Cover story: Making the sustainable material choice

The question of which materials are or are not environmentally-sustainable is a vexed one and is not as clear cut as is often thought. For instance, some materials seen as essential for environmentally-friendly products either cannot be extracted economically in sufficient quantities or come at an environmental cost that may make them unacceptable on a very large scale, or. While these factors may discourage the use of such materials in the course of the technical development of new products, they do mean that thought has to be given to looking for alternatives or finding ways of designing out the need for them. End user lifetime cost (including cost of disposal) is not a bad way of assessing which material to use, since cost includes the cost of energy to produce and ship, and if the suppliers are responsible – and it is increasingly hard to conceal bad environmental practices in the global village in which we all live – the cost of extracting it or producing it in an environmentally acceptable manner. Another major problem with the ability to assess the environmental impact of a material derives from the fact that precise and detailed information on the subject is hard to come by. This was one of the motivating factors behind Autodesk's decision to include the Eco Materials Adviser in its Inventor software. The tool uses information from Granta's database of design and environmental information on materials and is intended to allow the designer to make more informed and sustainable material choices at an early stage of the design process before any materials are 'locked in' to the design. However, while this is clearly a welcome development, it only serves to highlight the paucity of detailed information available on materials. Says Granta's Dr Jamie O'Hare: "This is not intended as a precise cost modelling tool." This becomes clear as one understands that the information on materials is derived from an international average and therefore cannot take into account local factors, alterations in cost, availability and other variables. Equally, it is not always possible to acquire accurate data from manufacturers and suppliers. Says O'Hare: "There is simply not the level of precision available for environmental data as there is for engineering data. It's simply not possible to get a precise value for a CO2 footprint as it is for, say, tensile strength." Sarah Krasley, Autodesk's product manager for sustainability, also acknowledges the issue, saying: "We're not seeing the same level of precision within the environmental data," she said. "But I would love this to be the start of a push down the supply chain and getting specific eco-indicators." A clear understanding of the available and sustainable alternatives is clearly crucial. However, that is easier said than achieved. A recent Knowledge Transfer Network meeting on 'Materials scarcity and critical materials' looked at materials for electric vehicles and asked whether electric vehicles themselves were as eco-friendly as some would have us believe. For instance, lithium is crucial to achieving maximum energy storage to weight ratio, but there is limited supply and the extraction process can pollute local water supplies. However, as Dr Colin Johnston, Materials KTN transport sector leader pointed out, there are alternatives. In hybrid vehicles, Formula 1 cars have shown the way to temporarily store braking energy in either flywheels or supercapacitors. It is also possible to store energy as compressed air and compressed nitrogen in hydraulic accumulators. If one must have batteries for battery electric cars, Dr Johnston asked what had happened to some of the high temperature batteries, relying on systems like sodium sulphur, which offer twice the storage capacity of lithium ion batteries. The answer, of course, is that, driven on by lower material costs and their higher energy densities, they are still being researched. And this, it would seem, is the key point: most potential material shortages or environmental problems can be engineered round by applying sufficient research and development. Another example of this can be seen regarding the potential shortage of rare earth metals used in permanent magnets for high efficiency motors. Prices of the most sought after rare earths have gone up by more than 1,000% in the last 12 months. However, permanent magnets are not crucial for electric motors. Most electric motors are induction motors and there are also switched reluctance motors that use no permanent magnets or rare earth metals at all. Starting torque for induction motors is less than for permanent magnet motors, at least at present, but research and development continues. Technology moves ever onwards changing materials needs. And even wood may come back into its own if the prices of oil derived plastics keep going up. Wood is largely cellulose, a natural polymer, and the German company, Tecnaro also produces a thermoplastic called 'Arborform' from lignin, the other main constituent of wood, which is discarded during paper making. Platinum is and always will be a scarce and valuable metal. It is the best catalyst material known, and as such is the material of choice in exhaust catalysts and fuel cells. There are alternatives but they are not as effective. Being valuable, 98% of production gets recycled, and Johnson Matthey, which is a British company, manages a large proportion of the supply. The remaining 2% not recycled is probably dispersed as dirt on the roads. There is talk of recovering this, too. Recycling is seen as crucial in conserving strategic materials, but there remain all kinds of practical problems and it is not a viable or eco friendly policy to expend vast amounts of energy and effort to recycle small amounts of material. Suppliers of lithium vehicle batteries take their batteries back and recycle them, but organising the same for batteries in laptop computers and mobile phones is probably not worth the trouble and not likely to happen on a full scale. The situation is even more fraught as regards recycling the tiny amounts of rare earth metals in low-energy and fluorescent lights, and the comment was made that the items that local authorities least want to collect – because they are potentially hazardous – are those that we most need to get back. Steel does tend to get recycled and so does copper. The reason that the price of copper keeps going up is that demand is exceeding supply. In North America, aluminium was extensively used for domestic wiring between about 1965 and 1973, as an alternative to copper. Unfortunately, care has to be taken with making connections with it, because when it oxidises, aluminium oxide is a good insulator and connection joints can overheat were responsible for a number of fires. After totally going out of fashion, technical advances have allowed it to be used again, but it is not allowed in the EU. Bars in the rotors of induction motors are normally made of aluminium and current busbars can either be made of aluminium or copper. Aluminium has only 62% of the electrical conductivity of copper but copper weighs three times as much and costs almost four times as much. There is no fundamental shortage of aluminium because when bauxite aluminium ore starts to run out, it can also be extracted from clay. The recycling of plastics is complicated. We described the production of 'EcoSheet' from mixed waste plastics in our February edition but most companies making products from waste plastics depend on having a steady and consistent supply of waste plastic of one particular type. For example, Eagley plastics in Chinley extrudes a wide range of products derived from recycled PVC from the building industry. These can be coated with a skin of virgin PVC if required. Similarly, Pipeline and Drainage Systems in Wakefield extrudes ceramic parts, mainly 'Envirokerb' drainage kerbs made from a mixture of LDPE – Low Density PolyEtheylene and limestone quarry dust. There was more concern expressed about possible difficulties that British users of composites might experience resulting from losing control of the production of high quality carbon fibre for composites. Everyone agreed that composites, many of which were originally British inventions, and which are the engineering materials of the future, now depend on supplies from abroad, particularly high modulus carbon fibre, which has to either come from the US and Japan. Adrian Waddams, manufacturing manager for the British Marine Federation is concerned about possible supply problems with resins and fibreglass for boat building. Carbon fibre may represent 60% of the UK composite industry in value terms, but is only a small fraction of the whole in volume terms. There is no fundamental shortage of carbon, no ecological problems associated with producing it, and big environmental advantages in making use of it to reduce weight, but we have to ask if it is wise to depend on production of a crucial component in two countries which are in many fields, strong business competitors. The solution, as always, is a need to look after British manufacturing and keep supporting research and development to a point where the UK can secure its supplies of strategic components and be agile enough to develop alternative strategies as and when required. Design Pointers • The vast majority of materials seen to be critical either have alternatives or can be designed out • The negative environmental impact of obtaining some materials could well outweigh the environmental usefulness of the products to be made from them • Recycling occurs to a high level where the rewards make it worthwhile but should not be blindly pursued for its own sake • Technology is moving on at such a rate that materials seen to be crucial today, could well turn out to be of little use in a few years time • R&D is essential to enable UK manufacturing to keep ahead of the game