| 1. |
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| 2. |
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| 3. |
- Axelsson, Maria, et al.
(author)
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Estimation of the pore volume at the interface between paper web and press felt
- 2006
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In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 21:3, s. 395-402
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Journal article (peer-reviewed)abstract
- A method for determining the water content at the interface between a press felt and a paper web has been developed. The water content was obtained by subtracting the estimated volume of the indented fibre web from the measured felt surface porosity of the press felt. The felt surface porosity was calculated from a topography map that was imaged with a Confocal Laser Scanning Microscope (CLSM) method. Here, the press felt was compressed against a smooth surface using a stress in the range of 0 to 10 MPa. Artefacts in the CLSM images were reduced using an image analysis method. The indentation of paper webs into the measured felt surface pores at different applied pressures was estimated using another image analysis method, simulating a rolling ball, with different radii of curvature for the different pressures and grammages, rolling over the felt surface. The ball radii were determined for a low and a high grammage web using the STFI-Packforsk Dewatering model. The method was evaluated in a case study with four press felts that had batt fibre diameters in a range between 22 and 78 μm. The indentation was calculated for webs with a low (15 g/m2) and a high grammage (105 g/m2), respectively. The evaluation showed that a considerable amount of porespace is available at the interface between the web and the felt. In most cases, the volume of the water-filled pores accounted for approximately 50% of the total surface porosity of the felt. Assuming a complete water saturation of the web/felt interface, approximately 10 g/m2 of water for the finest felt surface up to 40 g/m2 for the coarsest felt surface, could be located at the interface between the press felt and the paper web at a load of 10 MPa. This implies that a considerable amount of water is available for separation rewetting.
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| 4. |
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| 5. |
- Bergström, Jonas, et al.
(author)
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Application of a pitometer to measure the tangential velocity in a cylindrical through-flow hydrocyclone operated with a fiber suspension
- 2005
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In: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 20:1, s. 30-35
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Journal article (peer-reviewed)abstract
- This investigation evaluates a novel fluid velocity measurement method to measure the tangential velocity in a hydrocyclone. The hydrocyclone was operated with an opaque fiber suspension in order to investigate the influence of fiber presence on the tangential velocity distribution. The tangential velocity was measured with a one-hole pitometer, 0.9 mm in diameter, that was equipped with a micro pressure transducer. The pitometer was kept clean with a continuous purge flow. The probe was tested in a cylindrical through-flow hydrocyclone operated with water and 0.4 g/l and 0.8 g/l (0 %, 0.04 % and 0.08 %) addition of a bleached softwood kraft pulp. The velocity profiles measured in pure water agreed qualitatively with velocity distributions that are found in the literature. The outer section had a free vortex-like distribution and the inner section had a solid body rotation. The addition of small amounts of fibers changed the tangential velocity profile significantly. The radius of solid body rotation increased, the maximum tangential velocity decreased and the transition from solid body rotation to free vortex rotation was smoothened.
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| 6. |
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| 7. |
- Bergström, Jonas, et al.
(author)
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Literature review of experimental hydrocyclone flow field studies
- 2007
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In: Separation and Purification Technology. - : Elsevier BV. - 1383-5866 .- 1873-3794. ; 53:1, s. 8-20
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Journal article (peer-reviewed)abstract
- The complex flow field of hydrocyclones has been experimentally investigated on several occasions. Most studies present similar results for the tangential velocity component. In the inner part of the cyclone, it resembles a solid-body rotation, while it typically has a free-vortex-like behavior in the outer part. When looking at the axial velocity component, the results are more diversified. Most studies show a downward velocity close to the wall and an upward velocity in the center. However, some studies report a heavily varying axial velocity over short radii close to the centerline. The radial velocity component appears to be the most problematic one to measure. Dissimilarities in measurement results between the studies are often greater than similarities. However, later studies agree on an increasing inward radial velocity towards the hydrocyclone center. Despite the obvious relationship, extremely little experimental research work can be found in the literature where changes to the flow field are connected to changes in separation efficiency.
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| 8. |
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| 9. |
- Bergström, Jonas, et al.
(author)
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Tangential velocity measurements in a conical hydrocyclone operated with a fibre suspension
- 2007
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In: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 20:4, s. 407-413
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Journal article (peer-reviewed)abstract
- The tangential velocity flow field in a conical hydrocyclone was measured using a self-cleaning pitometer. The influence of pulp fibre concentration on the tangential velocity profile was of particular interest. The measurement, showed that the pulp fibres had a strong influence on the tangential velocity profile. When operating the hydrocyclone with pure water, the velocity profile showed the typical combination of free-vortex-like rotation close to the hydrocyclone wall and solid-body-like rotation in the proximity of the hydrocyclone axis. This profile changed significantly when pulp fibres were added. At a low fibre concentration (1.2 g/l), the fibres smoothened the transition between the free-vortex-like and the solid-body-like region of the velocity profile. The location of the maximum tangential velocity moved to a larger radius. At higher fibre concentration (7.5 and 11 g/l), the free-vortex-like behaviour in the outer area was virtually suppressed. Due to networking, the fibre suspension in the entire hydrocyclone behaved as a solid body. The radial acceleration profile and tangential rate-of-strain profile were determined. Based on these profiles, a hypothesis was proposed explaining the well-known observation that fractionation efficiency decreases significantly at higher fibre concentrations.
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| 10. |
- Bjärestrand, Annika, et al.
(author)
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Upgrading recycled pulp quality by fractionation and selective refining
- 2016
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In: International Paperworld IPW. - 1615-1720. ; 2016-January:12, s. 40-44
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Journal article (other academic/artistic)abstract
- As recycling rates increase and the consumption of graphic papers decrease it becomes more and more difficult to maintain the recycled fibre quality. Also, increasing ash content in the recycled pulp contributes to the strength challenge ahead for the paper and board producers. The fractionation of recycled fibre in this study was made in order to investigate possible routes for upgrading the recycled pulp strength. A recycled pulp for containerboard was fractionated in pilot scale using a pressure screen and hydrocydones. The pulp was first fractionated using a micro-perforated screen basket into a short fraction, with high ash and fines content, and a long fibre fraction. The following hydrocyclone fractionation of the screen short fraction resulted in a fine fraction with fibrillar fines and a coarse fraction containing low bonding fines and fibre fragments together with most of the ash. The short coarse fraction also had a high dirt content. When the screen long fibre fraction was split in the hydrocyclone fractionation, a fine fibre fraction containing good bonding fibres and fines and a coarse fibre fraction with coarse low bonding fibres were obtained. The coarse long fibre fraction was upgraded, to a strength level comparable to the good bonding fine fraction, by refining with an energy input of only 24 kWh/t calculated on the whole pulp. This selective refining of the coarse long fibre fraction resulted in an improvement of the pulp strength by 20 % when the pulp fractions were mixed back together in the same proportion as they had been separated. Further strength was gained when the low bonding short coarse fraction with high ash content was removed. This study showed that a recycled pulp can be upgraded by selective and appropriate treatment of the different streams, with different properties, produced in a fractionation process.
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| 11. |
- Björk, Elisabeth, et al.
(author)
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Fibre-based strength aids for increased board stiffness
- 2019
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In: PaperCon 2019. - : TAPPI Press.
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Conference paper (other academic/artistic)abstract
- A pilot scale study has been made of the concept of adding fibre-based strength agents (fines enriched (FE)-pulp or highly refined (HR)-pulp) in a board middle ply containing chemithermomechanical bleached pulp (CTMP) in order to increase bending stiffness of the board while maintaining Z-strength. It has been demonstrated that the bending stiffness of a sheet consisting of a top ply and a CTMP based middle ply could be improved by increasing the CTMP fraction and preventing Z-strength loss via addition of a fibre based strength agent. Compared with the reference pulp, both Z-strength and bulk increased for three of the compositions, namely 65% CTMP with 5% strength agent of either FE or HR type and 85% CTMP with 10% HR-pulp. FE-pulp was found to be more efficient than HR-pulp concerning bending stiffness improvement. While the highly-refined fibres of the strength agents had a negative effect on the drainage resistance and press dryness, an increased share of CTMP increased the press dryness linearly. FE-pulp and HR-pulp had the same impact on press dryness. Press solids could be improved by approximately 2% without significantly reducing the bulk by increasing press loads.
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| 12. |
- Björk, Elisabeth, et al.
(author)
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Fines-enriched pulp as a strength agent in a CTMP middle ply
- 2018
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In: PaperCon 2018. - : TAPPI. - 9781595102683 ; , s. 741-760
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Conference paper (peer-reviewed)abstract
- The objective of this pilot scale trial, was to evaluate fines-enriched pulp (FE-pulp) as a strength agent in amiddle ply of a board product.A typical CTMP-based middle ply was produced on the FEX pilot paper machine. The stock consisted of CTMP,refined hardwood and softwood pulp, and filler. FE-pulp as strength agent was compared with glue pulp, ahighly refined chemical pulp. FEX sheets and hand sheets made of pulp mixtures were evaluated. Also, thedewatering and pressing conditions on the paper machine were compared.The results confirmed the results of earlier experiments with handsheets; FE-pulp used as strength agent showedto be twice as efficient as glue pulp regarding strength properties without impairing the bulk. Further, thedewatering conditions and press dryness's on the paper machine was comparable at these additions. Thus, allthese results imply that addition of FE-pulp can replace the double amount of glue pulp as a strength agent.
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| 13. |
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| 14. |
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| 15. |
- Björk, Elisabeth, et al.
(author)
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Production of a fine fraction using micro-perforated screens
- 2020
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 35:4, s. 611-620
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Journal article (peer-reviewed)abstract
- The objective for this work was to investigate the possibility to use a pressure screen equipped with a micro-perforated screen basket to produce a fine fraction from bleached chemical pulp. Trials were performed with unrefined bleached chemical hardwood pulp, and with unrefined and refined bleached chemical softwood pulp. The effect of feed concentration, feed flow, and volumetric fine fraction flow was evaluated. The difference between the fine fraction (i. e. the particles passing the screen) and the feed was analysed by studying the fibre morphology. The results showed that high feed concentration was positive for both the fine fraction concentration and the separation efficiency. A higher fine fraction concentration was also obtained when using hardwood pulp, which was explained by the shorter fibre length. Refining of the pulp prior to the fractionation proved beneficial, as a larger share of the refined pulp passed the screen, resulting in a twice as high concentration of the fine fraction when compared to unrefined pulp.
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| 16. |
- Björk, Elisabeth, et al.
(author)
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Production of fines from refined kraft pulp by fractionation with micro-perforated screens
- 2021
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In: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 36:3, s. 456-
-
Journal article (peer-reviewed)abstract
- The objective in this work was to obtain a fine fraction of kraft pulp, with as high concentration as possible, in a pilot-scale fractionation with micro-perforated screen baskets. The influence of screen basket surface, hole size, feed concentration, pulp type and refining segment design was investigated. The results showed that a smooth screen basket surface improved the fractionation efficiency of the unrefined pulp compared to a profiled screen basket, despite a larger hole size. A significantly higher fine fraction concentration was obtained when using refined hardwood pulp compared to when using softwood pulp, which was explained with its lower average fibre length and narrower and thus more flexible fibre fragments. The pilot trials also showed that the screening process could be operated at feed concentrations similar to those directly after a refiner, 30-40 g/l. This was demonstrated in a process layout with partial recirculation where a refiner and a micro-perforated screen basket were operated in series in pilot scale.
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| 17. |
- Björk, Elisabeth, et al.
(author)
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Production of pulps with an extremely high fines content for use as strength agent
- 2018
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In: PaperCon 2018. - : TAPPI. - 9781595102683
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Conference paper (peer-reviewed)abstract
- The objective was to optimize the production of fines-enriched pulp (FE-pulp) from chemical pulp.The first trial was a continuous production of FE-pulp with unbleached and bleached never-dried softwood. Thepulp was refined using a JC00 equipped with SF filling, and screened with a micro-perforated screen basket with250 μm diameter holes, but the produced FE-pulp got low concentration, below 3 g/l.The second trial aimed at optimised conditions, using dried bleached softwood. Three fillings, microbar, AA andFF were evaluated in a JC01 refiner, where microbar was most energy efficient. Microbar and AA reachedtargeted FE-pulp concentration, 10 g/l. The refined pulps were screened with different hole diameters, where, asexpected, larger hole diameters resulted in higher concentration but also lower fines content in the FE-pulps.The last trial, the microbar filling was evaluated for never-dried softwood pulp, unbleached and bleached. Now,the refining of unbleached softwood gave 3 times more fines per kWh/ton compared with first trial.These trials demonstrated the importance of the right refining conditions regarding effect of refiner and type offilling to achieve glue-pulp with high enough fines content. With the right conditions, it was possible to produceFE-pulp with high concentration at moderate energy consumption.
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| 18. |
- Björk, Elisabeth, et al.
(author)
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Single-stage hydrocyclone fractionation of refined bleached softwood pulp
- 2017
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In: Paper Conference and Trade Show, PaperCon 2017: Renew, Rethink, Redefine the Future. - : TAPPI Press. ; , s. 878-905, s. 878-905
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Conference paper (other academic/artistic)abstract
- Refined bleached chemical softwood was fractionated using a hydrocyclone in a fine and a coarse fraction. The trials were done at three inject concentrations, three coarse fraction volume ratios, and with pulps refined with two refining levels.A large difference in sheet properties between fine and coarse fraction was observed. Compared with the feed pulp, the relative change in the sheet properties increased more in the fine fractions than it decreased in the coarse fractions. Increased fines proportion had a positive effect on all properties up to a certain level when a further improvement could not be observed. Interestingly, the fine fractions of both refining levels reached the same absolute strength level, both for the tensile properties and z-strength. The fine fractions at the highest coarse fraction mass ratios contained more fines, and the mean fibre was shorter and narrower. This led to higher density but also a decrease of the stretch-at-break and z-strength values.When comparing these results with previous fractionation results for unrefined pulp, it was found that inject concentration did not have a large effect on thickening in the present study. As for the refined pulp, the tensile index increased with fines proportion for the unrefined pulp, however, only up to a certain fines proportion where a maximum values was reached. The increase was larger for the refined pulps which had higher fines proportion.
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| 19. |
- Björk, Elisabeth, et al.
(author)
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Usage of Fines-enriched pulp to increase strength in CTMP
- 2017
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In: Paper Conference and Trade Show, PaperCon 2017. - : TAPPI Press. - 9781510847286 ; , s. 1607-1631
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Conference paper (other academic/artistic)abstract
- Fines-enriched pulp (FE-pulp) was benchmarked against glue pulp as strength agent in eucalypt CTMP. FE-pulp was produced by combining high intensity multiple-pass refining with a fractionation in a microperforated screen basket. The fraction passing through the holes of the screen is the FE-pulp. The FE-pulp comprises of secondary fines, created in the refiner, and flexible, fibrillated highly-refined fibres or fibre fragments. Glue pulp is highly refined kraft pulp, commonly added as a strength agent in middle plies of board products, or between plies to increase the plybond. Equal amounts of FE-pulp and glue pulp were added to the original CTMP as well as to washed CTMP, where most of the CTMP-fines had been removed. The effects of the strength agents were evaluated using laboratory sheets. Both glue pulp and FE-pulp increased the strength of the CTMP sheets. The bulk of the sheets decreased however. When 5 % FE-pulp was added, the tensile index increased by more than 50 %, and the tensile energy absorption and z-strength increased by more than 100 %. FE-pulp proved to be twice as effective as glue pulp. The addition of 5 % FE-pulp resulted in the same relative strength increase as an addition of 10 % glue pulp. The washed CTMP lost all strength when the CTMP-fines content was reduced from 17 % to 3% through washing. The addition of 5 % FE-pulp restored the strength values, and at a higher bulk. The drainability in terms of CSF of that stock was much higher when compared to the original pulp.
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| 20. |
- Björk, Elisabeth, et al.
(author)
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Use of fines-enriched chemical pulp to increase CTMP strength
- 2021
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In: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 20:4, s. 255-263
-
Journal article (peer-reviewed)abstract
- In this study, fines-enriched pulp (FE-pulp)-the fine fraction of highly-refined kraft pulp-was benchmarked against highly-refined kraft pulp (HRK-pulp) as a strength agent in eucalyptus chemithermomechanical pulp (CTMP). Both the FE-pulp and the HRK-pulp were produced from unbleached softwood kraft pulp, and equal amounts of those strength agents were added to the original CTMP, as well as to washed CTMP, where most of the fines had been removed. The effects of the added strength agents were evaluated with laboratory handsheets. The FE-pulp proved to be twice as effective as HRK-pulp. Both HRK-pulp and FE-pulp increased the strength of the CTMP handsheets. The bulk of the handsheets decreased, however, as well as the drainability. The addition of 5% FE-pulp resulted in the same strength increase as an addition of 10% HRK-pulp, as well as the same decrease in bulk and CSF. For the handsheets of washed CTMP, the strengths were not measurable; the CTMP lost the sheet strength when the CTMP-fines content was reduced through washing. The reduced strength properties were compensated for by the addition of chemical pulp fines that proved to be an efficient strength agent. The addition of 5% FE-pulp restored the strength values, and at a higher bulk and higher drainability. Application: In this study, we show how the strength of a CTMP sheet can be improved by adding fine material from kraft pulp.
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| 21. |
- Gabrielsson, Andreas, et al.
(author)
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Investigation of the dynamic liquid absorption properties of kitchen towel
- 2014
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In: Paper Conference and Trade Show, PaperCon 2014. - : TAPPI Press. - 9781510801288 ; , s. 1216-1239
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Conference paper (peer-reviewed)abstract
- The dynamic absorption of liquid in kitchen towel was investigated. A new method was developed. The method measures the radial spreading of the absorbed liquid using thermography. The method allows also for a controlled compression of the sample between two smooth surfaces during the absorption process. A pressure head at the inlet is avoided in order not to have an external pressure drop driving the flow. The dynamic absorption properties of kitchen towel samples comprising conventional dry creped samples with a two-and three-ply design, and a two-ply TAD sample were evaluated. The measurements were performed with the samples being compressed to different bulk levels. The absorption rate and the speed of the absorption in different directions were determined. For the conventional samples, the liquid spreading area had an oval shape, while it was approximately circular for the TAD sample. Artifacts like embossing structures had a clear effect on liquid spreading with the shape of the liquid spreading area becoming less uniform. Sample compression had a very strong influence on the dynamic absorption behavior.
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| 22. |
- Granberg, Hjalmar, et al.
(author)
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It’s a bird! It’s a plane! It’s a super multimaterial!
- 2015
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In: Paper Conference and Trade Show (PaperCon 2015). - : TAPPI Press. - 9781510818873 ; , s. 492-504
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Conference paper (peer-reviewed)abstract
- Matching market demands and technological solutions is not always straightforward. In this article, we report on one material, a cellulose-PLA multimaterial, which was made on a full-scale pilot paper machine and adapted to five different market applications having specialized and often conflicting demands. The material can be injection molded, 3D-printed, hot pressed, treated as a textile, used in a laminate, or converted as a paper board, giving it a wide range of possible properties depending on how it is processed.The five application areas presented here were identified as gaps in the marketplace where seemingly conflicting needs were desired: opacity and transparency; compact for transport but having an expanded size during use; stiffness and flexibility; strength and light-weight; and durability and degradability. These properties are exemplified in a number of material and product demonstrators, illustrating how tailored solutions can give products with distinctly different personalities. The material can be made flexible and given movement as graceful as the wing of a bird or be processed to be strong and light-weight enough to be used in vehicles like airplanes. By having one material that is produced on a large scale, but then processed according to specific market demands and expectations, the gap between needing scale and needing scope is bridged.
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| 23. |
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| 24. |
- Hyll, Caroline, et al.
(author)
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A method for measurement of the directional emittance of paper in the infrared wavelength range
- 2012
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In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:5, s. 958-967
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Journal article (peer-reviewed)abstract
- A method for measuring the directional emittance of paper and board samples was developed. The available literature showed that the influence of temperature and observation angle on the emittance of dry and moist paper had not been investigated in detail. Methods adapted for such investigations were not available. In the developed method, the emittance of a sample is determined by comparing its infrared radiation with the radiation emitted from a reference surface with known emittance. In order to investigate the influence of the wavelength range, two cameras, operating in the mid-wavelength and long-wavelength infrared range, respectively, were used. The method allows for the adjustment of the directional emission angle in a range from 0° down to 80°, and variation of the sample temperature between 30°C and 100°C. A study was performed to evaluate the method. Here, the directional emittance of handsheets made from thermo-mechanical pulp was measured at different wavelength ranges, sample temperatures and emission angles. The obtained emittance values and trends were in agreement with previous experimental work and theoretical predictions. The emittance of the samples was also measured using Fourier-Transform Infrared spectroscopy. Given the methodological differences between the two measurement approaches, the results were in good agreement.
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| 25. |
- Hyll, Caroline, et al.
(author)
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Analysis of the plastic and elastic energy during the deformation and rupture of a paper sample using thermography
- 2012
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In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 329-334
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Journal article (peer-reviewed)abstract
- Thermography has been used to quantitatively analyze the plastic and elastic energy during deformation of paper. Sack paper samples were subjected to uniaxial tensile testing until rupture occurred. The temperature of the sample was simultaneously recorded with an infrared camera. The mechanical energy invested in the deformation was determined based on the force and deformation data. The thermal energy that accumulated in the sample during testing was estimated using the temperature measurements. Here, special attention was put on using the correct emittance values for the sack paper by measuring it with a new method. When comparing exerted mechanical energy with released thermal energy up to the time of sample rupture, about 40% to 60% of the mechanical energy could be detected as thermal energy. The lacking share of heat was most likely lost due to cooling of the sample during the experiments, as a lower share of detected mechanical energy was obtained for longer experiments. When comparing the increase in thermal energy during rupture to the elastic energy stored in the sample, an agreement of better than 90% was found.
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| 26. |
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| 27. |
- Hyll, Caroline, 1984-, et al.
(author)
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Directional emittance of dry and moist paper
- 2014
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In: Nordic Pulp & Paper Research Journal. - Sundsvall : Mid Sweden University. - 0283-2631 .- 2000-0669. ; 29:2, s. 294-303
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Journal article (peer-reviewed)abstract
- The directional emittance of dry and moist paper and board samples was measured in two wavelength ranges; the mid-wavelength infrared (MWIR) range and the long-wavelength infrared (LWIR) range. The influence of pulp type, pulp drying, pulp refining, fibre orientation, additives, coating, and observation angle on the emittance of dry paper was examined. The influence of sample moisture and observation angle on the emittance of moist samples was also investigated. The emittance in the LWIR range was higher than the MWIR emittance. The emittance varied with pulp type, especially for TMP, which had a significantly lower emittance compared to the samples made of chemical pulp. The impact of different properties, such as pulp type, refining or coating, was much smaller in the LWIR range than in the MWIR range. Observation angle was found to significantly impact the emittance at angles larger than 60 degrees from the normal direction in the MWIR range, and angles larger than 70 degrees in the LWIR range. The emittance increased with increasing moisture ratio. This increase was most pronounced at low absolute moisture ratios, where an addition of an already small amount of water could impart a large change in emittance. It was found that the emittance and sample moisture could be correlated well using a linear combination of the emittance of dry paper and pure water.
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| 28. |
- Hyll, Caroline, 1984-
(author)
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Infrared Emittance of Paper : Method Development, Measurements and Application
- 2012
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Licentiate thesis (other academic/artistic)abstract
- Thermography is a non-destructive technique which uses infrared radiation to obtain the temperature distribution of an object. The technique is increasingly used in the pulp and paper industry. To convert the detected infrared radiation to a temperature, the emittance of the material must be known. For several influencing parameters the emittance of paper and board has not previously been studied in detail. This is partly due to the lack of emittance measurement methods that allow for studying the influence of these parameters.An angle-resolved goniometric method for measuring the infrared emittance of a material was developed in this thesis. The method is based on the reference emitter methodology, and uses commercial infrared cameras to determine the emittance. The method was applied to study the dependence on wavelength range, temperature, observation angle, moisture ratio, sample composition, and sample structure of the emittance of paper and board samples. It was found that the emittance varied significantly with wavelength range, observation angle and moisture ratio. The emittance was significantly higher in the LWIR (Long-Wavelength Infrared) range than in the MWIR (Mid-Wavelength Infrared) range. The emittance was approximately constant up to an observation angle of 60° in the MWIR range and 70° in the LWIR range, respectively. After that it started to decrease. The emittance of moist samples was significantly higher than that of dry samples. The influence of moisture ratio on the emittance could be estimated based on the moisture ratio of the sample, and the emittance of pure water and dry material, respectively.The applicability of measured emittance values was demonstrated in an investigation of the mechanical properties of sack paper samples. An infrared camera was applied to monitor the generation of heat during a tensile test of a paper sample. It was found that the observed increase in thermal energy at the time of rupture corresponded well to the value of the elastic energy stored in the sample just prior to rupture. The measured emittance value provided an increased accuracy in the thermal energy calculation based on the infrared images.
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| 29. |
- Hyll, Kari, 1984-
(author)
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Image-based quantitative infrared analysis and microparticle characterisation for pulp and paper applications
- 2016
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 30. |
- Jansson, Zheng, 1985-
(author)
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Characterization of Spruce Xylan and Its Potential for Strength Improvement
- 2013
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Licentiate thesis (other academic/artistic)abstract
- Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been shown to give higher pulp yield and better strength properties. This is economically interesting from an industrial point of view. Many studies have been done to investigate xylan behaviour during kraft cooking, to discover the xylan-cellulose attachment mechanism, to find the optimal xylan retention or adsorption process, and to discover relations between xylan structure and strength enhancement. Most of them have concentrated on hardwood xylan. However, softwoods are the major raw materials for the pulp industries in the northern hemisphere. Earlier studies have shown that the xylan characteristics, rather than simply the amount of xylan, influence the strength-enhancing effect of xylan. To obtain optimal utilization of spruce xylan as a strength enhancer, it is essential to know what the beneficial xylan characteristics are and how cooking conditions affect the characteristics.In this study, kraft cooking of spruce chips was performed under varied cooking conditions and the xylan in the black liquor was precipitated and characterized. It was found that dissolved spruce xylan had a much higher amount of bound lignin compared to previous studies on xylan dissolved from hardwoods. Increased cooking temperature increased the dissolution rate of xylan. The lower alkali charge and higher ionic strength of the cooking liquor resulted in a lower amount of dissolved xylan. Apart from the effect of the amount, cooking conditions also affected substitution of dissolved xylan. Higher temperature and higher ionic strength led to a lower amount of MeGlcA, while the MeGlcA amount of dissolved xylan was preserved during lower alkali cooking.By distinguishing how different cooking conditions affect the characteristics of the xylan dissolved in the black liquor, xylans with different structures were designed to study their effects on pulp strength, that is, the addition of black liquors with certain known xylan characteristics in the kraft cooking process. It was found that the best effect of xylan on tensile strength occurred when the xylan penetrated some distance into the subsurface of the fibre wall. Both low molecular weight and high degree of substitution lowered the tendency of xylan to aggregate, which enabled the dissolved xylan to penetrate some distance into the exposed fibre surface. Upon beating, this xylan was exposed, thus facilitating improvement of fibre-fibre joint formation, which led to increased tensile strength.
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| 31. |
- Kari, Hyll, 1984-, et al.
(author)
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Characterization of morphological changes of chemical pulp fibres and fines due to refining
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Other publication (other academic/artistic)abstract
- The influence of the refining process on the morphological changes of a chemical softwood pulp was investigated. An industrial-like laboratory refiner was used, where the pulp was refined with five refining segments with differences in bar widths, groove widths, and cutting angles. The refined pulp was characterized with a fibre analyser with a spatial resolution of approximately 4 µm/pixel and a wide size range. The fines fraction of the refined pulp was also characterized with an imaging flow cytometer with a spatial resolution of 0.33 µm/pixel and a narrower size range.The fibre analyser measurements showed that the mean length, width, and aspect ratio of the fines decreased monotonically with accumulated refining energy. The imaging flow cytometer with its higher spatial resolution showed little change in fines morphology with accumulated refining energy.The morphology of the fines was more dependent on the applied specific refining energy than the design of the refining segment. However, a segment with much finer grooves and bars, initially designed for hardwood, gave significantly less fibre shortening, fines generation, external fibrillation, kink, and fines that were more fibrillar, compared to the other segments.
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| 32. |
- Kemper, M, et al.
(author)
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Method for fractionating an aqueous paper fibre suspension and hydrocyclone for carrying out said method
- 2008
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Patent (pop. science, debate, etc.)abstract
- The invention relates to a method and to a device which is used to fraction aqueous paper fibre suspensions (S). Relatively large centrifugal forces are used, also in suspension components having essentially the same densities, in order to achieve good results. This is achieved by virtue of the fact that the paper fibre suspension (S) entering via the inlet (10) is guided initially in a first annular chamber (4) which narrows in an axial direction (4) and subsequently in a second annular chamber (5) which widens in an axial direction. As a result, good fractionating results can be obtained, in particular, when the fibre material consistency in the inlet area is approximately 0.5 - 2 % and also the necessary mass fluxes are maintained at a relatively low level. Said method can be used, for example, for fractionating fresh cellulose and/or wood pulp. It can also be used in the preparation of used paper, wherein said method is particularly economical.
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| 33. |
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| 34. |
- Ko, Jordan, et al.
(author)
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Numerical modeling of highly swirling flows in a through-flow cylindrical hydrocyclone
- 2006
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 52:10, s. 3334-3344
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Journal article (peer-reviewed)abstract
- This article aims to identify the most appropriate numerical methodology for simulating hydrocyclone flows with high swirl numbers. The numerical results are validated against the tangential velocity measurements from a cylindrical hydrocyclone with a swirl number of 8.1, which is twice the typical swirl magnitude of industrial hydrocyclones. The linear and quadratic formulations of the Reynolds stress transport (RST) model are used to simulate the anisotropic swirling turbulent flow three-dimensionally in the commercial software package Fluent (TM). The tangentical velocity profiles predicted by the quadratic RST model are in good agreement with experimental data. They also show Rankine vortex patterns over the entire flow domain. In contrast, the linear RST model fails to predict this important swirl flow feature. In addition, both models predicted a complex axial flow reversal pattern not previously reported in hydrocyclones. This study clearly shows that the quadratic RST model is preferable for future hydrocyclone simulations, especially when the swirl number is large. All necessary physical and numerical parameters used to obtain converged results are given in this article.
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| 35. |
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| 36. |
- Lucisano, Marco, et al.
(author)
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Stratified forming as a tool for resource efficient papermaking
- 2015
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In: Paper Conference and Trade Show (PaperCon 2015). - : TAPPI Press. - 9781510818873 ; , s. 767-785
-
Conference paper (peer-reviewed)abstract
- Pilot-scale demonstration of stratified forming with innovative design of vane technology. Stratified dosage of fillers tested for: •SC-paper •Fine paper Dosage of filler and retention aid through the liquid layers gives a wider window of operation (retention-formation). Filler content can be increased with no adverse effects on strength and structure.
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| 37. |
- Nilsson, Lars, 1966-, et al.
(author)
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The influence of grammage and pulp type on through air drying
- 2015
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In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 30:4, s. 651-659
-
Journal article (peer-reviewed)abstract
- The influence of grammage and pulp type on through air drying was studied. The temperature of a sample was measured during the drying process and the observed temperature changes were used to evaluate the drying process. Laboratory sheets with grammages 15- 60 g/m², from two softwood and two hardwood bleached chemical pulps were used. All samples were analysed with respect to formation, flow resistance, modified permeability, mean drying time, non-uniformity of drying time, and area- and mass-specific drying rate. The pulps had different modified permeabilities but showed similar behaviour when analysed as a function of grammage. A constant value was found for higher grammages, while an increase in modified permeability was found at decreasingly low grammages. Almost all pulp and grammage combinations had similar area-specific drying rates, but the mass-specific drying rates decreased with grammage. However, the samples with lower grammages had mass specific drying rates independent of modified permeability, where samples with increasing grammage showed an increasing dependency. This implies that the drying efficiency at low grammages was not controlled by the volume flow of the drying air. A good correlation was found between energy needed to evaporate water and energy supplied by the drying air as estimated from the surface temperature and air flow measurement. The surface temperature can therefore be used to quantify the drying process.
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| 38. |
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| 39. |
- Tysen, Aron, et al.
(author)
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Method for the quantification of in-plane drying nonuniformity
- 2015
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 30:2, s. 286-295
-
Journal article (peer-reviewed)abstract
- A method has been developed in order to determine the in-plane non-uniformity of drying of wet paper samples dried by an air flow. The surface temperature of the samples, recorded by an infrared camera, is used to determine a mean drying time and the local drying time of each pixel. Based on the initial dryness and the mean drying time, a mean drying rate can be obtained, and furthermore, the drying time of each pixel can be presented as a 2-dimensional map. Apart from conventional statistical information on the variation in drying time, the map also gives information regarding the size and shape of the drying non-uniformity. The pressure drop over the sample and the air flow rate through the sample were used to calculate a flow resistance as a function of grammage. Laboratory sheets with grammages between 15 and 45 g/m2, made from an unrefined bleached chemical hardwood pulp, were analysed. A considerable variation in local drying time was observed, despite their anticipated uniform formation. The mean drying time increased linearly with increasing grammages, thus the mean drying rate was not dependent on grammage. The flow resistance of the sheets increased with increasing grammage. The air flow rate through the sheet appeared not to be critical for the drying rate at the given experimental conditions.
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| 40. |
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| 41. |
- Tysen, Aron, et al.
(author)
-
The influence of grammage and pulp type on through air drying
- 2015
-
In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 30:4, s. 651-659
-
Journal article (peer-reviewed)abstract
- The influence of grammage and pulp type on through air drying was studied. The temperature of a sample was measured during the drying process and the observed temperature changes were used to evaluate the drying process. Laboratory sheets with grammages 15-60 g/m2, from two softwood and two hardwood bleached chemical pulps were used. All samples were analysed with respect to formation, flow resistance, modified permeability, mean drying time, non-uniformity of drying time, and area- and mass-specific drying rate. The pulps had different modified permeabilities but showed similar behaviour when analysed as a function of grammage. A constant value was found for higher grammages, while an increase in modified permeability was found at decreasingly low grammages. Almost all pulp and grammage combinations had similar areaspecific drying rates, but the mass-specific drying rates decreased with grammage. However, the samples with lower grammages had mass specific drying rates independent of modified permeability, where samples with increasing grammage showed an increasing dependency. This implies that the drying efficiency at low grammages was not controlled by the volume flow of the drying air. A good correlation was found between energy needed to evaporate water and energy supplied by the drying air as estimated from the surface temperature and air flow measurement. The surface temperature can therefore be used to quantify the drying process.
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| 42. |
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| 43. |
- Tysén, Aron, 1982-
(author)
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Through air drying : The influence of formation and pulp type on non-uniform drying and air flow
- 2014
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Licentiate thesis (other academic/artistic)abstract
- The removal of water is an integral part of tissue paper production. Through air drying (TAD) is used for water removal when producing premium tissue grade products, however, at the price of higher energy demand. A better understanding of TAD may therefore lower the energy demand.The objective was to investigate the influence of formation, pulp type and grammage on non-uniform drying and air flow through sheets. A laboratory method, based on infrared thermography, was used to determine drying time and area-specific and mass-specific drying rates. Air flow rate and pressure drop were used to determine flow resistance and modified permeability.Pulp type had a large influence on the air flow through the sheet. Modified permeability, i.e. the material property describing the air flow through the fibre network, was strongly dependent on grammage for lower grammages, while it approached a constant value for higher grammages. In contrast to that, mass-specific drying rates were similar for the different pulp types at lower grammages, but proved to be grammage-dependent for higher grammages. Formation did not influence the drying speed to any large extent.The results illustrate that industrial TAD processes operate under very special process conditions due to the low grammage sheets.
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| 44. |
- Tysen, Aron, et al.
(author)
-
Through air drying assisted by infrared radiation : The influence of radiator power on drying rates and temperature
- 2018
-
In: Nordic Pulp & Paper Research Journal. - : De Gruyter Open. - 0283-2631 .- 2000-0669. ; 33:4, s. 581-591
-
Journal article (peer-reviewed)abstract
- The use of infrared radiation for heating the web in the through air drying process was investigated in lab scale. The hypothesis was that infrared radiation should be a more efficient method to transfer drying energy to the wet web compared to hot air, but that a certain air flow is still required as a transport medium for the evaporated water. A trial program comprising handsheets made of two types of bleached chemical pulps, five grammages (15, 22, 30 and 60 g/m2), and dried with five radiator power levels was performed on a lab scale through air drying equipment. Drying times of the samples were determined from temperature data recorded with an infrared camera. The use of infrared radiation shortened drying times, especially for low grammage samples. The shortening of the drying time ranged between 10 and 45 %. The most substantial shortenings were obtained for the lowest grammages and the highest radiator power level. However, the increase of power did not linearly shorten drying time. After an initial shortening at the lowest power level, the positive effect of the IR heating decreased as the power was further increased. © 2018 Walter de Gruyter GmbH, Berlin/Boston.
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| 45. |
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| 46. |
- Vomhoff, Hannes, et al.
(author)
-
Evaluation of the compressibility of kitchen towel
- 2016
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In: Tappi Tissue 360 Forum.
-
Conference paper (other academic/artistic)abstract
- The out-of-plane compressibility of kitchen towels is a very important product property in order to achieve a high absorption capacity. A method for the measurement of the compressibility was therefore developed. It allows the compression of a tissue sample by a defined pressure in the range between 0 and 30 kPa. The thickness of the sample is measured. Both single-ply base paper samples and fully converted multi-ply products can be evaluated. The measurement can be performed on both dry or wet samples. Multiple compressions of the samples can also be performed in order to evaluate the difference in plastic deformation as a result of consecutive compressions. Under normal conditions, the applied pressure is gradually increased from 0 to 30 kPa and then decreased back to 0 kPa. This procedure can then be repeated. The compressibility of the sample was evaluated in terms of a bulk versus applied pressure.The compressibility of different tissue grades was evaluated and compared. A clear difference in compressibility between standard DCT and structured tissue samples was observed. The first compression cycle lead to a considerable irreversible, plastic deformation of the sample. The plastic deformation decreased then considerably during the consecutive compression cycles. Wetting the samples lead to a considerable decrease in compressibility. The results allow interesting conclusions in terms of the influence of base sheet production process and the converting processes on the absorption properties.
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| 47. |
- Vomhoff, Hannes, et al.
(author)
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Innventia Compression Test (ICT) : a method to measure compressibility of tissue products
- 2016
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In: Tissue World New Orleans 2016.
-
Conference paper (other academic/artistic)abstract
- The out-of-plane compressibility of kitchen towels is a very important product property in order to achieve a high absorption capacity. A method for the measurement of the compressibility was therefore developed. It allows the compression of a tissue sample by a defined pressure between 0 and 30 kPa. The thickness of the sample is measured. Both single-ply base paper samples and fully converted multi-ply products can be evaluated. The measurement can be performed on both dry or wet samples. Multiple compressions of the samples can also be performed in order to evaluate the difference in plastic deformation as a result of consecutive compressions. Under normal conditions, the applied pressure is gradually increased from 0 to 30 kPa and then decreased back to 0 kPa. This procedure can then be repeated. The compressibility of the sample was evaluated in terms of a bulk versus applied pressure relationship. In the presentation, the method will be explained and the compressibility of different kitchen towel products will be presented and discussed. Using some example of results, the effect of sheet structure, multiple compressions and wetting of the samples and will be illustrated.
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| 48. |
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| 49. |
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| 50. |
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