NMR spectroscopic studies on dissolution of softwood pulp with enhanced reactivity

N-methylmorpholine N-oxide (NMMO) is a known cellulose solvent used in industrial scale (LyoCel process). We have studied interactions between pretreated softwood pulp fibers and aqueous NMMO using nuclear magnetic resonance (NMR) spectroscopic methods, including solid state cross polarisation magic angle spinning (CP-MAS) 13C and 15N spectroscopies, and 1H high resolution MAS NMR spectroscopy. Changes in both cellulose morphology and in accessibility of solvents were observed after the pulp samples that were exposed to solvent species were treated at elevated temperature. Evidence about interactions between cellulose and solvent components was observed already after a heat treatment of 15 min. The crystalline structure of cellulose was seen to remain intact for the first 30 min of heat treatment, at the same time there was a re-distribution of solvent species taking place. After a 90 min heat treatment the crystalline structure of cellulose had experienced major changes, and potential signs of regeneration into cellulose II were observed.