Plastics get greener

Tom Shelley reports on some of the plastic innovations that were revealed at this year's 'K' show.

A significant number of exhibitors offering biopolymers and other 'green' or greener products was apparent at this year's 'K' – Kunstoffe – show, held from October 27th to November 3rd. At the same time, all the usual exhibitors were there with new blends and new applications for their products that push forward what is considered possible and likely to become the norm, particularly in the automotive sector, where potentially large orders continue to make it an important market for all major players.

The two driving forces to introducing more plastics into cars are to save weight and reduce manufacturing costs. Both goals are achieved in a complete, single part tailgate that has been developed by Bayer MaterialScience. Whereas a conventional tailgate is made of metal with an inserted glass window, the new part has a single seamless skin made of coated polycarbonate (PC). Non transparent areas are either back printed in a dark colour or back injected with a black frame material by two component injection moulding.

A rear spoiler and two styling lines are directly moulded in. Tail lamps, indicators, brake lights, license plate lights and the raised brake light are located behind the skin, so there is no need to seal lenses to bodywork. Fixings and guides can be directly integrated by the two-component back injection method. The license plate would also be behind the skin, deterring thieves.

It would also be quite conceivable, according to Volkhard Krause, head of the company's automotive glazing team, to integrate parts of the water management system. Instead of separately mounted locks and door handles, light sensors could be installed behind the skin for opening and closing the tailgate. The only problem is that, on its own, a PC skin would not be stiff enough to meet load specifications.

In order to remedy this, strips of sheet metal are inserted in grooves between the ribs and bonded with an adhesive that is sufficiently elastic to accommodate the difference in thermal expansion coefficients. The metal inserts additionally ease the attachment of locks, hinges and dampers, to allow the tail gate to be attached to the rest of the vehicle body. Despite this added metal, Krause estimates that overall weight saving over a conventional part is 30 to 40%.

Lanxess, the other half of what was formerly Bayer on the Leverkusen site, has also been involved in successfully applying metal plastic hybrid technology – this time to the front end of the Audi A8. To make it, semi finished 'Tepex' 'organic' sheet, made of woven glass roving in a plastic matrix, is supplied by Bond-Laminates in Brilon, Germany and formed to shape. It is then placed in an injection mould along with three aluminium sheets and over moulded in Lanxess 30% glass 'Durathan BKV 30 EF' PA (polyamide) to form reinforcements and ribbing.

The resulting structure incorporates a double torsion ring that significantly increases the stiffness of the front end of a vehicle. In the event of a head on collision, the resulting forces are distributed across three load planes and four load paths. The final part is 20% lighter than if it had been made out of aluminium alloy alone.

Seats too, can be made lighter using plastics, as was demonstrated by a new seat concept called the 'Susco 1.5' – an abbreviation of 'sustainable comfort'. It has been developed by three partners: BASF, which came up with a special 'Ultramid' PA for the project; Faurecia in France; and Performance Materials Corporation in California. It is made up from layers of continuous fibre reinforced plastic, over moulded with 'Ultramid' in a second step, and weighs 20% less than conventional car seats while being 30mm thinner. Serial production is expected to start in four years time.

Bioplastics
The French company Roquette chose 'K' to launch a range of plastics named 'Gaïalene', based on its 75 years of experience with processing starch. Michelle Serpelloni, Roquette's Gaïahub programme director, said: "Our resin transforms like thermoplastics but at a lower temperature, about 170°C. This requires less energy during transformation and improves the overall carbon footprint." The range, said to offer to offer characteristics such as shock resistance, softness and easy colouring and compounding, is aimed at applications presently using polyolefins, ABS (acrylonitrile butadiene styrene) and 'more technical polymers'.

FKuR Kunstoff, on the other hand, was offering 'Bio-Flex S 5630' based on PLA – polylactic acid and PBS – polybutylenes succinate which are both 100% biodegradable. Heat distortion temperature is 105°C. The company works closely with the Fraunhofer Institute UMSICHT and also offers 'Biograde', a cellulose ester compound and 'Fibrolon' natural fibre reinforced polymers.

Bioresins.eu is a UK based company distributing 'Ecomann' PHA (polyhydroxyalkanonate) made by Shenshen Ecomann Biotechnology in China, as well as TPS, thermoplastic starch and PLA, all of which are biodegradable and compostable. The PHA is made from maize starch and may be processed similarly to PE – polyethylene, but at lower temperatures.

Not particularly biodegradable, but with somewhat higher performance, is 'Arnitel' Eco, a thermoplastic copolyester (TPC) from DSM which is 20% to 50% derived from rapeseed oil. The product is said to show exceptional resistance against UV light and long term heat.

Plastics for new challenges
New engineering developments often require new thinking in materials. For example, robotics are mostly made in metal, but Hybrid Assistive Limbs (HAL) to help the elderly and partially disabled walk, stand up and climb stairs are best made out of plastic, according to Professor Yoshiyuki Sankai, CEO and founder of the Japanese company Cyberdyne. Exoskeleton elements are strapped onto human limbs and controlled via a computer that receives bioelectric signals from electrodes attached to the human skin.

"Bayblend improves the functionality considerably," Professor Sankai commented. It said that a HAL system can produce almost ten times the power available from muscles, and could be used to assist physical tasks in industry, as well as military situations, as has been featured in countless science fiction stories and films. 'Bayblend' is the name used by Bayer MaterialScience for its range of amorphous thermoplastic polymer blends based on PC and ABS as well as rubber modified PC and styrene-acrylonitrile copolymer (SAN) blends.

Another challenge area is protecting the electrics of photovoltaic systems because these have to be used outdoors and endure wet weather and a high temperature range. For this purpose, BASF is offering special variants of its 'Ultramid' PA products that are at the same time, strong, flame resistant and show high impact resistance and low temperatures.

New insulating foams can also do much to reduce carbon emissions, as well as costs, by improving thermal insulation in a wide variety of products including domestic and industrial refrigerators. Bayer Material Science is developing rigid PU (polyurethane) nanofoams which are to have pore sizes of the order of 150nm across instead of the 150µm that is typical at present. The company is working with Prof Reinhard Strey from the University of Cologne's Institute of Physical Chemistry which has applied for a patent on a process called POSME – Principle Of Supercritical Microemulsion Expansion – to produce them. Commercial production, however, is thought to be 'several more years' away.

At the same time, competitors, BASF offers insulating foams designated 'Neopor' (EPS, expandable polystyrene), 'Styrodur C' (XPS, extruded polystyrene) 'Elastoper H' and 'Elastopir' (rigid PU), 'Ultradur' (PBT – polybutylene terephthalate and 'Ultramid' (PA).

Design Pointers
• A whole car tailgate has been moulded in plastic that does away with the need for separate glazing or light covers • Significant weight savings can be achieved in high impact absorbing constructions combining rove glass mats, injection moulding and metal sheets • The number and variety of biopolymers is increasing. Most offer biodegradability or compostability as their main attraction but some offer lower processing costs and enhanced performance • Environmental benefits can also be achieved by improving or taking advantage of the performance of more traditional polymers

Author
Tom Shelley

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