Woven hemp fabric reinforced vinyl ester composite: effect of water absorption on the mechanical properties degradation

Natural fibre composites are potentially used in manufacturing industries and for that purpose, their water absorption properties are essential to be analysed. In this study, untreated and fire retardant chemical (FR) treated woven hemp fabrics (WHF) were used to reinforce vinyl ester resin. Water absorption tests were utilised to study the behaviour of water penetration into the composites. The diffusion coefficient were measured using Fick’s law while degradations of their mechanical properties were measured after 0, 168, 840 and 2688 hours of water immersion. It was found that the maximum water uptakes, times to saturation point and diffusion coefficient for fabricated composites were ranging 3.27-3.43%, 552-1848 hours and 1.45E-06 - 4.71E-06 mm2/s respectively. In terms of mechanical properties, the presence of water reduced the tensile strength and modulus up to 24% and 39% respectively due to the penetration of water which weakened the adhesion between the fibres and resin. The greater decline in tensile modulus than tensile strength due to the plasticisation of water on the vinyl ester and hemp fibres. Similar reasons can be applicable to the flexural properties for both samples since they show quite similar behaviour with tensile properties