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Distributions Of Fiber Characteristics As A Tool To Evaluate Mechanical Pulps
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. (FSCN)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mechanical pulps are used in paper products such as magazine or news grade printing papers or paperboard. Mechanical pulping gives a high yield; nearly everything in the tree except the bark is used in the paper. This means that mechanical pulping consumes much less wood than chemical pulping, especially to produce a unit area of printing surface. A drawback of mechanical pulp production is the high amounts of electrical energy needed to separate and refine the fibers to a given fiber quality. Mechanical pulps are often produced from slow growing spruce trees of forests in the northern hemisphere resulting in long, slender fibers that are well suited for mechanical pulp products. These fibers have large varieties in geometry, mainly wall thickness and width, depending on seasonal variations and growth conditions. Earlywood fibers typically have thin walls and latewood fibers thick. The background to this study was that a more detailed fiber characterization involving evaluations of distributions of fiber characteristics, may give improved possibilities to optimize the mechanical pulping process and thereby reduce the total electric energy needed to reach a given quality of the pulp and final product. This would result in improved competitiveness as well as less environmental impact. This study evaluated the relation between fiber characteristics in three types of mechanical pulps made from Norway spruce (Picea abies), thermomechanical pulp(TMP), stone groundwood pulp (SGW) and chemithermomechanical pulp (CTMP). In addition, the influence of fibers from these pulp types on sheet characteristics, mainly tensile index, was studied. A comparatively rapid method was presented on how to evaluate the propensity of each fiber to form sheets of high tensile index, by the use of raw data from a commercially available fiber analyzer (FiberLabTM). The developed method gives novel opportunities of evaluating the effect on the fibers of each stage in the mechanical pulping process and has a potential to be applied also on‐line to steer the refining and pulping process by the characteristics of the final pulp and the quality of the final paper.

The long fiber fraction is important for the properties of the whole pulp. It was found that fiber wall thickness and external fibrillation were the fibercharacteristics that contributed the most to tensile index of the long fiber fractions in five mechanical pulps (three TMPs, one SGW, one CTMP). The tensile index of handsheets of the long fiber fractions could be predicted by linear regressions using a combination of fiber wall thickness and degree of external fibrillation. The predicted tensile index was denoted BIN, short for Bonding ability INfluence. This resulted in the same linear correlation between BIN and tensile index for 52 samples of the five mechanical pulps studied, each fractionated into five streams(plus feed) in full size hydrocyclones. The Bauer McNett P16/R30 (passed 16 meshwire, retained on a 30 mesh wire) and P30/R50 fractions of each stream were used for the evaluation. The fibers of the SGW had thicker walls and a higher degree of external fibrillation than the TMPs and CTMP, which resulted in a correlation between BIN and tensile index on a different level for the P30/R50 fraction of SGW than the other pulp samples. A BIN model based on averages weighted by each fiber´s wall volume instead of arithmetic averages, took the fiber wall thickness of the SGW into account, and gave one uniform correlation between BIN and tensile index for all pulp samples (12 samples for constructing the model, 46 for validatingit). If the BIN model is used for predicting averages of the tensile index of a sheet, a model based on wall volume weighted data is recommended. To be able to produce BIN distributions where the influence of the length or wall volume of each fiber is taken into account, the BIN model is currently based on arithmetic averages of fiber wall thickness and fibrillation. Fiber width used as a single factor reduced the accuracy of the BIN model. Wall volume weighted averages of fiber width also resulted in a completely changed ranking of the five hydrocyclone streams compared to arithmetic, for two of thefive pulps. This was not seen when fiber width was combined with fiber wallthickness into the factor “collapse resistance index”. In order to avoid too high influence of fiber wall thickness and until the influence of fiber width on BIN and the measurement of fiber width is further evaluated, it is recommended to use length weighted or arithmetic distributions of BIN and other fiber characteristics. A comparably fast method to evaluate the distribution of fiber wall thickness and degree of external fibrillation with high resolution showed that the fiber wallthickness of the latewood fibers was reduced by increasing the refining energy in adouble disc refiner operated at four levels of specific energy input in a commercial TMP production line. This was expected but could not be seen by the use of average values, it was concluded that fiber characteristics in many cases should be evaluated as distributions and not only as averages.

BIN distributions of various types of mechanical pulps from Norway spruce showed results that were expected based on knowledge of the particular pulps and processes. Measurements of mixtures of a news‐ and a SC (super calendered) gradeTMP, showed a gradual increase in high‐BIN fibers with higher amounts of SCgrade TMP. The BIN distributions also revealed differences between the pulps that were not seen from average fiber values, for example that the shape of the BINdistributions was similar for two pulps that originated from conical disc refiners, a news grade TMP and the board grade CTMP, although the distributions were on different BIN levels. The SC grade TMP and the SC grade SGW had similar levels of tensile index, but the SGW contained some fibers of very low BIN values which may influence the characteristics of the final paper, for example strength, surface and structure. This shows that the BIN model has the potential of being applied on either the whole or parts of a papermaking process based on mechanical or chemimechanical pulping; the evaluation of distributions of fiber characteristics can contribute to increased knowledge about the process and opportunities to optimize it.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2015. , 170 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 211
Keyword [en]
Fiber, fibre, fiber characteristics, fiber dimension, fiber properties, mechanical pulp, FiberLab, raw data, distribution, fiber wall thickness, BIN, bonding ability influence, bonding indicator, bonding ability, fiber width, fibrillation, collapse resistance, laboratory sheet, fiber analyzer, optical analyzer, TMP, CTMP, SGW, sheet model, prediction, fiber characterization, hydrocyclone, fractionation, kernel density estimation, KDE, diffusion mixing, acoustic emission, F0.90, Norway spruce, Picea abies
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-24175ISBN: 978-91-86694-66-1 (print)OAI: oai:DiVA.org:miun-24175DiVA: diva2:782240
Public defence
2015-02-25, L111, Mittuniversitetet, Sundsvall, 09:15 (English)
Supervisors
Available from: 2015-01-20 Created: 2015-01-20 Last updated: 2015-03-13Bibliographically approved
List of papers
1. Measuring the bonding ability distribution of fibers in mechanical pulps
Open this publication in new window or tab >>Measuring the bonding ability distribution of fibers in mechanical pulps
2008 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 7, no 12, 26-32 p.Article in journal (Refereed) Published
Abstract [en]

Currently, the pulp and paper industry mainly uses average values of   mechanical pulp properties to characterize fibers, while printing paper   grammages keep decreasing, making every fiber more important for   strength, surface, and structure properties. Because fibers are   inhomogeneous, average values of the whole pulp may not be enough for   proper fiber characterization. This paper reports results from the   development of a method to measure the distribution of fiber bonding   ability in mechanical pulps.   Fibers from two commercial TMPs were fractionated into five   hydrocyclone streams, using a four-stage hydrocyclone system. The fiber   bonding ability of Bauer McNett fractions R16, P16/R30 and P30/R50   collected from each stream was analyzed. Five different methods of   evaluating fiber bonding ability all showed that fibers were separated   in the hydrocyclones according to their bonding ability.   Long fiber handsheets of the highest bonding fibers had up to 2.5 times   higher tensile strength for the P16/1330 fraction than handsheets from   the lowest bonding fibers. We also found that both the degree of   fibrillation and collapse resistance index (CRI) of the fibers obtained   from optical measurements are sufficient to predict quite accurately   the tensile strength of handsheets made from fiber fractions. Further,   we propose how to describe the distribution in fiber bonding ability   for mechanical pulps, by combining some of these five different   methods. A method to calculate fracture toughness of long fiber   handsheets based on acoustic emission is also illustrated.   A more rapid way to characterize fibers in mechanical pulps with   respect to their bonding ability distribution needs to be developed in   the future. It appears that it is time to move on from characterizing   pulp suspensions and handsheet properties using conventional approaches   based on average values.

National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-7381 (URN)000262544300005 ()2-s2.0-58749097112 (Scopus ID)
Available from: 2008-12-09 Created: 2008-12-05 Last updated: 2016-09-26Bibliographically approved
2. The influence of fiber dimensions on mechanical pulp long fiber tensile index and density
Open this publication in new window or tab >>The influence of fiber dimensions on mechanical pulp long fiber tensile index and density
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, 844-859 p.Article in journal (Refereed) Published
Abstract [en]

This study discusses how fiber dimensions affect the tensile index and density of long fiber laboratory sheets. Five commercial mechanical pulps (three TMP grades, one SGW and one CTMP) were fractionated into five streams in a hydrocyclone pilot plant. Fiber dimensions and fibrillation were analyzed of the P16/R30 and P30/R50 fractions and compared to the sheet properties. For comparison, samples were also analyzed by SEM cross-sectional image analysis and in a MorFi Lab optical analyzer. Fibrillation index showed a high positive influence on long fiber tensile index and density, whereas fiber wall thickness, fiber width, and collapse resistance index a negative. Fiber width showed the vaguest correlation to long fiber tensile index and density of the analyzed fiber properties, but this increased when combined with fiber wall thickness into collapse resistance index, CRI. The correlations between fiber properties and sheet properties were on different levels for the different mechanical pulping processes, but a combination of collapse resistance index and fibrillation index into the novel factor BIN, Bonding ability INfluence, gave one linear relation of high correlation to long fiber tensile index for all pulps, except the SGW P30/R50 fraction, which showed the same linear correlation on a slightly lower level. BIN should be a useful tool in characterizing mechanical pulp fibers.

Keyword
Bonding ability, Collapse resistance, Fiber characterization, Fiber wall thickness, Fiber width, FiberLab, Fibrillation, Mechanical pulp, MorFi Lab, Optical analyzer, SEM image analysis, Sheet properties
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-18300 (URN)10.3183/NPPRJ-2012-27-05-p844-859 (DOI)000313375400003 ()2-s2.0-84871766130 (Scopus ID)
Note

Language of Original Document: English

Available from: 2013-04-04 Created: 2013-01-16 Last updated: 2017-12-06Bibliographically approved
3. Weighted averages and distributions of fibre characteristics of mechanical pulps Part I: Various methods of weighting data from an optical analyser can give averages that rank pulps differently
Open this publication in new window or tab >>Weighted averages and distributions of fibre characteristics of mechanical pulps Part I: Various methods of weighting data from an optical analyser can give averages that rank pulps differently
2015 (English)In: Appita journal, ISSN 1038-6807, Vol. 68, no 4, 357-368 p.Article in journal (Refereed) Published
Abstract [en]

To improve the operation and energy efficiency of mechanical pulping processes, the effect of each stage of the process on the fibres should be carefully evaluated. Fibre-data from an optical analyser were used to predict tensile index by calculating BIN (Bonding ability /Nfluence). Wall volume weighted averages of wall thickness index and fibrillation index gave the most accurate predictions of the tensile index of laboratory sheets made from long fibre fractions of various mechanical pulps. Fibre width index, when used as a single factor, reduced the accuracy of the model. The ranking of some samples changed when fibre width was wall volume weighted compared to arithmetic. When fibre width was combined with wall thickness to give a collapse resistance index, no rankings changed. Weighted averages based on squared fibre length (length(2)) showed poor correlation to wall volume weighted averages for cross-sectional fibre dimensions, and resulted in different levels of correlation to long fibre tensile index for the five evaluated pulps.

Keyword
Fibre, bonding ability influence, B/N, weighted average, fibre characteristic, arithmetic, wall volume, FiberLab, optical analyser, collapse resistance index, length(2), hydrocyclone
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-24176 (URN)000364603600015 ()
Available from: 2015-01-20 Created: 2015-01-20 Last updated: 2017-12-05Bibliographically approved
4. Development of TMP fibers in LC- and HC-refining
Open this publication in new window or tab >>Development of TMP fibers in LC- and HC-refining
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, 860-871 p.Article in journal (Refereed) Published
Abstract [en]

Low consistency (LC) refining and high consistency refining (HC) has been studied in a TMP mill. When strength properties were increased, the development of fiber properties was different in LC- and HC-refining. Fiber curl decreased in LC-refining but increased in HC-refining. LC-refining decreased fiber curl and increased tensile index simultaneously in this study. It is therefore likely that the decreased fiber curl contributes to the increase of tensile index in LC-refining. Furthermore, fiber wall thickness decreased and external fibrillation increased in HC-refining, while these properties were only slightly influenced in the LC-refining. Fibrillation was found to decrease in most cases for LC-refining while fiber wall thickness index increased slightly but consistently, which might indicate a less dense structure of the fiber wall or its surface layers. Double-disc HC-refining with the same energy input as in a conical single-disc refiner resulted in fibers of higher external fibrillation, lower fiber wall thickness and higher fiber curl at a given fiber length. The results indicate that analyzing individual fiber dimensions could be a better tool for understanding how fibers develop in different kinds of refining than analyzing conventional handsheet properties.

Keyword
LC-refining, HC-refining, Mechanical pulp, TMP, Disintegration, Fiber dimensions, Fiber curl, Fiber wall thickness, Fiber width, Fibrillation, BIN, Sheet properties
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-18482 (URN)000313375400004 ()2-s2.0-84871738586 (Scopus ID)
Available from: 2013-03-06 Created: 2013-02-14 Last updated: 2017-12-06Bibliographically approved
5. Weighted averages and distributions of fibre characteristics of mechanical pulps – Part II: Distributions of measured and predicted fibre characteristics by using raw data from an optical fibre analyser
Open this publication in new window or tab >>Weighted averages and distributions of fibre characteristics of mechanical pulps – Part II: Distributions of measured and predicted fibre characteristics by using raw data from an optical fibre analyser
Show others...
2016 (English)In: Appita journal, ISSN 1038-6807, Vol. 69, no 1, 64-73 p.Article in journal (Refereed) Published
Abstract [en]

Characterisation of fibres in mechanical pulps is important for process evaluation and control, and necessary to be able to optimise the refining process with respect to the total electric energy consumption. There are large variations of cross-sectional fibre characteristics in the wood raw material which influence the properties of the product. Despite this, it is common to evaluate the fibre characteristics as averages instead of distributions. This study shows that the raw data from a FiberLab analyser can be used to make distributions of measured and predicted fibre characteristics. The factor BIN (Bonding ability /Nfluence), which correlates to long fibre tensile index, includes both the external fibrillation and wall thickness of each fibre. Distributions of BIN, fibrillation and wall thickness which take the Characteristics of each fibre into Consideration have higher resolution than histograms. These distributions weighted by length and wall volume with maintained resolution revealed more information about the pulps than average values.

Keyword
Fibre, distribution, weighted distribution, bonding ability influence, BIN, fibre characteristic, arithmetic, wall volume, FiberLab, optical analyser, collapse resistance index
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-24177 (URN)000371190200017 ()2-s2.0-85010817787 (Scopus ID)
Available from: 2015-01-20 Created: 2015-01-20 Last updated: 2017-12-05Bibliographically approved

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