Use of Composite Recyclate in Material Extrusion

Abstract

Composites in the form of fibre-reinforced polymers (FRP) are used more and more in many applications. They have a higher strength to weight ratio and can be applied in aircraft and automotive components to increase performance, specifically in fuel efficiency. As composite manufacturing technology advances, the application of the material has become wide-ranging from construction, sports equipment, military, medical, wind energy application, and other energy sectors. These have created a legacy for the use of composite waste manufacturing or end-of-life products, thus exposing a need for this material's use in a circular economy. To address the composite waste challenge, the aim of this research was to develop the knowledge base for using recycled composite in additive manufacturing. Composites can be recycled via various methods. The focus was on composite recyclate material from pyrolysis and the mechanical recycling process. These are currently mature recycling processes at an industrial scale. The research was based on the use of recyclate as reinforcement of polymer in material extrusion (MEX). Previous work done focused on virgin materials. Mathematical modelling was also developed to predict the critical parameters that can affect the properties of FRP with a predominant focus on reinforcement and tensile strength. This research involved developing the process capability to extrude filament that is reinforced with short fibres and its application in material extrusion. Fractional factorial experiments in the form of Taguchi orthogonal arrays were used to evaluate and optimise the extrusion process and the process chain for extrusion and material extrusion. The use of the design of experiments to optimise not just one process but to simultaneously optimise a process chain is an innovation in the methodology applied in this research. The studies covered the improvement of strength when acrylonitrile butadiene styrene (ABS) was reinforced with recyclate fibre from pyrolysis and mechanical recycling compared to virgin carbon fibre. The results showed an improvement in tensile strength by 43 %, 49 % and 69 % when mechanical recycled, pyrolysis recycled fibre and virgin fibre were used as reinforcement, respectively. When comparing recyclate fibres, the improvement in pyrolysis recycled fibre reinforced ABS was higher in comparison to mechanical. The variability was also low. This was attributed to the cleaner fibre for pyrolysis-recycled fibre compared to the mechanical recycling process. This suggests that the cleanliness of the fibre surfaces is an important factor in improving the bonding of the polymer to the fibre. Further research then focused on optimum parameters for producing pyrolysis recycled fibre reinforced polymer filament for additive manufacturing. An extensive study was also done using computed tomography (CT) scans to quantify and then minimise the porosity. The research was able to generate filaments whose porosity was significantly lower than the commercially available filaments. The next stage of the research focused on simultaneously optimising filament manufacture and the MEX process as a process chain. The research on the process chain optimisation considered factors namely extrusion temperature, fibre mass fraction and rotational speed, while for the MEX process factors were printing temperature, infill percentage and layer thickness. Through Taguchi analysis, it was concluded that printing temperature was the most significant factor. This was followed by rotational speed, extrusion temperature and fibre mass fraction. Layer thickness and infill percentage showed an almost negligible effect. Overall, the highest tensile strength was achieved when the extrusion temperature was 170 °C, fibre fraction 20%, a rotational speed of 40 rpm, printing temperature of 240 °C, infill percentage of 100% and layer thickness of 0.3 mm. The research has developed a viable process knowledge base to enhance the util

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paul Mativenga (Supervisor) & Muhammad Fahad (Supervisor)