1. Departments of Fibre and Polymer Technology and Chemistry, School of Chemical Science and Engineering, The Royal Institute of Technology, SE-100 44 Stockholm, Sweden, BIM Kemi AB, Box 3102, SE-443 03, Stenkullen, Sweden, Institute for Surface Chemistry, YKI, P.O. Box 5607, SE-114 86, Stockholm, Sweden, and STFI-Packforsk AB, Box 5604, SE-114 86 Stockholm, Sweden