Woven or unwoven fibres?

With evermore applications being found for reinforced composites, increasing questions are being asked about the best methods of using fibre and resin in a matrix.

There is debate in the materials world over the use of woven and nonwoven fibres. The trade off between directional fibres weaved together and put in to a lay-up is at odds with the random dispersion of fibres in some kind of thermoset or even thermoplastic resin.

The uniform dispersion of shorter fibres in a resin system is seemingly random, yet produces close to isotropic properties in the final cured material. Non-woven fibres and resin systems are much easier to apply to an automated process and are, in general, less costly to produce than that of weaved, aligned, fibres.

The technology has moved on since the days of the readymade fibreglass gloop that is still available from Halfords. The properties have got better in terms of costs, strength, stiffness as well as weight.

However, a relatively new development means another alternative is possible. High performance material manufacturer Technical Fibre Products (TFP) based in Cumbria produces the world's lightest non-woven fibre sheets. Its range of lightweight fibre veils – known as Optiveil – offer weights as low as 2g/m2 up to around 34g/m2. The big advantage, however, is its versatility and ability to have its properties tailored to suit particular applications. TFP has the ability to make custom blends of fibres, binders and particulates that are compatible with a broad range of resin systems.

Optiveil is manufactured from short-chopped fibres that are uniformly dispersed with a small amount of organic binder and, in some cases, additional particulates or fillers. TFP offers the capability to work with alternative, more specialised fibre types as well as manufacturing materials using precise fibre blends. The most popular fibre types include carbon, glass, aramid, polyester, thermoplastic and metal coated carbon.

Precise dispersion
TFP is a specialist in manufacturing of nonwoven fibres and uses a unique wet-forming process to enable precise dispersion that allows the fibres to be uniformly distributed in fine sheets. The material is available as continuous rolls or as custom cut sheets and even as complex shapes. The company also offers some second treatments to the Optiveil materials allowing the ability to form and consolidate multi-layer structures to produce a functional hybrid material.

Optiveil materials yield a high quality surface finishing and its even fibre distribution and tuneable aesthetic appearance have made it popular in achieving a quality, resin rich surface finish to 'Class A' standards.

Using these lightweight veils also delivers a weight and cost saving as it reduces the resin content in comparison to a woven or unidirectional composite, and the surface finish straight out of a mould can reduce or eliminate the need to grind or polish, potentially removing the entire process from a production line.

Optiveil has been used in a number of industries for applications such as EMI and RFI shielding for avionics, Class A surfaces in the automotive sector, as well as radar absorption materials in the defence sector.

The materials ability to be tailored and customised make it attractive to a number of potential applications where more exotic carbon fibre matrix and epoxy resin systems are perhaps not cost effective. The materials can be used with most resin systems with binders including poly vinyl alcohol (PVA), polyester, co-polyester, cross-linked polyester, styrene acrylic, phenoxy and polyurethane.

Justin Cunningham

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This is wonderful, now I want to know if what are the latest research topics on bio-composites.

Comment Siviwe Artwell Mfuywa, 19/03/2013

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