Exploded Wood Lignins From Pinus Radiata Wood. 2. The Effect of So2Pretreatment on Structure

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Abstract
The acetone soluble lignins of Pinus radiata wood, which had been steam exploded by the Australian Siropulper process, both with and without SO2 pretreatment, have been examined by 13C NMR spectroscopy. The marked structural effects of SO2 pretreatment are discussed. A brief comparison of the lignins from wood treated by the Siropulper and Canadian Iotech processes (without SO2 pretreatment) is also presented. The soluble lignins from exploded wood treated by either the Siropulper or the Iotech process are very similar in structure and in the relative abundances of structural units. In contrast, SO2 pretreatment markedly changed relative abundances. β-0-4 linked units were more extensively modified and β-5 linked units, which were stable in the absence of SO2 pretreatment, were also extensively modified. No sulphur incorporation was detected and some differences between the steam explosion treatment and acidic sulphite pulping are outlined.