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Sökning: WFRF:(Andreasson Håkan) > Mittuniversitetet

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2.
  • From, Malin, et al. (författare)
  • Tuning the properties of regenerated cellulose : Effects of polarity and water solubility of the coagulation medium
  • 2020
  • Ingår i: Carbohydrate Polymers. - : Elsevier Ltd. - 0144-8617 .- 1879-1344. ; 236
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents’ polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications.
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3.
  • Nejström, Malin, et al. (författare)
  • On Structural and Molecular Order in Cellulose Acetate Butyrate Films
  • 2023
  • Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 15:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Cellulose acetate butyrate (CAB) is a possible candidate, being a raw material derived from renewable resources, to replace fossil-based materials. This is due to its thermoplastic properties and the relative ease with which it could be implemented within the existing industry. With a significant amount of variation in CAB on the market today, a knowledge gap has been identified regarding the understanding of the polymer structural arrangement in films. This relates to the underlying mechanisms that regulate CAB film material properties, insights that are important in product development. In this study, commercially available CAB was investigated with XRD, SEM, AFM, and TOPEM DSC in order to obtain physicochemical information related to its micro-structural features in solvent-cast films. The film-forming ability relates mostly to the number of hydroxyl groups, and the semi-crystallinity of the films depends on the type and position of the side groups along the cellulose backbone. The appearance of signs of possible cholesteric ordering in the films could be connected to higher amounts of hydroxyl groups along the backbone that disturb the helix arrangement, while the overall order was primarily related to the butyrate substitution and secondarily related to the molecular weight of the particular CAB studied. Cold crystallization was also observed in one CAB sample.
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4.
  • Nejström, Malin (författare)
  • Structural impact on some physical properties of cellulose-based films
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Cellulose is a natural material that can be used both in its original form and as a building block for creating new types of materials. This work focused on regenerated cellulose (RC) and cellulose acetate butyrate (CAB) in which the hydroxyls on the cellulose backbone were substituted with ester groups. In this work both RC and CAB were formed as free-standing films via initial dissolution and characterized with respect to their structural and morphological aspects, as well as some other material properties. Cellulose pulp was dissolved in cold aqueous alkali urea solution and regenerated in either alcohols or esters to form RC films. Variations of commercially available CAB were dissolved in acetone and solvent cast to form CAB films.This work strove to understand the structural relations of cellulose-based films, the fundamental principles of these materials and how they affect the material properties. This work examined the effect of the polarity of the regeneration liquid on the crystallinity and on other material properties of dried RC films (Papers I and III). This work also investigated the variation in degree of substitution of butyrate and the variation in molecular weight of commercially available CAB and how those could affect the microstructural order of a solvent cast film to the degree that a measurable change in material properties could be observed (Paper II). This was done via structural analysisusing solid-state nuclear magnetic resonance (ss-NMR), x-ray diffraction (XRD), and temperature-modulated differential scanning calorimetry (TOPEM DSC), on RC and CAB films. The qualitative concept of “film formability” was used in this work to determine the practical film properties (related to the ease of handling a film) based on subjective observations.Both the RC films and the CAB films were transparent, with some variations. The CAB films were more fragile than the RC films, even when theCAB films were almost triple the RC films’ thickness. The RC films could be bent considerably, even sharply folded, whereas the CAB films were only slightly bendable before they snapped.The crystallinity of the RC films varied with the regeneration liquid used,and an increase in crystallinity was observed in the following order: EtOH
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  • Resultat 1-4 av 4

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