Experimental study on the recyclability and reusability of Plaster of Paris (POP) mould in ceramics manufacturing

In this research, the recycling process of used Plaster of Paris (POP) has been studied by involving the drying of POP powder to restore the original properties of Plaster of Paris that can be reuse in mould casting. This research was done by collecting used POP powder samples and drying them at different temperatures: 37°C, 150°C, 160°C, 170°C, 180°C and 190°C. This drying process aims to remove crystal water from the hydrated powder and return it to the hemihydrate form. Hence, this used POP is denoted as Recycle Plaster of Paris (RPOP). The results of the study show that temperature plays an important role in the recycling process. At the first stage, a drying temperature of 37°C, the dehydration process is incomplete producing used RPOP that cannot be reused, and the slurry does not freeze with low mechanical strength. At 150°C, a better partial dehydration occurs, but there is still moisture in the material. At 160°C, results are obtained with almost perfect dehydration, producing RPOP that is almost equivalent to New Plaster of Paris (NPOP) in chemical and physical properties that have been tested. The drying temperatures of 170°C, 180°C and 190°C cause some material degradation, although complete dehydration is achieved. Based on the results obtained, the optimal RPOP recycling process was found at a temperature of around 160°C, where RPOP can be converted back into hemihydrate with almost the same quality as NPOP. This process also indicates that increasing the temperature above 170°C does not provide significant additional benefits and can even damage the material. In the second stage, this study continues by testing the chemical and physical properties of RPOP through drying at a temperature of 160°C and adding the activator Silubit G80 to find out the reaction of RPOP with Silubit G80 whether the chemical and physical properties of RPOP + Silubit G80 are better or vice versa. This ensures that the final product has acceptable performance for casting use. The third stage, after all the tests were completed and the most optimal results were obtained, the mould making process using NPOP, RPOP 160℃ and RPOP 160℃ + Silubit G80 0.5% was tested again to estimate its casting capability. At this stage, the casting time and performing consistence were precisely analyzed to ensure that each mould could function properly. As a control reference, NPOP was used as a control in this evaluation. The testing was carried out using a simple form so that the comparison between NPOP, RPOP 160℃ and RPOP 160℃ + Silubit G80 0.5% could be evaluated objectively and directly before the intrate form was used. This study shows that used moulds can be reused by undergoing a recycling process. Furthermore, RPOP can produce an intracate mould shape without damage to the mould wall, especially in the geometrically angled part. Even so, the RPOP + Silubit G80 0.5% mould can still be used as a casting mould. This study contributes to the development of sustainable mould materials in the ceramics industry and helps reduce material waste.