Effect of Walnut Shell Powder and Nano-TiO2 on the Mechanical, Thermal, and Water Absorption Properties of Polyester Composites

This study investigates the potential of using ground walnut shell powder as a natural reinforcement for unsaturated polyester resin for sustainability and recycling, as an alternative to synthetic reinforcements. The main objective is to assess the effect of various filler contents 5%, 15%, and 25% wt. on the thermal and mechanical performance of the prepared composites. Hand lay-up technique was used to fabricate the casts, and the designated test specimens were cut according to the dimensions in the standard specification of each test (Impact strength, flexural strength, water uptake, and thermal conductivity). The results showed a significant improvement in the impact and flexural strengths at 15% wt. reinforcement, while thermal conductivity dropped with increasing filler weight fraction, suggesting enhanced thermal insulation. Water uptake increased at the first few weeks until a steady state is reached, after which the 25%wt. specimens showed the highest rate of water absorption, followed by the 15% and 5%wt. specimens, respectively. These findings show the suitability of using locally-available and inexpensive agricultural waste as an eco-friendly reinforcement for polymeric composites