Scission rate amorphous polymers

It is certain that the relaxation behavior of filled rubbers at large strains involves numerous complications beyond the phenomena of linear viscoelasticity in unfilled amorphous polymers. Breakdown of filler structure, strain amplification, failure of the polymer-filler bond, scission of highly extended network chains and changes in network chain configuration probably all play important roles in certain ranges of time, strain rate, and temperature. A clear understanding of the interplay of these effects is not yet at hand. 

The rate equation for polymer chain scission was presented in Chapter 3 for amorphous polymers and Chapter 4 for semi-crystaUine polymers. These equations are summarised in this section. The terms in these equations that are affected by the diffusion of short chains are highlighted. 

Photo-oxidation of PET will proceed, via formation and scission of hydroperoxides, in a similar manner to that described for thermal oxidation in Chapter 3 [12]. The main difference in this case will be (especially under outdoor exposure) the more ready availability of oxygen, at least on the surfaces of substrates. Diffusion of oxygen into and through the polymer must be considered. The rate of oxygen diffusion can be markedly affected by order in a polymer fibre or film (be it crystalline or ordered amorphous). It is generally considered that oxidation is largely limited to fully amorphous regions of the polymer matrix. 

The rate Equation [3.5] for chain scission, as presented in Chapter 3, can be applied to the amorphous phase of a semi-crystalline polymer. Using superscript amp to represent the amorphous phase, the rate equation can be rewritten as ... 

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