Oxidative delignification: The roles of lignin reactivity and accessibility

This study compared oxidative delignification of birch kraft pulp fibers to pulp fibers from acid hydrotropic fractionation (AHF) using p-toluenesulfonic acid (p-TsOH). Under oxygen delignification at 20% consistency, AHF pulps with lower hemicellulose content showed higher delignification than kraft pulps with similar lignin content despite its residual lignin (cellulosic enzymatic lignin, CEL) being less reactive with fewer beta-O-4 ether aryl linkages based on 2D(13)C-H-1 nuclear magnetic resonance (NMR) spectroscopy. The water retention value (WRV) of AHF pulp fibers, a measure of fiber accessibility to water or oxidative chemicals, was substantially greater than that of kraft pulp fibers. Similar comparison of various AHF pulps further suggested that fibers with lower hemicellulose content were easier to delignify (bleach) despite having more lignin with lower reactivity (fewer beta-O-4 linkages). Additionally, the present study also indicated that oxygen delignification was more effective at high fiber consistency, which can be attributed to thinner water films on the fiber surfaces at higher fiber loadings. These results indicated that mass transfer was the rate controlling process in oxidative delignification of wood fibers.

Automated summary

This study compared the oxidative delignification of birch kraft pulp fibers to pulp fibers from acid hydrotropic fractionation (AHF) using p-toluenesulfonic acid (p-TsOH). The results showed that AHF pulp fibers had higher delignification than kraft pulp fibers, despite having less reactive lignin. Additionally, the study found that higher fiber consistency resulted in better delignification.