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Degradation Of PLA During Long-term Storage | 58034
ISSN: 2155-6199
Journal of Bioremediation & Biodegradation
Open Access
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The degradation of PLA proceeds through hydrolysis of the ester linkages in the polymer backbone. This leads to a significant
reduction of molecular weight and thus to a deterioration of mechanical properties. However, up to now there are no
studies of PLA-hydrolysis performed under practical conditions and long-term storage. In this work, the influence of molecular
weight, granule size, crystallinity, air humidity and temperature on the hydrolytic degradation of PLA was investigated. Two
commercially available PLA types with different molecular weights were used in this study. Three different granule sizes were
prepared through compounding with a co-rotating twin-screw extruder. The granules were annealed at defined temperatures
so that crystallinity degrees in three different magnitudes were generated. Finally, all granules were stored at five different
temperatures in the range from 10 to 50�?ºC and a relative humidity of 33 and 75 % for six months. During this time, the viscosity
of the samples was monitored with a rotational rheometer. A simple linear function was used to define the relationship between
the weight average molecular weight and the zero viscosity in logarithmic form. By fitting the zero viscosity in the simplified
kinetic equation, the degradation rate constants for each sample at each temperature were determined and used afterward in
the Arrhenius equation to calculate the activation energy of the hydrolytic degradation for each sample. As most significant
influences on the hydrolytic degradation of PLA, temperature and air humidity were identified. The degradation rate constants
and therefore the rate of the hydrolytic degradation, increase significantly with increasing temperature and air humidity.
Furthermore, small granules, high crystallinity and high molecular weight increase the activation energy and thus reduce the
rate of PLA degradation during the long-term storage.