Dissolving pulp production from auto-hydrolyzed Kenaf stalk fibers by Soda-AQ process in biorefinery approach

Dissolving pulp, generally producing from wood and cotton linter and is determined as high α-cellulose which is widely used by numerus cellulosic products like microcelluloses, nanocelluloses and various cellulose derivatives. Huge attempts have been focused on non-woods as pulping raw materials, due to limitations of the resources of wood and cotton. Extreme exploitation of biomass via extraction and conversion of unsuitable components respect to a special application (non-cellulosic materials in dissolving pulp) is biorefinery purpose. Toward biorefinery approach, in this study Kenaf (Hibiscus cannabinus) stalk pre-hydrolyzed by hot water and the optimum residence time (40min) at 160 oC was selected based on the stalk yield loss (27 wt%) and then subjected to soda-anthraquinone pulping at different alkaline and time levels. Concerning optimum purity and brightness, the pulped biomass under 22 wt% alkalinity at 90 min with 17.8 kappa NO and pulping yield of 65.9 wt% was followed by AD1EpD2P bleaching sequences based on kappa factors of 0.3, 0.4 and 0.45. Pre-hydrolyze treatment revealed that the yield and acidity reduced due to hemicelluloses removal that were increased by longer times which is valuable respected to the biorefinery approach and α-cellulose requirements. Bleaching Kappa factor of 0.45 resulted in: kappa NO. 1, yield 30.6 wt% (based on the kenaf stalk), α-cellulose 94.1 wt%, viscosity 6.4 cP, ash content 0.51%, DP 1670, and brightness 80.9 respectively. Kappa factor increment led to yield (-2.2%) and ash (-0.25%) loss, together with increase in viscosity (+2%), brightness (+4.3%) and degree of polymerization (+360). Therefore, kenaf stalk could be used as a proper non woody feedstock for α-cellulose production.