Suitability of polymers and mechanical properties

The suitability of a polymer for a particular application depends on a number 

Many more questions of the type above have to be answered. On the 

Some of the answers have already been provided in the previous sections. All of these properties, however, have to be measured in quantitative and standard tests. This testing has done much to reassure the general public of the value and suitability of polymers. Many of these tests are carried out under conditions stipulated by ASTM (American Society for Testing and Materials). Not only new polymers are analysed by these techniques but also many new grades of old polymers. For example there are already dozens of grades of PE and nylon, new grades appear yearly, and data for all these grades are necessary. 

Rubbery polymers are illustrated by curve 4. Modulus is low, but high extensions (sometimes several hundred percent) are possible. Just before failure an increase in stress often occurs as a consequence of strain-induced crystallization (this is often demonstrated by a whitening of the polymer in this region) caused by molecular orientation in the direction of the stretch. 

A common requirement for a structural polymer is one which is hard (rigid) and has the toughness of a rubber. This can be achieved with engineering polymers but another way is to use blends of polymers and/or use additives such as fillers, plasticizers, etc. Indeed, most commercial grades of polymers are composites of this nature (section 1.14). 

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