| 1. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Arabinoxylan and Nanocellulose from a Kilogram-scale Extraction of Barley Husk
- 2019
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In: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 13:3, s. 6201-6220
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Journal article (peer-reviewed)abstract
- Processes of extracting hemicellulose from annual plants usually neglect the cellulose fraction. This study explored the possibility of obtaining both a hemicellulose and a cellulose fraction of sufficient quality for further use, with barley husks used as the raw material. An alkaline extraction was used to isolate the biopolymers by a process in which sodium dithionite replaced the traditional sodium borohydride as the reducing agent. The cellulose fraction was successfully transformed into nanocellulose by sulfuric acid hydrolysis, and the obtained hemicellulose (i.e., arabinoxylan) displayed carbohydrate composition characteristics similar to those previously reported in the literature for processes of extracting hemicellulose from barley husks. Using this methodology, both the cellulose and hemicellulose can be isolated in high quantities of dry material and used for transformation into new bio-based materials.
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| 2. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Branching of hemicelluloses through an azetidinium salt ring-opening reaction
- 2016
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In: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 428, s. 23-30
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Journal article (peer-reviewed)abstract
- During the last century there has been a steady increase in the number of publications on practical applications of hemicellulose. Due to the water and moisture sensitivity, poor film-forming ability and lack of thermal processability most of the hemicelluloses need to be chemically modified prior to processing into materials. Within this study we present the results of azetidinium salts as a new functional group for conjugation to polysaccharides. The reactivity of three azetidinium salts on xylan, arabinoxylan and galactoglucomannan was investigated. Carbonyl groups were found to be favorable for the reaction with azetidinium salts and thus the glucuronic acid content in the hemicellulose determines the degree of substitution. TEMPO-oxidation of the hemicelluloses was done which successfully increased the degree of substitution. The highly reactive azetidinium salts are easily synthesized from secondary amines and epichlorohydrin and can be used as a new tool toward functionalization of hemicelluloses into the after sought properties.
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| 3. |
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| 4. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Crystalline Nanocellulose — Preparation, Modification, and Properties
- 2015
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In: Cellulose - Fundamental Aspects and Current Trends. - 9789535122296 ; , s. 159-191
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Book chapter (other academic/artistic)abstract
- Cellulose is a linear biopolymer found naturally in plant cells such as wood and cotton. It is the worlds most abundant polymer in nature and possesses properties such as good biocompatibility, low cost, low density, high strength, and good mechanical properties. By mechanical or chemical treatment, the cellulose fibers can be converted into cellulose nanofibers (CNFs) or cellulose nanocrystals (CNCs) that possess outstanding properties compared with the original cellulosic fiber but also when compared with other materials normally used as reinforcements in composite materials such as Kevlar or steel wires. This review will describe the nanocellulose materials preparation techniques and cellulose sources, chemical modification both on the crystalline surface and during hydrolysis and its many properties and its use in biocomposite materials. Nanocellulose in its different forms shows an increasing interest in application areas such as packaging, paper and paperboard, food industry, medical and hygiene products, paints, cosmetics, and optical sensors.
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| 5. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Increased thermal stability of nanocellulose composites by functionalization of the sulfate groups on cellulose nanocrystals with azetidinium ions
- 2018
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 135:10
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Journal article (peer-reviewed)abstract
- Cellulose nanocrystals (CNCs) prepared via sulfuric acid hydrolysis are decorated with sulfate groups that yield a stable water suspension. To make the CNCs adaptable for use in composites, the hydroxyl groups on the surface are usually hydrophobized. In this article, an alternative hydrophobization method is described in which the sulfate groups are conjugated with azetidinium salts. The results of this study show that the sulfate groups can be functionalized with azetidinium salts and from thermal studies, it was discovered that the functionalization led to a 100 degrees C increase in thermal stability, compared with unmodified CNCs. The nanocomposites prepared by extrusion of CNC-coated low-density polyethylene powder displayed similar mechanical properties as the CNC-reference sample, but without the discoloration, due to the increased thermal stability. In conclusion, the azetidinium reagent reacts preferentially with sulfate groups, and this new type of chemical conversion of sulfate groups on polysaccharides will be beneficial in nanocomposite manufacturing. (C) 2017 Wiley Periodicals, Inc.
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| 6. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Periodate oxidation of xylan-based hemicelluloses and its effect on their thermal properties
- 2018
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 202, s. 280-287
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Journal article (peer-reviewed)abstract
- Hemicellulose from pulp mill process water and crop residuals from food production often end up in waste streams or burnt for energy contribution. These waste products contain valuable biopolymers but lack many attributes needed for use in applications such as food and medical or consumer products. This study reports on an investigation of the periodate oxidation of hardwood xylan and arabinoxylan (AX) from wheat bran to produce materials with new functionalities. The study explores how to control the oxidation degree and describes structural differences between the two xylan-based polymers. For the xylan samples, the oxidation resulted in a lowering of the glass transition temperature (Tg), indicating a more flexible chain due to ring-opening of the xylan anhydro-sugar units. For the AX samples, the arabinose side-groups were instead oxidized, hindering oxidation on part of the xylose units, which resulted in a crosslinked network with an unchanged Tgbut reduced intrinsic viscosity.
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| 7. |
- Börjesson, Mikaela, 1987
(author)
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Radiation crosslinking of cellulose fibers to obtain rigid lightweight paperboard
- 2013
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Licentiate thesis (other academic/artistic)abstract
- Cellulosic materials are used in a wide range of areas of application, and one of these is paperboard for packaging solutions. Paper or paperboard as a packaging material has benefits like low density, low costs, high stiffness, good printability, and paper is environmentally friendly. Compared to other packaging materials, such as plastics, paper has some weaknesses By improving some of its weaknesses, paper as a packaging material, can become more competitive on the market, and knowing how to utilize this resource in a more effective and sustainable way will become increasingly important in the future.One way to decrease the amount of fibers needed in paper and paperboard is by improving the strength properties of cellulose fibers. Greater fiber strength can be achieved by, for example crosslinking the fibers, and crosslinking can be achieved with only a small amount of chemicals. By using electromagnetic radiation, like ultraviolet (UV) radiation, the fibers can be crosslinked with the aid of a UV curing solution. Pretreatment of the fibers through an acrylic esterification reaction may enhance UV curing since polyester and acrylate groups are prone to be more reactive for UV radiation.In this thesis, UV curing of paper sheets with the aid of a UV curing solution is evaluated with tensile tests, microscopy and water retention measurements. Both acrylic esterified paper sheets and non-treated paper sheets are evaluated. Due to acid hydrolysis on the acrylic esterified paper sheets, the non-treated paper sheets showed the highest value in strength properties with a doubled increase in tensile index. Acrylic-acid-modified (AA-modified) sheets showed an increase in tensile index that was four times higher than non-radiated AA-modified sheets, but were weaker overall than the non-treated paper sheets due to the acrylic acid pre- treatment.
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| 8. |
- Börjesson, Mikaela, 1987, et al.
(author)
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Thermoplastic and flexible films from arabinoxylan
- 2019
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In: ACS Applied Polymer Materials. - : American Chemical Society (ACS). - 2637-6105. ; 1:6, s. 1443-1450
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Journal article (peer-reviewed)abstract
- Current interest in replacing fossil-fuel-derivedpolymers and materials in favor of renewable materials is high.An inherent difficulty with the use of biomass-derivedpolysaccharides and hemicelluloses in this context, however,is their stiffness and lack offlowability at temperatures relevantfor thermal processing, which severely limits their capacity forthermal processing. Here, we present a modification thatenables a heat-processable arabinoxylan (AX). The modifica-tion involves a ring-opening oxidation to a dialdehyde withsubsequent reduction of the aldehydes to alcohol, to increasethe number of OH groups, followed by an etherification withhydrophobic alkyl chains. The modified AX was successfullycompression molded with heat intofilmswhich becomethermoplastic in behavior and highlyflexibleandflows at temperatures above 130°C. Thefilms are stretchable up to 200%,and their strength and strain deformation are controlled by the degree of oxidation and substitution of the AX polymer. Thesefindings are highly encouraging and open up the potential use of modified AX alone or as a composite in applications thatincludefilms, food packaging, and barriers via hot-melt processing techniques.
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| 9. |
- Börjesson, Mikaela, 1987, et al.
(author)
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UV radiation of cellulose fibers and acrylic acid modified cellulose fibers for improved stiffness in paper
- 2015
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In: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 10:2, s. 3056-3069
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Journal article (peer-reviewed)abstract
- In this study, the strength and stiffness was measured on paper sheets with and without acryl ester functionalization grafted with UV-reactive molecules. Three different monomers with one, two, and three UV-reactive groups, respectively, were reacted with the unsaturated ester. The tri-functional monomer had the most influence on the strength properties of the three monomers and was added in concentrations of 5 to 20 wt% of paper (0.03-0.11 mol eq./AGU). The strength and stiffness properties were measured with tensile tests. An increase in elongation, tensile index, and Young's modulus was seen after irradiation. However, the paper sheets esterified with acrylic acid prior to radiation showed no improvement in stiffness compared to a non-treated paper. As a result, the esterification with acrylic acid to enhance the grafting effect did not have the ability to compensate for the loss in strength caused by the esterification treatment.
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| 10. |
- Härdelin, Linda, 1977, et al.
(author)
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Altered Thermal and Mechanical Properties of Spruce Galactoglucomannan Films Modified with an Etherification Reaction
- 2020
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 21:5, s. 1832-1840
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Journal article (peer-reviewed)abstract
- Native hemicellulose lacks many of the properties that make fossil fuel-based polymers excellent for use in today's industrial products and processes. The mechanical and thermal properties of the hemicellulose can, however, be modified, and its processability increased. We functionalized galactoglucomannan to lower its glass transition temperature (Tg) and thereby increase its processability. The functionalization was achieved through an etherification reaction with butyl glycidyl ether used at three molar ratios. Films were produced, and their mechanical and thermal properties were evaluated. Thermogravimetric analysis showed that increased substitution increased the degradation temperature and decreased the water content in the sample, implying increased hydrophobicity upon modification. Dynamic mechanical analysis indicated that butyl glycidyl ether functionalization alters the thermal properties of the modified films both in the absolute values of Tg and in the strength of the films. The etherification reaction resulted in a more ductile material than the unmodified galactoglucomannan (GGM).
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