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 degrees C (untreated), 55 degrees C, and 70 degrees 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 degrees 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/thermo-gravimetry (DSC/TG) data show that the heat-treated pure PMMAs become more challenging to undergo thermal degradation (i.e., mass drop).