PULPING AND BLEACHING OF CAD-DEFICIENT WOOD

Abstract

Mutant loblolly pine trees that are deficient in the enzyme cinnamyl alcohol dehydrogenase (CAD) have been obtained through directed breeding. The lignin in the wood of CAD-deficient trees has a different pool of precursors, resulting in high levels of pulping-resistant C-5 linkages. Wood from a 12-year-old CAD-deficient tree has been pulped under soda and kraft conditions in microdigestors. In comparison to a normal 12-year-old loblolly pine, the CAD-deficient wood was much more easily delignified. In addition, the pulp from CAD-deficient wood was as easy to bleach as a control pulp. The high reactivity of CAD-deficient wood may be related to the lignin size and phenolic content. The molecular weight of an isolated milled wood lignin from CAD-deficient pine was ∼35% less than that from a normal pine tree.

ACKNOWLEDGEMENTS

We are grateful to Dr. Jiebing Li for performing the KMnO₄ consumption tests and to Dr. Hiroki Nanko and Ms. Georgeta Maghiari for providing the STEM results. Support for this work came from a research grant from the US department of Agriculture, grant number 97–35103–4796.