Enhancing mechanical properties of PVC composites through surface composite modified calcium sulfate whiskers

To enhance the high-value utilization of industrial wastewater, this study used ammonium sulfate wastewater discharged from a rare earth plant as a raw material for producing anhydrous calcium sulfate whiskers (CSWs) through a hydrothermal method. Subsequently, the whiskers underwent modification using a C18H36O2–titanate coupling agent. The modification mechanism of CSW was investigated by comparing the surface contact angle before and after modification, along with characterization and analysis involving X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric-differential thermal analysis, and X-ray photoelectron spectroscopy. Finally, composite-modified calcium sulfate whiskers (CMCSWs) were incorporated into polyvinyl chloride (PVC) composites, and their mechanical properties were evaluated. The results indicated that at a modifier dosage of 15%, a modification time of 25 min, a modification temperature of 80°C, a stirring speed of 400 rpm, a drying temperature of 100°C, and a C18H36O2-to-titanate coupling agent compound ratio of 1:2, the contact angle reached 124.45°, and a nanoscale hydrophobic layer with a thickness of 15.63 nm was formed on the surface. Regarding PVC reinforcement, the tensile strength and elongation at the break of PVC composite with 15 parts of CMCSW added increased by 73 and 262%, respectively, compared to the material without CSW. This CSW serves as an innovative reinforcing agent for PVC composites. The study developed modified CSW with high hydrophobicity, offering theoretical insights for effectively modifying fiber-type whiskers and their reinforcement in PVC applications.