Plastics in the pipeline

Consumption of plastics continues to grow, even though the development of new plastics materials has almost dried up. Suppliers have changed their approach: instead of inventing new plastic molecules, they are boosting performance by refining existing materials and developing new additives. Many of the breakthrough applications – which deliver high temperature resistance, greater strength or a host of other engineering advantages – begin with the material, but then rely on addition or modification. One example is from GE Plastics, one of two major European suppliers of polycarbonate – the material used to create CDs and DVDs. Polycarbonate was introduced more than 50 years ago, but chemical modification is helping to expand its use. “Co-polymerisation and speciality co-polymers is a key focus for the future of our Lexan polycarbonate,” says Willem Sederel, global technical leader for the material at GE Plastics. “It’s a strategic direction we’ve been looking at since 1990.” In effect, GE is using different raw materials to make variants of standard polycarbonate. This clever chemistry has led to a number of completely new products – such as the DVD that ‘self destructs’ after 48 hours. “As long as the disk is in its package it is okay for a year,” says Sederel. “Once you open the package, the oxygen in the air starts to make it change from red to black. Then, it cannot be read by the laser.” An additive in the polycarbonate changes from red to black in the presence of oxygen. A disk made from standard polycarbonate would do this in just 12 hours, which was too short. For this reason, GE developed a co-polymer with a higher oxygen barrier, delaying the colour change. “As well as the higher oxygen barrier, this material has greater hardness and scratch resistance,” he says. “We did not plan for this, but it’s something we discovered that has value.” These physical attributes make the material suitable for applications such as longer-lasting windows and casings for mobile phones. It has also been used for TV bezels – the frame around the screen – and for “Market pull was for the oxygen barrier, but when we learnt about the scratch resistance we jumped on it.” Sederel says that these characteristics can be ‘dialled in’ – linking them closely with the chemical structure – though he admits that predicting scratch resistance is difficult. “We can start to put different building blocks together to make special materials,” he says. “We will engineer the materials based on chemical composition – but none of these have been commercialised yet.” At DuPont, Stewart Daykin – technology business manager for Europe – agrees that the strength of ‘market pull’ means that research must be better targeted at the market. “Major customers like Toyota are pulling us, on everything from bio-based plastics to fuel cells,” he says. “They are encouraging us to invest. They want suppliers that work hard to keep them at the leading edge.” Panel game One area that DuPont is attacking – albeit slowly – is plastic automotive body panels. Several models of car – notably from BMW and Renault – have already replaced metal front wings with plastics versions. The dominant material for these is Noryl GTX – a blend of polyamide and polyphenylene ether supplied by GE Plastics. Parts made from it can withstand the high temperature of the painting line, so can be processed in the same way as traditional metal panels. But new materials are lining up to challenge it. Rhodia, for example, has an all-polyamide material that is currently going through trials. And DuPont, with its PET-based ‘Shine-E Rynite’, believes it has the material of the future for body panels that will eventually replace Noryl GTX. “The industry does not believe that [Noryl GTX] is the future for body panels,” says Daykin. He claims that Noryl GTX is unsuitable for horizontal body panels such as bonnet lids because it will ‘sag’ under the excessive temperature of the paint line. And because automotive companies will not want separate technologies for horizontal and vertical body panels, the ‘horizontal’ technology will win out. “That means using thermosets or Shine-E Rynite,” says Daykin. In the last few months, DuPont has become the latest company to develop a corn-based polymer. Like GE, it re-invents its oldest materials. Delrin, the acetal material launched by DuPont exactly 50 years ago, has always relied on modification or blending to keep pace. In the past, one innovative application was a blend of Delrin and Kevlar, to make abrasion-resistant conveyor belts. Its latest modification to this is to add a proprietary additive. The fact that it can be picked up by metal detectors means that it can be used by the food industry – and any stray chips of the material can be picked up. Small wonder Nanocomposites, the additives that enhance the physical properties of plastics parts due to their smaller particle size, are also beginning to hit the mainstream. Major supply companies – including BASF, Bayer and Arkema – are ramping up production, while end users such as Ford are specifying them in commercial components. Small amounts of nanomaterials can enhance barrier properties, add surface conductivity and improve flow and flame retardancy of various plastics products. Nanomaterials fall into two main groups. Nanoclays, which rely on naturally occurring clay particles, and form the bulk of today’s commercial applications. And carbon nanotubes, which are created in the laboratory – and still largely confined to it. However, this is beginning to change as major suppliers – including Bayer and Arkema – ramp up commercial production. Nanotubes have been hailed as a ‘material of the future’ – and might one day be spun into carbon ‘nanowires’ that could lift an elevator to the moon – but for the present, researchers are content to try and drive their cost down. “Multi-wall carbon nanotubes cost around €1,000/kg,” says Martin Schmid, business manager for carbon nanotubes at Bayer Material Science in Germany. “We want to be considerably below that. One expectation is that by 2010, the cost will be €50/kg. With additional capacities coming up, that’s not out of the question.” Bayer was producing “several tonnes per year” of nanotubes – which it calls Baytubes – but increased this to 50 tonnes/year in July when it expanded its German manufacturing facility. “We are concentrating on polymer applications,” says Schmid. “This could be as a reinforcement, or for applications that require electrical conductivity.” He says that a nanotube-based paint could be sprayed onto surfaces to act as an EMI shield, for example – replacing a heavier silver-based paint. The prospect of a conductive plastic compound is also an attractive one for the automotive industry: conductive plastics panels could be painted directly, without the need for pre-treatment. But nanotubes are not the easiest additive to compound into a plastic. “There is a lot of work to do in terms of getting the product into polymers,” says Schmid. “It’s one thing to put it in as an additive in a granule. Then you have to mould and extrude it.” And while research continues, the dream of spinning carbon ‘nanowires’ is still some way off. “We cannot yet turn a carbon nanotube into a thread,” says Schmid. ** Next month, as part of our focus on plastics, Eureka speaks to Franz Brandstetter, head of polymer research at BASF’s competence centre in Ludwigshafen, Germany. **This is the first in a series of articles in which Eureka speaks to key supply companies to assess what is in their research pipeline. Motors, bearings, automation systems, materials, software – the whole spectrum of design components and systems – will be covered in future issues.