'Green' composites save money

Tom Shelley reports on two ways of making eco composites with financial benefits.

A new sheet polymer-based material with very useful engineering properties is being manufactured from mixed waste plastics. Strong, stiff, totally impermeable to water and light in weight, it is nonetheless a highly engineered product whose properties result both from the manufacturing process, and the careful blending of the waste materials that go into it. At the same time, natural fibres can be also used to be used to produce composites that are not only eco friendly, but sell for high price.

'EcoSheet', mainly intended as a superior alternative to plywood, is produced by 2K Manufacturing in Luton, by a process that head of sales Peter Ball describes as "Powder Impression Moulding". This involves mixing cleaned, shredded and blended plastic waste and cooking it together in machines which apply heat and pressure in a similar manner to a sandwich toaster. A foaming agent ensures a foam core between solid skins, with smooth outer surfaces on both sides, and a final density of around 615 kg/m3.

The process started in the US under the name 3DM, with the intention of recycling plastic from the auto industries, but the British arm was purchased through a management buyout, followed by the building of a pilot plant in Caerphilly, and further R&D assisted by the Wolfson Centre for Materials Processing at Brunel University, Pera, and a £600,000 grant from what was then the DTI. The Intellectual property is currently owned by Environmental Recycling Technologies, which is based on the Oxford Science Park. 2K Manufacturing has a global licence to make flat panels.

The waste inputs come from a very wide variety of sources, including unsorted post consumer waste, construction waste and auto shred – the mixed plastics left over from motor vehicle recycling after metals have been recovered, as well as used plastic hard hats and old mobile phone casings. Processes for separating mixed plastics do exist, but they all add cost. The problem with recycling mixed plastics together is that if melted, they do not mix and thus cannot form a single liquid. However, optimum properties of many metals and plastics come when they are made from mixtures of materials – composites, and this is what 'Ecosheet' effectively is. In the factory in Luton, human operators pick out unwanted material from the waste stream, after which it is shredded, dried, dust removed, pulverised, blended and moulded.

The end product sheets are then trimmed and sanded to produce sheets, 18mm thick, 2440mm long by 1220mm wide. Other products could be made, but a particular market has been identified in the building industry for 18mm thick flat sheets and so that is what is currently being produced. Price is around £10/m2 and first orders amount to more than 8,000 sheets. Customers who have successfully trialled the product include: Bovis Lend Lease, Apollo Group, ISG Pearce, Morgan Sindall and Wates. The Luton factory expects to reprocess 30,000 tonnes of low grade plastic in its first year of operation and clearly has room to expand. Eventually, it is planned to open more production sites near consumer waste streams that would enable to the production of up to 4 million sheets per year.

Although production has focused on producing a plywood replacement, it also is possible to adapt the process to produce a wide variety of other products. We were shown some sheet into which rubber crumb had been incorporated that could stop and absorb blows from a pickaxe. Energy and acoustic absorption and a certain degree of thermal insulation are inherent properties of the material products, and the formulations can be adjusted to enhance these properties.

The initial intention is to replace plywood, which is a material which itself has good engineering properties – the Mosquito aircraft was largely built of plywood, and we are told that when a more recent light aircraft was re-engineered from being made of plywood to being made out of glass fibre reinforced resin, the weight increased substantially because of uncertainties in the long term performance of the plastic composites. The downside of plywood is that it is liable to delaminate and warps when it gets soaked with water, and various insects and fungi can eat it, unless it is heavily soaked in chemicals.

'Ecosheet' on the other hand, does not suffer from any of these problems, and is a re-use of what originally were, fairly high performance, and in some cases, quite expensive engineering materials, making use of their properties, and by mixing them, in some cases, enhancing them. Nonetheless, it can be fastened with screws, 50mm round wire nails, other conventional fasteners and adhesives, and when worked, does not produce splinters. Peter Ball says that, as regards mechanical properties: "The product is still developing as different waste streams are trialled, but 2K intends to have performance figures out in time for the 'Ecobuild' show in March."

Current consumption of plywood in the UK is more than 25 million sheets per year, most of which only gets used once, after which none can be recycled and all of which has to end up in landfill. The UK currently uses about 5 million tonnes of plastic per year, 3 million tonnes of which ends up as waste. It is estimated that only about 7% of this is recycled. 'Ecosheet' can itself be recycled back into more 'Ecosheet'. It is not particularly attractive looking material being black with a foam core which is visible on its edges but it can be painted without requiring a primer coat.

For those who want to not recycle their current mobile phones or iPads but protect them, a French company has come up with recyclable composite cases that are made by an alternative heat and pressure moulding process, and which they are able to sell at considerably higher prices than 'Ecosheet'. 'FiberShell', made by an offshoot of the French technology company, RocTool, is made of polyamide impregnated linen, or for those who want greater strength, and a black pattern, carbon fibre. Manufacture starts by cutting material to size, after which several layers of fabric are placed in the mould to give the strength and thickness desired.

The mould is at room temperature but is quickly heated to a high temperature by electromagnetic induction, which is RocTool's particular, proprietary process. The hot mould melts the resin and impregnates the fibre, yielding a product that is strong with a high surface finish. The mould is cooled to remove the part which is subsequently trimmed, varnished and hand buffed Final mouldings for iPhones are only 0.8mm thick and weigh only 7g. They can be purchased for €45 each under the 'FiberShell' brand name.

The iPad cases are a little larger and cost €75. Because of the use of a thermoplastic resin, they are completely recyclable. The linen reinforced products are branded, 'EcoFiber' and the carbon fibre versions, the 'Performance collection'.

Design Pointers
• Ecosheet is stronger, stiffer and lighter than plywood
• It is totally impervious to water and can be screwed and nailed
• It is inherently energy and sound absorbing, and sound and thermal insulating with a foam core
• Mechanical properties can be tailored according to application

Author
Tom Shelley

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