Impacts of recycled carbon fibre and glass fibre as sustainable raw materials for thermosetting composites

Abstract

The fibre-reinforced polymer composites were implemented in various applications as a potential alternative to traditional metals. In particular, the carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) composites were heavily utilised in high-performance applications in the past two decades. As these composites reach their end-of-life stage, the consumers and waste management industries still rely on non-sustainable waste disposal options such as landfill and incineration. The cumulating tonnes of composite wastes contain valuable carbon fibres (CFs) and glass fibres (GFs), which still possess the potential to serve in applications for multiple cycles. When these composite wastes are adequately recycled and reused to close their life-cycle loop into new recycled composites, the wastes can be reduced. At the same time, the global demand for composites can be supplied without manufacturing virgin composites. However, there are certain challenges to overcome in order to achieve such goals. Thanks to the government regulations and public awareness on the environmental impacts of producing these virgin composites instead of reusing the existing composite wastes.

This dissertation focuses on overcoming such challenges in closing the life-cycle loop of the CFRP and GFRP composite materials with fibre recovery as a primary focus. The different types of recycling processes currently available were initially studied, focusing on the mechanical properties of the recycled fibres/composites and the environmental impacts of the recycling processes. Subsequently, a thermal recycling process was developed practically with optimised conditions to successfully recycle both the CFs and GFs from their respective composite wastes and remanufactured by compression moulding employing a fresh resin system. The mechanical properties of the recycled fibres and their newly produced composites were investigated using ISO standard tensile and impact tests both experimentally in the laboratory and numerically using finite element methods. Plus, the environmental impacts of the developed process were analysed and compared with traditional CFRP and GFRP composite waste disposal methods using life cycle analysis methods.

The results show that the developed thermal recycling process is capable of recycling both CFRP and GFRP composite wastes to produce unidirectional, long and continuous CFs and GFs. The mechanical properties of the recycled fibres and composites are in an acceptable range with similar results of recycled composites from literature. The environmental impacts are favourable to recycling CFRP wastes using the developed thermal recycling process and GFRP wastes using co-incineration as feedstock during cement production. Furthermore, discussions are made to overcome the challenges observed during this developed open-loop recycling process. When these challenges are addressed while upscaling the processes into a pilot and further to an industrial scale, a closed-loop recycling process can be achieved with mechanical properties of the recycled fibres/composites similar to their virgin counter. Thus, successfully establishing a circular economy.