High-performance eco-composites from walnut shells: evaluating raw silk and ramie as sustainable natural fiber reinforcements

Abstract

This study evaluates a novel composite material consisting of a polymer-based matrix reinforced with hybrid natural fibers (raw silk and ramie) and walnut shell powder. Natural fibers provide sustainability and lightweight benefits, while walnut shell powder provides lightweight benefits and durability. The present study was carried out to understand the water retention behavior and the mechanical behavior of epoxy composites made using walnut shell fillers, raw silk, and ramie fibers as reinforcements. First, it compares mechanical performance of composites involving fillers to those with only fiber. All specimens developed were made with 30% reinforcement (for fibers and for fillers) against 70% epoxy matrix. The experiments indicate that the walnut shell powder mixed with the fiber reinforcements reduces the void content. The composite epoxy/raw silk/walnut shell powder gave a void content of 1.37% as compared to other specimens, which was the best one. Among the other specimens studied, the composite of epoxy/raw silk/ramie/walnut shell powder demonstrated water absorption tests with the least amount of water uptake. For tensile property measurement, the composite of epoxy/ramie/walnut shell powder achieved a maximum tensile strength of 41 MPa, while epoxy/raw silk showed a maximum tensile modulus of 1.253 GPa. Maximum flexural strength is noted for the epoxy/ramie composite at 54.29 MPa. The blend of epoxy/raw silk composite has shown better impact strength than other configurations, at 9.1 kJ/m². The scanning electron microscopy (SEM) identified as main failure mechanisms studied after the mechanical testing fiber/matrix debonding, fiber rupture, and matrix fracture.