Enhancing Flexural Properties of Recycled Glass Fibre Reinforced Polyester with Eggshell-Derived Calcium Oxide

Today, sustainability has become a pressing issue, with waste ending up in landfills and polluting the environment. One significant source of waste is eggshells, which are rich in calcium carbonate (CaCO3) that can be calcinated to produce calcium oxide (CaO) filler. CaO filler has been proven to enhance the mechanical properties of composites. However, the impact of CaO filler loading on unsaturated polyester (UP) composites has not been explored. To address this gap, a study was conducted to investigate the effect of CaO filler loading on the flexural properties of UP and recycled glass fiber reinforced polyester (rGFRP)/UP composites. CaO filler was incorporated into UP resin, with filler percentages varying from 1–15wt.%, before selecting 1-7wt.% of CaO to be hybridized with rGFRP/UP composites containing 25wt.% of rGFRP. The flexural properties of the specimens were tested at a rate of 1.5 mm/min using the ASTM D790 standard. Incorporating 1 and 5wt.% CaO in UP shows an improvement in flexural modulus by approximately 90%, attributed to the optimal dispersion of CaO at these concentrations. Conversely, the flexural strength of CaO-filled UP decreased slightly by 5% to 10% with the addition of 1 to 10wt.% CaO, respectively. Reinforcing 25wt.% rGFRP to UP led to a notable 2.5-fold increase in flexural modulus. The further inclusion of 1 wt.% CaO in rGFRP/UP composites resulted in a slight improvement in flexural modulus from 3.94GPa to 4.02GPa. However, further increasing the CaO filler loading in rGFRP/UP composites resulted in a decrease in both flexural strength and modulus.