Water diffusion into transcrystalline layers on polypropylene

The diffusion constant of water through transcrystalline surface layers on isotactic polypropylene (i-PP) is reported. A suitable experimental techniq ue was developed, based on sorption or desorption measurements. The accompa nying change in sample weight is detected by the corresponding change in me chanical resonance frequency. The facility allows investigation of the diff usion current parallel to as well as perpendicular to the sample surface. T ests with commercial polyethylene films revealed that reproducibility and r eliability are better than 6%. The samples were prepared as thin films in w hich the transcrystallinity was controlled by use of several substrate mate rials and different thermal conditions during solidification of the melt. T he water diffusion constant of finely spherulitic i-PP turned out to be 15. 9 mu m(2)/s; whereas the values for transcrystalline material amounted to 1 9.6 mu m(2)/s parallel and between 12 and 10 mu m(2)/s perpendicular to the film surface, depending on the actual supermolecular structure. These resu lts are discussed with respect to the underlying transcrystalline texture a nd the texture of the amorphous percolation network. (C) 1994 John Wiley & Sons, Inc.