The modification mechanism and the effect of magnesium chloride on poly(vinyl alcohol) films

The modification mechanism and the effect of MgCl₂ on poly(vinyl alcohol) and the effect of water in the system were studied in this paper. The effect of MgCl₂ on different fully dried PVA was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimeter, thermogravimetric analysis, water content test, dynamic thermomechanical analysis and tensile test, respectively. The results showed that MgCl₂ was an effective strengthening agent, which could crosslink with PVA and then effectively decrease the crystallinity of PVA. With the addition of MgCl₂, the strength and rigidity of PVA increased and the melting temperature decreased. The effect of MgCl₂ on thermal stability of PVA was related to the alcoholysis degree of PVA. The tensile strength of PVA films modified with MgCl₂ were all over 120 MPa. Moreover, the effect of MgCl₂ on the dynamic thermomechanical properties and tensile properties of PVA with various content of water was studied. Water could interact with MgCl₂ to destroy the crosslink between MgCl₂ and PVA. In the presence of water, PVA modified with MgCl₂ became soft, with lower tensile strength and higher elongation at break.