Opportunity knocks for composites sector
A number of new materials have come to market in recent months that are offering a host of fresh opportunities for engineers. From resins to fibres, plastics to the more exotic; material innovations are helping deliver more economic and environmental solutions, as well as pushing the envelope of technical possibility.
Amber Composites announced that it is to supply a prepreg (pre-impregnated) composite with fibres made from sustainably-sourced woven flax. The flax fibres produced by Composites Evolution have a processing requirement similar to glass fibre but with lower weight and, of course, environmental impact. It also has good damping characteristics, which make it ideal for applications where vibration can be an issue such as in automotive structures.
Composites Evolution has been set up specifically to fill the niche of sustainable composite materials. These include fibre reinforcements, natural bio based resins, recycled as well as recyclable feed stocks.
Brendon Weager, managing director of Composites Evolution, says: "We have a lot of customers ask for prepreg using our Biotex flax fabric and we worked closely with Amber Composites to ensure this solution is now available."
The prepreg comes infused with Amber Composites Multipreg 8020 epoxy resin system. It is a low to medium cure prepreg which can be used in, but critically outside of, autoclave ovens. The initial fabric options are a 400g/m² 2x2 twill, and a 500g/m² plain weave. Like other bio based materials its strength limits it to semi structural and decorative applications, though improvements are continual.
One of the problems with using bio based fibres is ensuring the quality and reliability in the supply chain and making sure supply does not interfere with food crops. Jonathan McQueen, managing director of Amber Composites, says: "After evaluating many sources for sustainable fabrics, we are pleased to offer a proven solution from Composites Evolution which has created a capable material backed by a solid supply chain."
Last year the company showcased a canoe manufactured by Flaxland using flax fibre and resin derived from linseed oil. The aim was to showcase the possibilities and potential of the materials. It used marine plywood and European pine frame and covered it using the Biotex flax material impregnated with a UV cured bio resin.
Simon Cooper, owner of the builders Flaxland, is a traditional boat builder with a strong interest in using all natural materials. He says: "In recent years synthetic materials, such as coated polyester fabrics, have been used in boatbuilding. In an attempt to return to traditional boatbuilding methods, I became interested in the use of flax as a sustainable crop for the production of oil and fibre to make a boat. I wanted to find novel natural materials and in my search found the Biotex website."
Flaxland trialled many flax fabrics and found that Biotex had good impregnation, 'wet out' (the degree of resin impregnation) and very good tear strength which, it says, is equal to the synthetic materials. The result was a flexible and strong canoe which was made without a mould tool.
Flaxland has made seven prototypes, using both the Biotex flax 4x4 Hopsack and Biotex 3H Satin weaves. The Hopsack version offers a resilient and durable canoe which has a net weight of less than 12kg and the Satin version gives a lighter option at just 8kg for racing. The canoe is currently undergoing long term durability and water resistance tests and has, so far, shown good results. Cooper is looking to roll out the design to larger rowing boats in the future.
Meanwhile, Bayer Material Science has continued to develop its polyurethane based resin system that can be used instead of epoxy resin systems. Polyurethane can be used with most fibres and it hopes this will facilitate the renewable industries desire for longer, lighter, turbine blades. It says the polyurethane composite also improves fatigue and fracture toughness over commercial epoxy resin systems.
Wind turbine manufacturers are demanding lighter, and stronger, blades as gravity induced bending loads dramatically increase dynamic stress making blades over a certain length unviable for all but a few composite compositions.
Bayer's Baydur polyurethane system possesses low viscosity and long gelling properties and it says when compared to a commercial epoxy and vinyl ester based composite, the Baydur polyurethane provides several key advantages. These include ultra low volatile organic compounds (VOCs), faster infusion time, superior tensile fatigue, improved inter laminar fracture toughness and fatigue crack growth as well as the use of raw materials from sustainable resources.
Bayer principal scientist Dr. Usama Younes conducted tests comparing the properties of incumbent epoxy and vinyl ester resin systems with a polyurethane resin system. The testing included two sets of long flow, vacuum infusion experiments designed to compare the flow rates of the different resins.
It also studied the effect of multi walled carbon nanotubes on fibre reinforced composite properties. He says the results showed a clear trend toward improvement in the fracture toughness of the composites from the presence of multi-walled carbon nanotubes.
"Incorporation of a small amount of multi-walled carbon nanotubes improves the fracture of both polyurethane and epoxy composites by as much as 48%." says Younes. "The addition of carbon nanotubes is a viable option to improve the strength of wind turbine blades."
Another new composite structure comes from material scientists at ETH Zürich which is working on composite materials that mimic the structure of seashells. Such complex structures are produced using tiny magnetic particles which guide the composites' stiffer elements into place. This technique will enable technologies from more durable coatings to stronger and lighter materials.
Researchers discovered that they could enable a magnetic response in these nonmagnetic materials by attaching a small amounts of magnetic nano particles to the surface of the elements, just 1/1000th the diameter of a human hair.
This method only works for stiff elements of a defined size in the micrometer range, which happens to overlap with the sizes of key interest in the composite industry. Using stiffer elements on this scale provides orientation control using magnetic fields that are only 20 times that of the Earth. For comparison, credit card stripes emit magnetic fields approaching 2,000 times that of the Earth's field.
The team has already demonstrated that the technique can be used to produce an entire family of new composite structures, which exhibit programmable properties in any desired direction. The ETH team is currently working with commercial companies to put this technique into industrial use for lighter, cheaper, and stronger composite materials for the automotive, aerospace and renewable industries.
The general message from the composites industry is one of innovation. Almost all the companies involved in the supply chain, from the raw materials through to manufacture and disposal, are developing products and processes to better facilitate composite materials in to mainstream industry.
The message is clear, composite materials are going to play a vital role in the future. From cars to turbines, boats to buildings, the industry is developing materials that tick the check lists of designers and manufacturers.
However, at present composites are still considered a premium material with cost and manufacturing capital outlay massively limiting factors. But, the industrial machine will continue turning, and at speed, and many feel it is only a matter of time before composites are thought of in the same way as metals and plastics are today.
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