Structural changes and activation of cellulose by caustic soda solution with urea

Investigations on the activation of cellulose by mixed solutions of caustic soda and urea are reported. The structural effects of those solutions oil various dissolving pulps are studied by C-13-CP/MAS-NMR spectroscopy. In a series of steeping lyes, the concentration of NaOH was varied in a range from 0% to 8% and the urea-concentration in a range from 15% to 40% at ambient temperature and -25 degrees C. Using solely the single NaOH or urea solutions in the concentration ranges given above, no or only minor structural changes were found. In contrast to that, the cellulose I structure was partially or completely destroyed by using the bicomponent solution with urea added to caustic soda. The structural effect of the bicomponent solutions is comparable with the effect of solely caustic soda solutions of approx. 10% to 18% NaOH. However, the C-13-CP/MAS-NMR-spectra from the bicomponem pretreated samples indicate a structure different from the usual ordered structures of sodium cellulose I or II, namely a special urea-NaOH-cellu lose complex. The results show that for cellulose activation the NaOH concentration of the caustic soda can be remarkably reduced by adding urea. The improved activating effect of an optimized caustic soda solution with added area was proved to be useful for the synthesis of cellulose carbamate.