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PLA has a relative low point of glass transition, which can limit its application. The aim of the study was to observe the effect of humidity on glass transition. The glass transition of PLA films was determined under three different climates (nitrogen-atmosphere, wetted, and room conditions) by dynamic mechanical analysis with a tensile testing setup. The point of glass transition was calculated by interpretation of storage modulus (E’) and tan d curve as well. Although the applied humidity levels showed high variation, significant differences were observed. The glass transition temperature changed from 57.8 ± 1.5°C (E’)/62.5 ± 1.9°C (tan d) under dry condition to 46.5 ± 3.5°C (E’)/53.2 ± 3.1°C (tan d) at medium and 41.9 ± 4.8°C (E’)/45.2 ± 4.1°C (tan d) at high humidity.

Abbreviations: CA (Contact Angle); DMA (Dynamic Mechanical Analysis); DSC (Differential Scanning Calorimetry); Tg (Glass Transition Temperature). 

biopolymers, DMA, glass transition, humidity, PLA.