| 1. |
- Engberg, Birgitta A., Docent, 1975-, et al.
(författare)
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Abrasive refining of spruce TMP and CTMP fibers
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 57-62
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Most of the earlier proposed ways to reduce energy con-sumption in high consistency refining requires operating at a small disc gap. However, a small gap is often associated with a severe fiber length reduction and often lead to unsta-ble refining and a small operational window. To address these issues, the idea of utilizing abrasive segments surfaces is here revisited. Abrasive refiner segments, consisting of abrasive surfaces in combinations with traditional bars and grooves or flat abrasive surfaces without any bars or grooves, were evaluated in both pilot and mill scale. From the trials it could be concluded, that particularly stable refin-ing was achieved with less power variations compared to when using standard segments, even when refining at very small disc gaps. The lw-mean fiber length of the pulps was not reduced or only slightly reduced, even when refining at very small disc gaps. Tensile index could be increased more efficiently or equally efficient as when using standard seg-ments. Improved energy efficiency could be achieved when combining the abrasive surface with high intensity treat-ment.
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| 2. |
- Fjellström, Helena, 1977-, et al.
(författare)
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A novel method for studying the photo-stabilising properties of coating layers
- 2006
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new model system was developed which made it possible to study the reflectance and transmittance of thin coating layers (<10 g/m2) in a reproducible way, and to link this to the inhibition of the light-induced yellowing (Figure 1). The UV/VIS-screening properties of coatings of different coat weights containing common pigments such as kaolin, calcium carbonate (ground or precipitated) and titanium dioxide will be reported. The ability of a coating layer to protect a birch CTMP from light-induced discoloration will be exemplified using the evolved model system. An estimation of the contribution of different wavelength regions of the illuminating light to the photo-yellowing of various types of materials will also be shown. The developed method is a valuable tool for future photo-yellowing studies as well as for optimisation of the pigment coating formulation for various paper grades.
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| 3. |
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| 4. |
- Joelsson, Tove, et al.
(författare)
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High strength paper from high yield pulps by means of hot-pressing
- 2020
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 35:2, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- The hypothesis is that it should be possible to modify papermaking conditions in line with the softening properties of high yield pulp fibres and achieve similar strength properties to conventional chemical pulp based paper. We therefore investigated the rheological and physical properties of high yield pulp based papers during hot-pressing. Our results confirm that increased temperature combined with sufficient pressure enables permanent densification by softening of lignin, producing very high tensile strength. This treatment also significantly improved the wet tensile strength in comparison to bleached kraft pulp without using wet strength agents. The high yield pulps used here were spruce based thermomechanical pulp, chemi-thermomechanical pulp, and high temperature chemi-thermomechanical pulp, and birch-aspen based neutral sulphite semi chemical pulp, with spruce-pine based bleached kraft pulp as reference. Rapid Köhten sheets of 150 g/m 2 150\hspace{0.1667em}\text{g}/{\text{m}^{2}} and 50 % dryness were hot-pressed in a cylinder-press at 20-200 °C, 7 MPa, and 1 m/min. The mechanical properties showed great improvements in these high yield pulp papers, with tensile index increased to 75 kNm/kg and compression strength index to 45 kNm/kg; levels close to and better than bleached kraft. Wet strength increased to 16 Nm/g compared to 5 Nm/g for bleached kraft.
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| 5. |
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| 6. |
- Joelsson, Tove, et al.
(författare)
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Improving paper wet-strength by means hot-pressing and increased lignin content in pulp fibers
- 2019
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Ingår i: Paper Conference and Trade Show, PaperCon 2019. - : TAPPI Press. - 9781510893948 ; , s. 704-713
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Konferensbidrag (refereegranskat)abstract
- The research presented here show ways to improve wet strength by means of hot-pressing without strength additives when using lignin containing pulps as unbleached softwood chemical pulps (NSK) and lignin rich softwood chemithermomechanical pulps (CTMP). NSK (Northern Softwood kraft) laboratory scale produced pulps of 3 different levels of natural lignin (or kappa number) and two commercial pulps, NBSK (Northern Bleached Softwood kraft) and CTMP, were compared evaluating dry- and wet-strength properties. Staining methods and light microscope were used to study cross sections of paper sheets. The CTMP fibers collapse to an increasing degree with pressing temperature whereas NBSK/NSK do not change. The microscopy methods show the distribution of lignin within the paper structure. Sheets made from NSK show a significant increase in wet strength from 4kNm/kg to 23kNm/kg, when increasing temperature from 20°C to 200°C. CTMP show corresponding increase from 2kNm/kg to 16kNm/kg. No increase in dry strength or in density can be observed in case of NBSK/NSK, while the CTMP show an increase of 53% and 100% respectively. The SCT values show an increase up to 35% for lignin-rich NSK based paper sheets when hot-pressing.
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| 7. |
- Joelsson, Tove, et al.
(författare)
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Improving paper wet strength via increased lignin content and hot-pressing temperature
- 2020
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Ingår i: TAPPI Journal. - 0734-1415. ; 19:10, s. 487-499
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the strength properties of wood-based paper materials can be enhanced via hot-pressing techniques. Today, there is a desire not only for a change from fossil-based packaging materials to new sustainable bio-based materials, but also for more effective and eco-friendly solutions for improving the dry and wet strength of paper and board. Against this background, hot pressing of paper made from high yield pulp (HYP), rich in lignin, becomes highly interesting. This study investigated the influence of pressing temperature and native lignin content on the properties of paper produced by means of hot pressing. Kraft pulps of varied lignin content (kappa numbers: 25, 50, 80) were produced at pilot scale from the same batch by varying the cooking time. We then studied the effect of lignin content by evaluating the physical properties of Rapid When sheets after hot pressing in the temperature range of 20 degrees C-200 degrees C with a constant nip pressure of 7 MPa. The pilot-scale cooked pulps were compared with reference samples of mill-produced northern bleached softwood kraft (NBSK) pulp and mill-produced chemithermomechanical pulp (CTMP). Generally, the results demonstrated that lignin content had a significant effect on both dry and wet tensile index. All of the pilot cooked pulps with increased lignin content had a higher tensile index than the reference NBSK pulp. To obtain high tensile index, both dry and wet, the pressing temperature should be set high, preferably at least 200 degrees C; that is, well above the glass transition temperature (Tg) for lignin. Moreover, the lignin content should preferably also be high. All kraft pulps investigated in this study showed a linear relationship between wet strength and lignin content.
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| 8. |
- Kogevinas, Manolis, et al.
(författare)
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Exposure to substances in the workplace and new-onset asthma : an international prospective population-based study (ECRHS-II)
- 2007
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 370:9584, s. 336-341
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Tidskriftsartikel (refereegranskat)abstract
- Background The role of exposure to substances in the workplace in new-onset asthma is not well characterised in population-based studies. We therefore aimed to estimate the relative and attributable risks of new-onset asthma in relation to occupations, work-related exposures, and inhalation accidents. Methods We studied prospectively 6837 participants from 13 countries who previously took part in the European Community Respiratory Health Survey (1990-95) and did not report respiratory symptoms or a history of asthma at the time of the first study. Asthma was assessed by methacholine challenge test and by questionnaire data on asthma symptoms. Exposures were defined by high-risk occupations, an asthma-specific job exposure matrix with additional expert judgment, and through self-report of acute inhalation events. Relative risks for new onset asthma were calculated with log-binomial models adjusted for age, sex, smoking, and study Centre. Findings A significant excess asthma risk was seen after exposure to substances known to cause occupational asthma (Relative risk=1.6, 95% CI 1.1-2.3, p=0.017). Risks were highest for asthma defined by bronchial hyper-reactivity in addition to symptoms (2.4,1.3-4.6, p=0.008). Of common occupations, a significant excess risk of asthma was seen for nursing (2.2,1.3-4.0, p=0.007). Asthma risk was also increased in participants who reported an acute symptomatic inhalation event such as fire, mixing cleaning products, or chemical spills (RR=3.3, 95% CI 1.0-11.1, p=0.051). The population-attributable risk for adult asthma due to occupational exposures ranged from 10% to 25%, equivalent to an incidence of new-onset occupational asthma of 250-300 cases per million people per year. Interpretation Occupational exposures account for a substantial proportion of adult asthma incidence. The increased risk of asthma after inhalation accidents suggests that workers who have such accidents should be monitored closely.
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| 9. |
- Mirabelli, Maria C, et al.
(författare)
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Occupational risk factors for asthma among nurses and related healthcare professionals in an international study
- 2007
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Ingår i: Occupational and Environmental Medicine. - : BMJ. - 1351-0711 .- 1470-7926. ; 64:7, s. 474-479
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The authors examined the relations between self-reported work tasks, use of cleaning products and latex glove use with new-onset asthma among nurses and other healthcare workers in the European Community Respiratory Health Survey (ECRHS II). Methods: In a random population sample of adults from 22 European sites, 332 participants reported working in nursing and other related healthcare jobs during the nine-year ECRHS II follow-up period and responded to a supplemental questionnaire about their principal work settings, occupational tasks, products used at work and respiratory symptoms. Poisson regression models with robust error variances were used to compare the risk of new-onset asthma among healthcare workers with each exposure to that of respondents who reported professional or administrative occupations during the entire follow-up period (n=2481). Results: Twenty (6%) healthcare workers and 131 (5%) members of the referent population reported new-onset asthma. Compared to the referent group, the authors observed increased risks among hospital technicians (RR 4.63; 95% Cl 1.87 to 11.5) and among those using ammonia and/or bleach at work (RR 2.16; 95% Cl 1.03 to 4.53). Conclusions: In the ECRHS II cohort, hospital technicians and other healthcare workers experience increased risks of new-onset current asthma, possibly due to specific products used at work.
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| 10. |
- Norgren, Sven, 1973-, et al.
(författare)
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Strong paper from spruce CTMP - Part II : Effect of pressing at nip press temperatures above the lignin softening temperature
- 2018
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 33:1, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of the current study was to demonstrate that it is possible to enhance strength properties of sheets from spruce HT-CTMP and CTMP furnishes up to the same level as is common on sheets from softwood kraft pulps by changing conditions in papermaking. To achieve that, sheets of spruce HT-CTMP and CTMP were consolidated at densities close to that of the reference bleach kraft pulp by pressing at press nip temperatures well above the tack and softening temperatures of lignin. On sheets from spruce CTMP (CSF 420 ml), where the fibers were surface treated with cationic starch, it was possible to reach tensile index at the same level as on sheets from the untreated reference kraft pulp. The compression strength (SCT) of CTMP and HT-CTMP sheets, which were achieved at the highest press nip temperature (200 °C) in the study, was equal to or higher than that of the reference kraft pulp sheets. The results show that there is a great yet unexploited potential in papermaking from spruce HT-CTMP and CTMP furnishes, which could be utilized in manufacturing of products where very high requirements upon strength is demanded.
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