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Energy efficient fibre reinforced composite recycling
[Thesis]. Manchester, UK: The University of Manchester; 2016.
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Abstract
Composite materials are widely used in various sectors such as aerospace, automotive and wind energy. Global increase of demand, particularly for fibre reinforced plastic (FRP) composites, unavoidably lead to high volumes of manufacturing and end of life waste. Currently, the most common disposal route for composite waste is through landfill. However, current and impending legislations such as Directive on Landfill of Waste (1999/31/EC) and End of Life Vehicle (ELV) Directive (2000/53/EC), have limited the amount of composite waste permitted for landfilling. In addition, production of virgin composite materials requires higher energy input in comparison to other counterpart materials such as steel and aluminium. This calls for an urgent need for composite waste to be recycled and reused in close loop and cross sector applications. The composite materials have a heterogeneous nature. Thermoset matrixes, which are used in most high grade applications, have three dimensional cross-linked structures which make melting and remoulding impossible. Such complex nature requires appropriate composite recycling technologies, a number of which are currently under research and development. At this early stage it is important to select and develop sustainable solutions in terms of economic performance and reduced environmental impact. Unfortunately at present, there is limited high integrity environmental related data in literature to help assess the life cycle benefits of composite recycling. This information is vital in exploring environmental credentials of composite recycling processes, and to ensure resource efficient use of manufacturing and end of life composite waste. The work reported in this PhD thesis deals with the investigation of energy demand of composite recycling processes. Composite waste and demand in the UK market was captured through Sankey diagrams. The diagrams, combined with environmental footprints of virgin material and recycling processes, were used to identify resource benefits of composite recycling initiatives. Furthermore, environmental data for mechanical recycling of glass fibre composites was derived through new and novel bottom up process science inspired mathematical energy modelling approaches. It was found that the process specific energy demand is dependent on the processing rate. The effects of key process variables in mechanical recycling on process energy demand and recyclate quality were also investigated. This study highlights the importance of selecting the right conditions for running recycling processes and generating recyclate with a high market value. Potential of new recycling techniques, namely high voltage fragmentation, was also assessed. Performance of the method, which was originally developed for fracturing rocks, was compared to the mature mechanical recycling process. The final part of this study used a life cycle assessment method to evaluate end of life options for an automotive composite product with the highlights on positive environmental impacts of recycling scenarios. Collectively, the findings from this study have brought together considerations on environmental and maturity status of composite recycling processes, into a comprehensive and updated analysis. The vision is that the knowledge integration between environmental and performance aspects will promote the concept of sustainable use of composite materials and a circular economy. The new datasets developed will enable end of life options for composite waste to be evaluated in life cycle assessment. In the absence of such information, the life cycle impact of composite material use in products cannot be fully or correctly evaluated.