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Measuring the bonding ability distribution of fibers in mechanical pulps
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
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.

Place, publisher, year, edition, pages
2008. Vol. 7, no 12, 26-32 p.
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:miun:diva-7381ISI: 000262544300005Scopus ID: 2-s2.0-58749097112OAI: oai:DiVA.org:miun-7381DiVA: diva2:127394
Available from: 2008-12-09 Created: 2008-12-05 Last updated: 2016-09-26Bibliographically approved
In thesis
1. Bonding Ability Distribution of Fibers in Mechanical Pulp Furnishes
Open this publication in new window or tab >>Bonding Ability Distribution of Fibers in Mechanical Pulp Furnishes
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a method of measuring the distribution of fiber bonding ability in mechanical pulp furnishes. The method is intended for industrial use, where today only average values are used to describe fiber bonding ability, despite the differences in morphology of the fibers entering the mill. Fiber bonding ability in this paper refers to the mechanical fiber’s flexibility and ability to form large contact areas to other fibers, characteristics required for good paper surfaces and strength.

 

Five mechanical pulps (Pulps A-E), all produced in different processes from Norway spruce (Picea Abies) were fractionated in hydrocyclones with respect to the fiber bonding ability. Five streams were formed from the hydrocyclone fractionation, Streams 1-5. Each stream plus the feed (Stream 0) was fractionated according to fiber length in a Bauer McNett classifier to compare the fibers at equal fiber lengths (Bauer McNett screens 16, 30, 50, and 100 mesh were used).

 

Stream 1 was found to have the highest fiber bonding ability, evaluated as tensile strength and apparent density of long fiber laboratory sheets. External fibrillation and collapse resistance index measured in FiberLabTM, an optical measurement device, also showed this result. Stream 5 was found to have the lowest fiber bonding ability, with a consecutively falling scale between Stream 1 and Stream 5. The results from acoustic emission measurements and cross-sectional scanning electron microscopy analysis concluded the same pattern. The amount of fibers in each hydrocyclone stream was also regarded as a measure of the fibers’ bonding ability in each pulp.

 

The equation for predicted Bonding Indicator (BIN) was calculated by combining, through linear regression, the collapse resistance index and external fibrillation of the P16/R30 fractions for Pulps A and B. Predicted Bonding Indicator was found to correlate well with measured tensile strength. The BIN-equation was then applied also to the data for Pulps C-E, P16/R30, and Pulp A-E, P30/R50, and predicted Bonding Indicator showed good correlations with tensile strength also for these fibers.

 

From the fiber raw data measured by the FiberLabTM instrument, the BIN-equation was used for each individual fiber. This made it possible to calculate a BIN-distribution of the fibers, that is, a distribution of fiber bonding ability.

 

The thesis also shows how the BIN-distributions of fibers can be derived from FiberLabTM measurements of the entire pulp without mechanically separating the fibers by length first, for example in a Bauer McNett classifier. This is of great importance, as the method is intended for industrial use, and possibly as an online-method. Hopefully, the BIN-method will become a useful tool for process evaluations and optimizations in the future.

Abstract [sv]

Den här studien presenterar en metod för att mäta fördelning av fiberbindning i mekaniska massor. Metoden hoppas kunna användas industriellt, där i dagsläget enbart medelvärden används för att mäta fiberbindnings-fördelning, trots råvarans (fibrernas) morfologiska skillnader.

 

Fem mekaniska massor (Massa A-E) från olika massaprocesser men från samma råvara, norsk gran (Picea Abies), har fraktionerats i hydrocykloner med avseende på fiberbindningsförmåga. Från hydrocyklon-fraktioneringen bildades fem strömmar, Ström 1-5. Varje ström plus injektet (Ström 0) fraktionerades också med avseende på fiberlängd i en Bauer McNett för att kunna jämföra fibrerna vid samma fiberlängd (Bauer McNett silplåtarna 16, 30, 50 och 100 mesh användes).

 

Fiberbindingsförmåga i den här studien härrör till fiberns flexibilitet och förmåga att skapa stora kontaktytor med andra fibrer, vilket bidrar till papprets yt- och styrkeegenskaper.

 

Ström 1 visade sig ha den högsta fiberbindningsförmågan, utvärderat som dragstyrka och densitet av långfiberark, samt yttre fibrillering och kollaps resistans index mätt i den optiska analysatorn FiberLabTM. Akustisk emission och tvärsnittsanalyser visade samma resultat. Ström 5 visade sig ha den lägsta fiberbindningsförmågan, med en avtagande skala från Ström 1 till Ström 5. Andelen fibrer från injektet som gick ut med varje hydrocyklon-ström ansågs också vara ett mått på fibrernas bindningsförmåga i varje massa.

 

Genom att kombinera fiberegenskaperna kollaps resistans och yttre fibrillering från den optiska mätningen på varje fiber genom linjär regression, kunde Bindnings Indikator (BIN) predikteras. Medelvärdet av Bindnings Indikator för varje hydrocyklon-ström korrelerar med dragstyrka för långfiber-labark.

 

Det visade sig att predikterad Bindnings Indikator inte bara fungerade för Massa A och Massa B P16/R30 fraktionen, som var de fraktioner som användes i den linjära regressionen, utan även för Massa C-E, P16/R30, och Massa A-E P30/R50 som också visade goda korrelationer med långfiber-dragstyrka när de sattes in i BIN-formeln.

 

BIN-formeln användes sedan för varje enskild fiber, i den rådata som levererats från FiberLabTM. Detta gjorde det möjligt att få en BIN-distribution av fibrerna, d.v.s. en fördelning av fiberbindningsförmåga.

 

Den här rapporten visar också hur det går att få BIN-distributioner också från mätningar på hela massan, för valbara fiberlängder, utan att först mekaniskt separera massan efter fiberlängd. Det är viktigt, då metoden är tänkt att användas som en industriell metod, och eventuellt som en online-metod. Förhoppningsvis kommer BIN-metoden att bli ett användbart verktyg för processutveckling- och optimering i framtiden.

Place, publisher, year, edition, pages
Sundsvall: FSCN - Fibre Science and Communication Network, 2008. 91 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 31
Keyword
Fiber, mechanical pulp, bonding ability, fiber characterization, Bonding Indicator, BIN, acoustic emission, hydrocyclone, Fiberlab, collapse resistance, fibrillation, Fiber, mekanisk massa, bindningsförmåga, fiber karakterisering, Bindnings Indikator, BIN, akustisk emission, hydrocyklon, Fiberlab, kollaps resistans, fibrillering
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-8033 (URN)978-91-85317-90-5 (ISBN)
Presentation
2008-06-18, Granen, Stora Enso Kvarnsvedens Pappersbruk, Borlänge, 10:00 (Swedish)
Opponent
Supervisors
Projects
Bonding ability distribution of fibers in mechanical pulp furnishes
Note
FSCN – Fibre Science and Communication NetworkAvailable from: 2009-01-08 Created: 2009-01-07 Last updated: 2009-07-13Bibliographically approved
2. Distributions Of Fiber Characteristics As A Tool To Evaluate Mechanical Pulps
Open this publication in new window or tab >>Distributions Of Fiber Characteristics As A Tool To Evaluate Mechanical Pulps
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
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:nbn:se:miun:diva-24175 (URN)978-91-86694-66-1 (ISBN)
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

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