| 1. |
- Bosmans, Toon, 1988, et al.
(författare)
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Assembly of Debranched Xylan from Solution and on Nanocellulosic Surfaces
- 2014
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 15:3, s. 924-930
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Tidskriftsartikel (refereegranskat)abstract
- This study focused on the assembly characteristics of debranched xylan onto cellulose surfaces. A rye arabinoxylan polymer with an initial arabinose/xylose ratio of 0.53 was debranched with an oxalic acid treatment as a function of time. The resulting samples contained reduced arabinose/xylose ratios significantly affecting the molecular architecture and solution behavior of the biopolymer. With this treatment, an almost linear xylan with arabinose DS of only 0.04 was obtained. The removal of arabinose units resulted in the self-assembly of the debranched polymer in water into stable nanoparticle aggregates with a size around 300 nm with a gradual increase in crystallinity of the isolated xylan. Using quartz crystal microbalance with dissipation monitoring, the adsorption of xylan onto model cellulose surfaces was quantified. Compared to the nonmodified xylan, the adsorption of debranched xylan increased from 0.6 to 5.5 mg m(-2). Additionally, adsorption kinetics suggest that the nanoparticles rapidly adsorbed to the cellulose surfaces compared to the arabinoxylan. In summary, a control of the molecular structure of xylan influences its ability to form a new class of polysaccharide nanoparticles in aqueous suspensions and its interaction with nanocellulose surfaces.
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| 2. |
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| 3. |
- Eguees, Itziar, et al.
(författare)
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Corncob arabinoxylan for new materials
- 2014
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 102, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- Corncob agricultural waste was used as a source of arabinoxylan for preparation of films. Three arabinoxylan samples were prepared: crude extract (CCAX), purified by a washing step, and purified by bleaching CCAX. Films prepared with untreated CCAX were water soluble, yellowish in color and had poor mechanical properties. After the purification processes the Young's modulus increased from similar to 293 MPa to similar to 1400-1600 MPa, and strength was improved from similar to 9 MPa to around 53 MPa, while the strain at break was kept at similar to 8% both in untreated and purified CCAX. The contact angle was increased from similar to 21.3 degrees to 67-74 degrees after washing or bleaching CCAX. Acetylation of bleached CCAX showed the highest thermal resistance (325 degrees C), had low T-g (125 degrees C) and a high contact angle (80 degrees), and its films were stronger (strength similar to 67 MPa; Young's modulus similar to 2241 MPa) and more flexible (similar to 13%). These characteristics make purified CCAX a suitable material to be used as a matrix for film applications.
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| 4. |
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| 5. |
- Escalante, Alfredo, 1975, et al.
(författare)
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Flexible oxygen barrier films from spruce xylan
- 2012
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 87:4, s. 2381-2387
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Tidskriftsartikel (refereegranskat)abstract
- Arabinoglucuronoxylan was extracted from Norway spruce and films prepared by casting from aqueous solution. The sugar analysis and NMR confirmed that the spruce xylan was composed of arabinose, 4-O-methyl-glucuronic acid and xylose in a ratio of 1:2:11 respectively. Substitutions of 4-O-methyl-alpha-D-GlcpA at O-2 and of alpha-L-Araf at O-3 on the xylose backbone were found by NOE analysis. NOE cross-peaks indicated as well that there is at least one free xylose on the main chain present between two substitutions. Whether the distribution of side chains was random or in blocks was uncertain. The average molecular weight of the sample was determined by size exclusion chromatography to be 12,780 g/mol. Arabinoglucoronoxylan casting yielded transparent flexible films with an average stress at break of 55 MPa, strain at break of 2.7% and a Young's Modulus 2735 MPa. Wide-angle X-ray scattering analysis showed that the arabinoglucuronoxylan films were totally amorphous. Addition of sorbitol as plasticizer resulted in less strong but more flexible films (strain at break of 5%). Peaks of crystallinity could be seen in X-ray which corresponds to sorbitol crystallizing in distinct phases. The dynamic mechanical analysis showed that the arabinoglucuronoxylan film softened at a later relative humidity (80% RH) in comparison with plasticized films (60% RH). The films showed low oxygen permeability and thus have a potential application in food packaging.
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| 6. |
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| 7. |
- Stépán, Agnes, 1985, et al.
(författare)
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Arabinose content of arabinoxylans contributes to flexibility of acetylated arabinoxylan films
- 2012
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 125:3, s. 2348-2355
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Tidskriftsartikel (refereegranskat)abstract
- Arabinoxylans (AX) from rye were partly debranched by chemical hydrolysis methods, and AXs differing in arabinosyl substitution were acetylated using chemical methods. The resulting materials are film forming, and these films underwent molecular structural analysis and were tested for their material properties. The composition and structure of the modified polymers were determined using high performance anion exchange chromatography and two dimensional nuclear magnetic resonance; it was shown that all free hydroxyl groups (of both xylose and arabinose) were acetylated. Further characterizations were done by dynamic mechanical analysis and thermo-gravimetric analysis to evaluate the thermal behavior of the material. The observed glass transition temperatures (Tg) increased with a decrease in arabinosyl substitutions. The thermal degradation temperatures were all close to 380 degrees C. The mechanical properties were characterized with tensile tests of the films. Tensile tests showed that the strain at break, which reflects the flexibility of the material, was significantly higher at higher arabinosyl substitution levels. The elastic Young's modulus was not significantly affected, although a tendency was seen toward a less stiff material at higher arabinosyl substitution. The ultimate strength of the materials was remarkably high in all cases, around 60 MPa, with little difference between them. Considering these properties, a great potential is foreseen in the application of acetylated arabinoxylans as packaging films and as matrix for composites.
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| 8. |
- Stépán, Agnes, 1985
(författare)
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Bioplastics from Biomass - Acetylation of Xylans with Green Chemistry
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is social, environmental and increasing economic pressure on the industrial sector to substitute non-renewable resources with renewable ones as the increasing World population is exponentially depleting the fossil fuel supplies of the Earth. Each year about 260 million tons of plastics are produced from crude oil and most of it ends up as waste. Producing biodegradable plastics from renewable resources could be a contribution to a sustainable development. Hemicelluloses are the second most abundant biopolymers on Earth, with about 60 billion tons biosynthesized each year by plants. Xylans are the largest group of hemicelluloses and were designed by nature to primarily function as a matrix in plants. So far, they are unutilized valuable biopolymers with broad potential applications. Many xylans are acetylated in nature, and the degree and pattern of acetylation influences the material properties of the plant cell wall. Controlled chemical esterification is a powerful tool for tailoring the structure and material properties of hemicelluloses as a renewable raw material for bio-based plastic production.First, chemical acetylation was carried out on corncob arabinoxylan (CCAX), and the films were then compared with the unmodified pure CCAX films. There was clear improvement of the thermal and water resistant properties of the xylan films after acetylation. In following work, the structure-property analysis showed a positive effect of arabinose side chains on the elongation at break, the thermal stability and glass transition temperature of the acetylated xylan.To make hemicellulose acetylation more sustainable, green chemistry was applied. The first approach included the utilization of ionic liquids (IL) as reaction media. Rye AX and spruce AGX were both fully acetylated while maintaining a high degree of polymerization (DP) in a very fast reaction. Another green chemistry alternative is to use enzymes. In this thesis the surfaces of rye AX films were acylated with acetate and stearate using lipases and cutinases in a water-free environment. The advancing contact angle of the surfaces was increased, the stearated surface being most hydrophobic.Finally, AcAX was combined with spruce nanofibrillated cellulose (NFC) to form films. The thermal properties, stiffness and stress at break of the composite were superior to the neat AcAX films. The uniqueness of this composite is the water resistance and high elongation at break, even at a 10 % NFC content.This work is a contribution to the designing of novel xylan based materials and their feasible and environmentally friendly production. Acetylated arabinoxylans have a potential to replace many of the oil based plastics and become a future bioplastics.
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| 9. |
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| 10. |
- Stépán, Agnes, 1985, et al.
(författare)
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Enzymatic Transformation of Hemicelluloses to Bioplastics
- 2012
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Ingår i: 243rd ACS National Meeting, 25-29 March 2012, San Diego, CA, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Hemicelluloses being the second most abundant biopolymer on Earth are getting more attention in the recent years for having a great potential as a renewable source for materials, fine chemicals and fuels. The focus of this study is to modify molecular architecture of spruce arabinoglucuronoxylan (AGX) and to gain better understanding of structure-material properties relationships. Chemical acetylation and gradient debranching of arabinoxylan has been carried out and material properties have been evaluated. The recent work is more focused on enzymatic acetylation and acylation. Most of our enzymatic modifications are based on enzymes with a proven record in biocatalytic reactions. In parallel, we target the use of more specific acting enzymes as well. These enzymes are commercially not available yet, so this part includes enzyme cloning and production. The desired product is a thermoplastic biomaterial suitable for packaging or as binder / matrix in a biocomposite.
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