Influence of modified calcium sulfate hemihydrate whisker on the physical, mechanical, and microscopic properties of gypsum matrix composites

Fabricated calcium sulfate hemihydrate whiskers (CSHWs) were modified using the solubility product principle at about 20 °C. The designed structures and morphologies of the modified calcium sulfate hemihydrate whiskers (MCSHWs) were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. Three types of MCSHW/gypsum composites were prepared using MCSHWs as reinforcers. The physical, mechanical, and microscopic properties of the MCSHW/gypsum composites were studied. The surfaces of CSHWs modified by C6H9O7Na were considerably coarsened, which improved the interfacial properties of the MCSHW/gypsum composites. The initial and final setting times of the three types of MCSHW/gypsum composites exhibited decreasing trends, while the porosities decreased and then increased with the increase in the MCSHW content. The optimal flexural and compressive strengths of MCSHW/flue gas desulfurization gypsum composites were 5.41 and 9.37 MPa, respectively, when the MCSHW content was 10 wt%. The MCSHWs not only filled the material voids and reduced the porosity, but also connected the structural defects and prevented the development of cracks, effectively improving the mechanical properties of the MCSHW/flue gas desulfurization gypsum composites.