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Pulps
What do we mean by reinforcement?
The main use of softwood kraft pulps in papermaking
is to strengthen weaker papermaking furnishes without
significantly impairing other end-use properties. This
function is referred to as reinforcement.
Reinforcement fibres increase the strength of the wet
web, the dry sheet, and the sheet when rewetted. Reinforcement
fibres also improve the drainage of the furnish. Because
of the generally higher cost of reinforcement fibres
when compared to other furnish ingredients, it is normally
good practice to use the minimum amount possible while
ensuring that the desired strength properties are achieved.
While
the paper industry tends to be rather casual in the
way in which it uses the term strength,
the generally used mechanical strength properties
of paper are its elastic modulus and its fracture resistance.
Additionally we commonly include its tensile strength
and extensibility when referring to its strength. The
manner in which fibres interact and the physical and
chemical ways in which they tangle or bond together
within a sheet to provide these strength properties
have been the subject of extensive research and is
quite well understood (see Further
Reading for more reference).
The particularly crucial role of fibre morphology in
defining
the reinforcement
potential of a fibre is described elsewhere on this
site.
So what makes one pulp better than another from
the point of view of reinforcement on the paper
machine, the coater or the pressroom?
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