Polymer device degradation chain scission

Erosion is defined as the physical disintegration of a polymer matrix as a result of degradation [33,42]. Upon incubation, water penetrates into the polymer matrix, advancing towards the center of the device, and induces chain scission. Once a sufficiently low molecular weight is reached, the degradation products formed will diffuse to and dissolve in the degradation medium and be transported away from the polymer matrix, i.e., erosion [33]. 

Diffusion processes are ignored in the model presented in this chapter which could be important. For example, if diffusion of the calcium and phosphate ions in the polymer phase is slow comparing with the polymer scission rate, then the model would over-predict the effect of the TCP phase and hence under-predict the degradation rate. On the other hand, if the short chains can diffuse out of the device quickly such as in a very thin sample, then the TCP phase will be less useful and the model will over-predict the degradation rate of the polymer. It is possible to build these diffusion processes into the model to analyse aU the different possible scenarios. 

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