Degradation of high barrier ethylene–vinyl alcohol copolymer under mild thermal‐oxidative conditions studied by thermal analysis and infrared spectroscopy

Abstract

A study of the thermal-oxidative degradation of a high barrier ethylene±vinyl alcohol copolymer with 32 mol% of ethylene (EVOH) has been carried out by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) under mild temperature conditions above melting. It was found that time exposures of up to 11 h at temperatures between 9 and 33°C above the EVOH melting point resulted in polymer weight losses of up to 3.6% with colour formation. The weight loss was faster at short times and slowed down with increasing exposure time. DSC showed a small decrease in crystallinity and melting point, melting-peak broadening and a slight increase in the glass transition temperature of the samples subjected to the more severe thermal-oxidative treatment. The FTIR experiments showed transformation of the vinyl alcohol hydroxyl groups into carbonyl groups and creation of double bonds. Changes in degradation kinetics and perhaps in mechanisms are thought to occur with increasing exposure time. Moreover, FTIR measurements suggest that transformation of the hydroxyl groups leads to a weakening of the overall hydrogen bonding strength in the degraded samples, and therefore a reduction in intermolecular cohesion can be anticipated.

Influence of processing on the ethylene-vinyl alcohol (EVOH) properties: Application of the successive self-nucleation and annealing (SSA) technique

“…Artzi et al [19] working with EVOH/nanocomposites pointed out that when EVOH is processed at high temperatures, two competitive mechanisms may take place, namely thermal degradation (with chain scission) and grafting and oxidative crosslinking reactions. Similar results have been reported by Lagaron et al [20] under thermo-oxidative conditions (about 2 h at 215°C) without shearing. Considering that some traces of acetoxyl groups from incomplete saponification of EVA precursor could be present, some intermolecular transesterification reactions between the ester and hydroxyl groups could be taking place, resulting in some cross-linking and/or chain extension reactions.…”

Development of EVOH-kaolinite nanocomposites

“…According to Zanneti's model, the thermal stability increase is explained by the fact that the clay, together with the solid degradation products, lead to a dense coating that hinders the development of further degradation by opposing a strong mass transport resistance to the agents involved in the reaction, resulting in a decrease of the degradation kinetics. Similar degradation steps, as those reported for the EVA copolymers, have been found in a previous study on EVOH [22].…”

Subcritical gas‐assisted processing of ethylene vinyl alcohol + nanoclay composites

“…In Figures and , the TGA weight loss percent and the derivative weight loss are shown for the samples with and without NC. Several studies show that EVOH is easily degraded during thermal processing, like extrusion . The method of degradation is thermally induced chain‐scission via oxidation.…”