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Optical methods for fines and filler size characterization: Evaluation and comparison
KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics. Innventia AB. (Manufacturing and Metrology Systems)ORCID iD: 0000-0002-1467-7413
Innventia AB, Sweden . (Stock Design)
KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics. (Manufacturing and Metrology Systems)
2016 (English)Report (Other academic)
Abstract [en]

The pulp fines and mineral fillers in the fine fraction of a papermaking stock influence process conditions and sheet properties. The influence is largely dependent on the size and shape of the particles. Quantitative characterization of the size and shape of fines and fillers would aid in process control and prediction of product properties.  Thus, the aim of the study was to evaluate and compare optical instruments which can be used to quantitatively characterize the fine fraction of a papermaking stock. The compared instruments were the Mastersizer2000 from Malvern, based on diffraction scattering of a laser beam, the ImageStream from Amnis, and the Fiber Tester and Fiber Tester Plus from ABB Lorentzen & Wettre. The last three instruments are all based on imaging of the particles and have spatial resolutions ranging from 0.33 µm to about 10 µm per pixel.

All instruments overestimated the size of calibration spheres with known sizes. In several cases, calibration particles that were smaller than the spatial resolution of the instrument were detected. In these cases, the relative measurement error was large, likely due to positioning and quantization errors. It is also suggested that the oversizing was partly due to dissimilar optical properties of the calibration particles, compared to the typical sample, and that better calibration materials for fines need to be developed.

For the image-based instruments, the relative share of fines and filler particles increased with as the size of the measured particles decreased. Thus, with higher spatial resolution, more particles were detected. However, the shape of the particle size distribution depended on the resolution and the field-of-view. The ImageStream resolved single PCC particles, which has not previously been done using flow microscopy. Due to its limited field-of-view, the ImageStream could not measure the largest fines, which were detected by the Fiber Tester and Fiber Tester Plus. While the Fiber Tester Plus did not resolve single PCC particles, it detected, due to its higher resolution, a higher share of smaller particles than the Fiber Tester. Overall, the ImageStream and the Fiber Tester Plus were found to be complementary.

The diffraction-based method struggled to measure small fines. It is proposed that small fines diffracted light insufficiently to be detected by the instrument. The obtained result was also highly sensitive to the choice of refractive index; a fact that some of the previous users apparently were not aware of.

In summary, image-based methods were found to perform better than the diffraction-based method when measuring on fines and mixtures of fines and fillers, while the highest resolution image-based instrument and the diffraction-based method were best when measuring on pure fillers.

Place, publisher, year, edition, pages
Stockholm: Innventia AB , 2016. , 55 p.
, Innventia Report, 717
Keyword [en]
Stock, fine fraction, fines, fillers, size, shape, morphology, particle size distribution, particle characterization, flow microscopy, laser diffraction, flow cytometry
National Category
Paper, Pulp and Fiber Technology Reliability and Maintenance
Research subject
Production Engineering; Fibre and Polymer Science
URN: urn:nbn:se:kth:diva-180719OAI: diva2:896445
Swedish Energy AgencyVINNOVAÖnnesjö Foundation

QC 20160122

Available from: 2016-01-21 Created: 2016-01-21 Last updated: 2016-01-22Bibliographically approved
In thesis
1. Image-based quantitative infrared analysis and microparticle characterisation for pulp and paper applications
Open this publication in new window or tab >>Image-based quantitative infrared analysis and microparticle characterisation for pulp and paper applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Measurements of process variations and particle morphology are widely employed in the pulp and paper industry. Two techniques with high potential, infrared thermography and microparticle characterisation, are mainly used qualitatively. Quantitative thermography requires knowledge of the emittance, a material property which has not been measured under many process-relevant conditions. Quantitative characterisation of microparticles, e.g. pulp fines and mineral fillers, requires the analysis of a large number of particles, which can be accomplished using flow microscopes. Flow microscopes for pulp analysis have had insufficient spatial resolution to resolve fines and fillers. Additionally, there has been a lack of methods which can differentiate between fines and fillers in a mixed suspension.

State-of-the-art instruments for particle image analysis were evaluated and compared to laser diffractometry, a measurement method based on scattering by diffraction. Laser diffractometry was found to be highly sensitive to the complex refractive index of the particles, and especially to its change due to moisture absorption. A high-resolution imaging flow cytometer and a high-resolution fibre analyser were found to be complementary for characterisation of pure fines and fines/filler mixtures, and superior to laser diffractometry. A method for differentiating between fines and fillers in a suspension based on their autofluorescence and side-scattering was proposed and qualitatively evaluated.

Furthermore, a method for measuring the directional and integrated emittance of paper was developed and its accuracy was determined. Measurements on a wide range of samples showed that the emittance of fibre-based materials vary significantly with wavelength, pulp type, observation angle, and moisture content. By applying measured quantitative values of the emittance, the thermal energy emitted by sack paper samples during mechanical deformation could be quantitatively calculated. The increase in thermal energy at the time of rupture was found to correlate well with the elastic share of the mechanical energy that was stored in the sample during its elongation.

In summary, the results of this work have facilitated the use of quantitative microparticle analysis and infrared thermography for pulp and paper applications. 

Abstract [sv]

Mätningar av processvariationer och partiklars form och storlek utförs i stor skala inom massa- och pappersindustrin. Två mättekniker med stor potential, infraröd termografi och mikropartikel-karaktärisering, används mest kvalitativt idag. Kvantitativ termografi kräver att provets emittans är känd. Emittansen är en materialegenskap som inte har mätts för många förhållanden som är relevanta inom papperstillverkning. Kvantitativ karaktärisering av partiklar kräver att ett tillräckligt stort antal partiklar analyseras, något som kan göras med flödesmikroskop. Flödesmikroskop för mäldanalys har haft otillräcklig upplösning för att karaktärisera mikrometerstora partiklar, t.ex. fines och fyllmedel. Det har heller inte funnits någon metod som kan särskilja mellan fines och fyllmedel i en blandning.

Högupplösta mätinstrument för bildbaserad mikropartikelkaraktärisering utvärderades och jämfördes med en laserdiffraktometer, en mätmetod baserad på ljusspridning genom diffraktion. Laserdiffraktometerns mätresultat påverkades starkt av det brytningsindex som antogs för provet, och hur brytningsindexet ändrades med fukthalt. En högupplöst bildbaserad flödescytometer och en högupplöst fibermätare konstaterades komplettera varandra vid mätningar av mäldens finmaterial. De var även pålitligare än laserdiffraktometern vid mätningar av organiskt finmaterial. En metod för att skilja mellan organiskt och oorganiskt finmaterial i en mäld baserat på deras autofluorescens och ljusspridning presenterades och utvärderades kvalitativt.

En metod för att mäta den vinkelberoende och våglängdsintegrerade emittansen hos fiberbaserade material utvecklades och dess mätnoggrannhet utvärderades. Mätningar på ett stort antal prover visade att emittansen varierade betydligt med våglängd, mäldtyp, observationsvinkel, och fukthalt. Genom att använda den uppmätta emittansen kunde den termiska energin som frigjordes av ett säckpappersprov vid brottögonblicket beräknas. Denna energi korrelerade väl med den elastiska energi som lagrades i provet medan det töjdes, fram till tidpunkten för brottet.

Sammanfattningsvis har resultaten av detta arbete möjliggjort kvantitativ användning av mikropartikel-karaktärisering och infraröd termografi i massa- och papperstillämpningar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 132 p.
TRITA-IIP, ISSN 1650-1888 ; 16:01
Metrology, stock, papermaking, refining, fibrillation, fines, filler, morphology, classification, flow microscopy, fibre analyser, flow cytometry, laser diffraction, dynamic image analysis, process variation, thermography, emittance, emissivity, infrared, MWIR, LWIR, goniometer
National Category
Reliability and Maintenance Paper, Pulp and Fiber Technology
Research subject
Production Engineering; Fibre and Polymer Science
urn:nbn:se:kth:diva-180722 (URN)978-91-7595-843-9 (ISBN)
Public defence
2016-02-12, Innoversum, Innventia, Drottning Kristinas Väg 61, Solna, 10:00 (English)
Swedish Energy AgencyÖnnesjö Foundation

QC 20160122

Available from: 2016-01-22 Created: 2016-01-21 Last updated: 2016-01-22Bibliographically approved

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