Fibre-reinforced plastics (FRPs) have replaced conventional materials such as steel and wood for a wide range of products because they combine light weight, good mechanical properties and corrosion resistance. Weight reduction alone can make FRP products highly attractive to end users in industries such as road transport, where they can save at least 500 kg on a 7.5 tonne truck.

Approximately 240,000 tonnes of FRP products are now moulded annually in the UK but growth is only running at 3.7%. A limiting factor is that around 85% of the total is made using thermosetting resins, which cannot be recycled, making it impossible to meet the latest legislative requirements such as the EU End of Life Vehicles Directive. When most thermoset composites reach the end of their service life they have to be landfilled or burned.

Manufacturing processes too, are not fully sustainable as they tend to be labour intensive and require strict control of emissions of VOCs (volatile organic compounds), which are hazardous to health. ‘‘More and more, sustainability is becoming a key aspect for the industry‘‘, explains Dr Matthew Turner, Composites Engineer with project managers Europrojects LTTC Ltd (EPL), an independent consultancy specialising in application of thermoplastic composites. ‘‘Composite components offer light weight and user fuel efficiency but traditional composites are not recyclable. That is where thermoplastic composites win out. You don‘‘t have to waste precious resources on manufacturing something just once and then burying it or burning it. You can re-use it over and over again.‘‘

As well as having excellent mechanical properties, thermoplastic composites are fully recyclable and no VOCs are given off during manufacture. However until now production processes such as vacuum bagging have been very slow and labour intensive and the main alternative, compression moulding, requires expensive tooling.

The new process developed with support from the Sustainable Technologies Initiative will enable more producers to switch to the latest thermoplastic composite materials. In the SUSTCOMP collaborative project, leading industrial partners teamed up with researchers to develop a large prototype diaphragm-forming machine capable of operating at high production speeds. Moulding and heating are carried out between two thin silicone rubber diaphragms, producing high quality mouldings with inexpensive tools and greatly reduced energy consumption. ‘‘We wanted to speed the whole process up and by doing that increase sustainability of the production process,‘‘ says Dr Turner. ‘‘Our prototype machine is 16 times quicker than the vacuum bagging process, taking just 15 minutes instead of four hours or more to produce typical FRP components. Energy usage is tiny in comparison because you only heat the composite material instead of the composite and the tooling.‘‘

Trials showed that production costs are already competitive with hand lay-up methods and researchers have identified how production rates could be increased by up to 500% in future versions, making the process even more competitive. Tooling costs are much lower than other processes, a particular attraction for manufacturers making wide ranges of components.

A comprehensive Life Cycle Analysis carried out by Queen Mary University London demonstrated that the process is highly sustainable, has zero emissions of solvents and low labour requirements. Investigations confirmed that waste can be recycled into thermoplastic sheet and as much as 20% can be re-used in new products with no loss of performance.

Case studies were carried out on a lid for oil storage tanks and a prototype wind turbine blade section, designed to be lighter, stronger and, more importantly, faster to produce than traditional blades.

The results coul