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Effect of Annealing Temperature and Time on Tensile Strength of Poly(lactic acid) Films
Summary
Researchers studied how different annealing temperatures and times affect the tensile strength of poly(lactic acid) (PLA) films, a biodegradable plastic considered an alternative to conventional microplastic-generating plastics. Heating during secondary processing alters crystal structure and affects mechanical performance.
In recent years, poly(lactic acid) (PLA) was attracted the attention for alleviating environmental problems such as the microplastic pollution and/ or the exhaustion of petroleum resources, because PLA can be synthesized from plants and hydrolyzed in the natural environment. The mechanical properties of PLA can be improved by secondary processing after molding as drawing. However, heating in this secondary processing might change crystal structure of PLA and affect the mechanical properties. In this study, effect of annealing conditions on mechanical properties and crystal structure of PLA film was investigated as a basic study. The crystal structure of annealed PLA film was investigated through the measurement of crystallinity by differential scanning calorimetry and crystal diameter by polarization observation. As a result, the crystallinity and the crystal diameter were increased with annealing temperature, and reached a maximum at 130 °C. This result was suggested that crystal growth rate was maximum at 130 °C. In comparison with annealing time, the crystallinity and the crystal diameter were saturated at 3.5 h. And, there was no distinct effect of annealing time in the tensile test.