Effects of Caustic Extraction on Properties of Viscose Grade Dissolving Pulp

Viscose, a cellulose-based commodity fibre, is produced by pulping and bleaching of wood, yielding a high quality “dissolving pulp” which is then spun. During pulping and bleaching, effective hemicellulose extraction is required to allow fibre production. We present a design of experiments (DoE) approach to optimise caustic extraction in a total chlorine free (TCF) bleaching sequence (O-CE-Z-P) of beech wood sulphite pulp. Temperature and sodium hydroxide concentration were varied to identify highest xylan extraction yield, and a maximum xylan removal of 83% was achieved at 20 °C and 120 g/L NaOH. Additionally, caustic extraction conditions were derived from the DoE model that led to pulps with high yield, high alpha cellulose content or uniform cellulose molecular weight distribution. Pulps from verification experiments exhibited good reactivity in viscose application tests. Hence, the presented O-CE-Z-P bleaching sequence can be considered as suitable for integrated viscose fibre production. We assume that the presented caustic extraction model will be useful for pulp and biorefinery researchers who work on caustic biorefinery processes involving hardwood feedstocks.