Comparative mechanical properties between biocomposites of Epoxy and polyester matrices reinforced by hemp fiber

Abstract

Natural fibers have, in past decades, been increasingly used as reinforcement of polymer matrix composites in substitution for synthetic fibers. This work presents a comparative study on the mechanical properties of both epoxy and polyester composites reinforced with promising hemp fiber. The comparison would allow which of these thermoset matrices is more adequate for novel biocomposites to be used in technological applications. Amounts of 10, 20 and 30 vol% of continuous and aligned hemp fibers were mixed with either epoxy or polyester inside steel molds kept under pressure and cured for 24 h at room temperature. Plain epoxy and polyester plates were also fabricated for control samples. Basic characterization by Fourier transform infrared spectroscopy was preliminarly performed. Mechanical properties were obtained in flexural and tensile tests according to ASTM standards. Results were statistically compared by ANOVA and Tukey tests. Fracture was analyzed by scanning electron microscopy. For higher amount, 30 vol% of reinforcing hemp fiber, the epoxy composites disclosed superior strength than those of polyester composites. Indeed, for epoxy composites the flexural and tensile strength, 76.7 and 50.5 MPa, respectively, are higher than corresponding 49.1 and 25.4 MPa, respectively, for polyester composites. As for the elastic modulus, the flexural of 30 vol% hemp fiber/epoxy composites, 3.8 GPa, was superior to 30 vol% hemp fiber/polyester, with 1.2 GPa. These results indicate a potential application of hemp fiber/epoxy composites as part of multilayered armor systems for personal ballistic protection. Keywords: Hemp fiber, Epoxy composite, Polyester composite, Mechanical properties