Devolatilization of Particulate Polymer

Theoretical description of devolatilization of particulate polymer can generally be achieved with a relatively high degree of accuracy. In most cases, the process will be diffusion controlled. The diffusion coefficients in solid polymers are very low, ranging from about 10 mys to 10 mys. The temperature in the polymeric particle can usually be taken as constant since the thermal diffusivity (a 10 mys) is many orders of magnitude higher than the diffusion coefficient. 

In the case of spherical particles with low concentrations of volatile components for which the concentration dependence of the diffusion coefficient can be neglected, the diffusion equation in spherical coordinates can be written as  

If Ce is the equilibrium concentration at the interface and C the initial concentration, then the solution to Eq. 5.98 can be written in terms of the average concentration C as a function of time [30]  

The equilibrium concentration Cg is usually very small relative to the initial concentration Co, therefore, the Ce term is often neglected. In this case  

If the temperature cannot be assumed constant, then the equations have to be solved numerically. The same is true if the diffusion coefficient is dependent on the concentration. 

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