| 1. |
- Fardim, P, et al.
(författare)
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Critical comparison of methods for surface coverage by extractives and lignin in pulps by X-ray photoelectron spectroscopy (XPS)
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60, s. 149-155
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Tidskriftsartikel (refereegranskat)abstract
- Different methods for estimation of the surface coverage by extractives and lignin were critically compared. For data collection, four state-of-the-art X-ray photoelectron spectroscopy (XPS) instruments located in four different laboratories were used. Hand sheets of one mechanical and two chemical pulp samples were prepared in one laboratory and distributed among the other participants. The XPS results based on O/C ratios and curve fitting of the C 1s peak had very good intra- and interlaboratory variation for extracted and non-extracted pulp samples. The estimations of surface coverage by extractives and lignin also had acceptable intra- and interlaboratory variation. However, significant differences were observed between the results for the various methods. Estimation of surface coverage by extractives based on O/C ratios was much higher than that based on the C1 component analysis in the case of mechanical and unbleached chemical pulp. The surface coverage by lignin of mechanical pulp was reproducibly detected based on O/C ratios, C1 component analysis and by labelling with mercury acetate. The same data were, however, rather scattered if they were collected with these three methods for bleached and unbleached chemical pulp. In spite of the differences, similar trends regarding the pulp type could be observed. We interpret the results as indicating that the surface coverage for both extractives and lignin should not be considered as absolute “true” values, but rather as relative values, which are reliable only for comparison of samples for the same instrument. Even for relative comparisons, we recommend the selection of a strict experimental set-up for spectral acquisition and data treatment when applying any of the instruments and calculation models currently available.
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| 2. |
- Heijnesson Hultén, A, et al.
(författare)
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Comparison of different XPS methods for fiber surface analysis
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:1, s. 14-19
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Tidskriftsartikel (refereegranskat)abstract
- Three different XPS methods based on the O/C atomic ratio, C1 carbon content, and Hg amount are compared in this study to quantify the surface coverage of various pulp fiber surfaces by lignin and extractives. The sensitivity of the methods to drying technique and the stability of organically bound mercury when subjected to X-ray irradiation were also investigated. Results reveal that the surfaces of all pulp fibers have a higher content of lignin and extractives than the bulk of the fibers. Similar lignin surface coverage was obtained for thermomechanical pulp fibers using the Hg, O/C, and C1 carbon methods, while the Hg method gave lower values for kraft pulp fibers than the O/C and C1 carbon methods. The O/C and C1 carbon methods are sensitive to the drying technique, i.e., air-dried samples showed a higher amount of lignin on the fiber surface than freeze-dried samples, while no or only minor differences in results were obtained using the Hg method. The Hg method was more reproducible than the other methods. Special care must be exercised during XPS analysis to minimize mercury degradation.
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| 3. |
- Johansson, L-S, et al.
(författare)
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An XPS round robin investigation on analysis of wood pulp fibres and filter paper
- 2005
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 584:1, s. 126-132
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) has been applied to pulp and paper research for decades. However, there has been no attempt to standardise or even systematically compare experimental and analysis procedures, even though it is known that fibrous, nature-derived and insulating fibre materials pose remarkable challenges to reliable surface analysis. The experimental problems are mainly linked with neutralisation, energy resolution, contamination and X-ray induced degradation. We have tested applicability, reliability and reproducibility of XPS analysis on real pulp samples with varying lignin and extractives contents in a small round robin investigation. We also tested the instrumental set-ups with an acetone-extracted filter paper, used as a reference sample. The data, collected at four different laboratories with state-of-the-art instruments indicate that reproducible results can be obtained, despite minor differences in experimental and analysis procedures. However, we found that a specified sample handling procedure and limited X-ray exposure are crucial for reproducible, reliable data. Based on the round robin data we recommend dose restricted monochromatic measurements, a cellulosic in situ reference and a consistent sample handling procedure. The data confirms that a paper-based reference material and the correlation of high-resolution C 1s data with O/C atomic ratios can be used in testing instruments and experimental set-ups for pulp and paper materials.
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