Estimation of diffusion coefficients for regulatory purposes

In this respect one solution for the estimation of a Dp-value is to correlate the diffusion coefficient with the relative molecular mass, Mr, of the migrant and with matrix specific parameters at a given temperature T in Kelvin. This approach has already been successfully used (Piringer 1993,1994 Limm and Hollifield 1996). The estimation of the diffusion coefficient can be achieved for example using the following heuristic correlation (Piringer 1994 Baner et al. 1996)  

The parameter AP accounts for a specific contribution of the plastic material to the diffusion process. Phenomenologically speaking AP has the role of a conductance of the polymer matrix towards the diffusion of the migrant (Chapter 6). Higher values of AP in such polymers as PE lead to increased DP-values while in stiff chain polymers such as polyesters and polystyrenes lower AP-values account for smaller diffusion coefficients for the same migrant. The parameters b and c account for the specific contributions of the migrant and the diffusion activation energy respectively. 

In Chapter 11 it was shown that Limm and Hollifield (1996) proposed a somewhat similar approach to calculate DP for migration estimation purposes  

The results obtained are in a reasonable agreement with experimental data. To calculate the DP one needs for each polymer a set of values for the three parameters, D0, K and a, which are obtained from experimental diffusion data. For polyolefins the following sets of values are given  

To pursue the goal of obtaining a simple formula for the estimation of DB which does not rely on experimental diffusion data, reference Eq. (6-20) for all plastic materials was developed (Brandsch et al. 1999). The theoretical assumptions for this equation are given in Chapter 6. Following the approach treated in Chapter 6 a refined equation for DP resulted  

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