The effect of increased pulp yield using additives in the softwood kraft cook on the physical properties of lowgrammage handsheets

Hafizur Rahman,Per Engstrand,Peter Sandström,Lennart Salmén,Mikael E Lindström

doi:10.3183/npprj-2017-32-03-p317-323

Abstract

Highlights

The effect of increasing the pulp yield by the addition of sodium borohydride (NaBH4) or polysulfide (PS) in softwood kraft cooking, i.e. enhancing the retention of glucomannan, on the physical properties of low-grammage handsheets was studied
The degradation of lignin, cellulose and hemicellulose depends on the chemical conditions in the kraft cook, and the overall pulp yield can be increased by using different additives in the kraft cook (Aurell, Hartler 1965a; Paavilainen et al 1989)
According to Wang et al (2005) Sodium borohydride reduces the aldehyde end groups in the hemicellulose to stable alcohol end groups while polysulfide oxidises the aldehyde end groups to carbonyl end groups, and reduced end group is more stable towards peeling than an oxidised end group

Summary

Introduction

The effect of increasing the pulp yield by the addition of sodium borohydride (NaBH4) or polysulfide (PS) in softwood kraft cooking, i.e. enhancing the retention of glucomannan, on the physical properties of low-grammage handsheets was studied. The degradation of lignin, cellulose and hemicellulose depends on the chemical conditions in the kraft cook, and the overall pulp yield can be increased by using different additives in the kraft cook (Aurell, Hartler 1965a; Paavilainen et al 1989). Polysulfide sulfur in the cooking liquor stabilises hemicellulose at lower temperatures (100°C120°C) by oxidizing the reducing end groups of the polysaccharides into alkali-stable aldonic acids, and this reduces the carbohydrate degradation in kraft cooking (Hägglund 1946). Polysulfide addition has been found to have an slightly positive effect on delignification when cooking to low kappa numbers (Lindström, Teder 1995)

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Results

Conclusion