Synthesis and characterization of cellulose derivatives prepared in NaOH/urea aqueous solutions

We successfully synthesized hydroxypropyleellulose (HPC) and methylcellulose (MC) in high yields from cellulose in 6 wt% NaOH/4 wt% urea aqueous solutions at 25 degreesC. The cellulose derivatives were characterized with NMR, size exclusion chromatography/laser light scattering, gas chromatography (GC), ultraviolet, and solubility measurements in different solvents. According to the results of solution C-13 NMR and GC, the individual degree of substitution (DS; i.e., the average number of substituted hydroxyl groups in the monomer unit) at C-2 hydroxyl groups was slightly higher than the DS values at C-3 and C-6 hydroxyl groups for HPC and MC. In comparison with traditional systems, NaOH/urea aqueous solutions were proved to be a stable and more homogeneous reaction medium for preparing cellulose ether with a more uniform microstructure. The low limits for the average number of moles of the substituent groups per monomer unit and the DS value of water-soluble HPC were 1.03 and 0.85, respectively. MC (DS = 1.48) had good solubility in both water and organic solvents, and the precipitation point occurred at about 67 degreesC for a 2% (w/v) aqueous solution. In this way, we could provide a simple, pollution-free, and homogeneous aqueous solution system for synthesizing cellulose ethers. (C) 2004 Wiley Periodicals, Inc.