Understanding the Effect of Water Absorption on the Microstructure, Molecular Kinematics, and Relaxation Behavior of Polyvinyl Butyral Films

The effects of water molecules on the chemical structure, microstructure, molecular kinematics, and relaxation behavior of polyvinyl butyral (PVB) films were investigated. The 2D ATR-FTIR results demonstrated that water molecules initially interacted with free O–H and C═O, subsequently with hydrogen-bonded O–H and C═O between the hard and soft segments, and ultimately with hydrogen-bonded O–H and C═O in the hard segments. The SEM, AFM, DSC, and SAXS-WAXS results indicated that the microphase separation structure of PVB was formed by soft and hard domains, and the entry of water molecules disrupted the original structural regularity of the hard segments of the PVB films, resulting in a decrease in microphase separation degree. The BDRS results showed that water absorption had a significant effect on the molecular kinematics of the soft segments and the hard–soft interface. The results of the stress relaxation behavior showed that the relaxation properties of PVB films deteriorated after water absorption.