Enzyme Pretreatment of Hardwood Chips in Kraft Pulping

Abstract

This bachelor’s thesis concerns the application of enzymes pretreatment of hardwood chips in Kraft pulping. The purpose of this work is to understand the basic knowledge about enzymes and Kraft pulp, and meanwhile, to find out their effect on hardwood chips in Kraft pulping. Through comprehensive study, the knowledge was accumulated which brought a clear understanding for the enzymes' structure and properties of pulp, together with their working principles for pulp.

In the experiment part, four different cooking types of Kraft pulp were studied: Pulp with auto-hydrolysis treated (Pulp A), pulp with untreated (Pulp B), pulp with cellulase treated (Pulp C) and pulp with xylanase treated (Pulp D). These pulps were obtained after pulping fresh birch chips in liquid circulated batch digester by Kraft pulping process. Screened pulps were beaten in PFI mill to three different revolutions (0, 3000 and 6000). Then the kappa number, viscosity and fiber length were measured from pulps; Additionally, tensile strength, tear strength and air permeability were measured from hand sheets.

Beating brought significant changes in the fiber properties. Untreated pulp has the highest kappa number, and pulp with xylanase treated has the lowest kappa number. Viscosity values were decreased as the revolutions increasing. Tensile index was rising after each beating. As an important remark, beating had negative effect on the tear strength. Fiber length decreased because of beating, which directly reduces the web strength of paper made from it. Air permeability decreased to a quite low value after beating, which is a required property for paper making.