Development and characterization of hemp/carbon and hemp/glass hybrid and novel functionally graded hybrid composites for structural applications

Abstract The main objective of this study is to investigate the effect of combining natural and synthetic fibers on the mechanical characteristics of hybrid and novel functionally graded hybrid composites by considering hemp as natural fiber and carbon and glass as synthetic fibers. Before manufacturing, the natural fibers were treated with sodium hydroxide (NaOH) solution to remove the impurities on the fiber surface. The fibers were reinforced in an epoxy‐based matrix using a hand‐layup technique. The volumetric fraction of the hybrid composites was 40% fibers and 60% matrix. Different types of composites, such as plain fiber reinforced polymer (FRP), sandwich hybrid (SH), alternative hybrid (AH), and functionally graded hybrid (FH), were manufactured from hybridizations of hemp/carbon and hemp/glass. In accordance with ASTM standards, the tensile, compression, flexural, short beam shear, water absorption, and wettability properties of composites were determined. FH composites with hemp fiber at the top surface had the highest improvement in tensile strength, stiffness and compressive strength compared with pure hemp FRP (HFRP) composites. Hemp SH composites had the highest improvement in flexural and short beam properties in both hybridizations compared with HFRP composites due to the stacking of synthetic fiber at the outer layers. Scanning electronic microscopic (SEM) studies identified the failure mechanism of the tensile failure specimens and also the effect of mercerization on fiber surfaces. In conclusion, this work identified the structural capacity of hybrid composites and emphasizes that FH and hemp SH composites can replace glass FRP composites in structural applications. Highlights Treating hemp fiber with 2 g/L of NaOH for an hour had a better impact. Functionally graded composites had better in‐plane strength and stiffness. Composites made with synthetic fiber on the outer layers were good at bending. In structural applications, hemp/carbon hybrid composites can replace GFRP.