Preparation of oriented poly(lactic acid) thin films by a combination of high temperature rubbing and thermal annealing: Impact of annealing parameters on structure, polymorphism and morphology

Abstract

High temperature rubbing is a fast and low-cost method to prepare highly oriented films of polymers. This contribution describes the fabrication of smooth and pin-hole-free poly(lactic acid) (PLA) thin films of controlled structure and morphology using a combination of rubbing at moderate temperature (T ≤ 100°C) and thermal annealing. We investigate the impact of annealing temperature and duration on the structure of rubbed PLLA and stereo-complex (SC) thin films. The importance of annealing parameters on polymorphism, crystallinity, crystal dimensions and in-plane orientation are analyzed using Transmission Electron Microscopy, Differential Scanning Calorimetry and FTIR spectroscopy. Regarding SC PLA films, the conditions are identified to fully transform the equimolar PLLA-PDLA blend films into pure oriented SC films without presence of homocrystals.