Conventional injection moulding and gas-assisted injection moulding of rice husk-filled high density polyethylene and polypropylene eco-composites

高密度聚乙烯和聚丙烯的谷殼環保復 [i.e. 複] 合材料之注塑及氣輔注塑研究

Student thesis: Doctoral Thesis

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  • Mount Tsun Dominic MAK


Awarding Institution
Award date15 Feb 2013


The continued consumption of petrochemical-based polymers has caused significant concern. Thus, there is an immediate need to develop environmentally-friendly eco-composite materials to replace conventional, petrochemical-based polymers. An effective approach in this development is filling of polyolefins with natural fibres or blended agricultural composites to reduce the demand on petroleum-based polymers. However, blended agricultural composites have several weaknesses, including: low melt-flow indexes, which do not flow effectively inside the moulds in conventional injection moulding, weak interfacing bonding between the hydrophilic natural filler and hydrophobic polymer, and increased shear viscosity with an increase in natural and agricultural filler content. While there are a large number of findings and research reports on the injection moulding of products with simple geometries, such as tensile bars, only a few successful cases have been reported on the injection moulding of eco-composite products with complicated products geometries. With additives and appropriate moulding parameters, the newly-blended composite can be injection-moulded with fewer moulding defects, even in complicated designs. In this study, eco-composites from rice husks filled with high-density polyethylene and polypropylene were blended by twin-screw extrusion and processed successfully using conventional injection moulding and gas-assisted injection moulding technology. Injection moulding is one of the most commonly used manufacturing processes in the production of polymeric materials in the plastics industry. An extremely versatile process, it can be used for both simple and complicated geometries in various sizes and wall thicknesses. The injection moulding process allows for the manufacture of a wide range of polymeric materials. The process obtains high production rates, high yields and repeatable high tolerance. The gas-assisted injection moulding process is also widely used in the plastics industry to improve moulding quality. This is achieved by hollowing out the internal section to reduce material consumption and costs in conventional petrochemical-based polymers, and it is particularly well suited for thick, moulded products. In addition, it possesses the following unique features: prevention of sink marks for the moulding of thick parts, consumption of fewer materials, and less mould clamping force and injection pressure are required, thus saving energy. However, there are certain challenges in the adoption of injection moulding and Gas-assisted Injection Moulding to natural fibre/agricultural-filled eco-composites. The incorporation of natural and agricultural filler will naturally increase the melt shear viscosity, which will make the moulding of certain delicate features more challenging. The increase in melt temperature can reduce shear viscosity, but this is a challenge as natural fibres and agricultural fillers have a relatively lower thermal degradation temperature. This study is the first attempt to use rice husk-filled eco-composite materials in a gas-assisted injection moulding process. The developed eco-composite also uses fewer petrochemical-based polymers which will reduce the negative impact on the environment.

    Research areas

  • Injection molding of plastics, Polypropylene, Rice hulls