1. SP Trätek, SP Technical Research Institute of Sweden, Box 5609, Drottning Kristinas väg 67, SE-114 86, Stockholm, Sweden, and Department of Fibre and Polymer Technology and Wallenberg Wood Science Centre (WWSC), Department of Fibre and Polymer Technology, School of Chemical Science and Engineering, KTH, Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, Sweden