Study on Alkali-Accessible Chromophores from Unbleached Kraft Pulp

Abstract

Summary An approach to a chromophore composition study using the direct size-exclusion chromatography (SEC-UV) analysis of an alkaline extract of pulp fibre walls is described. Absorbance in the 290–405 nm range of 2% and 18% NaOH extract from unbleached pulps obtained by conventional and extended kraft delignification of black alder wood is compared. The effect of cooking conditions on the localisation and accessibility of chromophores is elucidated. The alkali-soluble lignin from pulp produced by extended cooking was less oxidised, less conjugated, and less coloured as compared with the conventional kraft lignin. A chromophore accessibility index is proposed. The chromogenic structures in pulps obtained by extended cooking were more resistant to alkali solutions than those in conventional kraft pulps.

Properties of Rice Straw Extract after Subcritical Water Treatment

“…Maximum absorption at about 220 nm might indicate the presence of carboxyl and carbonyl groups. 18,19) The absorption maximum around 280 nm probably indicates various phenolic substances originating from lignin and protein. 20,21) Figure 3 shows the ratio of the absorbance at 280 nm to that at 220 nm for extracts obtained at different temperatures.…”