| 1. |
- Wang, Miao, et al.
(författare)
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Colloidal Ionic Assembly between Anionic Native Cellulose Nanofibrils and Cationic Block Copolymer Micelles into Biomimetic Nanocomposites
- 2011
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 12:6, s. 2074-2081
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Tidskriftsartikel (refereegranskat)abstract
- We present a facile ionic assembly between fibrillar and spherical colloidal objects toward biomimetic nanocomposites with majority hard and minority soft domains based on anionic reinforcing native cellulose nanofibrils and cationic amphiphilic block copolymer micelles with rubbery core. The concept is based on ionic complexation of carboxymethylated nanofibrillated cellulose (NFC, or also denoted as microfibrillated cellulose, MFC) and micelles formed by aqueous self-assembly of quaternized poly(1,2-butadiene)-block-poly(dimethylaminoethyl methacrylate) with high fraction of the NFC reinforcement. The adsorption of block copolymer micelles onto nanocellulose is shown by quartz crystal microbalance measurements, atomic force microscopy imaging, and fluorescent optical microscopy. The physical properties are elucidated using electron microscopy, thermal analysis, and mechanical testing. The cationic part of the block copolymer serves as a binder to NFC, Whereas the hydrophobic rubbery micellar cores are designed to facilitate energy dissipation and nanoscale lubrication between the NFC domains under deformation. We show that the mechanical properties do not follow the rule of mixtures, and synergistic effects are observed with promoted work of fracture in one composition. As the concept allows wide possibilities for tuning, the work suggests pathways for nanocellulose-based biomimetic nanocomposites combining high toughness with stiffness and strength.
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| 2. |
- 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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| 3. |
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| 4. |
- Junka, Karoliina, et al.
(författare)
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Titrimetric methods for the determination of surface and total charge of functionalized nanofibrillated/microfibrillated cellulose (NFC/MFC)
- 2013
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 20:6, s. 2887-2895
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Tidskriftsartikel (refereegranskat)abstract
- Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed.
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| 5. |
- Morales, Luis Orlando, 1974-, et al.
(författare)
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Effects of residual lignin and heteropolysaccharides on the bioconversion of softwood lignocellulose nanofibrils after SO2-ethanol-water fractionation
- 2014
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Ingår i: Bioresource Technology. - : Elsevier. - 0960-8524 .- 1873-2976. ; 161, s. 55-62
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Tidskriftsartikel (refereegranskat)abstract
- The amount of residual lignin and hemicelluloses in softwood fibers was systematically varied by SO2-ethanol–water fractionation for integrated biorefinery with nanomaterial and biofuel production. On the basis of their low energy demand in mechanical processing, the fibers were deconstructed to lignocellulose nanofibrils (LCNF) and used as substrate for bioconversion. The effect of LCNF composition on saccharification via multicomponent enzymes was investigated at different loadings. LCNF digestibility was compared with the enzyme activity measured with a quartz crystal microbalance. LCNF hydrolysis rate gradually decreased with lignin and hemicellulose concentration, both of which limited enzyme accessibility. Enzyme inhibition resulted from non-productive binding of proteins onto lignin. Near complete LCNF hydrolysis was achieved, even at high lignin and hemicellulose content. Sugar yields for LCNF were higher than those for precursor SEW fibers, highlighting the benefits of high surface area in LCNF.
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| 6. |
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| 7. |
- 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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| 8. |
- Orelma, Hannes, et al.
(författare)
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Affibody conjugation onto bacterial cellulose tubes and bioseparation of human serum albumin
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 4:93, s. 51440-51450
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Tidskriftsartikel (refereegranskat)abstract
- We attached anti-human serum albumin (anti-HSA) affibody ligands on bacterial cellulose (BC) by EDC–NHS-mediated covalent conjugation and physical adsorption and demonstrate their application for tubular biofiltration of blood proteins. The BC fibrils were first modified by carboxymethyl cellulose (CMC) by incorporation of CMC in the BC culture medium, producing in situ a CMC–BC tubular network that was used as biofilter. Alternatively, BC carboxylation was carried out by alkaline TEMPO–NaBr–NaClO oxidation. The BC and modified BC, grown in the form of tubes or flat films, were characterized by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and conductometric titration. Anti-HSA affibody conjugation onto carboxylated cellulose thin film was verified from sensogram data obtained by surface plasmon resonance (SPR). The HSA specific binding capacity of the carboxylated cellulose conjugated with anti-HSA via EDC–NHS was approximately eight-fold larger when compared to the carboxylated cellulose surface carrying physically adsorbed anti-HSA (∼81 compared to 10 ng cm−2, respectively). Further proof of protein binding via anti-HSA affibody conjugated on tubules of CMC- and TEMPO-oxidized BC was obtained by fluorescence imaging. Specific binding of tagged HSA resulted in a linear increase of fluorescence intensity as a function of tagged HSA concentration in the contacting solution.
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| 9. |
- Sundman, Ola, et al.
(författare)
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Layer-by-Layer Adsorption of Two Cellulose-Based Polyelectrolytes on Cellulose Fibers. Dependence of pH and Ionic Strength on the Resulting Charge Density as Measured by Polyelectrolyte Titration
- 2013
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126. ; 8:4, s. 4827-4836
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Tidskriftsartikel (refereegranskat)abstract
- The charge density of a bleached Kraft hardwood pulp, subjected to layer-by-layer adsorption of the oppositely charged cellulose derivative polyelectrolytes hydroxyethylcellulose ethoxylate, quaternised (HECE), and carboxymethyl cellulose (CMC), was studied by polyelectrolyte titration as a function of pH and ionic strength. The experimental design included a simultaneous variation of the experimental parameters, and the trends were evaluated with the help of partial least squares regression. As expected from the literature, the data indicate that both pH and ionic strength influence the charge of cationic fibers. It is also obvious that CMC as an outermost layer is more sensitive to changes in pH than the deprotonation of COOH groups suggests. High ionic strength seems to be beneficial for the adsorption of HECE, while the pH dependence seems much more complicated. The non-linear pH dependence indicates that, in addition to electrostatic interactions, entropy factors and hydrogen bonding between OH groups on both the substrates and ligands are responsible for the adsorption, which is in agreement with literature on the subject.
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| 10. |
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