Morphological, thermal and mechanical properties of polyamide and ethylene vinyl alcohol multilayer flexible packaging after high-pressure processing

Abstract

The effect of high-pressure processing on the morphological surface, thermal and mechanical properties of three PA and EVOH based multilayer flexible packaging materials were evaluated. LDPE/PA/LDPE, LDPE/EVOH/LDPE and PET/LDPE/PA/EVOH/PA/LDPE packaging samples were processed under three different conditions (600 MPa/25 ºC/10 min, 600 MPa/90 ºC/10 min and 0.1 MPa/90 ºC/10 min) and an unprocessed sample was used as control. The LDPE/PA/LDPE and LDPE/EVOH/LDPE samples showed good thermal stability and no surface defects after processing, because of the greater thickness of the external material, the film withstood the compression and decompression of the processing, consequently resulting in the protection of the other layers. The PET/LDPE/PA/EVOH/PA/LDPE sample showed a significant increase in the Tm of PET, LDPE and PA after processing at 600 MPa/90 ºC/10 min. Regarding the mechanical properties, reductions in the tensile strength of the PET/LDPE/PA/EVOH/PA/LDPE sample were observed after processing at 600 MPa/90 ºC/10 min. In addition, a significant reduction in heat seal strength was observed in the three materials after processing at 600 MPa, but these values are accepted in practice. Therefore, in terms of morphological, thermal and mechanical properties, LDPE/PA/LDPE and LDPE/EVOH/LDPE materials are recommended for the processing conditions of this study, whereas PET/LDPE/PA/EVOH/LDPE materials require further evaluation of other functional properties.