| 1. |
|
|
| 2. |
- Branström, J., et al.
(författare)
-
Compression wood in knots and the effect on surface roughness.
- 2005
-
Ingår i: proceedings from IMPC 2005.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The microstructural and ultrastructural characteristics of knot wood were examined and related to paper properties. Norway spruce (Picea abies) chips were laboratory fractionated and sorted into a knot containing assortment and a non knot containing reference assortment. The proportions of compression wood in these two assortments were then assessed and the two chip assortments refined in pilot refiners. The knot containing portion was divided into wood from the upper branch, wood from the lower branch compression wood and wood surrounding the branch. Fibres from the three knotwood portions and the reference chips were extracted and measurements were made of fibre properties including fibre length, fibre width and cell wall thickness. The two chip assortments were refined in a pilot plant and the surface properties of laboratory sheets were measured. The knot containing chips had adverse effects on several paper properties. However, no clear relationship was established between surface roughness and the presence of compression wood fibres in knot wood. (6 fig, 12 ref)
|
|
| 3. |
- Engberg, Birgitta A., Docent, 1975-, et al.
(författare)
-
Abrasive refining of spruce TMP and CTMP fibers
- 2022
-
Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 57-62
-
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.
|
|
| 4. |
- Fjellström, Helena, 1977-, et al.
(författare)
-
A novel method for studying the photo-stabilising properties of coating layers
- 2006
-
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.
|
|
| 5. |
- Fjellström, Helena, et al.
(författare)
-
A novel method of studying the ability of coating layer to retard the photo-yellowing of the base paper
- 2007
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:3, s. 343-349
-
Tidskriftsartikel (refereegranskat)abstract
- A method was developed which made it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing. The ability of a coating layer to retard the photo-yellowing of a hydrogen-peroxide-bleached birch chemithermomechanical pulp (CTMP) is exemplified using this method. It is shown that the repeatability of the model system is excellent, even for coat weights below 10 g/m2. Furthermore, the transmittance in the UV-region is strongly correlated with the coating layers ability to protect the birch CTMP against photo-yellowing.
|
|
| 6. |
|
|
| 7. |
- Fjellström, Helena, et al.
(författare)
-
Influence of coating formulation on light-induced brightness stability of mechanical and chemimechanical pulp sheets
- 2005
-
Ingår i: International Mechanical Pulping Conference: IMPC 2005, Oslo, Norway, 7-9 June 2005. ; , s. 339-343
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The light-induced brightness reversion of different types of high-yield pulps has been studied under accelerated and long-term ambient ageing conditions. It was found that accelerated ageing (xenon lamp used as light source) overestimates the yellowing tendencies of hardwood pulps, whereas it was possible to predict the yellowing characteristics of softwood pulps. The lignin content of the pulps was found to be correlated to the degree of photo-yellowing for long-term ambient ageing. A model system was developed which made it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing. The yellowing characteristics of a coated birch CTMP is exemplified using the evolved model system.
|
|
| 8. |
- Fjellström, Helena, et al.
(författare)
-
Inhibition of light-induced brightness reversion of high-yield pulps : the UV-screening properties of coating layers containing kaolin or calcium carbonate pigments
- 2007
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:3, s. 350-355
-
Tidskriftsartikel (refereegranskat)abstract
- A newly developed method making it possible to study the reflectance/transmittance of thin coating layers and to link this to the inhibition of the light-induced yellowing, was used to describe the photo-stabilising properties of different types of commercial kaolin and calcium carbonate pigments. A base paper produced from a hydrogen-peroxide-bleached birch chemithermomechanical pulp (CTMP) was used throughout the study.The transmittance of the coating layers in the UV-region (300-385 nm) was found to be very low (below 1.0% at coat weights < 5g/m2) for all of the tested pigments, it strongly depends on the coat weight especially for coat weights below 10 g/m2. The kaolin pigments examined were found to be better in inhibiting the brightness reversion compared to the calcium carbonate pigments, even though the differences between the pigment types were only a few brightness units. The coating layer was, however, able to conceal some of the colour formed through the light-induce brightness reversion. For example, a coating layer consisting of kaolin pigments (coat weight of 15.6 g/m2) could conceal about 30% of the discoloration of the CTMP base paper.
|
|
| 9. |
- Fjellström, Helena
(författare)
-
Inhibition of light-induced colour reversion of wood-containing papers by means of coating
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main purpose of this thesis was to find ways to maintain a low level of light‐induceddiscolouration at an increased addition of mechanical and chemimechanical pulps in coated highqualityfine paper and magazine paper grades. Current technology allows the production of highyieldpulps such as thermomechanical and chemimechanical pulps with properties suitable formanufacturing high‐quality paper or paperboard with a low basis weight. Coating of woodcontainingpaper will probably be necessary for photo‐stability reasons if lignin‐containing pulps areto be used as the main fibre furnish in long‐life and high‐value products.In order to find the most suitable pulp for this purpose, light‐induced discolouration of a variety ofpaper samples from unbleached and bleached softwood and hardwood pulps was studied under bothaccelerated and long‐term ambient light‐induced ageing conditions. Hardwood high‐yield pulps,especially aspen pulps, were proven to be more photo‐stable compared to softwood pulps. Hardwoodpulps should therefore be the first choice for applications where a high permanence is desirable.Evaluating ageing characteristics using the CIELAB colour system showed that accelerated ageingconditions tend to mainly increase the b* value and decrease the L* value (i.e. yellow the pulp),whereas long‐term ambient ageing also increases the a* value, which makes the pulp more reddish.A new method for studying the influence of the UV‐screening properties of coating layers on abase paper was developed, and used to investigate the effect of pigment, pigment size distribution,binder and UV‐absorbing additives. The coat weight and pigment type were found to be the mostimportant factors for reducing the transmittance of UV‐radiation. Coating colours containing kaolinpigments had a lower UV‐transmittance than calcium carbonate pigments. Of the calcium carbonates,precipitated calcium carbonates were better than ground calcium carbonates and the difference wasgreater at higher coat weights. The particle size distribution should preferable be narrow. When thebest pigment (bleached kaolin) and the best binder (styrene butadiene latex) were combined withtitanium dioxide, the UV‐transmittance could be reduced by about 90% at a coat weight of ~10 g/m2.At a coat weight close to 20 g/m2, the transmittance was close to zero. This shows that it is possible tomore or less fully protect a double coated base paper from harmful UV‐radiation, when the coatinglayer has an optimum composition for that purpose. A prerequisite to reach so far is that the coatinglayer has an even coat weight.
|
|
| 10. |
- Fjellström, Helena, et al.
(författare)
-
Light-induced yellowing of mechanical and chemimechanical pulp sheets : influence of wood raw material, process and ageing method
- 2007
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:1, s. 117-123
-
Tidskriftsartikel (refereegranskat)abstract
- The light-induced brightness reversion of different types of unbleached and bleached high-yield pulps was studied under both accelerated and long-term ambient light-induced ageing conditions. It was found that accelerated ageing conditions that mimic indoor daylight exposures overestimate the yellowing tendencies of hardwood high-yield pulps (especially aspen pulps) compared to long-term ambient aging with no indirect sunlight present. It was, however, possible to predict the yellowing characteristics of softwood high-yield pulps. The lignin content of the pulps was found to be strongly correlated with the degree of photo-yellowing in the case of long-term ambient light-induced ageing. The presence of small amounts of birch chemithermomechanical pulp (CTMP) in a fine paper furnish resulted in extensive light-induced discoloration. The extent of photo-yellowing was found to be nearly linearly related to the amount of birch CTMP in the paper.
|
|
