Effects of cross-linking by MgCl₂ as an initiator on the properties of EVOH

Ethylene vinyl alcohol (EVOH) with excellent barrier properties has insufficient thermomechanical properties. The introduction of magnesium chloride (MgCl₂) as an initiator in EVOH blends improved its properties by cross-linking. Torque behavior and gel experiment analysis indicated that a cross-linking in EVOH was formed. The cross-linking mechanism was confirmed through ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) and Fourier-transform infrared (FTIR) spectrometry. In ¹³C NMR spectra, the splitting peaks of CH carbon and CH₂ carbon tended to disappear, and the stretching vibration peak of –C=C– was observed in the FTIR spectra. The formation of hydrogen bond between MgCl₂ and EVOH destroyed the intramolecular and intermolecular hydrogen bonds of EVOH, which contributed to the dehydration of –OH to form –C=C–, and –C=C– was the basis for a cross-linking reaction. The thermal analysis of blends demonstrated that the melting temperature and crystallization temperature decreased, and the crystallinity gradually disappeared when the MgCl₂ content increased. Glass transition temperature significantly increased as the intermolecular force enhanced. Thermogravimetric analysis showed that a cross-linked structure could improve the thermostability of EVOH with an increase in the MgCl₂ content. Mechanical test results revealed a remarkable increase in the tensile strength of EVOH as the MgCl₂ content increased.