| 1. |
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| 2. |
- Elsik, Christine G., et al.
(författare)
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The Genome Sequence of Taurine Cattle : A Window to Ruminant Biology and Evolution
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 324:5926, s. 522-528
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Tidskriftsartikel (refereegranskat)abstract
- To understand the biology and evolution of ruminants, the cattle genome was sequenced to about sevenfold coverage. The cattle genome contains a minimum of 22,000 genes, with a core set of 14,345 orthologs shared among seven mammalian species of which 1217 are absent or undetected in noneutherian (marsupial or monotreme) genomes. Cattle-specific evolutionary breakpoint regions in chromosomes have a higher density of segmental duplications, enrichment of repetitive elements, and species-specific variations in genes associated with lactation and immune responsiveness. Genes involved in metabolism are generally highly conserved, although five metabolic genes are deleted or extensively diverged from their human orthologs. The cattle genome sequence thus provides a resource for understanding mammalian evolution and accelerating livestock genetic improvement for milk and meat production.
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| 3. |
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| 4. |
- Ander, Paul, et al.
(författare)
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CRUW Mechanical Pulping sub-project 1: Effect of different refining pressures and energy using spruce TMP pulps from Braviken
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The mechanical pulping industry faces continued rising energy costs and increasing competition for raw material. In order to produce improved products based on mechanical pulp at lower energy consumption it is necessary to have a better understanding of the development of fundamental fibre properties during the processes. In particular, changes in fibre collapsibility, fibre fibrillation and fibre and surface development are of great interest. The overall goal of the CRUW Mechanical Pulping project is “Support development of more energy efficient mechanical pulping processes by increasing the knowledge on ultrastructural phenomena in mechanical pulping”. This project is working closely together with the Industrial Research College for Mechanical Pulping Technology bringing in the ultrastructural competence to more clearly understand and explain phenomena observed in these projects thus making it easier to develop new and improved processes to reduce energy consumption. This report presents results from CRUW Mechanical Pulping sub-project 1: ”Effect of different refining pressures and energy using spruce TMP pulps from Braviken”. The influence of temperature on the softening of lignin and hence improved (easier) fibre separation and treatment was noted earlier (Becker et al. 1977; Salmén 1984). Based on this knowledge, different process alternatives have been suggested to reduce energy demand for the refining process. One of the earliest publications on a technical system utilizing higher temperature and pressure was by Höglund et al. 1997 (Thermopulp). These results have been reproduced in many studies and are today considered general knowledge. There are however many practical problems with such a system. For example, the resulting very small refining gaps are difficult to control and it has therefore taken time to establish this technology in the industry. In the new TMP line at Braviken, the refiners are equipped to run at higher temperature/pressure than normal and it has therefore been interesting to study these pulps in order to explain the effects on pulp/fibres at an ultrastructural level. It should be noted that in a fibre-water-steam system, temperature and pressure are not independent variables and higher pressure means higher temperature and vice versa
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| 5. |
- Ander, Paul, et al.
(författare)
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Sub-project 10: CRUW Mechanical Pulping Enzyme treatment of chips for energy reduction in TMP
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In order to evaluate the possibilities of using enzymes for pre-treating softwood chips as a means of lowering the energy demand in mechanical pulping, impregnation and refining trials were performed using a set of different enzymes. The enzymes tested pectinase, xylanase and mannanase gave increased sugar release in the impregnation trials indicating that most of the sugar released occurred in the first 60 minutes and that activities thereafter seemed to level off. Refining trials using a small Wing refiner showed that for chips treated for 60 minutes with pectinase, xylanase and mannanase no energy savings to a given freeness level was observed. The property development was similar to that of reference pulps in the case of pectinase and xylanase while for chips treated with mannanase a less favourable development of the tensile index was noted. For chips treated for two hours, using xylanase or pectinase, energy savings could be observed for pectinase treated chips down to a freeness level of 200 CSF. However when refined further, the properties approached those of the reference pulp. Considering the much higher enzymatic activity reached when the initial fibre material was further disintegrated it is assumed that the possibilities for enzymes to attack desired structures of the intact fibre wall may have been too few even in the case of Impressafiner treated material.
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| 6. |
- Daniel, Geoffrey, et al.
(författare)
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Development of fiber properties in full scale HC and LC refining
- 2016
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Konferensbidrag (refereegranskat)abstract
- The aim of this work was to evaluate in more detail how fibers are developed during high consistency (HC) and low consistency (LC) refining. Three TMP mainline processes in mill operations were investigated for two configurations, one with only HC refining and the other with HC refining followed by LC refining. LC refining gave a similar increase in tensile index with increasing specific energy for the three lines, despite differences in the fiber property profiles of the feed pulps. At a given tensile index, LC refined pulps had a lower light scattering coefficient compared with only HC refining in the respective TMP line, but similar fiber length, strain at break, tear index and freeness. For two of the three lines, tensile index increased more with specific energy in LC than in HC refining. Whether installation of LC refining in a TMP line improves energy efficiency or not, depends on which pulp property(ies) the efficiency is related to, and also on the possibilities to optimize efficiency in the HC stages. Fiber curl decreased significantly for all LC refiners and remained unchanged or increased with higher energy in HC refining, although samples were tested after hot disintegration. Thus, the decrease of fiber curl contributed to the increase in tensile index in LC refining. When assessing the performance of LC refiners, fiber curl needs to be considered. Other fiber properties developed in different ways in HC and LC refining, resulting in different fiber property profiles for the two configurations.
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| 7. |
- Daniel, Geoffrey, et al.
(författare)
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Energy consumption in refining of Scots pine and Norway spruce TMP is governed by fibre morphology and ultrastructure
- 2009
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Ingår i: SPCI meddelande / The Swedish Association of Pulp and Paper Engineers. - 0280-6800. ; , s. 82-86
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Konferensbidrag (refereegranskat)abstract
- Studies on the different behaviour of Scots pine and Norway spruce during thermomechanical pulping were conducted to find reasons for explaining the greater energy consumption of pine. Well characterized wood samples from clear-cut trees and thinnings were used in pilot scale trials to produce highly characterized pulps. Structural and topochemical differences found between pine and spruce likely to have a strong negative impact on energy included: i) presence of a greater proportion of latewood fibres in pine annual rings with thick secondary cell walls and concomitant reduced fibre collapsibility; ii) ultrastructural differences in the location of fractures at the fibre secondary wall level during primary refining with pine showing greater resistance to refining although it defibrated easier than spruce; iii) that fibre separation and fibre development were sequential processes in pine and not concurrent as in spruce; and iv) the greater amounts of extractives in pine and their redistribution onto the surfaces of fibres and fines during processing
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| 8. |
- Daniel, Geoffrey, et al.
(författare)
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Inocula selection in microbial fuel cells based on anodic biofilm abundance of Geobacter sulfurreducens
- 2016
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier BV. - 1004-9541. ; 24, s. 379-387
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Tidskriftsartikel (refereegranskat)abstract
- Microbial fuel cells (MFCs) rely on microbial conversion of organic substrates to electricity. The optimal performance depends on the establishment of a microbial community rich in electrogenic bacteria. Usually this microbial community is established from inoculation of the MFC anode chamber with naturally occurring mixed inocula. In this study, the electrochemical performance of MFCs and microbial community evolution were evaluated for three inocula including domestic wastewater (DW), lake sediment (LS) and biogas sludge (BS) with varying substrate loading (L-sub) and external resistance (R-ext) on the MFC. The electrogenic bacterium Geobacter sulfurreducens was identified in all inocula and its abundance during MFC operation was positively linked to the MFC performance. The LS inoculated MFCs showed highest abundance (18%+/- 1%) of G. sulfurreducens, maximum current density [I-max = (690 +/- 30) mA.m(-2)] and coulombic efficiency (CE = 29% +/- 1%) with acetate as the substrate. I-max and CE increased to (1780 +/- 30) mA.m(-2) and 58% +/- 1%, respectively, after decreasing the R-ext from 1000 Omega to 200 Omega, which also correlated to a higher abundance of G. sulfurreducens (21% +/- 0.7%) on the MFC anodic biofilm. The data obtained contribute to understanding the microbial community response to L-sub and R-ext for optimizing electricity generation in MFCs. (c) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Das, Atanu Kumar, et al.
(författare)
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Multi-blade milling from log to powder in one step : Experimental design and results
- 2021
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 378:A, s. 593-601
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles<1.0 mm), the specific milling energy ranged from 99 to 232 kWh t(-1) DM. The mass per cent of particles <0.5 mm in MBSM powders ranged from 55 to 80% compared to 41% from hammer-milled powders. Powder bulk density varied from 138 to 264 kg m(-3) DM and the moisture content of the milled log was the only significant (p < 0.05) factor affecting the bulk density of resulting powders (dried). MLR models show that the milling energy is inversely proportional to the moisture content, which indicates that moisture influences MBSM milling in a similar way as in the sawing of wood and opposite to that of impact-based mills (i.e. hammer mills).
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| 14. |
- Das, Atanu Kumar, et al.
(författare)
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Multi-blade milling from log to powder in one step – Experimental design and results
- 2021
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 378, s. 593-601
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles<1.0 mm), the specific milling energy ranged from 99 to 232 kWh t(-1) DM. The mass per cent of particles <0.5 mm in MBSM powders ranged from 55 to 80% compared to 41% from hammer-milled powders. Powder bulk density varied from 138 to 264 kg m(-3) DM and the moisture content of the milled log was the only significant (p < 0.05) factor affecting the bulk density of resulting powders (dried). MLR models show that the milling energy is inversely proportional to the moisture content, which indicates that moisture influences MBSM milling in a similar way as in the sawing of wood and opposite to that of impact-based mills (i.e. hammer mills). (C) 2020 The Author(s). Published by Elsevier B.V.
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| 15. |
- Fernando, Dinesh, et al.
(författare)
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Applications of Simons' stain in characterizing mechanical pulp fibres at the cell wall level for understanding pulp property development
- 2010
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Konferensbidrag (refereegranskat)abstract
- The morphological and chemical characteristics of wood fibre cell walls govern their response to mechanical pulping processes like thermomechanical pulping (TMP) and thus determine most pulp and paper properties. Therefore for understanding fundamental aspects of TMP property development, a suitable method should be employed for characterizing morphological and structural changes at the cell wall level due to mechanical and other pre-treatments (e.g. temperature) during pulping processes. In the present work, TMP fibres were characterized according to micro/ultra-morphological changes reflecting cell wall delamination/internal fibrillation (D/IF) as a response to different TMP process conditions. Industrially produced (Holmen Paper, Braviken, Sweden) never-dried TMP pulp samples with varying pulp properties produced under different process conditions were used in the study. A modified method of Simons’ stain that addresses different levels of D/IF of the pulp fibre cell wall was developed. The stain was used to visualize unbeaten fibres that stain blue from beaten/treated pulp fibres that stain orange/yellow where D/IF of the cell wall has occurred. Whole fibre population of the pulp were categorized into five different sub-fibre populations based on their response to Simons’ stain where fibres stained with different intensities from blue to yellow/orange reflecting five levels of severity of fibre wall damage and/or D/IF (i.e. from none to high). Light microscopy was used to identify the sub-fibre populations. Data from these sub-populations were statistically analysed using the nonparametric statistical procedure Ordinal Logistic Regression to assess differences in the degree of D/IF for different pulp types. Transmission electron microscopy (TEM) was used to visualize features of D/IF of the fibre cell wall at the ultrastructural level. Results from statistical analysis using SAS showed there was a significant effect of refining pressure (p value- 0.0054) on the degree of cell wall D/IF of pulp fibres, while energy input at a given pressure level had the most significant effect (p value- < 0.0001). Simons’ stain was successfully employed to statistically compare different pulp types for the degree of D/IF caused by different process conditions and the results gave fundamental reasons related to pulp property development such as tensile index. Results of Simons’ stain on Bauer McNett fractions (10, 30 and 50 mesh) of the pulp type 6,4_1660 showed a clear trend for the severity of cell wall D/IF among different fractions. There was a very high significant difference on the degree of D/IF (p value- < 0.0001) among different fractions with 10, 30 and 50 in increasing order. Furthermore, results showed that the degree of D/IF correlated well with the tensile index of the pulp. TEM studies on fibres from fraction 30 having none, low and high degrees of cell wall D/IF are currently being conducted. It is concluded that the present method of using Simons’ stain for characterizing mechanical pulp fibres can successfully be applied in mechanical pulping processes leading to an improved understanding of the fundamentals behind pulp property development due to different treatments
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| 16. |
- Fernando, Dinesh, et al.
(författare)
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Cell wall configuration and ultrastructure of cellulose crystals in green seaweeds
- 2021
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 28, s. 2763-2778
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Tidskriftsartikel (refereegranskat)abstract
- Green seaweeds (Chlorophyta) are often considered a nuisance, but may in fact constitute a potential climate-friendly renewable resource in the new bioeconomy. Utilization of green seaweed polysaccharides could in particular enable a new type of green growth in coastal regions in developing countries e.g. in West Africa. The carbohydrate constituents, including cellulose, are lignin-free, but only limited knowledge is available on the cellulose ultrastructure and cellulose crystallinity in commonly occurring green seaweeds. Abundantly available green seaweeds along the coast in West Africa include Chaetomorpha linum, Caulerpa taxifolia, Ulva fasciata and Ulva flexuosa. Here, using X-ray diffraction (XRD), on cellulose gently purified from the green seaweeds, we determined that mainly cellulose I-alpha was present in both C. linum and U. flexuosa. We also found that the crystallite diameter was particularly large, 16 nm, in both the Ghanaian and the Danish C. linum samples, especially compared to the crystallite diameter of 2.5-5 nm in most terrestrial vascular plants (Tracheophytes), which mainly contain cellulose I-beta. For U. flexuosa, increasing crystallinity of the cellulose was achieved during purification. Cellulose purification was not achievable for C. taxifolia, indicating that in this species the glucose is mainly a constituent of other carbohydrates, presumably notably of starch. Transmission electron microscopy (TEM) confirmed the large size of the crystallites of C. linum showing the cellulose forming a multi-lamellar structure with alternating perpendicular and parallel layers along the fibre axis. The cell wall nano-structure appeared amorphous in C. taxifolia and as a network in U. fasciata and U. flexuosa. As glucose was most abundant in C. linum and its cellulose was crystalline, this green seaweed species appears particularly promising as a source for manufacturing of novel cellulose-based materials, e.g. specialized paper or cellulose-based composite materials. Graphic
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| 17. |
- Fernando, Dinesh, et al.
(författare)
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Characterization and biological depectinization of hemp fibers originating from different stem sections
- 2015
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Ingår i: Industrial Crops and Products. - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 76, s. 880-891
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Tidskriftsartikel (refereegranskat)abstract
- The wide variation of mechanical properties of natural fibers limits their applications in matrix compos-ites. The aim of this study is to evaluate the properties of hemp fibers from different stem sections (top,middle and bottom) and to assess fungal retting pretreatment of hemp from different stem sections withthe white rot fungi Phlebia radiata Cel 26 and Ceriporiopsis subvermispora. For the untreated hemp fibers,no apparent difference in tensile behavior for fiber bundles from different stem sections was observed,and more than 90% tested samples demonstrated plastic flow behavior. Fiber strength and stiffness werehighest for the fibers from the top and middle stem sections. These properties were related to the compositional make up and morphological properties of hemp fibers, notably the secondary fiber cell contents.In fungal retting, there was a strong dependence of depectinization selectivity on stem section, whichdecreased from bottom to top presumably due to the significantly higher lignin content in the bottomsection than in the top section (middle section was in between). Consequently, the fungal retting caused alower reduction in strength of fibers from the bottom section than in those from the top stem section, andessentially reversed the influence of stem section on fiber tensile strength through depectinization selec-tivity. At whole hemp stem level, the fungal retting with P. radiata Cel 26 exhibited better mechanicalproperties with an ultimate tensile strength, strain and stiffness of 736 MPa, 2.3% and 42 GPa, respec-tively, while fibers treated with C. subvermispora exhibited lower mechanical properties of 573 MPa, 1.9% and 40 GPa, respectively. The study thus also showed that less variable and high strength fibers may beproduced using the dependence of depectinization selectivity on stem section for composite application
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| 18. |
- Fernando, Dinesh, et al.
(författare)
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Characterization of fiber development in high- and low-consistency refining of primary mechanical pulp
- 2013
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67, s. 735-745
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Tidskriftsartikel (refereegranskat)abstract
- Primary refined softwood was subjected to highconsistency (HC) or low-consistency (LC) secondary refining, and the nature of the development of the internal and external fiber microstructure and ultrastructure has been compared. The primary refining of mixed softwood as a raw material was performed in pilot scale by the advanced thermomechanical pulp process. The study was aiming at the comparative characterization of LC and HC pulps at the fiber level when produced with similar and well-characterized handsheet properties. The formerly described Simons ’ staining method was applied. A significant degree of fiber wall delamination/internal fibrillation (D/IF) was observed during both LC and HC refining. Both the energy input and the refining consistency had a significant impact on elevating the degree of fiber wall D/IF. The statistical evaluation of internal fiber development indicated that the fiber populations in LC- and HC-refined pulps had a similar degree of fiber wall D/IF despite having a large difference in refining energy input (420 kW h odt in LC than in HC refining. The characteristic of the external fiber development from HC and LC refining was very different. Secondary LC refining promoted fiber surfaces with ribbons of thin hairlike threads arising from the inner secondary S2 layer that occasionally developed along the whole fiber length. Broad sheet- and lamellaetype external fibrillation from the S2 was typical for HC refining, and these characteristics were rarely observed in the LC pulps. The mechanisms for LC and HC fiber development are proposed. The cell wall characteristics (internal and external) of the pulp fibers appear to govern most of the physical and optical properties in handsheets.Primary refined softwood was subjected to highconsistency-1 ), confirming that D/IF was promoted more energyefficiently Keywords: (D/IF), fiber characterization, fiber development, surface ultrastructure of fibers, HC refining, LC refining, SEM, Simons’ stainingATMP, delamination/internal fibrillation
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| 19. |
- Fernando, Dinesh, et al.
(författare)
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Characterization of spruce thermomechanical pulps at the fiber cell wall level: a method for quantitatively assessing pulp fiber development using Simons’ stain
- 2010
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Ingår i: Tappi Journal. - 0734-1415. ; 9, s. 47-55
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Tidskriftsartikel (refereegranskat)abstract
- Fiber development of mechanical pulps is normally assessed by a combination of conventional numerical analyses of fiber features using FiberMaster, PulpEye, and Kajaani instruments. When observed, changes in fiber morphology are normally subjective with use of light- and electron microscopy observations of representative fibers. Thus, visualization and quantification of changes in the fiber cell wall, like delaminaton/internal fibrillation (D/IF) induced during processing, would offer a great advantage. Here, we developed a method using Simons’ stain (SS) that allows quantification of pulp fiber development in terms of fiber wall D/IF during different process conditions, as well as statistical analysis of whole pulp fiber populations of different thermomechanical pulp (TMP) types for the degree of D/IF developed in pulp fibers. The attributes of SS for producing different colored reactions (blue, green, orange, etc.) in pulp fibers through cell wall modification during processing were used in correlation with light microscopy. The method readily measured the degree of cell wall D/IF of pulp fibers from different double-disc refined TMPs produced using varying levels of specific energy and refining pressures. The SS method revealed the presence of five sub-fiber populations in a whole pulp of a given TMP type representing different categories of fibers that possessed varying degrees of cell wall D/IF as a result of process conditions/treatments. Results of statistical analysis indicated that, while D/IF was significantly induced by both the applied refining pressure and specific energy, the effect of energy had the greatest influence. Based on statistical analysis for Bauer McNett fractions of 10, 30, and 50 mesh, we suggest that fraction 30 is the most suitable fiber fraction for the analysis of TMPs using fiber characterization procedures, as this fraction possesses the most treated fibers. The method provided useful information regarding pulp fiber development at the cell wall level that has the potential to explain pulp and paper properties developed in furnishes. The present SS method represents a valuable tool for assessing fiber development at the cell wall level in mechanical pulping. Application: The present SS method can be used as a simple yet effective tool in mechanical pulp fiber characterization at the fiber level. The method provides useful information relating to fiber treatment in terms of morphological variations in the pulp fiber structure that determine most pulp and paper properties developed during processing
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| 20. |
- Fernando, Dinesh, et al.
(författare)
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Comparison of traditional field retting and Phlebia radiata Cel 26 retting of hemp fibres for fibre-reinforced composites
- 2017
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Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Classical field retting and controlled fungal retting of hemp using Phlebia radiata Cel 26 (a mutant with low cellulose degrading ability) were compared with pure pectinase treatment with regard to mechanical properties of the produced fibre/epoxy composites. For field retting a classification of the microbial evolution (by gene sequencing) and enzyme profiles were conducted. By phylogenetic frequency mapping, different types of fungi, many belonging to the Ascomycota phylum were found on the fibres during the first 2 weeks of field retting, and thereafter, different types of bacteria, notably Proteobacteria, also proliferated on the field retted fibres. Extracts from field retted fibres exhibited high glucanase activities, while extracts from P. radiata Cel 26 retted fibres showed high polygalacturonase and laccase activities. As a result, fungal retting gave a significantly higher glucan content in the fibres than field retting (77 vs. 67%) and caused a higher removal of pectin as indicated by lower galacturonan content of fibres (1.6%) after fibres were retted for 20 days with P. radiata Cel 26 compared to a galacturonan content of 3.6% for field retted fibres. Effective fibre stiffness increased slightly after retting with P. radiata Cel 26 from 65 to 67 GPa, while it decreased after field retting to 52 GPa. Effective fibre strength could not be determined similarly due to variations in fibre fracture strain and fibre-matrix adhesion. A maximum composite strength with 50 vol% fibres of 307 MPa was obtained using P. radiata Cel 26 compared to 248 MPa with field retting.
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| 21. |
- Fernando, Dinesh, et al.
(författare)
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Controlled retting of hemp fibres: Effect of hydrothermal pre-treatment and enzymatic retting on the mechanical properties of unidirectional hemp/epoxy composites
- 2016
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Ingår i: Composites Part A: Applied Science and Manufacturing. - : Elsevier BV. - 1359-835X. ; 88, s. 253-262
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to investigate the use of hydrothermal pre-treatment and enzymatic retting to remove non-cellulosic compounds and thus improve the mechanical properties of hemp fibre/epoxy composites. Hydrothermal pre-treatment at 100 kPa and 121 oC combined with enzymatic retting produced fibres with the highest ultimate tensile strength (UTS) of 780 MPa. Compared to untreated fibres, this combined treatment exhibited a positive effect on the mechanical properties of hemp fibre/epoxy composites, resulting in high quality composites with low porosity factor (αpf) of 0.08. Traditional field retting produced composites with the poorest mechanical properties and the highest (αpf) of 0.16. Hydrothermal pretreatment at 100 kPa and subsequent enzymatic retting resulted in hemp fibre composites with the highest UTS of 325 MPa, and stiffness of 38 GPa with 50% fibre volume content, which was 31% and 41% higher, respectively, compared to field retted fibres.
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| 22. |
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| 23. |
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| 24. |
- Fernando, Dinesh, et al.
(författare)
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Effect of harvest time and field retting duration on the chemical composition, morphology and mechanical properties of hemp fibers
- 2015
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Ingår i: Industrial Crops and Products. - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 69, s. 29-39
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Tidskriftsartikel (refereegranskat)abstract
- The large variability in the mechanical properties of hemp fibers creates difficulties for using them in high-grade composites. The objective of the present study was to determine the optimal growth stage for harvesting hemp fibers for use in composites and to evaluate the effect of field retting time on mechanical performance of the fibers. Reduction in bast content and thickness of the primary bast fiber layer in stems were found to be highly significant (P ˂ 0.01) with plant maturity. A significant increase in the secondary fiber fraction occurred with maturity, reaching a maximum value of 10% at seed maturity. A highly significant reduction in cellulose deposition in fiber cell walls was reflected by reduced fiber wall thickness with plant maturity and was related to the development and ripening of hemp seeds. A statistically significant increase in lignin deposition and slight decrease in pectins in hemp fiber cell walls was also noted with stem maturity. Microscopy observations and histochemical analyses corroborated results from chemical analyses and showed variations in morphological aspects and spatial micro-distributions of carbohydrates and lignin within the cell structure of the hemp stems between early- and late growth phases. Fibers harvested at the beginning of flowering exhibited high tensile strength and strain, which decreased with plant maturity. Reduction in strength was related to the increase in proportion of secondary fibers and decrease in cellulose deposition leading to inferior properties of the primary fibers. A negative effect of field retting occurred only after long term field retting (i.e. 70 days) which was presumably due to accelerated degradation of cellulose by the action of microorganisms.
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| 25. |
- Fernando, Dinesh, et al.
(författare)
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Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites
- 2016
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Ingår i: Composites Part A: Applied Science and Manufacturing. - : Elsevier BV. - 1359-835X. ; 90, s. 724-735
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endopolygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG -> 0% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04. (C) 2016 Elsevier Ltd. All rights reserved.
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