The conversion from cellulose I to cellulose II in NaOH mercerization performed in alcohol–water systems: An X-ray powder diffraction study

The slurry-mercerization (SM) processes in 2-propanol–water and 2-propanol–ethanol–water and wet-mass-mercerization (WMM) process in ethanol–water solvents are investigated. Based on X-ray diffraction measurements in the earlier reports, we have derived a mathematical method to evaluate more exactly the conversion of cellulose I (CI) to cellulose II (CII) and used it to survey the effects of different alkali treatments on cellulose crystals. This method is very useful when the crystal system changes in a certain set of experiments are compared with each other. The optimal alcohol concentration in SM processes was found to be 80–92 w/w-% in 2-propanol–water solution, 85–90 w/w-% in 2-propanol–ethanol–water solution and 45–55 w/w-% in the WMM process. In the WMM mercerization, the effect of the solvent/cellulose ratio showed that the conversion to CII increased linearly with a decreasing solvent/cellulose ratio. Temperature increase, as well as higher lye concentration, had a positive effect on the conversion of CI to CII. This study confirms also our earlier results that the concentration of soluble lye in the used solvent system is the most important factors in the mercerization of cellulose.