Effect of water absorption on mechanical properties of soybean oil thermosets reinforced with natural fibers

Natural fiber composites are known to absorb more water than glass fiber reinforced composites. In this study, hybrid natural fiber composites were prepared by combining different fiber reinforcements, and both the water absorption and the mechanical properties were studied. Compression molding technique was used to manufacture composite laminates from a bio-based resin (acrylated epoxidized soybean oil) and natural fibers: non-woven and woven jute, non-woven regenerated cellulose mat (Lyocell and viscose), and woven glass fiber. The composite laminates were cured at 160–170°C and 40 bar, with a fiber content of 40 wt%. We investigated effect of pretreatment of regenerated cellulose fiber using 4% NaOH solution. The gravimetric water absorption was tested by exposure to water for 10 days. Specimens were cut from composites with laser-cutting technique according to ISO standards, and tested for tensile, flexural, and impact strength. To determine the influence of water absorption on the mechanical properties, specimens were immersed in distilled water for 10 days before testing. As a reference, dry specimens were tested. The results showed that water absorption was reduced by producing hybrid composites with jute fibers, glass fiber, and Lyocell fiber. The tensile, flexural, and impact properties were improved by inclusion of glass fiber and Lyocell in the composite. The tensile and flexural properties of natural fiber reinforced composites were mostly affected by the influence of water, but this was improved considerably by hybridization with glass and Lyocell fibers. The viscoelastic properties of the manufactured composites and hybrid composites were studied using dynamic mechanical thermal analysis.