| 1. |
- Bjurhager, Ingela, et al.
(författare)
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State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
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Tidskriftsartikel (refereegranskat)abstract
- In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.
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| 2. |
- Chunilall, V., et al.
(författare)
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A CP/MAS 13C-NMR study of cellulose fibril aggregation in eucalyptus dissolving pulps during drying and the correlation between aggregate dimensions and chemical reactivity
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:6, s. 693-698
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Tidskriftsartikel (refereegranskat)abstract
- Changes in supramolecular properties of cellulose I, namely its lateral fibril aggregate dimension (LFAD), in bleached hardwood acid bisulphite pulp during drying was studied using cross-polarization/magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C-NMR) in combination with spectral fitting. A significant change in aggregate dimensions was noticed when each of the pulp grades were oven dried. The effect of drying was further investigated with pulp samples subjected to different drying methods. A comparison of a harsh oven drying, mild and rapid air drying, and a very mild and slow condition drying showed that the LFAD of the material decreases in the following order: oven drying > air drying > condition drying. The correlation between the total extractable material S10 (%) and LFAD and also the LFAD increment (ΔLFAD in %) are presented and shown to be intimately related. This means that the method of drying influences the size of the fibril aggregate dimensions and depends on the presence of extractable material within the fibre cell wall. Reactivity studies were carried out based on the acetylation of cotton linters and commercial 96α pulp. Results indicate that the initial reaction rate is proportional to the specific surface area of the two cellulose pulp samples. Accordingly, the specific surface area is directly related to initial reactivity of the performed acetylation. We demonstrated that it is possible to control the LFAD and hence specific surface area in laboratory-produced pulps 91α, 92α, and 96α by the drying method. Thus controlling LFAD can probably be one viable route for controlling the initial reactivity of dissolving pulp towards acetylation.
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| 3. |
- Dedic, Dina, et al.
(författare)
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Analysis of lignin and extractives in the oak wood of the 17th century warship Vasa
- 2014
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:4, s. 419-425
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Tidskriftsartikel (refereegranskat)abstract
- The wood in the 17th century Swedish warship Vasa is weak. A depolymerization of the wood's cellulose has been linked to the weakening, but the chemical mechanisms are yet unclear. The objective of this study was to analyze the lignin and tannin moieties of the wood to clarify whether the depolymerization of cellulose via ongoing oxidative mechanisms is indeed the main reason for weakening the wood in the Vasa. Lignin was analyzed by solid-state nuclear magnetic resonance [cross-polarization/magic-angle spinning (CP/MAS) C-13 NMR] and by means of wet chemical degradation (thioacidolysis) followed by gas chromatography-mass spectrometry (GC-MS) of the products. No differences could be observed between the Vasa samples and the reference samples that could have been ascribed to extensive lignin degradation. Wood extracts (tannins) were analyzed by matrix- assisted laser desorption ionization (MALDI) combined with time-of-flight (TOF) MS and C-13 NMR spectroscopy. The wood of the Vasa contained no discernible amounts of tannins, whereas still-waterlogged Vasa wood contained ellagic acid and traces of castalagin/vescalagin and grandinin. The results indicate that the condition of lignin in the Vasa wood is similar to fresh oak and that potentially harmful tannins are not present in high amounts. Thus, oxidative degradation mechanisms are not supported as a primary route to cellulose depolymerization.
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| 4. |
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| 5. |
- Dedic, Dina, et al.
(författare)
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Cellulose degradation in the Vasa : The role of acids and rust
- 2013
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Ingår i: Studies in Conservation. - 0039-3630 .- 2047-0584. ; 58:4, s. 308-313
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Tidskriftsartikel (refereegranskat)abstract
- The oak timbers of the Swedish warship Vasa are deteriorating. High amounts of oxalic acid have been found along with a low pH and low molecular weight cellulose deep in the wood timbers. The iron-rich surface wood differs from the interior wood in that it displays higher pH and cellulose with higher molecular weight. The objective of this study was to determine why there is a difference in cellulose degradation, pH, and oxalic acid amount between the surface region and the interior of the Vasa timbers. Analysis of cellulose weight average molecular weight by size exclusion chromatography was performed, as well as quantification of oxalic acid and iron by high-performance anion exchange chromatography and atomic emission spectroscopy, respectively. It was found that a decrease in iron content coincides with an increase in oxalic acid concentration and a drop in pH at a certain depth from the wood surface. When iron-rich surface wood samples from the Vasa were mixed with an aqueous solution of oxalic acid, a fast increase of pH over time was observed. Neither interior wood poor in iron nor the fresh oak reference showed the same neutralizing effect during the time of measurement. This indicates that the presence of iron (rust) causes a neutralization of the wood, through the formation of iron(III) oxalato complexes, thus protecting the wood from oxalic acid hydrolysis. This effect was not observed to the same extent for other acids observed in Vasa wood (sulfuric, formic, glycolic, and acetic acids).
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| 6. |
- Dedic, Dina, et al.
(författare)
-
Chemical analysis of wood extractives and lignin in the oak wood of the 380 year old Swedish warship Vasa
- 2011
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Konferensbidrag (refereegranskat)abstract
- In order to map the source of oxalic acid in the interior wood of the Vasa ship, an analysis of wood extractives (tannins) was conducted. Samples used for analysis were PEG-impregnated dry Vasa wood, waterlogged Vasa wood and a reference material (fresh oak). The wood material was ground and extracted with an acetone/water-mixture. In the reference sample, several types of tannins were found such as the isomers castalagin/vescalagin and grandinin and their dimmers roburin A/D and roburin B/C respectively. The results have been confirmed by NMR spectroscopy and MALDI-TOF. The interior of the waterlogged Vasa wood contained small amounts of monomers, whereas the dry, PEG treated Vasa revealed no discernible amounts of hydrolysable tannins or other easily soluble compounds. Furthermore, an analysis of lignin was made by means of chemical degradation (thioacidolysis). A decrease in the amount of β-O-4 bonds in the lignin structure would imply a formation of easily oxidized free phenolics. The products were analyzed by GC-MS, which revealed no dramatic differences between the Vasa samples and the reference. The results were confirmed by CP/MAS NMR by analyzing the differences in the aromatic region (150∼160 ppm) as well as the carbonyl region (190∼200 ppm).
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| 7. |
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| 8. |
- Ek, Monica, et al.
(författare)
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A comment on the effect of carbonyl groups on the light-induced reversion of groundwood pulp
- 1990
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 5:4, s. 159-160
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Tidskriftsartikel (refereegranskat)abstract
- Sodium borohydride redn. of stone groundwood pulp from spruce (Picea abies) had no dramatic effect on the light-induced brightness reversion. This indicates that the direct scission of phenacyl aryl ether linkages is not an important step in the initial chromophore formation.
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| 9. |
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| 10. |
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| 11. |
- Ek, Monica, et al.
(författare)
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WOBAMA : wood based materials and fuels
- 2014
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 48:9-10, s. 773-779
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Tidskriftsartikel (refereegranskat)abstract
- WOBAMA - Wood Based Materials and Fuels is a biorefinery oriented scientific research project supported by Wood Wisdom-Net Research Programme and ERA-NET Bioenergy. In this project, the wood based raw materials were converted to a range of value added products through unconventional techniques. So far, many demonstrators have been prepared, such as the dissolving pulps with high cellulose content, the regenerated cellulose films with high tenacity, the hydrophobic materials based on cellulose and birch bark suberin, as well as the adhesives based on polysaccharides.
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| 12. |
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| 13. |
- Halonen, Helena, et al.
(författare)
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Mercerized cellulose biocomposites : A study of influence of mercerization on cellulose supramolecular structure, water retention value and tensile properties
- 2013
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 20:1, s. 57-65
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Tidskriftsartikel (refereegranskat)abstract
- In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.
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| 14. |
- Halonen, Helena, 1982-
(författare)
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Structural changes during cellulose composite processing
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two approaches for creating a new all-cellulose composite material have been studied: the biosynthesis of compartmentalised bacterial cellulose fibril aggregates and the compression moulding of commercial chemical wood pulps processed with only water. The objective was to study the structural changes during processing and the complexity of relating the mechanical properties of the final biocomposites to the nanoscale structure was highlighted.Solid-state CP/MAS 13C NMR spectroscopy was utilised to determine both the fibril aggregate width and the content of the different crystalline cellulose forms, cellulose I and cellulose II. Using this method, the quantities of hemicellulose present inside the fibre wall and localised at the fibre surfaces could be determined.The formation of cellulose fibrils was affected by the addition of hydroxyethylcellulose (HEC) to a culture medium of Acetobacter aceti, and the fibrils were coated with a thin layer of HEC, which resulted in loose bundles of fibril aggregates. The HEC coating, improved the fibril dispersion in the films and prevented fractures, resulting in a biocomposite with remarkable mechanical properties including improved strength (289 MPa), modulus (12.5 GPa) and toughness (6%).The effect of press temperature was studied during compression moulding of sulphite dissolving-grade pulps at 45 MPa. A higher press temperature yielded increases in the fibril aggregation, water resistance (measured as the water retention value) and Young’s modulus (12 GPa) in the final biocomposite. The high pressure was important for fibril aggregation, possibly including cellulose-cellulose fusion bonds, i.e., fibril aggregation in the fibre-fibre bond region. The optimal press temperature was found to be 170°C because cellulose undergoes thermal degradation at higher temperatures.The effect of hemicellulose was studied by comparing a softwood kraft paper-grade pulp with a softwood sulphite paper and a softwood sulphite dissolving-grade pulp. A significant fibril aggregation of the sulphite pulps suggested that the content and distribution of hemicellulose affected the fibril aggregation. In addition, the hemicellulose structure could influence the ability of the hemicellulose to co-aggregate with cellulose fibrils. Both sulphite pulp biocomposites exhibited Young’s moduli of approximately 12 GPa, whereas that of the kraft pulp was approximately half that value at 6 GPa. This result can be explained by a higher sensitivity to beating in the sulphite pulps.The effect of mercerisation, which introduces disordered cellulose, on the softwood sulphite dissolving-grade pulp was also studied under compression moulding at 170°C and 45 MPa. The mechanisms causing an incomplete transformation of cellulose I to II in a 12 wt% NaOH solution were discussed. The lower modulus of cellulose II and/or the higher quantity of disordered cellulose likely account for the decrease in Young’s modulus in the mercerised biocomposites (6.0 versus 3.9 GPa).
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Lennholm, Helena, et al.
(författare)
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Photoyellowing of groundwood pulps
- 1994
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 9:1, s. 10-15
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Tidskriftsartikel (refereegranskat)abstract
- The photoyellowing of spruce groundwood pulps (GWP) has been studied by use of UV/VIS diffuse reflectance- and FTIR-transmission spectroscopy. Brightness reversion was induced by exposing unbleached, hydrogen peroxide-bleached and sodium borohydride-reduced spruce GWP to simulate daylight for various exposure times. Spectra were recorded and principal component anal. was used to evaluate the spectral data. The information obtained indicates the presence of two alternative photo-induced processes proceeding in parallel during the irradn. The first process, more pronounced during the initial phase of the photoyellowing was ascribed to redox reactions involving structures with absorption bands at 340 or 380 nm and 440 nm in the UV/VIS-spectra. These absorption bands could results from photo-induced transformations involving quinonoid redox couples. The second process, pronounced during both the initial and final phase of the photoyellowing, was interpreted as non-specific oxidns. of lignin causing major chromophore formation.
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| 20. |
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| 21. |
- Li, Dongfang, et al.
(författare)
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Biocomposites based on birch suberin
- 2012
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Ingår i: Abstracts of Papers of the American Chemical Society. - : American Chemical Society (ACS). - 0065-7727. ; 243
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 22. |
- Li, Dongfang, et al.
(författare)
-
Biocomposites based on birch suberin
- 2012
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Ingår i: NWBC 2012 - 4th Nordic Wood Biorefinery Conference. - : VTT Technical Research Centre of Finland. ; , s. 342-343
-
Konferensbidrag (refereegranskat)abstract
- The suberin monomer, cis-9,10-epoxy-18-hydroxyoctadecanoic acid (epoxy fatty acid or EFA), was isolated from birch (Betula verrucosa) outer bark. The crude EFA was purified and polymerized via lipase-catalysis. The resulting polyesters were characterized by MALDI-TOF MS and SEC. Biocomposites were prepared through grafting EFA onto cellulose. The products were characterized by FTIR.
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| 23. |
- Li, Dongfang, et al.
(författare)
-
Hydrophobic materials based on cotton linter cellulose and an epoxy-activated polyester derived from a suberin monomer
- 2015
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X.
-
Tidskriftsartikel (refereegranskat)abstract
- Suberin is a natural hydrophobic material that could be used to improve the water repellency of cellulose surfaces. It is also abundant in the outer bark of birch (Betula verrucosa); birch bark is a side-stream product in Scandinavia from the forest industry, which is generally burned for energy production. A suberin monomer, cis-9,10-epoxy-18-hydroxyoctadecanoic acid, was isolated from birch outer bark and polymerized via lipase (immobilized Candida antarctica lipase B). The resulting epoxy-activated polyester was characterized by nuclear magnetic resonance (NMR) imaging, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, and size exclusion chromatography. Then the polyester was cured with tartaric or oxalic acid, and the crosslinked polyesters were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry. Hydrophobic materials were prepared by compression molding of polyester-impregnated cellulose sheets, and the final products were characterized by FTIR, cross-polarization magic angle spinning 13 C NMR, and field-emission scanning electron microscopy. The water contact angle was significantly increased from 0 ° for the original cellulose sheets to over 100 ° for the produced hydrophobic materials.
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| 24. |
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| 25. |
- Lindfors, Eva-Lisa, et al.
(författare)
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Polysaccharide degradation in waterlogged oak wood from the ancient warship Vasa
- 2008
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 62:1, s. 57-63
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Tidskriftsartikel (refereegranskat)abstract
- A rather extensive degradation of cellulose and hemicelluloses was found in waterlogged oak wood samples from the ancient warship Vasa by size exclusion chromatography with the solvent system lithium chloride/ N,N-dimethylacetamide (LiCl/DMAc). The degradation has mainly occurred after salvage of the wreck, probably as a consequence of keeping iron contaminated wood in contact with air. The most likely explanation is Fenton type of reactions degrading the wood polymers and oxidising reduced sulphur forms to sulphuric acid. An increased degradation rate of the Vasa wood can be anticipated in the future if the sulphuric acid cannot be neutralised and the oxidative reactions cannot be quenched.
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| 26. |
- Lindfors, Eva-Lisa, et al.
(författare)
-
Polysaccharide degradation in waterlogged oak wood from the ancient warship Vasa
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:1, s. 57-63
-
Tidskriftsartikel (refereegranskat)abstract
- A rather extensive degradation of cellulose and hemicelluloses was found in waterlogged oak wood samples from the ancient warship Vasa by size exclusion chromatography with the solvent system lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). The degradation has mainly occurred after salvage of the wreck, probably as a consequence of keeping iron contaminated wood in contact with air. The most likely explanation is Fenton type of reactions degrading the wood polymers and oxidising reduced sulphur forms to sulphuric acid. An increased degradation rate of the Vasa wood can be anticipated in the future if the sulphuric acid cannot be neutralised and the oxidative reactions cannot be quenched.
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| 27. |
- Malm, Erik, et al.
(författare)
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The surface structure of well-ordered native cellulose fibrils in contact with water
- 2010
-
Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 345:1, s. 97-100
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Tidskriftsartikel (refereegranskat)abstract
- CP/MAS C-13 NMR spectroscopy was used in combination with spectral fitting to examine the surface structure of hydrated cellulose I fibrils from Halocynthia and Gluconoacetobacter xylinus. To increase the spectral intensities and minimize signal overlap, G. xylinus celluloses site-specifically enriched in C-13 either on C4 or on both C1 and C6 were examined. The experimental data showed multiple C4 and C6 signals for the water accessible fibril surfaces in the highly crystalline celluloses. These signal multiplicities were attributed to structural features in the surface layers induced by the fibril interior, and could not be extracted by spectral fitting in celluloses with a lower degree of crystallinity such as cellulose from cotton.
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| 28. |
- Monica, Ek, et al.
(författare)
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A study on the mechanism of the photoyellowing of partially acetylated groundwood pulps
- 1992
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 7:3, s. 108-112
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Tidskriftsartikel (refereegranskat)abstract
- The effects of partial acetylation on the photoyellowing of unbleached, peroxide-bleached, and borohydride-reduced groundwood pulps were studied. Quinone structures and quinone precursors, such as hydroquinones and catechols, are important reactants in the photoyellowing process.
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| 29. |
- Nilsson, Helena, et al.
(författare)
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A non-solvent approach for high-stiffness all-cellulose biocomposites based on pure wood cellulose
- 2010
-
Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 70:12, s. 1704-1712
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Tidskriftsartikel (refereegranskat)abstract
- All-cellulose composites are commonly prepared using cellulose solvents. In this study, moldable all-cellulose I wood fiber materials of high cellulose purity (97%) were successfully compression molded. Water is the only processing aid. The material is interesting as a "green" biocomposite for industrial applications. Dissolving wood fiber pulps (Eucalyptus hardwood and conifer softwood) are used and the influence of pulp origin, beating and pressing temperature (20-180 degrees C) on supramolecular cellulose nanostructure is studied by solid state CP/MAS C-13 NMR. Average molar mass is determined by SEC to assess process degradation effects. Mechanical properties are determined in tensile tests. High-density composites were obtained with a Young's modulus of up to 13 GPa. In addition, nanoscale cellulose fibril aggregation was confirmed due to processing, and resulted in a less moisture sensitive material.
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| 30. |
- Nilsson, Helena, et al.
(författare)
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Bark Suberin as a Renewable Source of Long-Chain omega-Hydroxyalkanoic Acids
- 2008
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Ingår i: Macromolecular Symposia. - : Wiley. - 1022-1360 .- 1521-3900. ; 272:1, s. 104-106
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Tidskriftsartikel (refereegranskat)abstract
- Polycondensations of cis-9,10-epoxy-18-hydroxyoctadecanoic acid, isolated from birch outer bark, were performed at 75 degrees C in toluene as solvent and at 85 degrees C in bulk using immobilized Candida antarctica lipase B as catalyst. The polycondensation performed in toluene in presence of molecular sieves gave a polyester with DP 50 after 24 h. The same DP was obtained at much shorter reaction time (3 h) by bulk polymerization in an open vial without any drying agent present.
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| 31. |
- Nilsson, Helena, et al.
(författare)
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Birch bark as a source for fine chemicals
- 2008
-
Ingår i: 2008 Nordic Wood Biorefinery Conference - Proceedings. - 9789186018139 ; , s. 125-128
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Konferensbidrag (refereegranskat)abstract
- In this study we report polycondensation and co-polymerization of cis-9,10-epoxy-18-hydroxyoctadecanoic acid (1) isolated from birch outer bark using immobilized Candida antarctica lipase B (Novozyme 435) as catalyst to give epoxy activated straight chain polyesters and cyclic macromonomers.
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| 32. |
- Nilsson, Helena, et al.
(författare)
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Compression molded wood pulp biocomposites : A study of hemicellulose influence on cellulose supramolecular structure and material properties
- 2012
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:3, s. 751-760
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.
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| 33. |
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| 34. |
- Nilsson, Johanna, et al.
(författare)
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The Validation of Artificial Ageing Methods for Silk Textiles Using Markers for Chemical and Physical Properties of Seventeenth-Century Silk
- 2010
-
Ingår i: Studies in Conservation. - : Informa UK Limited. - 0039-3630 .- 2047-0584. ; 55:1, s. 55-65
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Tidskriftsartikel (refereegranskat)abstract
- The Royal Armoury in Stockholm has conducted a project to experimentally evaluate conservation methods used for historic costumes. As the historic value of authentic artefacts precludes their use in experimental work, artificially aged standard silk needs to be used as a substitute. This study aimed to find a suitable artificial ageing method for standard silk resulting in a degradation state that simulated that of silk from seventeenth-century costumes. Four artificial ageing methods were studied: (1) thermal oxidation it, dry air, (2) exposure to different relative humidity (RH), (3) immersion in solutions of varied pH, (4) accelerated ultraviolet (UV) exposure at 50 +/- 2 degrees C, 95% RH. Different chemical and physical properties for silk were evaluated using Fourier transform infrared spectroscopy, size exclusion chromatography and tensile tests, which were employed as analytical indicators for comparison between the artificially aged silk and samples front seventeenth-century costumes. Of the ageing methods tested in this study, thermo-oxidation at 125 degrees C in dry air for 28-56 days produced silk with properties most like those of-historic silk samples.
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| 35. |
- Nilsson, Johanna, 1961, et al.
(författare)
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The validation of artificial ageing methods for silk using markers for chemical and physical properties of seventeenth-century silk
- 2010
-
Ingår i: Studies in Conservation. - 0039-3630. ; 55:1, s. 55-65
-
Tidskriftsartikel (refereegranskat)abstract
- The Royal Armoury in Stockholm has conducted a project to experimentally evaluate conservation methods used for historic costumes. As the historic value of authentic artefacts precludes their use in experimental work, artificially aged standard silk needs to be used as a substitute. This study aimed to find a suitable artificial ageing method for standard silk resulting in a degradation state that simulated that of silk from seventeenth-century costumes. Four artificial ageing methods were studied: (1) thermal oxidation it, dry air, (2) exposure to different relative humidity (RH), (3) immersion in solutions of varied pH, (4) accelerated ultraviolet (UV) exposure at 50 +/- 2 degrees C, 95% RH. Different chemical and physical properties for silk were evaluated using Fourier transform infrared spectroscopy, size exclusion chromatography and tensile tests, which were employed as analytical indicators for comparison between the artificially aged silk and samples front seventeenth-century costumes. Of the ageing methods tested in this study, thermo-oxidation at 125 degrees C in dry air for 28-56 days produced silk with properties most like those of-historic silk samples.
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| 36. |
- Nocanda, Xolani, et al.
(författare)
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Cross polarisation/magic angle spinning C-13-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process
- 2007
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:6, s. 675-679
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Tidskriftsartikel (refereegranskat)abstract
- Cross polarisation/magic angle spinning C-13 NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92 alpha and 96 alpha. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96 alpha pulp was found to be more aggregated than the freely dried 92 alpha pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92 alpha pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92 alpha and 96 alpha pulps during free drying.
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| 37. |
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| 38. |
- Persson, Per Valdemar, et al.
(författare)
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Selective organocatalytic ring-opening polymerization : A versatile route to carbohydrate-functionalized poly(e-caprolactenes)
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:16, s. 5889-5893
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Tidskriftsartikel (refereegranskat)abstract
- Cationic catalysis using simple carboxylic acids to combine the ring-opening polymerization of c-caprolactone and the regioselective acylation of carbohydrates has been investigated. L-Lactic acid catalyzed the acylation of methyl beta-D-glucopyranoside and sucrose with epsilon-caprolactone in high yield by bulk polymerization at 120 degreesC. The main products were regioselectively acylated on the primary hydroxyl groups of the carbohydrate end groups. The overall conversion to methyl beta-D-glucopyranoside-functionalized poly(epsilon-caprolactone) was more than 90%, M-w 2000 and polydispersity index 1.5, with one major product methyl 6-O-poly(epsilon-caprolactone)-beta-D-glucopyranoside, in agreement with the corresponding Candida antarctica lipase B-catalyzed acylation
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| 39. |
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| 40. |
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| 41. |
- Zhou, Qi, et al.
(författare)
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Nanostructured biocomposites based on bacterial cellulosic nanofibers compartmentalized by a soft hydroxyethylcellulose matrix coating
- 2009
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 5:21, s. 4124-4130
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Tidskriftsartikel (refereegranskat)abstract
- Biomimetic approaches involving environmentally-friendly synthetic pathways provide an opportunity to elaborate novel high-performance biocomposites. Here we have developed a low-energy biosynthetic system for the production of a high-strength composite material consisting of self-assembled and nanostructured cellulosic nanofibers. This biocomposite is analogous to natural composite materials with high strength and hierarchical organization such as wood or tendon. It was generated by growing the bacterium Acetobacter, which naturally produces cellulosic nanofibers, in the presence of hydroxyethylcellulose (HEC). Individual cellulose fibrils were coated by HEC and exhibited a smaller lateral dimension than pure bacterial cellulose (BC) fibrils. They self-assembled to form compartmentalized nanofibers and larger cellulose fibril aggregates compared to pure BC. The tensile strength of nanocomposite films prepared from the compartmentalized cellulosic nanofibers was 20% higher than that of pure BC sheets and wood cellulose nanopapers, and 60% higher than that of conventional BC/HEC blends, while no strain-to-failure decrease was observed. The thin nanoscale coating consisting of hydrated HEC significantly increased the mechanical performance of the nanocomposite films by provoking compartmentalization of individual fibrils.
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