Effect of silica aerogel – Aluminium trihydroxide hybrid filler on the physio-mechanical and thermal decomposition behaviour of unsaturated polyester resin composite

Abstract

Aluminum trihydroxide (ATH) is an eco-friendly and economical additive used in polymers as a flame retardant (FR), but its low thermal stability has become an important issue that is critical in determining the fire protection and thermal stability of the composites. The present study was an attempt to enhance the thermal stability of ATH to some extent by combining it with nano-porous silica known as silica aerogel (SA) as a hybrid FR filler in unsaturated polyester resin (UPR). Ultra-low density SA (0.07 g/cm3) in the form of fine particles was extracted from renewable resources (i.e. rice husk), through a sol-gel process, surface modification and dried at atmospheric pressure. From our findings, it is found that the addition of the hybrid filler into UPR results in interesting properties such as lightweight, flame retardancy and enhanced thermal stability whose properties cannot be gained by composites with single filler. From thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gas analysis using Fourier transform infrared spectroscopy (FTIR); it is evident that doping the ATH with SA helps to improve the thermal stability via synergistic effect, by extending the ATH decomposition process over a wider temperature range. As a result, the UPR filled with SA/ATH hybrid demonstrates higher thermal stability when compared to the composites filled with only ATH or SA. Furthermore, the SA/ATH hybrid also provides sufficient flame retardancy in UPR as evaluate by ASTM D635-14 (UL–94) horizontal burning test. For mechanical properties, a sharp increase in tensile strength was observed for UPR filled with ATH or SA while the addition of SA/ATH hybrid filler only slightly increases the tensile properties of UPR due to particle agglomerations and porosities.