The use of recycled PET for high performance injection moulded components

Abstract

Recycling plays a crucial part in a circular economy. However, due to contamination and material degradation during a material’s use phase, the material properties of recycled material is reduced significantly, many times being used for second class applications. Instead, this project aims to upscale the properties of recycled PET (rPET) such that to achieve high performance mechanical properties with an injection moulding process. Hence, the aim of this project is to increase the tensile properties and thermal properties of rPET, in order to reach high performance properties, such as PEEK. Studies have shown that with the use reinforcing fibres, such as, E-glass or Basalt fibres, the tensile properties increases significantly. Ceramic fillers, coupling agents and nucleating agents may also increase the tensile properties, as the two former enhance the adhesion and bonding between the two phases of the composite, while the latter increases the crystallinity of the material. To increase the melting temperature, the chemical composition of the polymer would need to be amended; however, composites with added glass fibres demonstrate significant greater strength at elevated temperatures. Calculations show that Basalt and S-glass fibres are an attractive sustainable alternative to the more commonly used E-glass fibres, as other than displaying greater strength, they display better environmental properties. Tensile specimens, designed according to the ISO527 standard, were produced with rPET and additional E-glass and S-glass reinforcing fibres. Fibres were cut and added manually into the hopper, which proved to be significantly hard due to clogging and clumping of the fibres. In fact, for samples made of E-glass fibres, only a fibre content of less than 1% was obtained. At such a low fibre content, no increase in tensile properties was observed. However, the maximum fibre content obtained for S-glass fibres was nearly 12%. Although at 12% the strength only increased by 6.4%, the Young’s Modulus increased by 65% reaching a maximum value of 4.41GPa, exceeding that of PEEK. This increase is significantly lower than the predicted calculations where, at 12% fibre content, the Young’s Modulus should have increased by 109%. Only a 65% increase was obtained primarily due to the inhomogeneous mixture observed from micrograms as well as significant material degradation from the injection moulding process. This was due to difficulty when trying to input the glass fibres as well as the disuse of an extrusion or compounding process.