Polymer degradation effective diffusion coefficient

Siepmaim et flZ." suggested that the effective diffusion coefficient can be considered to be linearly proportional to the porosity. Empirical expressions of are mostly dependent on Af or degradation time rather than real structures of polymer systems. Empirical expressions can be utilised in the same polymer system from which they were derived. They are, however, not valid for a different polymer system. 

There is no data on the effect of temperature on compatibility of antiblocking, release or slip additives, but such data can be found on other polymer additives or products of their degradation. Figure 6.4 shows the data on diffusion coefficient of bisphenol A and dimethyl phthalate vs. temperature. It is immediately obvious that increased temperature causes increase in diffusion coefficient. Also diffusion coefficient of liquid additive (dimethyl phthalate) is substantially higher than that of solid additive (bisphenol A). This shows that polymer additives will migrate to the surface more readily if they have higher melting point and process occurs at elevated temperature. Compatibility of additves with polymer decreases with temperature increase. 

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