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Toughness and impact resistance of Zytel

Du Pont Engineering Polymers : 30 May, 2003  (Company News)
The world
Zytel® ST was selected by French manufacturer Pactuco International of Roche La Molière, near Lyon (France) as the material for the central ‘peak and crest’ (or ‘raised cap’) section of the helmet, which houses a periscope-like system of three mirrors that ‘bends’ the image over the wearer’s head. This system enables the wearer to benefit from comprehensive rear views without the need to turn or look over the shoulder – and with no loss of vision of the road in front.

General Manager at Pactuco International, Antoine Monville, said: “Because it is on top of the helmet, its impact strength is critical to the overall safety of the helmet. During the development phase, we submitted the helmet to flat surface and kerbstone impact (sharp edge) tests under a variety of conditions – hot, cold and wet. The impressive impact resistance of Zytel® ST means that the helmet could easily withstand international drop tests of 5 kg from 1.5 meters under these conditions. Zytel® ST is the ideal material for the critical cap part because although it is flexible to a degree, it does not become overly flexible in hot weather - nor does it become brittle in the cold. With its outstanding toughness and impact resistance over a wide range of environmental conditions, DuPont’s super tough nylon is perfectly adapted to this application.

“In fact, the excellent overall performance of Zytel® ST enabled us to reduce the thickness of the original helmet design by 50 per cent (24 mm to 12 mm thickness), meaning that the helmet could be even more streamlined and lightweight than originally envisaged. As a thermoplastic, Zytel® ST can be easily injection moulded so that we had the design freedom to make the cap and the overall helmet very attractive.”

The Reevu helmet is moulded by Joly Plastics of Ezy sur Eure (near Paris) France, a leading French specialist moulder of thermoplastic helmets for building and mining applications. Alain Henry, chairman of Joly Plastics, commented that his company often incorporates Zytel® ST to improve the effectiveness of its line of injection-moulded safety helmets.

Chief Executive of Reevu, Bill Morgan, confirmed that there were three main specifications for the helmet. It had to meet all international safety standards in order to afford the wearer as much head protection as possible. The mirror system had to be tough, lightweight, highly reflective and crack resistant – and yet require minimum maintenance. Lastly, the helmet needed to be light and comfortable with high levels of airflow.

Morgan said: “The Reevu helmet rear view system was designed to address a failing in the very heart of cycle design and operation. It is against the law not to have a rear view mirror system in a car or on a motorbike, but on a pedal cycle no such rules apply. We take the view that accident prevention is just as important as the protection of the user. Our design goal was that wearers of our helmet will continually glance at what is going on behind them in much the same way as car drivers do – but will continue to face ahead.”

“The idea for our system came about when a colleague’s son fell off his bike while glancing over his shoulder before turning right. He wobbled, clipped the kerb and fell off. The obvious solution is to provide some method of keeping an eye on what’s happening behind you, but that’s not easy on a bicycle. Mirrors on handlebars tend to vibrate and distort; they’re easily broken and, when you turn the handlebars, the mirror points in the wrong direction. That’s why we came up with the idea of putting a mirror inside the helmet.

“This dramatically increases the level of road safety for cyclists. Although it can never replace the golden rule of always looking over your shoulder before manoeuvring, it does mean that riders can be fully aware of traffic approaching them while keeping their eyes on the road ahead. It will also encourage people to wear helmets while riding bicycles because it not only provides them with vital protection in the event of falling off, but it can help them be aware of and keep clear of potential dangers from behind at all times.” As an added plus, the cavity produced by its rear view system creates a chimney effect that pulls cool air through and over the top of the wearer’s head that helps to keep the head cool.

Morgan concluded: “The design for this helmet has been tested to destruction – we like to describe it as ‘bullet-proof’! It conforms to all known international impact standards for protective cycle helmets. It withstands all of the dirt and rain that nature can produce, requires low maintenance and simply needs to be wiped with a damp cloth to keep it clean. The fit system allows maximum adjustment to ensure that the helmet maintains an optimal angle on the wearer’s head and stays comfortable in the process.”
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