Sustainable biobased composites: Fumaric acid-based epoxy resin synthesis and modified natural waste reinforcements

The increasing demand for sustainable alternatives to petroleum-based polymers has accelerated the development of biocomposites to mitigate environmental impact. In this study, a novel bio-based epoxy resin (EFA) was synthesized via the reaction of fumaric acid (FA) and epichlorohydrin (ECH), and characterized using FT-IR, ¹H NMR, viscosity, mass spectrometry, and epoxy group analysis. Apricot kernel shell (APKSh), an agricultural waste, was used as a natural reinforcement, modified with citric acid (CA) and levulinic acid (LA) to improve interfacial compatibility. Composites were produced with filler contents ranging from 5 to 30 wt% and tested for FT-IR, SEM, TGA, DMA, mechanical, thermal, and surface properties. The 15 wt% CA-modified composite exhibited a tensile strength of 105.7 MPa, an elastic modulus (e-modulus) of 8.7 GPa, and a Shore D hardness of 80, representing up to 222 % improvement in tensile strength and 107 % improvement in hardness compared to the neat ER-EFA (7:3 weight ratio). The LA-APKSh composites showed a char residue of 26.9 % at 800 °C and a T_g value of 106.01 °C. Contact angle (C.A.) measurements revealed enhanced hydrophobicity, with values exceeding 99.6° for CA-APKSh composites. The weight gain data in seawater indicated that all composites had higher values compared to the neat ER-EFA matrix (7:3 weight ratio). ANOVA analysis highlighted the influence of filler type and content on composite properties. This study presents a promising approach to developing high-performance, eco-friendly epoxy composites using chemically modified lignocellulosic waste.