Hemp Fibre Reinforced Sheet Moulding Compounds

Abstract

Glass fibres are by far the most extensively used fibre reinforcement in thermosetting composites because of their excellent cost-performance ratio. However, glass fibres have some disadvantages such as non- renewability and problems with ultimate disposal at the end of a materials lifetime since they cannot be completely thermally incinerated. The possibility of replacing E-glass fibres with hemp fibres as reinforcement in sheet moulding compounds (SMC) is examined in this thesis. The composites are manufactured with existing SMC processing techniques and similar resin formulation as used in the commercial industry. An attempt is made to enhance/optimise the mechanical properties of hemp/polyester composites. For this the fibre-matrix interface is modified via chemical modifications with alkaline and silane treatments. Influence of hemp fibre volume fraction, calcium carbonate (CaCO3)filler content and fibre-matrix interface modification on the mechanical properties of hemp fibre-mat-reinforced sheet moulding compounds (H-SMC) is studied. The results of H-SMC composites are compared to E-glass fibre-reinforced sheet moulding compounds (G-SMC). In order to get a better insight in the importance of these different parameters for the optimisation of composite performance, the experimental results are compared with theoretical predictions made using modified micromechanical models such as Cox-Krenchel and Kelly- Tyson for random short-fibre-reinforced composites. These models are supplemented with parameters of composite porosity to improve the prediction of natural fibre composite tensile properties. The influence of impact damage on the residual exural strength of the H-SMC composites is investigated to improve the understanding of impact response of natural fibre reinforced composites. The result of penetration and absorbed energies during non-penetrating impact of H-SMC composites are investigated and compared to values for G-SMC. A simple mechanistic model has been developed for H-SMC composites and is used to get an insight into the impact behaviour of these composite as well as to provide a guideline to compare the experimental results with theoretically calculated data. The fracture toughness properties in terms of the critical-stress-intensity factor KIc, and critical strain energy release rate, GIc, of H-SMC and G-SMC composites are studied using the compact tension (CT) method. It was shown that fracture toughness of H-SMC composites is significantly lower than that of glass fibre reinforced composites (G- SMC). However, results show that with an optimum combination of fibre volume fraction, (CaCO3) filler and surface treatment of the hemp fibres can result in H-SMC composites that have fracture toughness properties that can be exploited for low to medium range engineering applications. It is recommended that to further improve the fracture toughness properties of these natural fibre reinforced composites more research needs to be devoted to the optimization of the fibre-matrix interface properties and ways of reducing porosity content in these composites. Finally, environmental impact of H-SMC composite with conventional G-SMC composite for automotive and non-automotive applications was compared. The composites were assumed to be made in a traditional SMC manufacturing method. Two different types of performance requirements; i.e. stiffness and strength were investigated for both the non-automotive and automotive parts. Two different disposal scenarios: landfill and incineration of the SMC product at the end of life was considered. The LCA results demonstrate that the environmental impact of H-SMC composites is lower than the reference G-SMC composites. G-SMC composites have a significantly higher environmental impact on climate change, acidification and fossil fuels than H-SMC composites. Where as H-SMC composites have a much higher impact on land use and ecotoxicity than G-SMC composites.