA samples (PLA1). Mainly mechanical properties of PLA were affected by incubation temperature and time since 68% tensile strength loss was observed in PLA3 samples which were pre-treated at 55ºC and 34% decrease in tensile strength was observed in PLA2 samples. Thermal behaviour of PLA was also influenced by incubation time and temperature as degree of crystallinity decreased 2 and 5% in PLA2 and PLA3 samples, respectively. Deformation of CH bonds and amorphous phase degradation were revealed by FTIR analyses in PLA2 and PLA3 samples.
PAPER REVISED: 2018-12-28
PAPER ACCEPTED: 2019-01-05
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