Removal of residual lignin of ethanol-based organosolv pulp by an alkali extraction process

Organosolv pulps usually have high kappa number. This research investigated an alkaline extraction method prior to bleaching for reducing the kappa number of organosolv pulp. Ethanol wheat straw pulp with a kappa number of 58.2 was extracted with 1% NaOH solution. The results show that the ethanol pulp has a large amount of lignin particles on the fiber surface. After 1 min alkali extraction, the kappa number of the ethanol pulp is reduced by 60%, to 22.2, and both the number and the size of the lignin particles on the fiber surface are significantly reduced. In comparison with a further ethanol washing/extraction, the alkali extraction is much more effective in terms of lignin removal. X-ray photoelectron spectroscopy results show that a thin layer of lignin remained on the fiber surface after alkli extraction, but this did not reduce the internal bond strength. (c) 2007 Wiley Periodicals, Inc.