Taguchi optimization and ANOVA-based evaluation of hybrid epoxy composites reinforced with agricultural and industrial wastes for thermal insulation applications

Abstract This study aims to develop low-density sustainable composites by incorporating hemp fiber, rice husk, and glass fiber reinforced plastic (GRP) pipe waste obtained from industrial pipe cutting waste into an epoxy matrix. The effects of material ratios and matrix type on physical, mechanical, strength, and thermal properties were investigated within a two-level experimental design. Composites produced by hand-laying were characterized in terms of density, porosity, water absorption, Shore-D hardness, compressive strength, and thermal conductivity. Samples showed ultra-low bulk density in the range of 193–279 kg m −3 , and a strong inverse relationship was determined between density and porosity. While GRP waste acted as a densifying phase, water absorption values (26–41 %) were largely controlled by porosity. Epoxy A exhibited better interfacial integrity by providing lower moisture absorption. Mechanical results showed that hemp-rich and epoxy A-based compositions offered higher hardness and compressive strength. In contrast, the lowest thermal conductivity value of 0.0487 W m −1 K −1 was obtained in Epoxy B-based systems. ANOVA confirmed that matrix type is the dominant factor influencing thermal performance. The findings demonstrate that fiber ratio and matrix selection are critical in optimizing the performance of lightweight insulation composites and offer a viable strategy for waste-based building materials.