several hours. One could obtain a family of linear isotherms (with strong hysteresis), and corresponding to 2,3 or 4 h of equilibrium for each point.
'The strong affinity of chloroethane for chlorinated polymers was also revealed by measurements on PVDC.
At 293 K there is adsorption (and no longer penetration) of CH,CH,CI and the isotherm is linear up to pipo = 0.5, corresponding to an approximate coverage of 8 = 2.
The adsorption equilibrium is reached after 45 min. only but there is a strong hysteresis on desorption, indicating some kind of retention.
About 40 h of pumping were needed to clean the surface. This contrasts with the behaviour of sulfur dioxide, neopentane and butane adsorbed on PVDC in the same temperature range [I, 21 and which have surface areas similar to the surface area of chloroethane.
Conclusion.
-The present study, combined with previous investigations, shows that at low temperatures PVC and PVDC may be similar because of the C1 groups present on both surfaces. At higher temperatures, however, penetration effects appear with PVC. This may be caused by the poor cristallinity of the solid, owing to its atactic structure. In the case of PVDC, on the other hand, the structure is much simpler and the cristallinity is higher. Hence, there are fewer or no penetration sites at all between the chains. This is also in agreement with the (relatively) lower penetration of water into a chlorinated PVC (63% Cl), as observed by Babkin & al. [4] near room temperature. hcknowlcdgmcnts are due t o I)r. Helen StoeckZi-Evans for X-ray photographic work and β¬31 H1,IOGRAPHY interpretations.