Surface Modification of Calcium Sulphate Whiskers: Methodologies, Modifiers and Composite Synergistic Modification Strategies

Calcium sulphate whiskers (CSWs) are a family of one-dimensional calcium sulphate crystals with different hydration states, which can be generally expressed as CaSO4·nH2O, where n = 2, 0.5, or 0 for calcium sulphate dihydrate whiskers (DH-CSW), calcium sulphate hemihydrate whiskers (HH-CSW), and anhydrous calcium sulphate whiskers (AH-CSW), respectively. Owing to their high strength, high modulus, low density, and favourable thermal stability, these whiskers have significant application potential in polymer composites, building materials, papermaking, and environmental remediation. However, the agglomeration issues arising from CSW’s highly polar surface and large specific surface area lead to insufficient interfacial compatibility with the matrix, severely limiting its reinforcement and toughening efficacy. Consequently, this paper provides a systematic review of surface modification techniques for CSW, focusing on modification methods, modifier structural selection, and surface interaction mechanisms. Particular emphasis is placed on composite synergistic modification: through organic-organic, inorganic-inorganic, and inorganic-organic composite strategies, complementary synergies between different modification mechanisms are achieved, effectively enhancing the interfacial bonding stability and functional integration of the modified layer. Finally, the paper notes that current research still faces key challenges, including insufficient microscopic analysis of modification mechanisms, unclear structure-effect relationships between modifiers and modification outcomes, and a lack of green, scalable processes. Future efforts should integrate multi-scale interfacial characterisation with molecular simulations, optimise modifier selection and composite synergistic strategies, develop eco-friendly and efficient modification systems, and establish a controllable, functionalised framework for interfacial design. This will provide a theoretical foundation for the high-value application of CSW in high-performance composites and advanced functional materials.