Physical properties of zircon-filled poly(methyl methacrylate) composites following heating around its glass transition temperature

Zircon-filled poly(methyl methacrylate) (PMMA) composites were synthesized, and their physical properties after ambient heat treatments were investigated. The sub-micron zircon filler was obtained by purifying local zircon sand. The heat treatments were at 25°C (untreated), 55°C, and 70°C, around the glass transition temperature of PMMA. The crystal and molecular structures of the samples were investigated using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The thermomechanical, optical, and thermal (between RT and 550°C) properties of all composites were examined using dynamic mechanical analysis (DMA), UV–Vis spectroscopy, and differential thermal/thermogravimetric analysis (DT/TGA) instruments. XRD patterns showed that there were no crystal structure changes. FTIR peaks were reduced due to the heat treatment indicating the presence of PMMA molecular degradation in the heat-treated samples. Meanwhile, DMA data showed that the heat-treated samples exhibit a much lower room temperature storage modulus, that is, up to half as compared to the untreated ones. Furthermore, the heat treatment also affects the optical properties, including a slight drop of transmittance in UV-A and visible regions but a slight increase of transmittance in UV-B and UV-C regions. Finally, the differential scanning calorimetry/thermogravimetry (DSC/TG) data show that the heat-treated pure PMMAs become more challenging to undergo thermal degradation (i.e., mass drop).