The Isolation and Properties of Lignins Obtained by the Acidolysis of Spruce and Aspen Woods in Dioxane–water Medium

A study has been made of the isolation of a lignin fraction from spruce and aspen wood meals using a low temperature (90–95 °C) acidolysis involving a dioxane–water (9:1) solvent medium containing the equivalent of 0.2 N hydrochloric acid. The effect of extraction time on the yield of precipitated lignin and ether-soluble material, and on the methoxyl content of these products, was investigated. For both species prolonged extraction times led to greater yields of lignin with lower methoxyl content.Further acidolysis of isolated spruce lignin led to no significant loss of methoxyl indicating the stability of this group to these reaction conditions. With increasing times of acidolysis of the aspen wood, a slow rise in the carbon–methyl/methoxyl ratio was observed for the isolated lignins. This is in agreement with earlier findings for the spruce lignin. The yields of vanillin and syringaldehyde from aspen lignin on alkaline nitrobenzene oxidation were much less than those from wood meal, and the relative yield of syringaldehyde was higher.It is suggested that this type of lignin may be only mildly modified during extraction and hence suitable for subsequent chemical investigation. The significance of the findings is discussed.