Investigation into the improvement of recycled polypropylene for use in automobile manufacturing

Abstract

The increasingly strict legislation on plastic recycling and the public concerns about environmental protection have driven the waste plastics recycling industry and the development of recycled plastics applications. However, recycled plastics are rarely used in high-value-added applications, especially in the automobile industry. This thesis aimed to investigate the feasibility of utilising recycled plastics for auto parts manufacturing. It started with the background study focused on the use of plastics in automobiles and the status of waste plastic recycling in China. Recycled polypropylene (RPP) was selected as the focused material because it is widely used for the manufacturing of automobiles parts. A literature review of recycled plastics was conducted to understand the degradation mechanism and reinforcing techniques in detail. The experimental study consists of four sections: 1) Development and characterisation of the RPP/Talc composites for the manufacturing of the armrest box. The prepared formula processed the industrial trial, the products meet all the mechanical requirements of the armrest box, and it can save 35.2% of material cost. 2) Preparation of RPP-based blends for automobile bumper. With the addition of 20 wt% of maleic anhydride grafted linear low-density polyethylene (LLDPE-g-MA), the notched impact strength of the RPP composites improved by 252.6%. And 10 wt% LLDPE-g-MA filled RPP3 meet the mechanical requirements for the middle-end bumper. 3) Process development for the use of recycled short milled carbon fibre (rSMCF) as a filler and investigation of its effects on the mechanical properties of the composite. By adding 5 wt% rSMCF, the tensile modulus and flexural modulus of RPP composites increased by 52.3% and 47.3%, respectively. And the coupling agent maleic anhydride grafted polypropylene (MAPP) significantly improved the interfacial adhesion between rSMCF and PP matrix. At 5 wt% MAPP loading, The tensile strength and flexural strength of 5 wt% RSMCF filled PP composites was increased from 21.8 MPa to 24.3 MPa and 27.2 MPa to 31.7 MPa, respectively. This study shows that only a small amount of rSMCF addition will contribute to significant improvement of polypropylene (PP) based composites in tensile and flexural properties. 4) Evaluating the effects of hollow glass bead (HGB) on weight reduction, mechanical behaviours and flame retardancy. The effects of MAPP on compatilising RPP and fillers were analysed, the interfacial effects were studied by the microscale observation. By addition 10 wt% of HGB, the total weight of VPP and RPP composites have a reduction of around 4%. The reduction of impact properties is the major drawback of HGB. By adding 10 wt% of HGB in RPP3 and RPP4, the un-notched impact strength reduced by 54.1% and 48.5%. The processed cone calorimeter test shows by adding 10 wt% HGB to VPP, the heat release rate decrease from 766.6 kW/m2 to 536.6 kW/m2 . The mechanism of the flame retardancy of HGB was further analysed by scanning electron microscopy, during the burning HGB can form an effective protection layer floating on the melted plastics to suppress the flame and thus improve the flame retardancy of PP composites. This study found that it is possible to partially replace virgin polypropylene (VPP) with RPP in some specific automobile applications. The novelty of this research is the utilisation of well-developed techniques (filler addition, polymer blending) to develop recycled composite to meet the requirement from manufacturers and evaluate its performance in real automobile parts. It presented a crucial step from the lab-scale study to the large-scale industrial use of recycled plastics in the automobile industry. This study developed a process for manufacturing rSMCF filled PP composites. By only using a small amount

Date of Award	8 Jul 2021
Original language	English
Awarding Institution	Univerisity of Nottingham
Supervisor	Philip Hall (Supervisor), Peter Summers (Supervisor) & Michael George (Supervisor)