Effect of long-fibred reinforcement pulp on
mechanical properties of short fibred-based paper

Authors*: Eero Hiltunen
Hannu Paulapuro

Keywords: Activation, fibre length, fracture toughness, interfibre
bonding, runnability

Abstract
The purpose of long-fibred reinforcement pulp in printing paper
furnish is to improve the runnability of paper. Here the dry web
runnability was evaluated primarily based on flaw-resisting ability
of paper and secondarily based on in-plane tensile properties.
Flaw-resisting ability was measured as tear strength and, more
importantly, as fracture toughness. We modified the fibre length
and bonding potential of chemical softwood pulp–mechanical pulp
mixture. Fibre length was manipulated by proportion of pulps and
interfibre bonding potential by beating level and cooking conditions
of chemical pulp. Results clearly showed that higher average fibre
length improved the flaw-resisting ability of dry paper. As expected,
beating of reinforcement pulp and sulfite cooking (vs. kraft) increased
the interfibre bonding of pulp mixtures. However, contrary to our
expectation, improved bonding increased the flaw-resisting ability
only a little. According to our analysis, low-freeness mechanical pulp
has, as such, rather good interfibre bonding. Other factor is that
beating of chemical pulp improves specific elastic modulus largely
due to increased fibre segment activation, and only to smaller part
due to bonding. The flaw-resisting ability of reinforced paper can be
best controlled by modifying the average fibre length of the furnish
- controlling the bonding ability seems not as critical. On the other
hand, tensile properties like elastic modulus are not dependent
on fibre length, instead they depend on fibre segment activation,
interfibre bonding and fibre strength.

Authors’ references:
Aalto University, School of Chemical Technology, P.O. Box 16300, 00076 Aalto, Helsinki, Finland.
E-mail: Eero.Hiltunen@aalto.fi
Corresponding author: Eero Hiltunen – E-mail: Eero.Hiltunen@aalto.fi

O PAPEL vol. 72, num. 8, pp. 42 - 48 AUG 2011