Glassy polymers plastic deformation, crazing mechanics

Glassy polymer-diluent mixtures deformed in a temperature range close to are susceptible to exhibit a cavitational mode of plasticity at hi stresses and strains. Activation of this mechanism in mixtures of polycarbonate with esters of the phthalic acid results in extensive fibrillation and stress whitening of the material. There is strong evidence that the diluent plays an important role in enhancing chain slippage, which is required for the formation of craze fibrils. One of the most fundamental problems which is still unsolved is the elucidation of the molecular mechanism by which diluents become active. 

It is well known that the mechanical behavior of glassy amorphous polymers is strongly influenced by hydrostatic pressure. A pronounced change is that polymers, which fracture in a brittle manner, can be made to yield by the application of hydrostatic pressure Additional experimental evidence for the role of a dilatational stress component in crazing in semicrystalline thermoplastics is obtainai by the tests in which hydrostatic pressure suppresses craze nucleation as a result, above a certain critical hydrostatic pressure the material can be plastically deformed. 

Enhancement of impact toughness in some semicrystalline polymers is similar to techniques used for some glassy polymers. Usually an elastomeric phase is melt-blended into the host polymer, resulting in a dispersion of spheroidal elastomeric particles or a network. Compatibilization is obtained by copolymerization or chemical reaction at the interface. The toughening mechanisms may include both massive crazing and cavitation-plastic deformation, depending on the... 

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