Title
Characterization of subabul heartwood and sapwood pulps after cooking and bleaching
Authors
MADHURI PYDIMALLA NIKHIL SAINATH REDDY and RAMESH BABU ADUSUMALLI

Received September 9, 2018
Published Volume 53 Issue 5-6 May-June
Keywords heartwood, sapwood, kraft cooking, bleaching, Klason lignin, black liquor

Abstract
This study aimed to investigate the effect of cooking temperature (165 °C, 140 °C) on subabul heartwood and sapwood pulps separately, and the effect of bleaching on the mixed subabul wood pulp. The pulps cooked at 165 °C had high cellulose content, high water retention value and low lignin content, compared to those obtained at 140 °C. Microscopic analysis confirmed the integrity of the pulps obtained at 140 °C, while those cooked at 165 °C presented loose and collapsed fibres. The water retention value and the cellulose and ash contents of sapwood pulp were much higher in comparison to those of heartwood pulp, for both temperatures, and it could be due to the differences in their lignin and extractive contents. Bleached pulp had high cellulose content, high brightness and was thermally stable up to 300 °C. For packaging applications requiring processing temperatures of up to 600 °C, unbleached fibres are recommended due to the integrity of their cell wall. UV-visible spectroscopy data revealed that 2 h cooking time was sufficient for effective removal of lignin from the heartwood, but the situation was different in the case of sapwood.