Impacts of hemp fiber diameter on mechanical and water uptake properties of polybenzoxazine composites

The waste hemp fibers (HF) were alkali treated; then shredded, ball milled, and sieved. The 20, 40, and 80 mesh collected HF was reinforced in polybenzoxazine. The effects of fiber diameter and vol.% loading on tensile, impact, flexural and water uptake properties of composites have been studied. On 30 vol.% loading of 20 mesh HF, an increase of 91%, 43%, 168%, 137%, and 73% in tensile strength, flexural strength, impact strength, tensile modulus, and flexural modulus, respectively. The additional enhancement was observed in all mechanical properties as fiber diameter was reduced from 311.5 +/- 42.9 to 198.3 +/- 40.7 mu m (20-80 mesh). The similar behavior was confirmed by Halpin-Tsai model. The water uptake was also increased as vol.% loading increased and HF diameter decreased, 28.2% higher water uptake was observed on 20 vol.% loading as the diameter was reduced from 20 to 80 mesh.