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

Abstract: 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.