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Authors
Advisor(s)
Abstract(s)
The goal of this thesis is to set up a methodology to establish a relationship
between pulp properties, namely morphological and physical, and paper properties,
specifically structural, optical and strength, with the operating variables of refining
and the physical and chemical properties of the raw material. The goal is to contribute
to the analysis of the beatability of chemical pulps for paper production.
The beatings took place in a laboratory Valley beater, and the studied variables
were the charge on the roll, the rotor speed of rotation and the specific applied
energy. For its feasibility, one fitted the following adaptations to the Valley: a rotor
speed of rotation variation controller, a sensor to measure the distance between rotor
and stator and an electrical power consumption meter.
The effects for three different bleached Kraft pulps were studied, one being
pine and the others Portuguese eucalyptus and birch. At the fibre level, its
morphology was analysed by image analysis, such as the average fibre length and
distribution, its width, coarseness, curl, kinks, fibrillation and fines proportion; the
intrinsic fibre resistance was evaluated, such as its water retention value and wet
flexibility. At the paper level, one measured its density, tensile strength, burst
strength, tear strength, brightness, opacity and its scattering and absorption
coefficients. One implemented methodologies to evaluate the relative bonded area and
the bond strength in the paper structure using optical and mechanical methods.
The hydromechanics of the beating was analysed for the three pulps. So the
beating effects on the specific edge load was studied, the normal and tangential forces
were evaluated, the pulp apparent viscosity evolution during refining was determined,
the distance between rotor and stator was measured and also the energetic efficiency
was quantified. One obtained relationships between the apparent viscosity and the
rotor-stator gap, and another between the first one and the rate of shear.
One explored the experimental results in order to develop control relationships
for the pulp properties to paper production. One essayed an optimization of the
refining conditions for each pulp for specific types of industrial papers, namely in
terms of paper properties and the energy consumption in the Valley beater.
The pulp suspension presents rheofluidificant behaviour and the apparent
viscosity diminishes along the refining. The different pulps reveal different rheological behaviour, which leads to the inference that from the hydrodynamical
point of view one should treat pulps with different morphological characteristics
separately.
The obtained adjustment equations for the different studied properties permit
the comparison between the pulps and the study of the effects of the operating
conditions. As expected, the pine revealed the best strength performance, the
eucalyptus showed the best optical properties, and the birch showed a better
mechanical performance relatively to the other hardwood. In what concerns the
analysis of the operating conditions, one verified that the rotor speed of rotation has a
major influence on the pulp and paper properties. One also inferred that the birch
reveals an opposite behaviour comparatively to the pine and the eucalyptus, from the
standpoint of the sped of rotation and the specific edge load.
Description
Keywords
Ciência e Tecnologia do Papel Refinação Refinabilidade Pastas químicas Avaliação de pastas Valley Hidromecânica Propriedades das fibras Propriedades da pasta Propriedades do papel