Thermal Transformation of Selected Non-Steroidal Anti-Inflammatory Drugs Trapped in Silica Beads via Amine-Functionalised Silica Gel

This study presents solid dispersions of naproxen and sodium ibuprofen in porous SiO2 pellets (manufactured via the hard template method) before and after additional phase manufacture from amine-functionalised silica gel. Nanoscopic pore evolution of the investigated materials was examined at all stages of synthesis using positron annihilation lifetime spectroscopy (PALS). The TG–DSC–FTIR/MS in He and synthetic air provided information on the systems’ thermal transformations. PALS showed that both drugs preferentially occupied smaller mesopores in SiO2 pellets. Thermal analysis revealed distinct atmosphere- and drug-dependent behaviour. Silica confinement delayed naproxen’s thermal degradation but decreased sodium ibuprofen stability. Interestingly, thermal decomposition of sodium ibuprofen most likely also occurred through the evolution of volatile ibuprofen, as signals assigned to it were detected in both atmospheres, although less extensively in air. Encapsulation of naproxen in the investigated systems made it more resistant to high temperature, whereas for sodium ibuprofen the opposite tendency was observed. The amine-functionalized silica phase increased the overall thermal stability of both dispersions in helium, whereas oxidation in synthetic air seemed to be governed mainly by the NH2-SiO2 phase degradation.