Polyolefin strain resistance

TPE grades are often characterized by their hardness, resistance to abrasion, cutting, scratching, local strain (deformation), and wear. The generic types of TPE are styrenics, thermoplastic polyolefins (TPO), polyurethane thermoplastic elastomers... 

Polymers which yield extensively under stress exhibit nonlinear stress-strain behavior. This invalidates the application of linear clastic fracture mechanics. It is usually assumed that the LEFM approach can be used if the size of the plastic zone is small compared to the dimensions of the object. Alternative concepts have been proposed for rating the fracture resistance of tougher polymers, like polyolefins, but empirical pendulum impact or dart drop tests are deeply entrenched forjudging such behavior. 

Plastics are bonded to one another or to other materials. They differ widely in their affinity for bonding. Some plastics are easy to bond (e.g., PVC-U, ABS, PS), whereas others can be bonded only after special preparation (e.g., PTFE). On account of the low polarity and surface tension of certain plastics (e.g., polyolefins) there are still no adhesives for pipe joints which are durably resistant to shear strain and pressure. The choice of adhesive is determined by the substrate and the mechanical, thermal, and chemical requirements [69] - [75]. 

In comparison with other polyolefin materials, PB-1 has a higher level of resistance to strain under continually applied stress over long periods of time. This is known as creep behavior (Fig. 2.24) and the graph illustrates the increasingly superior performance of PB-1—at times in excess of 100 h. 

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