The Formation and Quantity of Diphenylmethane Type Structures in Residual Lignin during Kraft Delignification of Douglas-Fir

Document Type

Article

Publication Date

1-1-1988

Abstract

Kraft delignification of Douglas-fir (Pseudotsuga menziesii) was carried out from 90°C to a final pulping temperature of 170°C at a heating rate of 1°C/min. At various stages of delignification the quantity of phenyl nuclei that were condensed into the diphenylmethane moieties in residual lignins were determined directly on delignified wood by a method combining alkaline nitrobenzene oxidation and phenyl nucleus exchange reactions. The results indicate that the formation of diphenylmethane structures does not occur before the pulping temperature had reached 170°C. As delignification proceeded, the quantity of diphenylmethane moieties in residual lignins increased steadily. After 2 hours at 170°C (~ kappa 30) the residual lignin consisted of 54 mol% phenyl nuclei that were associated with the diphenylmethane structural units, 37 mol% other type of condensed and 9 mol% noncondensed phenyl nuclei. In this study, the quantity of structural units of the diphenylmethane type in residual lignin was determined for the first time. Further confirmation of the validity of our current results is under investigation using other analytical methods. Copyright © 1988 Walter de Gruyter

Publication Title

Holzforschung

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