In this study, temperature-responsive composite films were developed using polylactic acid (PLA), polyethylene glycol (PEG), and montmorillonite nanoclay by melt blending method. PEG (35 wt%) as a phase change material with a molecular weight of 35,000 g/mol was compounded with nanoclay using a twin-screw extruder. Subsequently, PEG/nanoclay composite introduced to PLA as the main polymer matrix using cast extrusion process. Different concentrations of nanoclay (3%, 5%, 7% and 10%) were added to the composite films to improve the shape stability and heat transfer during microwaving. The chemistry of composite films was investigated using Fourier transform infrared spectroscopy in which the chemical interactions between PLA-PEG and PEG-nanoclay were identified. Differential scanning calorimeter thermograms showed that glass transition temperatures and melting point of PLA film did not significantly change with addition of PEG and nanoclay. In addition, the addition of PLA and nanoclay reduced the tensile strength of PLA but increased the elongation at break. Furthermore, scanning electron microscope was employed to observe the microstructural morphologies, showing a uniform morphology in the cross-section and top-surface images, which maintained the barrier properties of composite films at the lower temperatures. Temperature-dependent oxygen permeability at different temperatures showed a permeable jump in vicinity of the PEG phase transition temperature (60-70 centigrade) approximately 4 times bigger than PLA film. The addition of nanoclay assisted with the better heat transfer in the composite film matrix in which the composites films containing nanoclay showed a bigger permeable jump. It is worth noting that the temperature-dependent permeability in this study imparted a self-releasing feature to the composite films at a temperature range before the accumulation of steam inside the packaging due to microwaving. Therefore, these smart composite films can be applied as a monolayer material for microwave packaging to safely release steam generated by food and avoid bursting in the microwave.

Eco-friendly temperature-responsive permeable films derived from PLA/PEG/nanoclay composite for steam self-releasing microwave packaging

ACS Spring 2022

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