The effects of kneading and enzymatic treatments on properties of viscose-grade dissolving wood pulp

Abstract

Dissolving wood pulp (DWP) is a high-purity form of cellulose that is produced by pulping and bleaching lignocellulosic biomass to obtain a cellulose content greater than 90%. DWP is used as the feedstock for many applications with viscose production being the most dominant. DWP of high purity and quality can be produced through chemical, mechanical, and enzyme treatments. Mechanical and enzymatic treatments are currently of interest as they lower the environmental impact by limiting the volume of chemicals used in the production of viscose. This study aims to improve the critical properties of DWP through a combination of mechanical (kneading) and endoglucanase enzyme treatments. The critical properties of DWP for viscose production are reactivity and viscosity. The study was divided into three distinct phases. In the first phase, two different formulations of endoglucanase enzyme were investigated at a bench-scale level, using a range of incubation times and enzyme concentrations. In the second phase, the scale was, firstly, increased to pilot plant level using the most effective enzyme concentration, formulation, and incubation time. And then, secondly, the most effective sequence of mechanical kneading and enzymatic treatments was investigated to further enhance the pulp properties. In the final phase, viscose was produced using the treated pulp from the previous phase to validate the results and conclude whether the treatments could be effective to improve the quality of DWP. The bench-scale investigation showed that endoglucanase could be used to reduce the viscosity by up to 50 mL/g (8.8%) with the most effective overall incubation time of 2 hours. The Ecopulp R formulation did not significantly increase the reactivity, but the NS 51179 did. It was thus concluded that the Ecopulp R formulation was the most effective of the two. The second phase of investigation found kneading to be a harsh mechanical treatment that resulted in increased amounts of degraded cellulose without decreasing the viscosity or improving the reactivity of the pulp. Additionally, kneading also caused compression of the pulp fibres that resulted in decreased enzyme and chemical efficiency by reducing the available surface area of the pulp fibres. This was demonstrated when the combination of kneading followed by enzyme treatment resulted in a lower pulp reactivity compared to the control, while the viscosity was not reduced as much as the enzyme-treated pulp. Both enzyme treatment alone and enzyme treatment followed by kneading resulted in similar viscosity changes, with the key difference being that the combination of enzyme treatment and kneading resulted in lower reactivity, indicating that chemical accessibility was hindered by introducing kneading. It was therefore concluded that using enzyme treatment alone, without kneading, was the most effective way to decrease viscosity and improve reactivity.

The final phase of the investigation found that all viscose results were highly variable with no significant improvement of viscose quality being observed. Therefore, the combination of kneading and enzymatic treatments was not effective in producing DWP of higher quality.