Synthesis and thermomechanical characterization of PEG/cristobalite composites

Synthesis and thermomechanical characterization of polyethylene glycol-silica cristobalite composites have been successfully performed. Commercial Polyethylene glycol (PEG) 4000 and natural-silica-sand-derived cristobalite (SiO₂) powders were used in this research. The cristobalite ceramic powder was produced by a coprecipitation method using silica sand from Tanah Laut, South Kalimantan as the raw material. XRD data analysis for the cristobalite powder showed that it contained 98.8 wt% cristobalite and 1.2 wt% tridymite - both are polymorphs of silica. The PEG-cristobalite composition was varied in the composites at PEG weight fraction of 100, 80, 60 and 40 %. PEG and cristobalite dry powders were simply mixed and then uniaxially pressed before a heat treatment at 50 °C to form dense composite prior to characterization. Further FTIR and XRD data analyses for the densed samples showed the success of the formation of the composite. The thermomechanical properties was characterised using Dynamic mechanical analysis (DMA) instrument with shear mode. In general, at all measurement temperatures, the storage modulus (G’) of the composites was significantly improved with the addition of cristobalite, e.g. its values for 60 % cristobalite sample was 13 times that of the pure PEG sample. The pure samples showed a rubbery plateau behaviour which was not found in the composite samples. It was also found that by increasing the amount of cristobalite, the glassy transition temperature (T_g) increase from 56 °C for the pure and 68 °C for the 60 % cristobalite samples respectively.