SORPTION AND DIFFUSION OF N-ALKANES INTO BROMOBUTYL RUBBER MEMBRANES

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25-60 degrees C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34 x 10(-7) cm(2)/s (n-hexadecane) to 9.94 x 10(-7) cm(2)/s (n-hexane). The activation energy for diffusion varied from 14 kJ/mol (n-hexane) to 27 kJ/mol (n-hexadecane). Heat of sorption ranged from -1.4 kJ/mol for n-heptane to 2.0 kJ/mol for n-hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain-entanglement-crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative effects on the polymer.