1,720,967 research outputs found
Polysaccharide thin film studies - Adsorption of oxidized xylan on cellulose [Elektronisk resurs]
No full textWood xylans are renewable natural materials that have potential for future use in bio-based products. However, their high price and low production capacity restrict their industrial use and current applications. This research aimed to explore the potential of wood xylans for film applications. Most xylans extracted from wood do not dissolve in water, which is a common solvent in many industries, such as the pulp and paper industry. Furthermore, bio-based materials are expected to be processed in a green approach, where water is a preferable solvent, and has benefit in terms of low-cost, and being an environmentally benign solvent. The poor water interaction of xylans hinders dissolution and film production, but can be overcome by chemical modification of xylan to alter its properties. Regioselective oxidation—a well-known modification in polysaccharides—can increase the flexibility and water interaction of xylans by opening their monosaccharide ring and equipping them with aldehyde groups. The research employed quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) to study the adsorption of macromolecules on film surfaces. The analytical combination was first established for studying protein adsorption on cellulose film with different morphology, and structure, and then oxidized xylan adsorption on nanocellulose films, which was the focus of this research. The influence of the molecular weight of oxidized xylan on adsorption in aqueous conditions, and its effect on film swelling were explored. The behavior of oxidized xylan in solution was observed using dynamic light scattering, showing that high molecular weight oxidized xylan formed larger aggregates when the concentration increased compared to low molecular weight oxidized xylan. The QCM-D and SPR investigations revealed that a high molecular weight grade adsorbed preferentially on a neutral cellulose surface, while both grades were adsorbed independently of molecular weight on a negatively charged surface. The impact of oxidized xylan on the swelling of cellulose films, regardless of molecular weight, was due to oxidized xylan bringing more water to the non-charged films, while the opposite was true of negatively charged films. Also, applying the combination of QCM-D and SPR techniques to oxidized xylan adsorption on cellulose, water content and adsorbed dry mass were obtained. This study provides a stepping-stone toward the future use of bio-based materials obtained from forest sources
Wood xylan and modified xylan - Solubilization, film formation and water interactions
Full text linkWood xylans are biopolymers that are valuable for future materials and renewable engineering solutions. In this study, xylan solubility in polar solvents and film formation were investigated. Most wood xylans are poorly soluble in polar solvents, such as water, and this can be a critical hindrance for facilitating new uses of xylan, especially in solution-based processes. Modification via oxidation using sodium periodate was selected as a potential prospect to improve xylan solubility. The influence of modification, such as the degree of oxidation, was investigated using solutions and thin films. Surface-sensitive analytics were used to quantify the properties of modified xylan as films and film additives, with a focus on their interaction with water. Furthermore, a correlation between film morphology and material solubility of modified xylan and unmodified xylan in blend systems was observed using atomic force microscopy. The findings expand the possibility of utilizing wood xylan in solution-based processes
Wood xylan and modified xylan - Solubilization, film formation and water interactions [Elektronisk resurs]
No full textWood xylans are biopolymers that are valuable for future materials and renewable engineering solutions. In this study, xylan solubility in polar solvents and film formation were investigated. Most wood xylans are poorly soluble in polar solvents, such as water, and this can be a critical hindrance for facilitating new uses of xylan, especially in solution-based processes. Modification via oxidation using sodium periodate was selected as a potential prospect to improve xylan solubility. The influence of modification, such as the degree of oxidation, was investigated using solutions and thin films. Surface-sensitive analytics were used to quantify the properties of modified xylan as films and film additives, with a focus on their interaction with water. Furthermore, a correlation between film morphology and material solubility of modified xylan and unmodified xylan in blend systems was observed using atomic force microscopy. The findings expand the possibility of utilizing wood xylan in solution-based processes
Polysaccharide thin film studies - Adsorption of oxidized xylan on cellulose
Full text linkWood xylans are renewable natural materials that have potential for future use in bio-based products. However, their high price and low production capacity restrict their industrial use and current applications. This research aimed to explore the potential of wood xylans for film applications. Most xylans extracted from wood do not dissolve in water, which is a common solvent in many industries, such as the pulp and paper industry. Furthermore, bio-based materials are expected to be processed in a green approach, where water is a preferable solvent, and has benefit in terms of low-cost, and being an environmentally benign solvent. The poor water interaction of xylans hinders dissolution and film production, but can be overcome by chemical modification of xylan to alter its properties. Regioselective oxidation—a well-known modification in polysaccharides—can increase the flexibility and water interaction of xylans by opening their monosaccharide ring and equipping them with aldehyde groups. The research employed quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) to study the adsorption of macromolecules on film surfaces. The analytical combination was first established for studying protein adsorption on cellulose film with different morphology, and structure, and then oxidized xylan adsorption on nanocellulose films, which was the focus of this research. The influence of the molecular weight of oxidized xylan on adsorption in aqueous conditions, and its effect on film swelling were explored. The behavior of oxidized xylan in solution was observed using dynamic light scattering, showing that high molecular weight oxidized xylan formed larger aggregates when the concentration increased compared to low molecular weight oxidized xylan. The QCM-D and SPR investigations revealed that a high molecular weight grade adsorbed preferentially on a neutral cellulose surface, while both grades were adsorbed independently of molecular weight on a negatively charged surface. The impact of oxidized xylan on the swelling of cellulose films, regardless of molecular weight, was due to oxidized xylan bringing more water to the non-charged films, while the opposite was true of negatively charged films. Also, applying the combination of QCM-D and SPR techniques to oxidized xylan adsorption on cellulose, water content and adsorbed dry mass were obtained. This study provides a stepping-stone toward the future use of bio-based materials obtained from forest sources
Current opportunities and challenges in biopolymer thin film analysis–determination of film thickness
Full text linkPolymer thin films with thickness below 100\ua0nm are a fascinating class of 2D materials with commercial and research applications in many branches ranging from coatings to photoresists and insulating materials, to mention just a few uses. Biopolymers have extended the scope of polymer thin films with unique materials such as cellulose, cellulose nanocrystals, cellulose nanofibrils with tunable water uptake, crystallinity and optical properties. The key information needed in thin biopolymer film use and research is film thickness. It is often challenging to determine precisely and hence several techniques and their combinations are used. Additional challenges with hydrophilic biopolymers such as cellulose are the presence of humidity and the soft and often heterogenous structure of the films. This minireview summarizes currently used methods and techniques for biopolymer thin film thickness analysis and outlines challenges for accurate and reproducible characterization. Cellulose is chosen as the representative biopolymer
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Oxidized xylan additive for nanocellulose films – A swelling modifier
Full text linkPolymeric wood hemicelluloses are depicted to join cellulose, starch and chitosan as key polysaccharides for sustainable materials engineering. However, the approaches to incorporate hemicelluloses in emerging bio-based products are challenged by lack of specific benefit, other than the biomass-origin, although their utilization would contribute to sustainable material use since they currently are a side stream that is not valorized. Here we demonstrate wood-xylans as swelling modifiers for neutral and charged nanocellulose films that have already entered the sustainable packaging applications, however, suffer from humidity sensitivity. The oxidative modification is used to modulate the water-solubility of xylan and hence enable adsorption in an aqueous environment. A high molecular weight grade, hence less water-soluble, adsorbed preferentially on the neutral surface while the adsorbed amount on a negatively charged surface was independent of the molecular weight, and hence, solubility. The adsorption of the oxidized xylans on a neutral cellulose surface resulted in an increase in the amount of water in the film while on the negatively charged cellulose the total amount of water decreased. The finding of synergy of two hygroscopic materials to decrease swelling in hydrophilic bio-polymer films demonstrates the oxidized macromolecule xylan as structurally functional component in emerging cellulose products
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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