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- 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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| 2. |
- 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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| 3. |
- Bodvik, Rasmus
(författare)
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Bulk and interfacial properties of cellulose ethers
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work summarizes several studies that all concern cellulose ethers of the types methylcellulose (MC) hydroxypropylmethylcellulose (HPMC) and ethyl(hydroxyethyl)cellulose (EHEC). They share the feature of negative temperature response, as they are soluble in water at room temperature but phase separate and sometimes form gels at high temperatures. The different types of viscosity transitions occurring in these three cellulose ethers are well-known. However, earlier studies have not solved the problem of why both HPMC and EHEC, as the temperature increases, exhibit a viscosity decrease just before the viscosity increases, whereas MC only has one transition temperature where the viscosity increases. With our investigations we have aimed to compare the effect of temperature on bulk solutions and on adsorbed layers of the different polymers using a range of techniques.Light scattering and cryo transmission electron microscopy (cryo-TEM) was employed to study aggregation of MC, HPMC and EHEC in solution. The solvent quality of water is reduced for all three polymers in solution as the temperature increases, and this infers an onset of aggregation at a certain temperature. The aggregation rate follows the order EHEC > HPMC > MC. Cryo-TEM pictures of solutions frozen from high temperatures showed closely packed fibrils forming dense networks in MC solution. Some fibrils were also found in HPMC solution above the transition temperature, but they did not interconnect readily. This is explained by the bulky and hydrophilic hydroxypropyl groups attached to HPMC. EHEC has similar substituents, while MC only has short and hydrophobic methyl groups attached to the main chain.An amphiphilic liquid, diethyleneglycolmonobutylether (BDG) was used as an additive to change the properties of MC solutions in water. With 10 wt% BDG added, the effect was similar in viscosity and light scattering measurements as well as cryo-TEM pictures, inducing a temperature response resembling that of HPMC in pure water. 5 wt% of BDG was enough to change the aggregation type and induce a transition temperature with viscosity decrease. The effect of the additive is rationalized by BDG acting as a hydrophobic and bulky substituent in MC, similar to the large substituents in HPMC and EHEC.Two instruments, a quartz crystal microbalance with dissipation (QCM-D) and an ellipsometer, were used in parallel to determine the changes with temperature on an adsorbed layer of MC and HPMC on silica kept in water and in polymer solution. The silica needed to be hydrophobized for significant adsorption to take place. Adsorption was similar for both polymers at low temperatures, whereas a sharp transition in several layer properties occurred for HPMC, but not for MC, close to the solution viscosity transition temperature. Atomic force microscopy (AFM) was used to measure attractive and repulsive forces and also friction forces between MC layers in polymer solution. The small changes in normal forces with temperature infer that the hydrophobic groups in MC are mostly depleted from the surface. The surface–polymer interactions increase with increasing temperature and the layer becomes more cohesive, which induces a higher load bearing capacity and lower friction when measured at high loads. AFM imaging was employed to obtain the height distribution in MC adsorbed layers. These images indicate that fibril-like structures were formed at a lower temperature in the surface layer than in bulk solution.The different preferences for adsorption and for aggregation in MC and HPMC above the solution transition temperatures are explained by the fibril formation in MC shielding hydrophobic parts of the polymer from the solution, and thus counteracting adsorption, but also fast aggregation. The viscosity decrease in HPMC and EHEC is conferred to intra-chain contraction and aggregation into less extended structures.
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