Polymer strengthening mechanisms

Polymer chain stiffening A polymer strengthening mechanism significandy different from linear, branched or cross-linked. It has a monomer that is physically large and unsymmetrical. The ability of a chain to flex is impaired. A typical example is with polystyrene plastic. 

Years ago, it was predicted (by Herman Mark) that an important advance would come from the combination of thermoplastics technology with thermosetting technology, that is, by use of all four of the strengthening mechanisms named earlier (Figure 1) in a single polymer. Numerous laboratories have worked on various aspects of this approach, but the big breakthrough is apparently still to be made. 

Cracks can be initiated during shrinkage, mechanical testing, sample preparation or SEM analysis. Therefore, all samples were prepared and handled in the same way. It is observed that the polymer strengthens the cement matrix and increases the internal cohesion. Similar observations are made by Muller using ultrasonic auscultation technique [10]. 

Methods for mechanical testing of materials are briefly introduced along with various strengthening mechanisms. The number and siu-face area of the slip systems in metals and in ceramics are shown to be responsible for the ductility (or the lack of it) and for ductile-to-brittle transitions. Griffith s theory of brittle fracture is used to introduce fracture mechanics and to develop the concept of fracture toughness. The viscoelastic behavior of polymers is briefly discussed. 

There is also a significant drawback the inherently higher fuel permeability of polymers. The strengthening of environmental regulations (PZEV Partial Zero Emission Vehicle) leads to severe requirements concerning fuel impermeability, needing modification of the techniques now in use. Moreover, some carmakers such as Ford and GM require higher mechanical and thermal resistance, and conductive materials. 

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