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Aggregation studies of pinus radiata wood extractives under increased system closure.

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Lee, R and Stack, KR and Richardson, DE and Lewis, T and Garnier, G (2011) Aggregation studies of pinus radiata wood extractives under increased system closure. In: 65th Appita Annual Conference, 10-13 April, Rotorua, New Zealand.

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Abstract

Within the pulp and paper industry, the recycling of
process water to reduce water consumption leads to
accumulation of colloidal Material in this water and
greater risk of deposition. A major factor in the colloidal
stability of these substances, which arise from the wood
extractives, is the presence of natural polymers
originating from the wood as well as salts that
accumulate in the process water as a result of increased
system closure. This work explores the factors that
affect the stability of wood extractive colloids under
varying conditions of ionic strength, ionic valency,
shear, pH, mixtures of cations and wood polymers
released from pinus radiata thermomechanical pulp.
Coagulation of a colloidal wood extractive
solution by a single salt was found to follow the
Schultz-Hardy rule, with the critical salt coagulation
concentration (CCC) strongly influenced by salt valency
(z). Changes to both pH and shear experienced by the
colloid, were observed to affect the concentration of salt
required to destabilise the colloid. However, on
addition of a second salt to the solution, the CCC
decreased for calcium + sodium in comparison to when
only a single salt was present.
Addition of wood polymers to an aqueous
dispersion of wood extractives caused two stages of
destabilization of the wood extractive colloids, which
were separated by an apparently stable region. The
behaviour was typical of aggregation by polymers in
which polymer bridging at low polymer additions caused
firstly colloid destabilization, followed by steric
stabilisation of the colloids at medium concentration of
the polymer, then depletion flocculation followed finally
by depletion stabilization at higher polymer
concentrations.

Item Type: Conference or Workshop Item (Paper)
Keywords: wood extractives, pitch, aggregation, photometric dispersion analyzer, critical coagulation concentration, polysaccarides, shear
Date Deposited: 05 Jul 2011 02:39
Last Modified: 18 Nov 2014 04:20
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