Impact of fiber treatment and nanoclay addition on water soaking effects of coir fiber reinforced epoxy composites

Polymer composites reinforced with natural fibers provide sustainable alternatives to synthetic materials, thanks to their biodegradability, low cost, and favorable strength-to-weight ratio. However, their hydrophilic nature leads to moisture absorption and mechanical degradation over time. The study examines the effect of alkaline fiber treatment and nanoclay incorporation on the water absorption and mechanical properties of coir fiber-reinforced epoxy composites. The compression molding method is used to fabricate composites using 20, 30, and 40 wt.% untreated and treated coir fibers with varying nanoclay contents (0, 2, and 4 wt.%). Water absorption tests reveal that the combination of treated fibers and nanoclay reduces water uptake by up to 35% compared to untreated composites. Mechanical testing reveals a steady increase in tensile strength with rising fiber content. With fiber treatment and the addition of nanoclay, the tensile strength increases from 57.75 MPa to 97.02 MPa, while the flexural strength improves from 78.31 MPa to 114.24 MPa under the same conditions. The C3N2 composite, comprising 40 wt.% alkaline-treated coir fiber and 4 wt.% nanoclay, retains over 91% of its tensile properties and 93% of its flexural properties after soaking. In contrast, composites with untreated coir fiber show a declining trend in strength retention with increasing fiber content. SEM analysis confirms enhanced bonding between the matrix and fiber interface, accompanied by reduced microstructural degradation. The findings demonstrate the potential of using surface modification and nanofillers to improve the resilience and mechanical integrity of natural fiber composites in harsh environments.