Low molecular weight lignols with intact side chains were produced by mild hydrolysis of spruce wood, of unbleached and hydrogen peroxide bleached spruce groundwood and of chemithermomechanical pulp (CTMP). The major monomeric, dimeric and trimeric lignin products derived were isolated by HPLC and characterized by GC-MS and NMR. The behaviour of these products towards photo-oxidation in the solid state on filter paper was studied. Coniferaldehyde structures, the major leucochromophores originally present in spruce wood lignin, were reduced during the CTMP process and eliminated after bleaching with hydrogen peroxide. Diguaiacyl stilbene originating from diarylpropane structures and produced during hydrogen peroxide bleaching were found to be the predominant leucochromophoric structure present in the hydrogen peroxide bleached pulps and these were found to be responsible for the fast photoyellowing of these pulps.
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