The influence of fibre curl on the shrinkage and strength properties of paper

Fibres become curled during high consistency treatments in the pulp mill. This changes the properties of paper, for instance it is belived that the shrinkage during drying is increased. The drying shrinkage is an important factor to control, one reason is that it can lead to misprint in multi colour printing. In this thesis the influence of fibre curl on the shrinkage and mechanical properties of paper is studied. One chemical and two mechanical methods are used to introduce different degrees of fibre curl. The papers are dried in a biaxial dryer, which allows the paper to shrink or be stretched in two directions while the stresses and strains are measured. The drying stresses occuring in the paper are used to determine the shrinkage potential of paper. Both in-plane and out-of-plane properties are evaluated. It was found that the influence of fibre curl on the shrinkage potential and tensile properties depended on the beating. Shrinkage potential and tensile strength, for unbeaten pulps, were increased with increasing fibre curl while they were decreased for beaten pulps. The z-strength increased with increasing fibre curl. It was also found that wet strain is the determining parameter for tensile properties, which means that the tensile properties in cross direction can be changed without affecting tensile properties in the machine direction.Validerat; 20101217 (root