| 1. |
- Berglund, Linn
(författare)
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From bio-based residues to nanofibers using mechanical fibrillation for functional biomaterials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bio-based resource utilization in different forms has been driven by societal, industrial and academic research interests towards the development of “green”, sustainable materials from renewable sources. Within this context, exploiting biomass from different industrial residues is further advantageous from an environmental and economic point of view, leading to minimization of residues by means of waste treatment and to the development of high-addedvalue- products. Breaking down the cell wall structure to its smallest structural components is one means of turning bio-based residues into high-value products, leaving us with nanofibers. The aim of this work has been to understand how these nanofibers can be liberated from various cellulosic sources using mechanical fibrillation and how they can be assembled into functional hydrogels.The production of bio-based nanofibers as a sustainable bio-based material is in the early stages of commercialization and considerable research has been devoted to explore different methods of reaching nanoscale. However, the extraction process by chemical and/or mechanical means is still associated with a relatively high energy demand and/or cost. These are key obstacles for use of the material in a wide range of applications. Another challenge is that methods to characterize nanofiber dimensions are still being developed, with few options available as online measurements for assessing the degree of fibrillation. Allowing for assessment during the fibrillation process would enable not only optimization towards a more energy efficient fibrillation, but also matching of the nanofiber quality to its intended function, since different applications will require widely different nanofiber qualities. Energy-efficient fibrillation and scalability from industrial residues were explored using upscalable ultrafine grinding processes.Nanofibers from various industrial bio-residues and wood were prepared and characterized, including the development of a method for evaluation of the fibrillation process online via viscosity measurements as an indication of the degree of fibrillation down to nanoscale. Furthermore, the correlation of viscosity to that of the strength of the nanopapers (dried fiber networks) was evaluated for the different raw materials.Switchable ionic liquids (SIL) were tested as a green pretreatment for delignification, without bleaching of wood prior to fibrillation, with the aim to preserve the low environmental impact that the raw material source offers.In order to employ the hydrophilic nature and strong network formation ability of the fibrillated nanofibers, they were utilized in the preparation of functional biomaterials in the form of hydrogels. Firstly, brewer’s spent grain nanofibers were used to promote and reinforce hydrogel formation of lignin-containing arabinoxylan, resulting in a hydrogel completely derived from barley residues. In addition, alginate-rich seaweed nanofibers from the stipe (stem-like part of the seaweed) were used directly after fibrillation as an ink and hydrogels were formed via 3D printing.
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| 2. |
- Farooq, Muhammad, et al.
(författare)
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Well-Defined Lignin Model Films from Colloidal Lignin Particles
- 2020
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 36:51, s. 15592-15602
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Tidskriftsartikel (refereegranskat)abstract
- The transformation of a molecularly complex and irregularly shaped lignin into a nanoscale spherical architecture is anticipated to play a pivotal role in the promotion of lignin valorization. From the standpoint of using colloidal lignin particles (CLPs) as building blocks for a diverse range of applications, it has become essential to study their interactions with soluble compounds of varied origin. However, the lack of model films with well-defined surface properties similar to those of CLPs has hindered fundamental studies using surface-sensitive techniques. Here, we report well-defined and stable thin films prepared from CLPs and demonstrate their suitability for investigation of surface phenomena. Direct adsorption on substrates coated with a cationic anchoring polymer resulted in uniform distribution of CLPs as shown with atomic force microscopy (AFM). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments revealed higher adsorbed mass of cationic lignin onto the CLP-coated substrate in comparison to the film prepared from dissolved lignin, suggesting preferential adsorption via the carboxylic acid enriched surfaces of CLPs. QCM-D further enabled detection of small changes such as particle swelling or partial dissolution not detectable via bulk methods such as light scattering. The CLP thin films remained stable until pH 8 and displayed only a low degree of swelling. Increasing the pH to 10 led to some instability, but their spherical geometry remained intact until complete dissolution was observed at pH 12. Particles prepared from aqueous acetone or aqueous tetrahydrofuran solution followed similar trends regarding adsorption, pH stability, and wetting, although the particle size affected the magnitude of adsorption. Overall, our results present a practical way to prepare well-defined CLP thin films that will be useful not only for fundamental studies but also as a platform for testing stability and interactions of lignin nanoparticles with materials of technical and biomedical relevance.
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| 3. |
- Gustafsson, Emil, 1982-
(författare)
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Tailoring adhesion and wetting properties of cellulose fibers and model surfaces
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The layer-by-layer (LbL) technique was used to modify the surface of cellulose fibers by consecutive adsorption of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) followed by a final adsorbed layer of anionic paraffin wax colloids. Paper hand sheets made from the modified fibers were found to be highly hydrophobic with a contact angle of 150°. In addition to the significantly increased hydrophobicity, the sheets showed improved mechanical properties, such as a higher tensile strength. Heat treatment of the prepared sheets further enhanced both the mechanical properties and the hydrophobicity. These results demonstrate the flexibility and robustness of the LbL technique, which allows us to combine the known adhesive effect of PAH/PAA LbL films with the functionality of wax nanoparticles, creating a stronger and highly hydrophobic paper.It was further observed that LbL modified sheets without wax also displayed increased hydrophobicity when heat treated. The mechanism was studied through model experiments where LbL films of PAH/PAA were assembled on flat non-porous model cellulose surfaces. Contact angle measurements showed the same trend due to heat treatment of the model films, although, the absolute value of the contact angles were smaller. Analysis using the highly interfacial sensitive vibrational sum frequency spectroscopy technique showed an enrichment of CH3 groups (from the polymer chain ends) at the solid/air interface. These results indicate that during the heat treatment, a reorientation of polymer chains occurs to minimize the surface energy of the LbL film.In the second part of this work, the adhesive interactions between the main constituents of wood fibers were studied using high-resolution measuring techniques and well-defined model films of cellulose, hemicellulose and lignin. Successful surface modification of polydimethylsiloxane (PDMS) caps, needed in the Johnson-Kendall-Roberts (JKR) measuring methodology, by LbL deposition of nanofibrillated cellulose (NFC) and poly(ethylene imine) (PEI) allowed for the first known all-wood biopolymer JKR measurements of the adhesion between cellulose/cellulose, cellulose/lignin and the cellulose/glucomannan surfaces. The work of adhesion on loading and the adhesion hysteresis were similar for all three systems, suggesting that adhesion between the different wood biopolymers does not differ greatly.
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| 4. |
- Ibn Yaich, Anas, 1986-
(författare)
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Strategies for Renewable Barriers with Enhanced Performance
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Forest biomass is expected to play an increasingly important role in tomorrow´s global bio-economy as one of the main renewable sources of materials, chemicals and energy. In the framework of the biorefinery concept, the forestry industry is looking for new processes to utilize several fractions in the biomass (cellulose, hemicelluloses, lignin etc.), thereby generating value-added by-products, an economically sustainable process, and new market opportunities. The work presented in this thesis aims to develop oxygen barrier films and coatings based on the hemicelluloses-rich biorefinery fraction, referred to as wood hydrolysate (WH). These WHs were obtained from the aqueous process liquor after the hydrothermal treatment of hardwood. The WH-based films and coatings are intended to meet the increasing demand of bio-based and biodegradable barrier materials in multi-layered laminates for the food-packaging sector. This work has employed four strategies to provide control and enhancement of the mechanical and barrier properties of WH: I) a selective choice of up-grading pre-treatments of the WH aqueous liquor, II) the incorporation of layer silicates into the barrier formulation, III) chain-extension of the hemicellulose chains present in the WH via reductive amination, and IV) the development of wood hydrolysate polyelectrolyte complexes (PEC) with quaternized cellulose (QC). It has been demonstrated that the crude WH, with almost no upgrading pre-treatment, produced coatings with the best performance in terms of low oxygen permeability. Furthermore, the addition of naturally occurring layered silicates into the WH-based film formulations led to a decrease in water vapor permeability, and a considerably lower oxygen permeability at 80% relative humidity. Moreover, the chain-extension approach was shown to significantly enhance the formability and mechanical performance of WH-based films, making it possible to produce cohesive films with a higher proportion of WH, 70–85% (w/w) and to reduce the content of co-components in the films. The WH/QC-PEC-based films exhibited by far the best tensile properties, better than those previously obtained with carboxymethyl cellulose as a co-component in an equal amount, with a tensile strain-at-break as high as 7 %.
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| 5. |
- Junka, Karoliina, et al.
(författare)
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Multilayers of cellulose derivatives and chitosan on nanofibrillated cellulose
- 2014
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Ingår i: Carbohydrate Polymers. - : Elsevier. - 0144-8617 .- 1879-1344. ; 108, s. 34-40
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to study the effect of solution conditions and polysaccharide structure on their Layer-by-Layer (LbL) deposition on nanofibrillated cellulose (NFC). Multilayer build-up of cellulose derivatives and chitosan on NFC model surfaces was studied using Quartz Crystal Microbalance with Dissipation (QCM-D) and Colloidal Probe Microscopy (CPM). The type of cationic polysaccharide was found to significantly affect the multilayer build-up and surface interactions. Cationic cellulose derivative quaternized hydroxyethyl cellulose ethoxylate (HECE) formed highly water-swollen layers with carboxymethyl cellulose (CMC), and the build-up was markedly influenced by both the ionic strength and pH. The ionic strength did not significantly influence the multilayer build-up of chitosan–CMC system, and adsorbed chitosan layers decreased the viscoelasticity of the system. Based on the results, it was also confirmed that electrostatic interaction is not the only driving force in case of the build-up of polysaccharide multilayers on nanofibrillated cellulose.
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| 6. |
- Leppänen, Ann-Sofie, et al.
(författare)
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Targeted functionalization of spruce O-acetyl galactoglucomannans-2,2,6,6-tetramethylpiperidin-1-oxyl-oxidation and carbodiimide-mediated amidation
- 2013
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 130:5, s. 3122-3129
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Tidskriftsartikel (refereegranskat)abstract
- Modified spruce O-acetyl galactoglucomannans (GGMs) can be used as molecular anchors to alter the surface properties or to activate the surface of cellulose. To selectively introduce functionalities, GGMs were oxidized on C-6 of hexoses by 2,2,6,6-tetramethylpiperidin-1-oxyl-mediated oxidation. Different degrees of oxidation were successfully obtained by varying the reaction parameters. Low degrees could be obtained by performing the oxidations in bromide-free conditions. The formed uronic acids were further modified by a carbodiimide-mediated amidation reaction, which opens a window for introducing various functionalities selectively on hexoses. The adsorption of the modified GGMs to various cellulose samples was investigated. Indirect bulk sorption to fibers was compared to direct adsorption to nanofibrillated cellulose ultrathin films. GGMs with low degrees of oxidation showed high affinity to cellulose surfaces and could be sorbed onto cellulose in pure water. Moderate amounts of GGMs with high degree of oxidation could be sorbed onto cellulose in the presence of salts.
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| 7. |
- Nordgren, Niklas, 1975-, et al.
(författare)
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Mediation of the Nanotribological Properties of Cellulose by Chitosan Adsorption
- 2009
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Ingår i: Biomacromolecules. - USA : American Chemical Society. - 1525-7797 .- 1526-4602. ; 10:3, s. 645-650
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Tidskriftsartikel (refereegranskat)abstract
- Cellulosic model surfaces functionalized with chitosan, a naturally occurring cationic biomacromolecule, by in-situ adsorption have been studied with an atomic force microscope (AFM) in colloidal probe configuration. The interaction forces on approach and separation, as well as the nanotribological properties, were shown to be highly pH-dependent and a significant difference in the behaviour was seen before and after chitosan adsorption. In general, all forces on approach showed a highly repulsive interaction at shorter distances due to deformation of the probe. At high pH, before chitosan adsorption, a long-range electrostatic repulsion was observed, consistent with DLVO theory. However at low pH no electrostatic contribution was found before adsorption probably due to charge neutralization of carboxyl groups. After chitosan adsorption, repulsive forces acting over a much longer distance than predicted by DLVO theory were present at low pH. This effect was ascribed to chain extension of the chitosan species of which the magnitude and the range of the force increased dramatically with higher charge at low pH. In all cases, a typical saw-tooth patterned adhesion was present with pull-off events occurring at different separations. The frequency of these events after chitosan adsorption was greatly increased at longer distances. Additionally, the adsorbed chitosan markedly reduced the friction where the largest effect was a 7-fold decrease of the friction coefficient observed at low pH.
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| 8. |
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| 9. |
- Olszewska, Anna, et al.
(författare)
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Non-ionic assembly of nanofibrillated cellulose and polyethylene glycol grafted carboxymethyl cellulose and the effect of aqueous lubrication in nanocomposite formation
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 9:31, s. 7448-7457
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Tidskriftsartikel (refereegranskat)abstract
- facile route to significantly lower the frictional forces between cellulose nanofibrils (NFC) has been presented. The concept is based on the surface modification of NFC by adsorption of polyethylene glycol grafted carboxymethyl cellulose (CMC-g-PEG) via non-ionic interactions. The adsorption was studied using quartz crystal microbalance with dissipation (QCM-D). The changes in viscoelastic properties of the adsorbed layers, upon changes in pH were evaluated and attributed to the conformation of CMC. Surface forces and frictional properties of NFC films were examined using the AFM colloidal probe technique and were shown to be highly pH dependent. A significant difference in behaviour was observed upon the surface modification of NFC. After adsorption of CMC-g-PEG, repulsive forces were acting over a much longer distance than predicted by DLVO theory. This was ascribed to the CMC-g-PEG chain extension, the effect of which was even more pronounced at higher pH due to the deprotonation of carboxyl groups on CMC. A higher anionic charge resulted in increased water content and swelling of the layer. Additionally, the adsorption of CMC-g-PEG onto NFC films markedly increased the lubrication by the reduction of the friction coefficient by 65% and 88% at pH 4.5 and pH 7.3, respectively.
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| 10. |
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