Optimization of ternary blends based on poly (lactic acid) according to physical and biological properties

 Increasing plastic wastes of the packaging industry and concerns about their environmental problems, have attracted many researchers to use biopolymers. Therefore, the preparation of cheap biodegradable films with desirable properties for using in the packaging industry can be an attractive challenge.

In this study, poly (lactic acid) (PLA) based ternary blends were prepared by experimental design (mixture method). For this purpose, thermoplastic starch (TPS) was first prepared using 28 wt% sorbitol and 14 wt% glycerol. Then, PLA / PCL (poly (caprolactone), PCL) / TPS ternary blends at different concentrations were prepared using the melt mixing method. Morphological, physical (tensile, water vapor permeability), biodegradability, and rheological tests were also carried out. Finally, the optimum sample was determined using Minitab software.

Scanning electron microscope (SEM) images revealed incompatibility and phase separation in the blends. Moreover, with increasing PCL and TPS contents, flexibility enhanced due to the plasticization effect of PCL and mechanical properties declined, respectively. The permeability test results showed that the samples containing less TPS due to its hydrophilic nature and more PCL leads to increase the crystallinity of the matrix, had lower water vapor permeability. The effect of TPS on the biodegradability test was also well established. In this way, the sample containing 35 wt% TPS loses about 50% of its weight within 14 weeks. Finally, the sample with 50/25/25 (PLA / PCL / TPS) composition was selected as the optimum sample by Minitab software. The results showed that the formulated films in this study have the potential to be used in biodegradable packaging materials with good mechanical and barrier properties.