Natural rubber, toluene diffusion

It is possible that the lower than required values of D2 reflect a problem with incorrect values of Q, which if too large would result in smaller values of D2. In an interferometric study of the diffusion of toluene in an uncrosslinked natural rubber sample, Mozisek (15) reported results for the mutual diffusion coefficient which were similar to the results of Hayes and Park. In the absence of thermodynamic data from Mozisek s work, correction factors calculated for the present work were applied to his data. The results are shown in Figure 7, which reproduces Mozisek s data along with the values for D2. The extrapolated value at 1, would exceed the self diffusion coefficient for toluene by about two orders of magnitude, similar to the discrepancy seen with Hayes and Park s data. This indicates that the fault with the results in the present case is not due to overly high values of the correction factors. Moreover, the method of calculating D from D12 has been confirmed experimentally by Duda and Vrentas (16) in a comparison of vapor sorption results for toluene diffusion in molten polystyrene with the values of D1 obtained directly using radio-labeled toluene. 

Figure 7. Comparison of Dj versus volume fraction of solvent in natural rubber, calculated from results of Von Mozisek using thermodynamic correction factors from present study, with self-diffusion coefficient for pure toluene. D, obtained using Q from Rory—Huggins (Chi=0.36).

Figure 8. Dj for heat corrected data in unfilled, crosslinked, natural rubber sample, versus volume fraction of solvent, compared with empirical extrapolation (dashed line) to the self-diffusion constant for toluene.

H. C. Obasi, O. Ogbobe and I. O. Igwe, Diffusion Characteristics of Toluene into Natural Rubber/Linear Low Density Polyethylene Blends, Inter. J. Polymer Sci., 2009, 1. 

---