| Polyurethane is a collective term for a number of different materials found in many different forms. They are widespread throughout society, and most of us encounter them every day, such as hard or soft foam in impact-absorbing interior car fittings, shoe soles and cushioning in running shoes, backing for wall-to-wall carpets, furniture padding, insulation in white goods, watertight and durable protective coatings and sealants, paints and lacquers, adhesives and synthetic fibres, and much more. The name of a polymeric group of materials refers to its common chemical characteristic as a regularly recurring element in the polymer chain, in this case the urethane group, a typical molecular component of all polyurethanes. Though it is a member of the big polyurethane family, urethane rubber must be further divided up into different categories based on differentiating but typical components of its polymer chains. The most frequently occurring urethane rubbers are polyether, polyester and polycaprolactone, but there are more, and within these subgroups there are also several different subcategories. The manufacturer of a customised end product can choose between several differentiating components determined by the reaction that creates the polyurethane structure. This also applies to the reaction that creates cross-linked and elastic rubber structures. In certain systems, in addition to urethane, carbamide groups are also formed in the polymer chain, and in the cross-linkings certain reactions lead to the formation of allophanate and/or biuret groups. The rubber-elastic hardnesses are governed firstly by the main components’ molecular weights, and secondly by the choice and quantity of other reacting components. Softening agents or other fillers, which are inevitable in other rubber production, do not need to be used. Vulcanised multicomponent urethane rubber can be produced entirely through chemically bonding without catalysts and/or stabilisers, which is impossible with any other sort of rubber. In addition to the entire scale of rubber-elastic hardnesses, urethane rubber can actually be manufactured in nearly 100 separate chemical structures, and this bewildering diversity has far-reaching practical significance for the user with regard to choosing the right variant for the right purpose. Even if you take into consideration the fact that many variants are very special, very expensive, very complicated in terms of manufacturing technology, not ready for the market, or not commercially availablefor other reasons, the established and cost effective multiplicity is greater than for any other sort of rubber. If you add to this the fact that hard urethane rubber can subsequently be processed using more mechanical methods than with any other sort of rubber, it becomes even more obvious that urethane rubber is a material with many possibilities. The multiplicity of the chemical structures leads to • a very broad spectrum of largely unique physical (mechanical) properties • greatly varying behaviours in contact with chemicals, and in many contexts unique durability • many uses in wind and weather, seawater, ground acids, UV light, ozone, etc. • variants for very low cold-stiffening temperatures and relatively high operating temperatures. It can be safely assert that urethane rubber currently has the broadest technical usage of any type of rubber. |
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