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Continuous Fiber Thermoplastics

Combining Continuous Structural Fiber And Thermoplastic Resin

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Continuous Fiber Reinforced Thermoplastic (‘CFRT’ – not to be confused with carbon fiber reinforced thermoplastic) has been in use for about 25 years. It differs from other fiber reinforced thermoplastics such as long fiber reinforced thermoplastic (‘LFRT’) and glass mat reinforced thermoplastic (‘GMT’) in terms of fiber length. The term CFRT spans a range of formulations and technologies and the boundary between CFRT and LFRT is not always clear, with some manufacturers citing dictionary definitions in support of their own interpretation.

CFRT technology is at the high end of the physical properties spectrum in terms of the various fiber reinforced composites available (from GMT through LFRT to CFRT), but also at the highest cost end. Market demand for its superior properties is driving costs down as technology improves.

Fibers and Thermoplastics

CFRT composites span a wide range of fibers and thermoplastic formulations. Thermoplastics typically selected are polypropylene (PP), Nylon, PMMA, PPS, PEEK, PC, PEI, PC-ABS, PETG, UPPS, PU, PB. Fiber choices are just as wide ranging and include glass, carbon, aramid, basalt, ceramic and stainless steel in a range of conformations spans fabrics (woven) and non-woven (unidirectional and mat). Carbon fiber and stainless steel are useful where electrostatic charge dispersal is desirable.

Production Techniques

There are three main technologies. The first uses prepreg unidirectional tape which are themselves made up in a range of ways including hot melt impregnation and powder coating. The tapes can be used in pultrusion or compression molding. Another technique uses a low viscosity polymer which wets out the fiber and increases viscosity as it cools. This is used in pultrusion processes. Manufacturers are working to come up with practical ways of utilizing this material blend in resin transfer molding.

A third approach employs dry prepregs which blend thermoplastic fibers with the reinforcing fibers. In-process mixing of thermoplastic fibers and glass fibers delivers a lower cost material because the approach is capable of high volumes. Just one fiber runs through the output.

Although continuous fiber does not lend itself to injection molding technology, co-molding is possible in DLFT and LFT compression & injection molding processes. Production processes are still evolving, and the complexity of the variables at press-time can be challenging to manage if consistent product quality is to be achieved.

The fiber length introduces some design limitations for compression moldings - holes and vents in a product may require secondary milling/drilling operations for example, and some manufacturers offer design guides (e.g. performancematerials.com ).  Other limitations depend on the particular fiber used – for example aramid fibers should not be sanded, and achieving a highly polished finish is not usually possible.

Advantages of CFRT

High strength, high performance and high impact resistance are often cited as advantages, but these clearly depend on the properties of the particular fiber reinforcement.

In the automotive industry, low cost tooling and corrosion resistance are clearly advantageous.

The other material advantage of thermoplastic over thermosets such as epoxy resins are the ability to recycle and a lack of volatile organic compounds (VOCs) in the production process. Flexibility and durability are also key advantages.

The Future of CFRT

The relatively high costs of the technology meant that CFRT composite materials were only used in niche applications in aerospace and defense markets. In the last ten years though, the market has since grown exponentially (at 100%+ per annum according to some observers) in automotive, sporting, transportation, industrial and other categories.

The technology and processes are still evolving, and machinery is expensive (creating high barriers to market entry), though inevitably the superior performance will continue to drive demand and therefore competition will reduce costs.

How about an automobile fender – the days of chromium are over, and the days of CFRT are here.

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