ABSTRACT
Methacrylate-based polyhedral oligomeric silsesquioxane (POSS) is one of the new composites used as a dental resin. Both monofunctional methacryl isobutyl POSS (MIPOSS) and multifunctional methacryl POSS (MAPOSS) are reported to be possible resins that possess the desired properties for using them as dental resins. Our group's previous comparative study on these two resins showed that the MAPOSS composite has superior mechanical properties compared with the MIPOSS composite. In this article, molecular dynamic simulations (MD simulations) are performed to study the water sorption in these two composites. Water sorption in dental composites can have several effects on the material properties, performance, and longevity of dental restorations. Water sorption in MAPOSS and MIPOSS composites is analyzed by studying the hydrogen bonding, cluster analysis, density projection calculations, and diffusion coefficient calculation of water molecules within the resin matrix. MD simulations results are further used to understand the interaction of water molecules with the resin matrix comprehensively, which governs the composite's mechanical properties. The water sorption study showed that the MAPOSS composite has less water sorption capacity than the MIPOSS composite. The practical significance of this study is to find properties that affect dental restoration and longevity, which can help in the design of better materials for dental applications.
ABSTRACT
Phosphogypsum releases have a detrimental effect on flora and fauna and also cause economic loss due to the loss of sulfur. This study contributes to solving this problem using a process that consists of the valorization of this byproduct. A new sustainable method that consists of using sulfuric acid is proposed to process the Algerian phosphogypsum to recover the sulfur, which is imported in huge quantities until today. The experiments carried out in this investigation have enabled us to recover sulfur in the form of SO2 using appropriate additives such as silica, alumina, clay, and charcoal as reducing agents. These additives accelerate the desulfurization process and decrease the decomposition temperature of calcium sulfate. As a result, these additives allow the reduction of energy used and simultaneously increase the concentration of SO2. X-ray diffraction shows that thermochemical decomposition is not complete and that the sulfur present in the residue exists in the form of CaSO4 and CaS at 1150 °C. After calcination of phosphogypsum, the analysis of the residues obtained shows that they have a chemical composition almost identical in terms of quality to that of clinker, which can further be used in the cement production.
