Impact-absorbing elastomers

When this work began, an important application for TPU elastomers was in automobile exterior body components associated with impact absorbing bumper systems. Cold impact strength, resilience, resistance to heat distortion at paint oven temperatures and rapid injection molding cycles were all required. 

Okitsu K and Murabayashi K (1985) Polycaprolactone-polyamide elastomer impact absorbers, JP Patent 61,171,731, to Daicel Chemical Ind., Chem 105 192699. 

A commercial grade of high-impact (notched Izod > 900 J/m) POM resin (Delrin 100 ST, DuPont) is believed to be a blend of POM with >30 wt% of a thermoplastic poly(ester-urethane) elastomer derived from poly(l, 4-butane adipate) diol and methylene-bis-(4,4 -diphenyl diisocyanate) (MDl) (Hexman 1989). This blend is reported to have a cocontinuous or semi-interpenetrating network of the elastomer in a matrix of the polyacetal (Flexman et al. 1990). The toughening effect in such a blend of IPN-type morphology was interpreted to occur partly through a rubber band mechanism by which the fracture energy is absorbed. The bands of rubbery domains were believed to span the crack and participate in the deformation process. 

The last example of application of smart materials to PPE described in this chapter deals with shock absorbers. With shear thickening fluids, complete flexibility is maintained in static conditions while the material instantaneously hardens upon impact at high rate. Products based on elastomer foam and 2D and 3D impregnated fabrics are already on the market, with a particular target at sports, defense, and law enforcement applications. 

Impact Modifiers, impact modifiers function by absorbing the impact energy and dissipating it in a nondestructive fashion. Typically elastomers, they are added to a wide range of thermoplastic materials at levels up to... 

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