Page 52 - Curriculum Visions Dynamic Book

Polyurethane
Polyurethane is made by a reaction of the chemicals polyols and polyisocyanates. The reaction is designed to form two types of building block – one rigid, the other one elastic. The elastic sections stretch, while the rigid ones give the fibre a shape. This kind of stretchable fibre is called spandex.
Olefin fibres
Olefins are a group of synthetic fibres of which the two most important are polypropylene (PP) and polyethene (PE). Both products are made using propylene and ethylene gases.
All olefin fibres are practically inert, and they do not absorb water. As a result, any chemicals on the surface (stains) can often be removed simply with warm, soapy water. Polypropylene is more useful than polyethene because it has a higher melting point. However, the melting point of both materials is low. Furthermore, neither type of fibre can be dyed, so the colour has to be introduced into the polymer before it is spun.
Olefins have good low-static properties, they
wear well, they are colourfast (because the colour is
in the fibre), and they dry quickly because they do not absorb moisture. They resist dirt and stains, and do not deteriorate in sunlight. They are good at being natural wicks, carrying body moisture to the surface, where it evaporates. They feel very comfortable to wear and are the lightest-weight fibre available.
(Left and right) Polyurethane fibres known as spandex are used in stretch fabrics such
as supporting leg and wrist bandages, in sportswear, and in swimsuits. Lycra®, Numa®, Spandelle®, and Vyrene®
are common trade names for spandex. Very often a fabric needs only a small proportion of these fibres to give it sufficient stretch. Spandex is often coated with nylon to give better durability.
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