| 1. |
- Alimohammadzadeh, Rana
(författare)
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Eco-friendly and Catalytic Surface Engineering of Cellulose and Nanocellulose
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The non-stop use of petroleum-based materials such as plastics can generate significant environmental problems, including pollution of the oceans and increased CO2 levels, and cause diseases like cancer due to the starting monomers. Consequently, increased use of sustainable and non-toxic polymers and monomers is required to address these issues. Cellulose, generously supplied by Mother Nature, is the most abundant biopolymer on Earth. Nanocellulose is a sustainable polymer extracted from the cellulose inwood or produced by bacteria and algae. This biodegradable nanomaterialhas recently been receiving intense research attention, since it has great potential for use in a broad range of industrial and biomedical applications. However, it has limitations such as moisture sensitivity and incompatibility with hydrophobic materials due to its hydrophilic nature. Chemical modification is necessary for it to fulfill the requirements for applications that require high moisture resistance and water repellency. Unfortunately, several of the existing methods involve harsh and toxic conditions or reagents. In this thesis, together with my co-workers, I have employed the toolbox of organocatalysis for accomplishing eco-friendly and innovative surface modification of cellulose and nanocellulose. The organocatalysts we usedmost in our research are the naturally abundant and industrially relevantorganic acids tartaric acid and citric acid.Direct catalytic esterification of cellulose nanocrystal (CNC) with thioglycolicacid was performed either in suspension or on solid surfaces such as films and foams. We found that the reaction was accelerated by tartaric acid but could also be autocatalytic with respect to the thioglycolic acid under certain conditions. The synthesized CNC-SH was further exploited as a heterogeneous reducing agent as well as a handle for further nanocellulose modifications. This was demonstrated by using CNC-SH as a heterogenous reducing agent of Cu(II) to Cu(I), which is essential for allowing the Cu to actas a catalyst for 2,3-dipolar cycloaddition reactions between azides andalkynes. We also showed that the thia-modified CNC could undergo further functionalizing via thiol-ene click chemistry reactions, for example, we attached fluorescent compounds such as TAMRA and quinidine.Herein we provide a fluorine-free method to prepare superhydrophobic CNC film with excellent water-resistance properties by combining self-assemblyand organocatalysis. Self-assembly of CNC via vacuum filtration resulted in xa film with a specific roughness at the microscale. Next, the catalytic silylation with a variety of alkoxysilanes in the presence of natural organic acids such as tartaric acid and citric acid was performed. The successful implementation of our method resulted in a super-hydrophobic CNC film (water contact angleover 150°) with excellent water-resistance. Thus, the combination of the selfassembly of a rough surface with catalytic surface modification resulted in a phenomenon like the “lotus effect” as exhibited by the leaves of the lotus flower. An investigation of the oxygen permeability of the octadecyltrimethoxysilane-modified CNC film revealed that it significantly decreased at high relative humidity compared with unmodified CNC films.In this thesis, the fabrication of hydrophobic and functionalized MTM/CNF nanocomposites using organocatalytic surface modification with a large variety of alkoxysilanes is also performed. The surface modifications are mildand the mechanical strength of the Nacre-mimetic nanocomposites is preserved. Elemental mapping analysis revealed that the silane modification occurred predominantly on the surface.A combination of organocatalyst and biopolyelectrolyte complex was appliedfor surface engineering of chemi-thermomechanical pulp (CTMP) and bleached sulfite pulp (BSP). The reaction was performed using a synergistic combination of an organocatalyst with a polyelectrolyte (PE) complex. Using this method, the strength properties of CTMP and BSP sheets were significantly increased (up to 100% in Z-strength for CTMP). Further investigations of the distribution of the PE complex were then performed using TAMRA and quinidine labeling and confocal laser scanningmicroscopy. This revealed that an even distribution of the cationic starch component of the PE complex had occurred within the CTMP-based paper sheets, which follows its lignin distribution pattern.
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| 2. |
- Alipour, Nazanin, 1978-
(författare)
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Structure and Mechanical/Transport properties of Single and Multilayer Polyethylene-based Materials
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current study discusses the structure, mechanical and transport properties of polyethylene-based materials into two parts. The first part deals with the migration and chemical depletion of active substance such as insecticides from moulded polyethylene sheets. Deltamethrin (DM) and synergist piperonyl butoxide (PBO) are often used for insect control purpose. It was found that DM as a powder was incapable of recrystallization and remained in liquid state after cooling to room temperature, and that the evaporation of a DM/PBO solution was greater than that predicted from the evaporation rates of pristine separate material components. Infrared spectroscopy and liquid chromatography showed that the loss of DM and PBO through polyethylene sheets was negligible over 30 days, when aged in air at 80 °C (60 and 80 %RH). However, significant migration of the active species was observed in aged polyethylene sheets which were exposed in liquid water (at 80 and 95 °C). In the second part, the structure and properties of multi–layered polymer films were studied in terms of crystallization kinetics, mechanical and transport properties. Previously, it has been shown that when the layer thickness decreases from micrometre-scale to nanometre-scale, leading to improvement of the film performance such as crack propagation and oxygen barrier properties. In this work, two multi-layered systems were considered based on compatible (i) or incompatible layers (ii). In the first case (i), metallocene polyethylene (mPE) and low-density polyethylene (LDPE) where investigated as 2, 24, and 288 adjacent layers. In the second case (ii) poly(ethylene-co-vinyl alcohol) (EVOH) and polyethylene adhesive was evaluated as 5 and 19 layers. The crystallization kinetic studies showed that the crystallization rate was retarded as the layers became thinner with increasing number of layers in the multi-layered films as compared to the reference films (2 and 5 layers). The observation was suggested to stem from greater association between layers (inter layer mixing) in the case of mPE/LDPE films with 2 layers. Furthermore, the crack growth resistance increased with increasing number of layers. The x-ray scattering and tensile testing showed that the films were orientated more in extrusion direction than in the transverse direction, besides the EVOH films (the incompatible system) showed higher orientation in the extrusion direction than mPE/LDPE films. The uptake of n-hexane was reduced significantly in multi-layered EVOH films due to the effective protective role of EVOH. Furthermore, it was revealed that non-homogenous swelling causing a folding/curling of bilayer films when exposed to the vapour of the solvent.
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| 3. |
- Almlöf, Heléne, 1968-
(författare)
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Extended Mercerization Prior to Carboxymethyl Cellulose Preparation
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carboxymethyl cellulose (CMC) is produced commercially in a two-stage process consisting of a mercerization stage, where the pulp is treated with alkali in a water alcohol solution, followed by an etherification stage in which monochloroacetic acid is added to the pulp slurry. In this thesis an extended mercerization stage of a spruce ether pulp was investigated where the parameters studied were the ratio of cellulose I and II, concentration of alkali, temperature and retention time. The influence of the mercerization stage conditions on the etherification stage, were evaluated as the degree of substitution (DS) of the resulting CMC and the filterability of CMC dissolved in water at a concentration of 1%. The DS results suggested that the NaOH concentration in the mercerization stage was the most important of the parameters studied. When the NaOH concentration in the mercerization step was low (9%), a high cellulose II content in the pulp used was found to have no negative impact on the DS of the resulting CMC compared with pulps with only cellulose I. However, when the NaOH concentration was high (27.5%), pulps with high content of cellulose II showed a lower reactivity than those with only cellulose I with respect to the DS of the CMC obtained after a given charge of NaMCA. The results obtained from the filtration ability study of CMC water solutions suggested that both the amount of cellulose II in the original pulp and the temperature had a negative influence on the filtration ability whereas the NaOH concentration in the mercerization stage had a positive influence. The filtration ability was assumed to be influenced highly by the presence of poorly reacted cellulose segments. A retention time between 1-48 h in the mercerization stage had no effect on either the DS or the filtration ability of the CMC. Using NIR FT Raman spectroscopy molecular structures of CMC and its gel fraction were analyzed with respect to the conditions used in the extended mercerization stage. Here it was found that the alkaline concentration had a very strong influence on the following etherification reaction. FT Raman spectra of CMC samples and their gel fractions prepared with low NaOH concentrations (9%) in the mercerization stage indicated an incomplete transformation of cellulose to Na-cellulose before carboxymethylation to CMC. Low average DS values of the CMC, i.e. between 0.42 and 0.50, were yielded. Such CMC dissolved in water caused very thick and semi solid gum-like gels, probably due to an uneven distribution of substituting groups along the cellulose backbone. FT Raman spectra of CMC mercerized with alkaline concentrations at 18.25 and 27.5% in the mercerization stage indicated, however, that all of the cellulose molecules were totally transferred to CMC of high DS, i.e. between 0.88 and 1.05. When dissolved in water such CMC caused gels when they were prepared from ether pulp with a high fraction of cellulose II.
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| 4. |
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| 5. |
- Ankerfors, Caroline
(författare)
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Polyelectrolyte complexes : their preparation, adsorption behaviour and effect on paper properties
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the formation of polyelectrolyte complexes (PECs) has been studied using a jet mixing method not previously used for mixing polyelectrolytes. The PECs were formed from two weak polyelectrolytes, i.e., polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH), with different mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The adsorption behaviour of the formed PECs on silicon oxide substrates and pulp fibres was analysed, and the results were compared with those for polyelectrolyte multilayers (PEMs) prepared from the same two polyelectrolytes. The results indicated that by using the jet mixer, the size of the formed PECs could be controlled, which was not the case with the polyelectrolyte titration method. The PECs produced by jet mixing were also found to be smaller than those produced by polyelectrolyte titration. From these results, a two-step mechanism for the formation of PECs was suggested: initial precomplex formation, which is a fast and diffusion-controlled process, followed by a reconformation process, during which the vigorous mixing in the jet mixer can partially limit secondary aggregation. When the complexes were adsorbed to silicon oxide or pulp fibre surfaces, adsorption studies indicated that it was impossible to reach the same adsorption levels for PECs as for PEMs. This was explained in terms of free energy, entropical, reasons rather than to any geometric limitation of the surface. Despite the smaller amount of polyelectrolyte adsorbed from the PEC treatment than from the PEM treatment of pulp fibres, the PEC treatment had the greatest effect on paper strength per adsorbed amount of polymer. This was thought to be because the three-dimensional structure of the PECs, versus the smoother structure of PEMs, allows for the formation of multiple contact points between the macroscopically rough fibres and increased molecular contact area. In the adsorption experiments, it was also found that net cationic complexes can adsorb to both anionic and cationic substrates. This phenomenon was explained by the occurrence of anionic patches on the surface of the net cationic PECs and the ability of the PECs, formed from weak polyelectrolytes, to partially change charge upon exposure to a surface of the same charge as the complex itself, due to a change of the degree of dissociation of the polyelectrolytes constituting the complex.
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| 6. |
- Axegard, Peter, et al.
(författare)
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Bleaching of softwood kraft pulps with H2O2, O3, and ClO2
- 1996
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Ingår i: TAPPI Journal. - 0734-1415. ; 79:1, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- Ozone or chlorine dioxide bleaching prior to hydrogen peroxide bleaching greatly improves the performance of the hydrogen peroxide stage. The efficiency is further improved by a chelating treatment immediately after the ozone or chlorine dioxide stage. With an optimal metal ion profile, laboratory bleached (OAZQP) softwood kraft pulps can reach brightness levels above 90% ISO, with 5-10% lower pulp strength properties and bleaching costs comparable to ECF bleaching. It also is possible to obtain full brightness with only hydrogen peroxide provided the metal ion profile is optimal, e.g., by using multiple QP treatments. The chemical consumptions, expressed as oxidation equivalents per decreased kappa number are the same as for sequences including ozone or chlorine dioxide. Ozone and chlorine dioxide are comparable as far as delignification and brightness efficiency go.
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| 7. |
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| 8. |
- Axelsson, Patrik, et al.
(författare)
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Bleachability of Alkaline Birch Pulps.
- 2000
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Ingår i: Proceedings 6<sup>th</sup> European Workshop on Lignocellulosics and Pulp..
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Konferensbidrag (refereegranskat)
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| 9. |
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| 10. |
- Axelsson, P., et al.
(författare)
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Influence of alkali profiling in birch kraft pulping on QPQP bleachability
- 2004
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 19:1, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- The influence of different aspects of alkali profiling in the kraft cook on QPQP bleachability of oxygen-delignified birch pulp was investigated. The use of a levelled-out alkali profile was compared to a conventional, and different modifications to the levelled-out alkali profile, like alkali charge, degree of delignification and amount of dissolved organic substance and ionic strength in the cooking liquor were studied. The alkali profile itself was found to have a significant effect where a levelled-out alkali profile showed a superior bleachability compared to a conventional one. The bleachability improved with an increased alkali charge towards the end of the cook, a high kappa number after cooking or by a cooking liquor exchange in order to decrease the amount of dissolved organic substance and the ionic strength towards the end of the cook. When a levelled-out alkali profile was used, the bleachability correlated well with the light-absorption of the lignin in the unbleached pulp, where a pulp with a brighter lignin consumed less peroxide in the QPQP sequence, for the pulp to reach 89% brightness.
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| 11. |
- Axelsson, P., et al.
(författare)
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The influence of alkali charge and temperature in the kraft cook on the QPQP bleachability and the kappa number composition of birch pulp
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:3, s. 206-212
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of this investigation was to study how the alkali charge and the temperature in the kraft cook influence the QPQP bleachability of oxygen-delignified birch pulp. The bleachability was evaluated as the normalised consumption of bleaching chemicals required to reach a certain light absorption coefficient of the pulp. All the pulps had a kappa number of about 17 after the cook and a kappa number of about 10 after oxygen delignification. The alkali charge significantly affected the bleachability and the best bleachability was obtained for an intermediate level alkali charge ([HO-](initial)=1,35 mol/L, corresponding to an effective alkali charge of 21.6% on wood). An increase in cooking temperature gave only a slight increase in bleachability. The contributions to the kappa number of lignin, hexenuronic acids (HexA) and other non-lignin structures were also investigated. Lignin contributed to about 60% of the kappa number in pulps after the cook, to about 40% in pulps after the oxygen delignification, and to about 30% after QPQP bleaching. Hexenuronic acids contributed between 3.7 to 4.7 kappa number units in all pulps, which makes them the largest contributors to the kappa number in oxygen-delignified and QPQP bleached pulps. Other non-lignin structures, were contributing about 3 kappa number units in pulps after the cook, but decreased to less than I kappa number unit after QPQP bleaching. No great differences in the composition of the kappa number could be seen between pulps produced under different pulping conditions, except that there was a somewhat lower hexenuronic acid content in the pulps produced with the highest alkali charge or at the highest cooking temperature.
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| 12. |
- Badia, J. D., et al.
(författare)
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Effect of sisal and hydrothermal ageing on the dielectric behaviour of polylactide/sisal biocomposites
- 2017
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Ingår i: Composites Science And Technology. - : Elsevier. - 0266-3538 .- 1879-1050. ; 149, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of virgin polylactide (PLA) and its reinforced composites with different weight amounts of sisal fibres were assessed at broad temperature (from −130 °C to 130 °C) and frequency ranges (from 10−2–107 Hz), before and after being subjected to accelerated hydrothermal ageing. The synergetic effects of both the loading of sisal and hydrothermal ageing were analysed by means of dielectric relaxation spectra. The relaxation time functions were evaluated by the Havriliak-Negami model, substracting the ohmic contribution of conductivity. The intramolecular and intermolecular relaxations were respectively analysed by means of Arrhenius and Vogel-Fulcher-Tammann-Hesse thermal activation models. The addition of fibre increased the number of hydrogen bonds, which incremented the dielectric permittivity and mainly hindered the non-cooperative relaxations of the biocomposites by increasing the activation energy. Hydrothermal ageing enhanced the formation of the crystalline phase at the so-called transcrystalline region along sisal. This fact hindered the movement of the amorphous PLA fraction, and consequently decreased the dielectric permittivity and increased the dynamic fragility.
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| 13. |
- Badia, J. D., et al.
(författare)
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Relevant factors for the eco-design of polylactide/sisal biocomposites to control biodegradation in soil in an end-of-life scenario
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 143, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- The eco-design considers the factors to prepare biocomposites under an end-of-life scenario. PLA/sisal biocomposites were obtained from amorphous polylactide and sisal loadings of 10, 20 and 30 wt% with and without coupling agent, and subjected to biodegradation in soil according to standard ISO846. Mass-loss, differential scanning calorimetry and size-exclusion chromatography were used for monitoring biodegradation. A statistical factorial analysis based on the molar mass Mn and crystallinity degree XC pointed out the relevance and interaction of amount of fibre and use of coupling agent with the time of burial in soil. During the preparation of biocomposites, chain scission provoked a similar reduction of Mn for coupled and non-coupled biocomposites. The amount of fibre was relevant for the increase of XC due to the increase of nucleation sites. The coupling agent accelerated the evolution of both factors: reduction of Mn and the consequent increase of XC, mainly during biodegradation in soil. Both factors should be balanced to facilitate microbial assimilation of polymer segments, since bacterial digestion is enhanced by chain scission but blocked by the promotion of crystalline fractions.
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| 14. |
- Badia, J. D., et al.
(författare)
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Water absorption and hydrothermal performance of PHBV/sisal biocomposites
- 2014
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 108, s. 166-174
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Tidskriftsartikel (refereegranskat)abstract
- The performance of biocomposites of poly(hydroxybutyrate-co-valerate) (PHBV) and sisal fibre subjected to hydrothermal tests at different temperatures above the glass transition of PHBV (T-H = 26, 36 and 46 degrees C) was evaluated in this study. The influences of both the fibre content and presence of coupling agent were focused. The water absorption capability and water diffusion rate were considered for a statistical factorial analysis. Afterwards, the physico-chemical properties of water-saturated biocomposites were assessed by Fourier-Transform Infrared Analysis, Size Exclusion Chromatography, Differential Scanning Calorimetry and Scanning Electron Microscopy. It was found that the water diffusion rate increased with both temperature and percentage of fibre, whereas the amount of absorbed water was only influenced by fibre content. The use of coupling agent was only relevant at the initial stages of the hydrothermal test, giving an increase in the diffusion rate. Although the chemical structure and thermal properties of water-saturated biocomposites remained practically intact, the physical performance was considerably affected, due to the swelling of fibres, which internally blew-up the PHBV matrix, provoking cracks and fibre detachment.
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| 15. |
- Bengtsson, Andreas
(författare)
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Biobased carbon fibers from solution spun lignocellulosic precursors
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon fibers (CFs) have excellent mechanical properties and a low density, making themattractive as a reinforcing fiber in composites. The use of CFs is limited to high-end applications,since they are produced from an expensive fossil-based precursor via an energy-intensivemanufacturing process, explaining the need for cheaper CFs from renewables. CFs can be madefrom strong cellulosic precursors, but the low carbon content of cellulose results in a lowconversion yield, and thus an expensive CF. Lignin has a higher carbon content than cellulose butCFs from melt spun lignin precursors have presented challenges, since these precursors have a lowstrength and are difficult to convert to CF in a realistic conversion time.In the present work, CFs from solution spun precursors consisting of blends of softwood kraftlignin and cellulose have been developed. The lignin-cellulose precursors (up to 70% lignin) wereprepared with air-gap spinning and wet spinning, using an ionic liquid and a water-based solventsystem for co-dissolution, respectively. Co-processing of cellulose and lignin was beneficial as theformer made the precursor strong and easy to handle, whereas the latter gave a higher conversionyield than precursors based solely on cellulose. The precursors were converted to CFs via bothbatchwise and continuous conversion, using industrially relevant times (< 2 h), with a yield up to45 wt% after incorporation of a flame retardant.These CFs have a moderate Young’s modulus and tensile strength up to 75–77 GPa and 1.2 GPa,respectively, i.e. similar to the values for CFs from fossil-based isotropic pitch and they can thusbe classified as general-grade CFs. These biobased CFs have a disordered turbostratic graphitestructure, and their tensile properties are affected by the precursor structure, the conversionconditions, and the final diameter. These CFs can potentially be used as a sustainable componentin non-structural and semi-structural applications.
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| 16. |
- Bengtsson, Andreas, et al.
(författare)
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Carbon Fibers from Lignin-Cellulose Precursors : Effect of Carbonization Conditions
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society. - 2168-0485. ; 8:17, s. 6826-6833
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Tidskriftsartikel (refereegranskat)abstract
- Carbon fibers (CFs) are gaining increasing importance in lightweight composites, but their high price and reliance on fossil-based raw materials stress the need for renewable and cost-efficient alternatives. Kraft lignin and cellulose are renewable macromolecules available in high quantities, making them interesting candidates for CF production. Dry-jet wet spun precursor fibers (PFs) from a 70/30 w/w blend of softwood kraft lignin (SKL) and fully bleached softwood kraft pulp (KP) were converted into CFs under fixation. The focus was to investigate the effect of carbonization temperature and time on the CF structure and properties. Reducing the carbonization time from 708 to 24 min had no significant impact on the tensile properties. Increasing the carbonization temperature from 600 to 800 °C resulted in a large increase in the carbon content and tensile properties, suggesting that this is a critical region during carbonization of SKL:KP PFs. The highest Young's modulus (77 GPa) was obtained after carbonization at 1600 °C, explained by the gradual transition from amorphous to nanocrystalline graphite observed by Raman spectroscopy. On the other hand, the highest tensile strength (1050 MPa) was achieved at 1000 °C, a decrease being observed thereafter, which may be explained by an increase in radial heterogeneity.
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| 17. |
- Bengtsson, Andreas, et al.
(författare)
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Carbon Fibers from Wet-Spun Cellulose-Lignin Precursors Using the Cold Alkali Process
- 2022
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Ingår i: FIBERS. - : MDPI AG. - 2079-6439. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, there has been extensive research into the development of cheaper and more sustainable carbon fiber (CF) precursors, and air-gap-spun cellulose-lignin precursors have gained considerable attention where ionic liquids have been used for the co-dissolution of cellulose and lignin. However, ionic liquids are expensive and difficult to recycle. In the present work, an aqueous solvent system, cold alkali, was used to prepare cellulose-lignin CF precursors by wet spinning solutions containing co-dissolved dissolving-grade kraft pulp and softwood kraft lignin. Precursors containing up to 30 wt% lignin were successfully spun using two different coagulation bath compositions, where one of them introduced a flame retardant into the precursor to increase the CF conversion yield. The precursors were converted to CFs via batchwise and continuous conversion. The precursor and conversion conditions had a significant effect on the conversion yield (12-44 wt%), the Young's modulus (33-77 GPa), and the tensile strength (0.48-1.17 GPa), while the precursor morphology was preserved. Structural characterization of the precursors and CFs showed that a more oriented and crystalline precursor gave a more ordered CF structure with higher tensile properties. The continuous conversion trials highlighted the importance of tension control to increase the mechanical properties of the CFs.
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| 18. |
- Bengtsson, Andreas, 1991-
(författare)
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Carbon fibres from lignin-cellulose precursors
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector. The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs. This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view. The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties. A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (<2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route.
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| 19. |
- Bergnor, Elisabeth, et al.
(författare)
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The role of metal ions in TCF-bleaching.
- 1994
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Ingår i: Proceedings 3<sup>rd</sup> European Workshop on Lignocellulosics and Pulp. ; , s. 284-289
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Konferensbidrag (refereegranskat)
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| 20. |
- Brolen, Gabriella, et al.
(författare)
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Hepatocyte-like cells derived from human embryonic stem cells specifically via definitive endoderm and a progenitor stage
- 2010
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 145:3, s. 284-294
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Tidskriftsartikel (refereegranskat)abstract
- Human embryonic stem cells offer a potential unlimited supply for functional hepatocytes, since they can differentiate into hepatocyte-like cells displaying a characteristic hepatic morphology and expressing various hepatic markers. These cells could be used in various applications such as studies of drug metabolism and hepatotoxicity, which however, would require a significant expression of drug metabolizing enzymes. To derive these cells we use a stepwise differentiation protocol where growth- and maturation factors are added. The first phase involves the formation of definitive endoderm. Next, these cells are treated with factors known to promote the induction and proliferation towards hepatic progenitor cell types. In the last phase the cells are terminally differentiated and maturated into functional hepatocyte-like cells. The cultures were characterized by analysis of endodermal or hepatic markers and compared to cultures derived without induction via definitive endoderm. Hepatic functions such as urea secretion, glycogen storage, indocyanine green uptake and secretion, and cytochrome P450-expression and activity were evaluated. The DE-Hep showed a hepatocyte morphology with sub-organized cells and exhibited many liver-functions including transporter activity and capacity to metabolize drugs specific for important cytochrome P450 sub-families. This represents an importantstep in differentiation of hESC into functional hepatocytes. (C) 2009 Elsevier B.V. All rights reserved.
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| 21. |
- Buchert, Johanna, et al.
(författare)
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Effect of pulping and bleaching on pulp carbohydrates and technical properties.
- 1996
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Ingår i: Proceedings Int. Pulp Bleaching. ; , s. 39-42
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Konferensbidrag (refereegranskat)abstract
- Pulping and bleaching have a profound effect on the carbohydrate chem. of kraft pulps. The chem. structure of xylan is modified due to the conversion of methylglucuronic acid side groups to hexenuronic acid side groups. Pulping conditions strongly affect the amt. of hexenuronic acid present in the pulp and subsequently modified kraft pulps have different carboxyl group profiles as compared with conventionally cooked pulps. Due to its reactivity, hexenuronic acid is readily degraded when chlorine dioxide or ozone are used as bleaching chems. However, TCF-pulps bleached with peroxide and oxygen contain high amts. of hexenuronic acid. Thus, depending on the pulping and bleaching method, the quality and quantity of carboxylic acids in different types of pulps varies significantly. The differences in the uronic acid content are in turn reflected in the macroscale properties of the pulps, such as brightness stability.
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| 22. |
- Buchert, Johanna, et al.
(författare)
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Significance of xylan and glucomannan in the brightness reversion of kraft pulps
- 1997
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Ingår i: TAPPI Journal. - 0734-1415. ; 80:6, s. 165-171
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Tidskriftsartikel (refereegranskat)abstract
- The brightness reversion of kraft pulps is caused by the presence of residual lignin, chlorinated extractives, or oxidized carbohydrates. The effect of hemicellulose content, i.e., xylan (I) and glucomannan (II), on the thermal stability of modern bleached kraft pulps was investigated. Different O-delignified hard- and softwood kraft pulps were bleached with different bleaching sequences contg. ClO2, H2O2, or O3. Hemicellulose-degrading enzymes, i.e., xylanase or mannanase, were used for selective removal of the resp. hemicellulose from the pulps, and the role of partially removed I and II on the brightness stability of these pulps was studied. Because of the structure of kraft I, enzymic removal of I also resulted in a decreased carboxyl group content in the pulps, whereas II removal did not affect the carboxyl group content. By decreasing the carboxyl groups in the pulps in conjunction with I removal, the thermal aging of the pulps was significantly decreased. The role of II was less significant. Thus, the uronic acids present in the pulp participate in the brightness reversion of kraft pulps.
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| 23. |
- Buchert, Johanna, et al.
(författare)
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The role of xylan and glucomannan in yellowing of kraft pulps.
- 1995
-
Ingår i: Proceedings 8<sup>th</sup> Int. Symp. Wood Pulp. Chem.. ; , s. 43-48
-
Konferensbidrag (refereegranskat)abstract
- The effects of xylan and glucomannan on the thermal stability of unbleached, partially bleached, and fully bleached pine and birch kraft pulps were studied. The choice of bleaching chems. strongly affected the brightness reversion. Compared with hydrogen peroxide or chlorine dioxide, bleaching with ozone reduced the amt. of carboxyl groups and subsequently the pc-nos. of oxygen-delignified pulps. Xylan removal reduced also the amt. of carboxyl groups in the pulps and this was reflected in improved brightness stability whereas glucomannan removal had no effect. Thus, the uronic acids bound to pulp xylan were found to participate in the brightness reversion of kraft pulps.
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| 24. |
- Bäckström, Marie, 1964-
(författare)
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The effect of environment on refining efficiency of kraft pulps
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the pulp and paper mill processes have been operational for long time there is still a need to understand the unit operations in paper making and how they interact with the ingoing pulp material. This is crucial in order to fully utilize the potential of the wood as well as of the unit operations. In order to do that it is vital to have an understanding about the produced pulp fibres, how they are constructed and how they respond to different conditions of their environment.The aim of this work has been to clarify how the environment influences the refining efficiency of kraft pulps in terms of energy requirement and paper property development. The main hypothesis has been that the swelling of the fibres, due to their inherited polyelectrolytic gel nature, will not only affect the fibre as such but also the strength and properties of the fibre flocs that are mechanically treated between bars in the refiner and in this way affect the refining efficiency.The main focus has been to study how the chemical environment, in particular the initial fibre swelling, affects the refining efficiency. Therefore, the influence of counter-ions to the charged groups, the number of charged groups, electrolyte concentration, pH and rheological behaviour was studied. Additionally, the importance of fibre flocculation for the refining efficiency was investigated by chemical means, i.e. to chemically flocculate and deflocculate a fibre suspension just before entering the refiner and evaluate the refining efficiency. An investigation to clarify the importance of refining homogeneity was also performed. The work was performed both on a laboratory scale and in pilot scale using industrial refiners to ensure the validity of the results.The importance of the counter-ions to the charged groups on refining was demonstrated. When the counter-ions was sodium the refinability, defined as the required energy input to reach a certain WRV or tensile index, was reduced by up to 50%. The more energy-efficient refining of pulps in the Na+-form may be explained as a co-operation between a higher osmotic pressure in the fibre wall and the mechanical stress applied during refining, so called “electrostatic repulsion-assisted refining”. When mechanical forces are applied on the fibre and the fibre wall, the electrostatic repulsion forces due to the ionization act as an additional aid to increase the swelling, and this in turn helps to delaminate the fibre wall. This “electrostatic repulsion-assisted refining” also resulted in another type of external fibrillation of the fibres than that produced for the reference pulp in calcium form. The fibrils were very short and tiny. The improved refining efficiency could not be attributed to any rheological effect such as floc strength or floc size.The number of charges correlated to refinabiliy of the pulp material, but there has to be a balance between the number of charges and ultrastructure of the pulp fibre. If too many charges were introduced, the internal ultrastructure was eventually damaged, and no property development was obtained in the refining.The importance of refining heterogeneity on paper properties was investigated by mixing less refined or unrefined pulps and highly refined pulps in different proportions giving a wide distribution on energy input to individual fibres, as well giving swelling distribution curves. The mechanical properties of the produced paper were surprisingly alike, and the influence of the extreme inhomogeneity was rather small. In a pilot paper machine trial, clear effects due to heterogeneous refining was only observed when 50% of the stock fed to the paper machine was unrefined. This implies that the mills can have large freedom in refining strategies without any significant negative impact on the tensile strength properties at a given density.
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| 25. |
- Cervin, Nicholas, 1982-
(författare)
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Porous Cellulose Materials from Nano Fibrillated Cellulose
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the first part of this work a novel type of low-density, sponge-like material for the separation of mixtures of oil and water has been prepared by vapour deposition of hydrophobic silanes on ultra-porous nanocellulose aerogels. To achieve this, a highly porous (> 99 %) nanocellulose aerogel with high structural flexibility and robustness is first formed by freeze-drying an aqueous dispersion of the nanocellulose. The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the nanocellulose dispersion before freeze-drying. The hydrophobic light-weight aerogels are almost instantly filled with the oil phase when they selectively absorb oil from water, with a capacity to absorb up to 45 times their own weight. The oil can also be drained from the aerogel and the aerogel can then be subjected to a second absorption cycle.In the second part of the work a novel, lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified NanoFibrillated Cellulose (NFC). Confocal microscopy and high-speed video imaging show that the long-term stability of the wet foams can be attributed to the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface which prevent the air bubbles from collapsing or coalescing. Careful removal of the water yields a porous cellulose-based material with a porosity of 98 % and a density of 30 mg cm-3. These porous cellulose materials have a higher Young’s modulus than other cellulose materials made by freeze drying and a compressive energy absorption of 56 kJ m-3 at 80 % strain. Measurements with an autoporosimeter reveal that most pores are in the range of 300 to 500 μm.
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| 26. |
- Ceynowa, Dylan J., et al.
(författare)
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Morning Glory Disc Anomaly in childhood - a population-based study
- 2015
-
Ingår i: Acta Ophthalmologica. - : Wiley. - 1755-375X .- 1755-3768. ; 93:7, s. 626-634
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: To report prevalence, ocular characteristics and coexisting neurological, behavioural, somatic and neuroradiological abnormalities in children and adolescents with morning glory disc anomaly (MGDA).Methods: In a cross-sectional population-based study, 12 patients with MGDA, aged 2-20years, were identified. All 12 agreed to ophthalmological assessments including visual functions, refraction, fundus photography, optical coherence tomography (OCT) and ocular motor score (OMS). Neurological examinations and behavioural/developmental screening were carried out. Data from previous or new neuroradiological investigations were collected.Results: The prevalence of MGDA was 2.6/100000. MGDA was unilateral in 11/12 patients with a best-corrected visual acuity (BCVA) in the MGDA eye ranging from hand motion to 0.65 (median 0.06). Severe microphthalmus prevented unilaterality to be determined in one adolescent. All patients had a binocular BCVA of 0.5. OMS showed abnormalities in pupil response, vestibulo-ocular reflex, stereo visual acuity, strabismus and convergence. OCT revealed peripapillary or macular oedema in 5/8 patients and foveal aplasia in 3/8 patients. Three patients had extensive capillary hemangiomas, of which one had PHACES syndrome and one had additional cerebrovascular anomalies and corpus callosum agenesis. Neuroradiology showed craniovascular anomalies in two patients. Neurology was mostly normal. Behavioural/developmental screening showed attention deficit hyperactivity disorder in one patient.Conclusions: The prevalence data, previously not reported, of morning glory disc anomaly was 2.6/100 000. Coexisting retinal peripapillary or macular oedema was common, as were cerebral abnormalities and/or cutaneous vascular malformations. The associated findings may not be discovered through routine ophthalmological examination why OCT and neuroimaging are called for.
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| 27. |
- Champ, Simon, et al.
(författare)
-
Biocidal coatings
- 2006
-
Patent (populärvet., debatt m.m.)abstract
- Biocidal multilayered system, characterized in that it comprises at least the following layers: - an anionic or cationic carrier, preferably cellulose as anionic carrier, - on this carrier alternating polymeric cationic and anionic layers starting with a layer having a charge opposite to that of the carrier, - wherein at least one layer is hydrophobically modified.
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| 28. |
- Chen, Chao, et al.
(författare)
-
Antibacterial evaluation of CNF/PVAm multilayer modified cellulose fiber and cellulose model surface
- 2018
-
Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 33:3, s. 385-396
-
Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that 3-layer-modified cellulose fibers with poly(acrylic acid) (PAA) as the middle layer between two cationic polyelectrolyte polyvinylamine (PVAm) layers have strong antibacterial efficacy in terms of both bacteria adsorption and bacterial growth inhibition. In the present work, the fossil-based PAA middle layer was replaced by sustainable wood-based cellulose nano-fibrils (CNF), i. e., the fibers were modified by a 3-layer PVAm/CNF/PVAm system. Interestingly, the antibacterial efficacy of this system was greater than that of the previous PVAm/PAA/PVAm system. A higher salt concentration and lower assembly pH in the multilayer build-up resulted in better bacterial reduction. As the surface of a cellulose fiber is heterogeneous, making it difficult to characterize and visualize at high resolution, more homogeneous cellulose model surfaces were prepared by spin coating the dissolved cellulose fiber onto a silica surface to model the fiber surface. With increasing ionic strength, more aggregated and heterogeneous structures can be observed on the PVAm/CNF/PVAm modified model surfaces. The adsorbed bacteria distributed on the structured surfaces were clearly seen under fluorescence microscopy. Adsorbed amounts of bacteria on either aggregate or flat regions were quantified by scanning electron microscopy (SEM). More adsorbed bacteria were clearly seen on aggregates than on the flat regions at the surfaces. Degrees of bacteria deformation and cell damage were also seen under SEM. The surface roughness of the modified model surfaces was examined by atomic force microscopy (AFM), and a positive correlation was found between the surface roughness and the bacterial adhesion. Thus, an additional factor that controls adhesion, in addition to the surface charge, which is probably the most dominant factor affecting the bacteria adhesion, is the surface structures, such as roughness.
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| 29. |
- Chen, Chao, 1989-, et al.
(författare)
-
Bactericidal surfaces prepared by femtosecond laser patterning andlayer-by-layer polyelectrolyte coating
- 2020
-
Ingår i: Journal of Colloid and Interface Science. - : Academic Press. - 0021-9797 .- 1095-7103. ; 575, s. 286-297
-
Tidskriftsartikel (refereegranskat)abstract
- Antimicrobial surfaces are important in medical, clinical, and industrial applications, where bacterial infection and biofouling may constitute a serious threat to human health. Conventional approaches against bacteria involve coating the surface with antibiotics, cytotoxic polymers, or metal particles. However, these types of functionalization have a limited lifetime and pose concerns in terms of leaching and degradation of the coating. Thus, there is a great interest in developing long-lasting and non-leaching bactericidal surfaces. To obtain a bactericidal surface, we combine micro and nanoscale patterning of borosilicate glass surfaces by ultrashort pulsed laser irradiation and a non-leaching layer-by-layer polyelectrolyte modification of the surface. The combination of surface structure and surface charge results in an enhanced bactericidal effect against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. The laser patterning and the layer-by-layer modification are environmentally friendly processes that are applicable to a wide variety of materials, which makes this method uniquely suited for fundamental studies of bacteria-surface interactions and paves the way for its applications in a variety of fields, such as in hygiene products and medical devices.
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| 30. |
- Chen, Chao, 1986-
(författare)
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Development of Non-leaching Antibacterial Approaches on Cellulose-based Substrates and Their Mechanisms
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The layer-by-layer (LbL) technique is becoming a powerful tool that has been applied in many surface coatings and functionalizations in recent years. It has many advantages including a fast and mild process, the flexibility of choice of substrate, and the easiness to scale-up. Novel antibacterial materials can be achieved using this technique, by immobilizing selected antibacterial agents on surfaces of desired substrates. An ideal antibacterial agent, a cationic polyelectrolyte, can be LbL-deposited onto the surfaces in mono or multi layers, make the surfaces lethal to the bacteria due to their positive charge. This approach is able not only to effectively control the spreading of bacteria but also to minimize bacterial resistance as well as the environmental impact.Cellulose fibres modified by different cationic polyelectrolytes including PDADMAC, PAH, PVAm as either monolayer or multilayer assembled with PAA using LbL deposition have shown more than 99.99 % bacterial removal as well as the inhibition of bacterial growth. Among these modifications, two layers of PVAm assembled with one layer of PAA have shown the highest antibacterial efficiency due to the highest adsorbed amount and charge density. Secondly, PAA was replaced by a bio-based cellulose nano-fibril (CNF), as a middle layer between two layers of PVAm, which decreases the carbon-footprint and expands the possibility of using LbL technique in antibacterial applications, since the LbL technique can be used long as the alternate layers are oppositely charged. The fibres modified with this approach have shown similar and even better antibacterial properties than those of PAA.To develop the antibacterial approach using LbL on cellulose fibres, it is also essential to understand the antibacterial mechanism. It was found that the charge density and surface structures are two important factors affecting bacterial adhesion and the bactericidal effect. To study this, different charged cellulose model surfaces were made by coating oxidized, regenerated cellulose followed by PVAm/CNF/PVAm LbL deposition, and a better antibacterial effect was observed on the higher charged surface. By calculating the force between the bacteria and charged surface, it was suggested that a higher interaction due to the higher surface charge causes a large stress on the bacterial cell wall which leads to the disruption of the bacteria. To further improve the bactericidal effect, the flat surfaces were patterned with micro and nano structures using a femtosecond laser technique. The weakening of the bacterial cell wall caused by the charged surface makes the bacteria more vulnerable and easier to disrupt. This approach has been shown to be valid on both Gram-positive S. aureus, and Gram-negative E. coli. The effect was greater on E. coli with a weaker membrane structure and higher surface potential, which shows that the antibacterial mechanism is a physical disrupt of the bacterial cell.
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| 31. |
- Chen, Chao, 1986-, et al.
(författare)
-
Effect of cationic polyelectrolytes in contact-active antibacterial layer-by-layer functionalization
- 2017
-
Ingår i: Holzforschung. - : WALTER DE GRUYTER GMBH. - 0018-3830 .- 1437-434X. ; 71:7-8, s. 649-658
-
Tidskriftsartikel (refereegranskat)abstract
- Contact-active surfaces have been created by means of the layer-by-layer (LbL) modification technique, which is based on previous observations that cellulose fibers treated with polyelectrolyte multilayers with polyvinylamine (PVAm) are perfectly protected against bacteria. Several different cationic polyelectrolytes were applied, including PVAm, two different poly(diallyl dimethyl ammonium chloride) polymers and two different poly(allylamine hydrochloride) polymers. The polyelectrolytes were self-organized in one or three layers on cellulosic fibers in combination with polyacrylic acid by the LbL method, and their antibacterial activities were evaluated. The modified cellulose fibers showed remarkable bacterial removal activities and inhibited bacterial growth. It was shown that the interaction between bacteria and modified fibers is not merely a charge interaction because a certain degree of bacterial cell deformation was observed on the modified fiber surfaces. Charge properties of the modified fibers were determined based on polyelectrolyte titration and zeta potential measurements, and a correlation between high charge density and antibacterial efficiency was observed for the PVAm and PDADMAC samples. It was demonstrated that it is possible to achieve antibacterial effects by the surface modification of cellulosic fibers via the LbL technique with different cationic polyelectrolytes.
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| 32. |
|
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| 33. |
- Chen, Chao, 1986-, et al.
(författare)
-
Influence of Cellulose Charge on Bacteria Adhesion and Viability to PVAm/CNF/PVAm-Modified Cellulose Model Surfaces
- 2019
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602.
-
Tidskriftsartikel (refereegranskat)abstract
- A contact-active antibacterial approach based on the physical adsorption of a cationic polyelectrolyte onto the surface of a cellulose material is today regarded as an environment-friendly way of creating antibacterial surfaces and materials. In this approach, the electrostatic charge of the treated surfaces is considered to be an important factor for the level of bacteria adsorption and deactivation/killing of the bacteria. In order to clarify the influence of surface charge density of the cellulose on bacteria adsorption as well as on their viability, bacteria were adsorbed onto cellulose model surfaces, which were modified by physically adsorbed cationic polyelectrolytes to create surfaces with different positive charge densities. The surface charge was altered by the layer-by-layer (LbL) assembly of cationic polyvinylamine (PVAm)/anionic cellulose nanofibril/PVAm onto the initially differently charged cellulose model surfaces. After exposing the LbL-treated surfaces to Escherichia coli in aqueous media, a positive correlation was found between the adsorption of bacteria as well as the ratio of nonviable/viable bacteria and the surface charge of the LbL-modified cellulose. By careful colloidal probe atomic force microscopy measurements, it was estimated, due to the difference in surface charges, that interaction forces at least 50 nN between the treated surfaces and a bacterium could be achieved for the surfaces with the highest surface charge, and it is suggested that these considerable interaction forces are sufficient to disrupt the bacterial cell wall and hence kill the bacteria.
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| 34. |
- Chen, Lan, et al.
(författare)
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A modified ionization difference UV-vis method for fast quantitation of guaiacyl-type phenolic hydroxyl groups in lignin
- 2022
-
Ingår i: International Journal of Biological Macromolecules. - : Elsevier BV. - 0141-8130 .- 1879-0003. ; 201, s. 330-337
-
Tidskriftsartikel (refereegranskat)abstract
- An ionization difference UV-Vis method (Delta epsilon-spectrum method) is the most potentially simple method for fast quantitation of phenolic hydroxyl groups (ph-OH) in lignin. However, the underestimated results were calculated from the conventional Delta epsilon-spectrum method using one- or two-point wavelengths measurement. In this study, a modified Delta epsilon-spectrum method using multi-point wavelengths measurement was developed and the negative absorbance was also considered. Four main typical lignin models, e.g. vanilla alcohol, 5-5 biphenyl, stilbenoid and vanillin, were applied as the guaiacyl-type (G-type) phenolic models for the determination of ph-OH by the modified Delta epsilon-spectrum method. The 2-methoxyethanol/water/acetic acid = 8/2/0.2 (V/V/V) was used as the acidic solvent system and the 2-methoxyethanol/0.2 M NaOH solution = 1/9 (V/V) was used as the alkaline solvent system. The ph-OH contents in the spruce milled wood lignin (SMWL) and the spruce Kraft lignin (SKL) were respectively quantified by the modified Delta epsilon-spectrum method as 1.078 and 4.348 mmol/g, which were comparable to the counterparts determined by P-31 Nuclear Magnetic Resonance Spectroscopy (P-31 NMR). The results revealed that the modified Delta epsilon-spectrum method can provide more accurate and reliable results compared to the conventional method.
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| 35. |
- Dedic, Dina, et al.
(författare)
-
Analysis of lignin and extractives in the oak wood of the 17th century warship Vasa
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:4, s. 419-425
-
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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| 36. |
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| 37. |
- Dedic, Dina, et al.
(författare)
-
Cellulose degradation in the Vasa : The role of acids and rust
- 2013
-
Ingår i: Studies in Conservation. - 0039-3630 .- 2047-0584. ; 58:4, s. 308-313
-
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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| 38. |
- 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
-
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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| 39. |
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| 40. |
- Dedic, Dina, 1985-
(författare)
-
The warship Vasa : A Study of Lignin, Extractives and Acids in the oak wood
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The oak wood timbers of the 17th century Swedish warship Vasa are weak. The weakening has been attributed to cellulose degradation, which is more extensive in the interior of the timbers compared to the surface regions. Further, the mechanism of cellulose degradation was attributed to oxidative reactions involving iron as a catalyst. In this work, the non-cellulosic wood components (lignin and extractives) in the wood of the Vasa have been studied in order to assess the level of degradation possibly caused by oxidative reactions. Because the interior of the wood timbers is more acidic and its cellulose more depolymerized than at the near surface regions, a general study of organic acidand iron concentrations with respect to different depths from the surface was also performed.Characterization of lignin in the wood of the Vasa was done by means of wet chemical degradation (thioacidolysis) and subsequent GC-MS analysis of the degradation products, as well as CP/MAS 13C NMR spectroscopy of the wood. Dry acetone- and water extracts of the wood were analyzed by 13C NMR spectroscopy and MALDI-TOF mass spectroscopy in order to study the presence of gallo- and ellagitannins. No severe lignin degradation and no discernible amounts of hydrolysable tannins in the oak wood of the Vasa were detected, indicating that oxidative reactions are not the primary route to cellulose depolymerization.High amounts of oxalic acid (analyzed by HPIEC) and a low pH have been found in the interior of the wood timbers, supporting acid hydrolysis as the main mechanism of cellulose depolymerization. Analysis of the iron distribution using ICP AES shows that iron is most abundant in the surface of the timbers and decreases as the concentration of oxalic acid increases. Experimental work also shows that some iron species (rust) in the Vasa neutralize oxalic acid, thereby protecting the surface wood from acid hydrolysis.
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| 41. |
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| 42. |
- 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
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 5:4, s. 159-160
-
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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| 43. |
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| 44. |
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| 45. |
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| 46. |
- Ek, Monica, et al.
(författare)
-
Biointeractive fibres : A sustainable way of fighting bacteria by using antibacterial cellulosic fibres
- 2010
-
Konferensbidrag (refereegranskat)abstract
- Bacterial growth is a risk of infection. Antibiotics did long time seem to be a soln. to the problem, but now the consequences are seen, as antibiotic-resistant strains are evolving. The substances are also eventually released into the environment, where they often are harmful to living organisms. Antibacterial surfaces state another option. However, a majority of the now existing surfaces are of leaching type i.e. assocd. with the same problems as the antibiotics. The non-leaching are a safer option, but until now the fabrication has been a problem with use of e.g. org. solvents. We present a sustainable way of forming an antibacterial material onto cellulose by using the polyelectrolyte multilayer technique. By step-wise adsorbing oppositely charged polyelectrolytes in an aq. soln. contg. fibers, at room-temp., the surface of the fibers are modified. The result is a non-leaching material with bacteria inhibiting properties. Also the fabrication is quite safe, as polymers have shown lower toxicity to humans than their monomeric counterparts. Cellulose is an excellent substrate for antibacterial surfaces. It is easy to modify with the present technique and is in itself a sustainable materials, with multiple applications. Combined this gives us in total a new, antibacterial material which also opens up for sustainable cellulose-based products.
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| 47. |
- Ek, Monica, et al.
(författare)
-
CELL 28-Biointeractive fibers with antibacterial properties
- 2008
-
Ingår i: ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY. ; , s. 28-CELL-
-
Konferensbidrag (refereegranskat)abstract
- Growth of bacteria on various surfaces may cause major concern if encountered in the wrong environment. The ability to impart antimicrobial properties onto surfaces is therefore desirable. Modification of both glass surfaces and cellulose membranes using weak polyelectrolytes as antimicrobial agent is presented. The aim was to incorporate a known carrier of antimicrobial activity into a multilayer structure of adsorbed polyelectolytes at different surfaces and evaluate the antibacterial activities. The approach involved screening for antimicrobial activity in soln. of modified and unmodified polymers. The polymers were evaluated against gram-neg. E. coli and gram-pos. B. subtilis. In order to elucidate the mode of action of the polymers, the charge was detd. This is done since earlier studies have shown that both charge and degree of hydrophobicity are of importance in terms of exerted activity. Results show that the chosen polymers exert activity in the immobilized state. Different techniques have been used to evaluate the mechanisms.
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| 48. |
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| 49. |
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| 50. |
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