1. Wallenberg Wood Science Center, Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
2. Department of Chemistry, University of Helsinki, A.I. Virtasen aukio 1, 00560 Helsinki, Finland
3. Lund University, Division of Solid Mechanics, SE-221 00 Lund, Sweden
4. Department of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden