Property enhancement of polylactic acid/thermoplastic starch blend using zeolite 5A incorporation and biaxial stretching process

Abstract

Importance of the work: Blended polylactic acid/thermoplastic starch (PLA/TPS) is a potential material for packaging; however, it still has poor mechanical and barrier properties.
Objectives: To improve the mixing and performance of PLA/TPS blends by incorporation of zeolite 5A (Z5A) and biaxial orientation of the PLA/TPS/Z5A composite.
Materials & Methods: PLA/TPS/Z5A pellets were prepared by melt-compounding using a twin-screw extruder. The composite pellets were converted into a sheet using cast sheet extrusion followed by biaxial stretching into films. The stretching rate was varied (75−150 mm/s). The microstructural, mechanical and gas barrier properties of the stretched films were investigated.
Results: Z5A incorporation and the stretching rate affected the morphology and properties of the stretched films. The presence of Z5A enhanced mixing of PLA and TPS by reducing the TPS dispersed phase size and improving dispersion of TPS in the blend matrix. The biaxial stretching process increased the ordered structure and crystallinityof the PLA in the PLA/TPS/Z5A films. These improvements led to significant increases in tensile strength and the oxygen and water vapor barriers of the PLA/TPS blend up to 100, 90 and 65%, respectively. Increasing the stretching rate from 75 mm/s to 150 mm/s improved the tensile and impact strength by 26% and 22%, respectively.
Main finding: This was the first report of simultaneous biaxial stretching of PLA/TPS/Z5A composite film. The mixing and performance (mechanical and barrier properties) of the blend were substantially improved by compounding with Z5A and biaxial stretching process.