Other Rubber-toughened Plastics

The loss of modulus caused by crazing becomes less pronounced as the draw ratio is increased, especially in tests carried out at lower stress levels. This observation supports earlier conclusions drawn from creep studies on other rubber-toughened plastics (6) if the specimen can reach a strain of 5% largely or entirely by shear mechanisms, the loss of modulus resulting from the creep and recovery program is quite small if, on the other hand, crazing is the dominant mechanism, the loss in modulus is large. 

Several methods of studies have been developed. Osmium-staining technique, pioneered by Kato [1967], is one of the most successful methods for observing crazing in rubber toughened plastics. It depends upon a reaction between osmium tetroxide, OsO, and double bonds in PBD and other unsaturated polymers. However, it is not suitable for saturated rubbers. 

These structures are illustrated in Figure 1.3. Through the leadership of Amos and others, polymer blends and grafts found uses as rubber-toughened plastics, which include high-impact polystyrene (HiPS) and acrylonitrile-butadiene-styrene (ABS) plastics. As further illustrated in Table 1.1, block copolymers containing a water-soluble block and an oil soluble block became important as surfactants through the work of Lunsted, while other block copolymers, composed of elastomer and plastic blocks, were useful as thermoplastic elastomers. 

Both the modulus-temperature relationships presented in the preceding sections and the tensile data presented above are strikingly similar to those demonstrated for other rubber-plastic combinations, such as the thermoplastic elastomers (see Chapter 4 and the model system presented in Section 10.13) and the impact-resistant plastics (Chapter 3). The IPN s constitute another example of the simple requirement of needing only a hard or plastic phase sufficiently finely dispersed in an elastomer to yield significant reinforcement. Direct covalent chemical bonds between the phases are few in number in both the model system (Section 10.13) and present IPN materials. Also, as indicated in Chapter 10, finely divided carbon black and silicas greatly toughen elastomers, sometimes without the development of many covalent bonds between the polymer and the filler. 

The drive sprocket is injection-moulded in rubber-toughened PA6.6, which is resistant to repeated impact over a wide range of temperatures, and which shows excellent abrasion resistance. The plastic sprocket absorbs the shock of gear changes better than metal, causes less wear on the chain, and provides a quieter ride. The polymer is resistant to lubricants and other liquids. Reduced firiction improves power transmission and, coupled with a lower weight, results in better performance. 

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