Self-reinforced plastics are a new family of composite materials, where the polymer matrix is reinforced by highly oriented polymer fibres, usually derived from the same polymer. Self-reinforced plastics (SRPs) have enhanced strength and stiffness compared to unreinforced plastics and they have improved recyclability and reduced weight compared to glass fibre-reinforced plastics. They also have outstanding impact energy absorption and the absence of abrasive fibres has advantages in terms of handling and tool wear.
To date, this technology has most commonly been applied to polypropylene (PP), which has a good balance of properties and is relatively low cost but has limited performance at elevated temperature.
There are two main techniques for producing self-reinforced PP materials, namely hot-compaction or co-extrusion. In the hot-compaction process, developed in 1989 at the University of Leeds, fibre fabrics are stacked together and consolidated by applying heat and pressure in a static press or, on an industrial scale, a double belt press. The process conditions are controlled precisely so that just the surface of the fibres melt and this molten polymer forms the matrix phase of the composite. In the coextrusion process, PP fibres are coextruded with a thin layer of a polypropylene-polyethylene copolymer, which has a lower melting temperature than the homopolymer fibre. On application of heat and pressure, the copolymer surface layer melts to form the matrix phase. Both processes have recently been commercialised and a number of SRPP materials are available, either as preconsolidated sheets, woven fabrics or tapes.
There are a wide range of potential applications for SRPs including:
• Automotive – body panels, parcel shelves, under-shields, load floors
• Off-road vehicles – high-impact exterior panels
• Marine – personal watercraft
• Sports – helmets, pads, guards
• Leisure – suitcases, loudspeaker cones
• Personnel protective equipment – safety helmets, anti-ballistic shields
• Medical – orthoses, temporary supports
• Construction – shuttering, formwork
