Polyurethane Brittle plastics

A comparison of the abrasive wear by Bohm (1990) found that the hard and more brittle plastics, such as polyacetals, polyamide-imide, and polycarbonates, are less abrasion resistant than softer and tougher materials such as the polyethylenes and polyurethanes. Table 7.2 details some comparative... 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

The reduction in modulus (and the reduction in brittleness) brought about by the absorption of a small molecule is known as plasticization the small molecule is known as a plasticizer. When the humidity increases over a nylon or polyurethane specimen the absorbed water content increases, which leads to a small increase in volume and a... 

Styrene-maleic anhydride copolymers (SMA) Excellent heat resistance compared to typical polystyrenes Can be reinforced with glass fiber to enhance heat resistance, and with rubber to prevent plastic from becoming too brittle. Are used in IP in BMW 3 and 5 series and in Fiat Coupe, covered with polyurethane foam. [63]... 

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