Browsing by Author "Silvy, Jacques"
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- 3-D Characterisation of Nonwoven Fabrics by means of an optical systemPublication . Pereira, Mário José Teixeira; Salvado, Rita; Fiadeiro, Paulo; Silvy, JacquesThe characterisation of fabric structure by means of quantified parameters is essential for the control of the fabrication processes and the resulting properties of the nonwoven materials. Important parameters of the structure are the porosity, the mean pore size and the pore size distribution, the specific area of the texture, the fibres orientation the last one needing to be characterised in the three dimension of the fabric web. In this research work we intend to evaluate the porous fibres orientation in geotextiles nonwovens using a procedure based on the fibres light conducting and their associated scattering. The interpretation of the phenomena is made through a modelisation concept of the pore fibre interfaces
- Energy efficiency in low consistency refining: a study using a Valley beaterPublication . Vaz, Álvaro; Espírito-Santo, António; Araújo, Pedro; Simões, Rogério; Silvy, JacquesThe purpose of this work was to study the influence of pulp fiber suspensions refining operating variables on energy efficiency coefficient. Three chemical pulps with different average morphological characteristics were used, obtained from bleached kraft Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The final objective was to establish the chemical pulps refining efficiency parameters. Refining hydromechanics and energy consumption profiles were analyzed. Average normal and tangential forces on pulp suspension in the gap clearance, resulting rotor-stator distance and no-load and refining conditions power consumption were obtained. The refining trials took place in a laboratory Valley beater, and the manipulated variables were charge on the roll and rotor rotation speed. Global relationships for tangential stress and energy efficiencies in terms of rotation speed and rotor-stator gap were obtained. A relationship between energy efficiency and shear stress was obtained. The results have shown that in a Valley beater increased rotor-stator gaps reduce energy efficiency, concomitantly increasing apparent viscosity and reducing shear stress. No-load power was seen to increase with crowding factor, and thus with flocculation. Inversely, crowding factor and ultimately flocculation had an adverse effect on energy efficiency.
- New method for the measurement of fibres orientation on the paper faces applied to the analysis of hygro-instability in paper sheetsPublication . Pereira, Mário José Teixeira; Costa, A. P.; Trindade, A. C.; Fiadeiro, Paulo; Silvy, Jacques; Tosio, J. M. SerraFor a given change in the humidity of a paper the hygro-instability of the sheet depends of two main factors: the sheet structural parameters which reflects its structure: the sheet porosity, the fibres orientation distribution mainly in the sheet plane and the variations of these parameters across the paper sheet thickness. the water reactivity of the components of the paper sheet which depends mainly of the sheet composition: the cellulosic and the fillers content, the nature of the fibres, softwood or hardwood, their degree of delignification, the beating degree of the pulp, the fines content, the conditions of the sheet drying with a more or less conditions of restraint. In this research initiated at the University of Beira Interior (UBI) with the collaboration of the Ecole Française de Papeterie (EFPG), we have tried to identify these main parameters of the paper hygro-instability. For this purpose we characterise the sheet structural parameters by optical methods developed at the Optical Centre of UBI.
- Paper surface diffraction to characterise the fibre orientation distributionPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo; Silvy, JacquesMany paper mills use ultrasonic techniques to measure the Tensile Stiffness Index, TSI, of the paper sheet. They then assume that the TSI value is the same as the fibre orientation anisotropy. This is true if the paper is allowed to dry without any internal tension or elongation, but does not apply to paper manufactured in a paper machine. The paper machine introduces tension and elongation as soon as the fibre is placed on the forming fabric. These factors increase through the press section and are accentuated in the drying section. In order to uniquely measure the fibre orientation anisotropy on the surfaces, the proposed method uses replicas of both paper surfaces to produce a laser diffraction pattern. The obtained pattern reveals an elliptical shape, which is related to the fibre orientation anisotropy of the paper surface. By measuring the ellipticity of the diffraction pattern and the deviation with respect to the machine direction, one can quantify the fibre orientation distribution. Different papers from the bench market have been successfully tested with the developed system. This article describes the new developed optical system and its innovative capabilities in the field to produce maps of the fibre orientation of a complete paper sheet surface. A selection of the obtained results to prove its feasibility is also presented.
- Refining rheological response of chemical pulp fibre suspensionsPublication . Vaz, Álvaro; Simões, Rogério; Silvy, JacquesThe purpose of this work was to study the influence of the refining operating variables on the rheological response of chemical pulp fibre suspensions using a Valley beater. Pinus sylvestris, Eucalyptus globulus and Betula verrucosa bleached pulps were used. The normal and tangential average forces exerted on the pulp suspension in the gap clearance were evaluated, the gap between rotor and stator was measured and the apparent viscosity evolution during refining was obtained. The refining essays took place in a laboratory Valley beater, and the studied variables were the load on the roll, the rotor speed of rotation and the specific applied energy. Relationships between apparent viscosity and shear rate were tested for the three species fibre suspensions, which showed shear-thinning behaviour (Fig.1). The results were analysed in terms of fiber and flock properties. The computed crowding factors, Nc, (Kerekes and Schell) decrease from pine to eucalypt to birch. Thus, flock dimensions and resistance are significantly higher for pine. Pine had significantly wider gap, due to its greater and more resistant flocks. This produced smaller shear rate and thus higher apparent viscosity. The smaller and weaker eucalyptus and birch flocks induced smaller gaps, higher shear rates and smaller apparent viscosity. For each pulp suspension, the apparent viscosity diminished with refining time due to increased fibre flexibility and shortening, which promoted smaller flocks and reduced gap clearance (producing higher shear rates). The different rheological behaviors under the same operating conditions for different pulps lead to the inference that from the hydrodynamical point of view one should treat pulps with different morphological characteristics separately, considering the optimization of the energy transfer efficiency in pulp refining.
- Structure of papers and NonwovensPublication . Pereira, Mário José Teixeira; Costa, A. P.; Salvado, Rita; Silvy, Jacques; Fiadeiro, PauloWe characterise the structure of fibrous materials: papers and nonwovens by diffraction and transmission of light. This allows the measurement of the fibres orientation distribution of the sample as a whole or for the surfaces using replicas. Applications of the methods are demonstrated in the case of paper for the control of the curl tendency and for two kinds of nonwoven materials, one used in the tailoring of surgical garments and the other used as components of the baby diapers.
- The effect of shear rate on apparent viscosity for different pulp suspensionsPublication . Vaz, Álvaro; Simões, Rogério; Silvy, JacquesThe goal of this work was to study the relationship between chemical pulps suspensions rheology and the operating variables of refining for three different paper fibres, namely Pinus sylvestris, Eucalyptus globulus and Betula verrucosa. The intention was the establishment of the best conditions for the refining of chemical pulps for paper production. In order to obtain that, the hydromechanics of the beating was analysed for the three pulps. So, the normal and tangential forces were evaluated, the distance between rotor and stator was measured and the pulp apparent viscosity evolution during refining was calculated. The refining essays took place in a laboratory Valley refiner, and the studied variables were the charge on the roll, the rotor speed of rotation and the specific applied energy. A global relationship between the apparent viscosity and the shear rate was finally obtained.
- The Surface Measurement of Fibre Orientation Anisotropy and Misalignment Angle by Laser DiffractionPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo; Jesus, M. E. P.; Silvy, JacquesThe dimensional stability in fibre webs mainly depends of the fibre anisotropy and its orientation on the surfaces. These parameters are influenced during the manufacturing process, where the length and type of the fibres is determinant. The web quality control, in general, is performed based on the measurement of these parameters in the bulk of the fibre webs. This paper presents an optical laser diffraction method to measure the fibre anisotropy and the fibre orientation distribution only at the paper surfaces. The developed system has been successfully used with a set of well-characterised paper sheets. The results shown a high correlation and accurate precision when compared with the results obtained by other techniques. This method has also been used successfully in non-woven fabrics.