Improvement in barrier properties of polymers used in packaging industry: pet/N-MXD6 blends

Official URL: http://192.168.1.20/record=b1225705 (Table of Contents)

Traditional packaging materials like glass and metal are increasingly replaced by plastics due to several advantages of plastics which are low density, less energy consumption, ease of processing, weight reduction and cost savings. Unfortunately plastics are permeable to gases while glass and metal are absolute barrier materials. Permeability is an important issue in packaging that relates to product quality and a reasonable shelf life. Improvement in barrier properties of polyester/polyamide blends used in packaging industry is the main objective of the present study. For this purpose polyethylene terephthalate (PET)/ poly (m-xylene adipamide) (Nylon-MXD6) (95/5 w/w) and PET-co-10I (polyethylene terephthalate-co-isophtahalate random copolymer containing 10 wt. % isophthalic acid (IPA)) / N-MXD6 (95/5 w/w) blends have been prepared with different compatibilizer types and combinations by using a co-rotating intermeshing twin screw extruder. The effects of biaxial orientation, crystallinity, morphology (tortuous pathway), and chemistry on oxygen gas permeability were analyzed by using different characterization techniques like scanning electron microscopy (SEM), differential scanning calorimetry (DSC), spectral-birefringence, and gas permeability analyzer. The morphological analysis revealed that PET copolymer that consists of 5% sodium sulfonated isophthalate (PET-co-5SIPA) was an effective compatibilizer for both PET/N-MXD6 and PET-co-10I/N-MXD6 blends. Spectral-birefringence technique and DSC analysis were used to understand the crystallization behaviour of the blends. Morphological analysis of films after biaxial stretching indicated that the spherical nylon phase was converted to 75 nm thick ellipsoids during stretching (aspect ratio L/W=6) that creates tortuous pathway for oxygen ingress. PET-co-10I films had low permeability before biaxial stretching compared to unoriented PET films. Stretching ameliorated barrier properties of PET/N-MXD6 films but increased the permeability of PET-co-10I/N-MXD6 blends.