Thermal oxidative stability and effect of water on gas transport and mechanical properties in PA6‐EVOH films

Abstract

The thermal oxidative stability and the effect of water on gas transport and mechanical properties of blends of polyamide 6 (PA6) with ethylene-co-vinyl alcohol (EVOH) and EVOH modified with carboxyl groups (EVOH-COOH) have been investigated. The presence of EVOH reduces water vapor and oxygen gas permeability of polyamide, as well as small amounts of EVOH-COOH further improve barrier properties, especially to oxygen. This has been explained in terms of improved interactions of the blend constituents in the amorphous phase, due to ionic linkages between the polyamide amino groups and the carboxyls of modified EVOH. The permeation to gases was found to increase with the amount of sorbed water. The morphology of the samples was found to have an effect on barrier properties, as the presence of EVOH causes the PA6 a crystalline form to increase, lowering the permeability to oxygen and water vapor. Mechanical properties are strongly affected by water sorption, as tensile modulus and strength decrease with increasing water content. Chemiluminescence (CL), infrared spectroscopy (FTIR), and tensile test were employed in order to assess the correlation between chemical composition and the thermal oxidative stability of the films aged at 110 8C in air. CL experiments suggest that the presence of EVOH and EVOH-COOH efficiently inhibits the formation of peroxidized species during the processing, and increases the thermal oxidative stability of the films. Infrared spectroscopy showed a build-up of carbonyl absorption in the range 1700-1780 cm À1 , due to the formation of oxidation products, which is greater in the case of the pure polymer. Tensile tests on films revealed a reduction in ductility as a result of ageing for neat PA6, whereas in comparison the blends exhibit a far better long-term stability. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 840-849, 2007

Linking morphology changes to barrier properties of polymeric packaging for microwave‐assisted thermal sterilized food

“…In terms of the crystallinity of the EVOH layer in Film B (ranging from 81.5% to 94.5%), there were no statistical differences found either after processing or during storage ( P > 0.05). Oxygen barriers are thought to be closely related to the crystal region of polymers, with higher crystallinity films having greater oxygen barrier properties . In this study, the changing pattern of PET crystallinity (%) followed well with the OTR changes in film A.…”

“…Oxygen barriers are thought to be closely related to the crystal region of polymers, with higher crystallinity films having greater oxygen barrier properties. 23,24 In this study, the changing pattern of PET crystallinity (%) followed well with the OTR changes in film A. However, film B did not show the same correlation.…”

Role of package headspace on multilayer films subjected to high hydrostatic pressure

“…However, the decrease in crystallinity was not statistically significant ( P > 0.05). The initial reduction in crystallinity of the EVOH‐based film could be due to plasticization by water (food simulant) absorbed during the process . The insignificant decrease in crystallinity of film A in the white spot may be due to the change in topography rather than the change in the morphology of the film's inner layer.…”

“…The initial reduction in crystallinity of the EVOH-based film could be due to plasticization by water (food simulant) absorbed during the process. 38,42,43 The insignificant decrease in crystallinity of film A in the white spot may be due to the change in topography rather than the change in the morphology of the film's inner layer. In contrast, film B showed a decrease in crystallinity of about 11% after processing at 600 MPa and 90°C, decreasing from 81% to 70%.…”

Thermal oxidation of clay-nanoreinforced polypropylene

“…To follow the evolution of the oxidation process over time, infrared micro-spectrometry measurements in transmittance mode are often performed [18,19]. However, its spatial resolution of about 25e30 mm does not permit the measurement of oxidation layers, whose individual thickness is of the order or even lower than this resolution.…”