Experimental investigation and flow visualisation of the resin transfer mould filling process for non-woven hemp reinforced phenolic composites

Resin transfer moulding (RTM) of glass fibre reinforced polymeric composite s offers the advantages of automation, low cost and versatile design of fib re reinforcement. A replacement of glass fibres with natural plant fibres a s reinforcement in polymeric composites provides additional technological, economical, ecological and environmental benefits. The resin transfer mould filling process has significant effects on different aspects, such as fibr e wetting out and impregnation, injection gate design, "dry patch" and void formation. Flow visualisation experiments were carried out using a transpa rent RTM mould to develop a better understanding of the mould filling proce ss for hemp mat reinforced phenolic composites. The mould filling of unrein forced phenolics was characterised by a "quasi-one-dimensional steady state " flow. In the case of hemp non-woven reinforced system, the mould filling process can be considered as the how of fluids through porous media. "Fibre washing" was a typical problem encountered during the injection process, l eading to poor property uniformity. In addition, a preferential flow path w as usually created near the edges and corners of the mould. The path exhibi ted low flow resistance and caused the resin flow front to advance much fas ter in these regions. The edge flow disturbed the steady flow, leading to d ifficulties in venting arrangement and "dry patch" formation. The edge flow and fibre washing were alleviated by reinforcement manipulation so steady state how could be achieved. The relationships between the filling time and injection pressure and between filling time and different fibre weight fra ctions have been established for certain specific injection strategies. (C) 2000 Elsevier Science Ltd. All rights reserved.