Effect of changes in fibres’ internal and external fibrillation on dewatering properties in paper making

Abstract

The papermaking process can be described as a process to remove water from pulp. The purpose of this thesis is to evaluate the effects to dewatering properties in each sub-process including forming, pressing and drying.

Lampen mill refiner and Voith LR-40 refiner is used to generate 4 different types of pulp which are subject to dewater with laboratory papermaking process. Moving belt former (MBF) was used to forming sheets and this machine also can generate different vacuum levels to remove the water from the wet web. Then the wet sheets are dewatered with MTS-press which can generate high pressure in a millisecond scale. IR-dryer was used to dry the sheets to evaluate the evaporation rate.

It is found that with the increasing energy level in refining, the heavily refined fibres are shorter, more fibrillation, straight and fines than that of lightly refined. Meanwhile, the Voith refined fibres have more fibrillation than Lampen refined pulp.

In forming part, the vacuum curves and surface level curves can be characterized by MBF. When high vacuum level applied on wet web, the heavily refined pulps or high fines content furnishes have higher vacuum curves and longer drainage time because the fibrillations and more fines result in the web denser and less permeable. Voith refined samples have higher vacuum curves and longer drainage time than that of Lampen mill refined samples.

The dry solid content was measured after each sub-step. Heavily refined samples have lower dry solid content than that of lightly refined samples and Voith heavily refined samples have lower dry solid content than that of Lampen heavily refined samples. The heavily refined pulps or more fines content have the lower speed to be dried. Lightly refined samples have higher evaporation rate than of heavily refined samples.