Effect of inorganic–organic surface modification of calcium sulfate whiskers on mechanical and thermal properties of calcium sulfate whisker/poly(vinyl chloride) composites

Abstract

Coupling agents are traditionally used to improve the interfacial adhesion between inorganic fillers and a polymer matrix; however, the application of this method is somewhat limited by the number of hydroxyl groups on the surface of inorganic fillers. In this study, a layer of calcium hydroxide (Ca(OH)₂) was coated on the surfaces of calcium sulfate whiskers (CSW) through hydroxylation modification using sodium hydroxide (NaOH) to increase the hydroxyl groups of the CSW, and then a polyether titanate coupling agent synthesized in our lab was used to modify Ca(OH)₂ coated CSW in order to improve their compatibility with poly(vinyl chloride) (PVC). The chemical structure and surface properties of the modified CSW were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA). Then, CSW/PVC and modified CSW/PVC composites were prepared via a two-roll mill, and the effects of the inorganic–organic surface modification of CSW on their mechanical and thermal properties were evaluated. The results show that hydroxylation modification can further improve the compatibility and the interfacial adhesion between CSW and the PVC matrix, which results in better mechanical and thermal properties.