Void content and moisture absorption behavior of hybrid vinyl ester composites reinforced with different forms of coconut shells and glass

Natural and hybrid composites are the preferred use at present and in the future in terms of enhancing environmental sustainability and reducing the use of non-biodegradable synthetic materials. From this perspective, vinyl ester reinforced chemically treated coconut and glass in powder, chopped, and fiber in weight fractions (20, 30, 40, and 50%) have been investigated to study their ability to absorb moisture by immersing them in water for 21 days and measuring their weight every day. The experimental density was less than the theoretical density across all samples, ranging from 0.249% in NSP at 40% weight fraction to 7.075% in NSF at 20% weight fraction. Additionally, the experimental density increased with the weight fraction, reaching a maximum of 1.406 g/cm 3 in hybrid NSP composites at a 50% weight fraction, making them suitable for structural applications requiring high density and moisture resistance. In addition, the chemical composition of the composites was explained through Fourier Transform Infrared (FT-IR) Spectroscopy. Based on these results, the water absorption showed that hybrid composites reduced moisture uptake by 45% compared to natural composites, with the lowest absorption recorded in glass-reinforced composites. Among the tested samples, six composites have the best-balanced combination (the lowest ability of moisture absorption with little void content) among 36 types; SP20 1.19% with void content 1.775%, SCH40 1.739% with void content 2.922% and NP50 2.5% with void content 0.690%.