New composite paper

Abstract

The principle objective of adding fillers to paper making s raw material economy and the secondary advantage is to increase specific properties such as opacity and brightness. The amount of filler added is limited because of paper strength.

In this thesis, changes in printing paper properties were studied by substituting fibres with micro-fines and pigments. The typical filler load in paper used in this work was between the ranges of 40% - 50%, which s clearly higher than current practice. The main scope and objective of this thesis was primarily to explore and research the essential and fundamental properties of fibrillar fines originating from different raw materials. Second objective was to study their behaviour with various inorganic pigments. The main technical target was to apply fibril - filler aggregates which form new type of web structures together with tailor-made pulp suspension, as a means to contrive a new composite paper.

In the first approach, two types of pigments- kaolin and PCC - were used together with fibres and fibrils. The results from two hardwood species and one annual plant, eucalyptus, birch and rice straw showed that all fibrils improved both optical and strength properties. Hand sheets made with straw fibrils showed poor strength and optical properties when compared to birch and eucalyptus sheets. Birch and eucalyptus fibrils behaved similarly though eucalyptus seems to give somewhat better optical and bonding properties.

In the second approach, TMP-based paper in combination with birch and eucalyptus fibrils from chemical pulp for filler loadings up to 40 %, were tested. Fibrils did improve the optical properties and tensile strength of the sheets as well as in chemical pulp-based paper. However, interfibre bonding (Scott bond) was not compensated as well. This is possibly because of the stiff fibre network formed by TMP fibres.

The new composite hand sheets developed in this study showed better tensile and internal bond strengths than to the reference sheets that were made from conventional furnish. A promising combination of higher filler content and high quality (strength, optical properties) was reached. Biggest challenge seems to be dewatering, which needs to be optimised using better process equipment.