Flowability prediction of recycled α-hemihydrate gypsum for 3D powder printing under combined effects of different glidants using response surface methodology

In this study, a high-value-added recycled α-hemihydrate gypsum (α-RHG) generated from WGP using the atmospheric pressure hydrothermal method (APHM) was utilized to manufacture a 3D printed material. The univariate and combined effects of affordable and high-performance glidants, including hydrophobic nano-silica (HNS) and soluble starch (SS), on the flowability of α-RHG were evaluated experimentally and modelled. The results revealed that the flowability of α-RHG can be enhanced by the proper univariate addition of HNS (e.g., <1.0 wt%) or SS (e.g., <3.0 wt%). In addition, the experimental and modelling results based on central composite design (CCD) using response surface methodology have consistently demonstrated that the optimal flowability of α-RHG can be achieved by incorporating an optimum combined addition of 1.0 wt% HNS and 3.0 wt% SS. Finally, a 3D printed sample with a flow rate of 3.16 g/s using the modified α-RHG powder with optimum addition of HNS and SS was successfully produced.