Mark Fletcher looks at a method of recycling plastic
materials into strong engineering components
Design Pointers
- The profiles exhibit the external features of an extrusion
with the mechanical properties of a pultrusion
- The parts are made using a single step process on a conventional
extruder
- Raw material costs are low and a variety of materials and fibre stocks can be used
A British company has developed a method of manufacturing strong thermoplastic profiles using continuous fibre reinforcement and recycled plastic bags.
Glass fibres run along the entire length of the component to impart strength to the finished profile. The part can itself later be recy-cled to form a high-value moulding compound.
Unlike other pultrusion processes - which tend to produce components with a rough surface - the continuous fibres are not noticeable. The prospect of making a profile with a smooth exterior finish should extend the potential uses of the technique.
The fibres allow a variety of reinforcement levels from 0 to 55 per cent, enabling different ranges of stiffness to be produced. Manufactured using a standard extrusion line, the process will accept a wide range of thermoplastics, giving it a much wider range of composite properties than previously available.
It has a potentially massive application base due to its mechanical properties and aesthetic appearance. Unlike conventional pultruded materials it is robust and can be richly coloured, post-formed and welded.
The developer, Imhotep, has demonstrated the technology with a range of simple pro-files. The profile range could be extended to take in complex shapes, depending on the mechanical requirements of the application. Licenses are available for the technology.
Thermoplastic composites are much simpler to process than thermosets and are usually made using a number of two-stage processes.
Imhotep's process, on the other hand, is a simple one-stage process that does not rely on expensive precursor materials. Manufactured using a single extruder, the company can produce a composite profile that exhibits all the external signs of an extrusion but with the mechanical attributes of a pultrusion, from a variety feedstocks.
The profiles exhibit a gel coating which is thick and durable and welded to the outer surface of the core which cannot be peeled off. It can also be coloured and can exhibit a variety of finishes. There is also scope for the ends to be thermally sealed to provide a smooth finish for exposed applications.
The strength of fibres can match that of conventionally pultruded material
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Reproduced from Eureka July 2000
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