Browsing by Department "Materials Chemistry of Cellulose"

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    Activation of TEMPO by ClO2 for oxidation of cellulose by hypochlorite — Fundamental and practical aspects of the catalytic system
    (2017-06-30) Pääkkönen, Timo; Pönni, Raili; Dou, Jinze; Nuopponen, Markus; Vuorinen, Tapani; Materials Chemistry of Cellulose; Department of Bioproducts and Biosystems; UPM
    Bromide-free TEMPO-catalyzed oxidation of the primary alcohols by sodium hypochlorite (NaOCl) does not proceed without a prior activation of the catalyst. Here were demonstrate an immediate in situ activation of the catalyst with an equimolar addition of chlorine dioxide (ClO2) relative to TEMPO. Sodium bromide (NaBr) had a similar role in activating the catalyst although NaBr was needed in excess and the activation took several minutes depending on the dosage of NaBr. The activation method, or the concentration of NaBr, did not affect the bulk oxidation rate. The selectivity of the ClO2 initiated oxidation remained high up to NaOCl addition of 3 mol/kg bleached birch kraft pulp after which additional loss in yield and depolymerization of cellulose were emphasized with negligible increase in carboxylate content. A carboxylate content of 0.8–1 mol/kg, sufficient for easy mechanical fibrillation of the pulp, was achieved under mild conditions with NaOCl addition of 2-2.5 mol/kg pulp.
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    Humidity Response of Cellulose Thin Films
    (AMERICAN CHEMICAL SOCIETY, 2022-03-14) Reishofer, David; Resel, Roland; Sattelkow, Jürgen; Fischer, Wolfgang J.; Niegelhell, Katrin; Mohan, Tamilselvan; Kleinschek, Karin Stana; Amenitsch, Heinz; Plank, Harald; Tammelin, Tekla; Kontturi, Eero; Spirk, Stefan; Graz University of Technology; VTT Technical Research Centre of Finland; Materials Chemistry of Cellulose; Department of Bioproducts and Biosystems
    Cellulose-water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.
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    Nanocellulose-based mechanically stable immobilization matrix for enhanced ethylene production
    (ROYAL SOC CHEMISTRY, 2021-05-21) Rissanen, V.; Vajravel, S.; Kosourov, S.; Arola, Suvi; Kontturi, E.; Allahverdiyeva, Y.; Tammelin, T.; VTT Technical Research Centre of Finland; University of Turku; Materials Chemistry of Cellulose; Department of Bioproducts and Biosystems
    Cell immobilization is a promising approach to create efficient photosynthetic cell factories for sustainable chemical production. Here, we demonstrate a novel photosynthetic solid-state cell factory design for sustainable biocatalytic ethylene production. We entrapped cyanobacteria within never-dried hydrogel films of TEMPO-oxidized cellulose nanofibers (TCNF) cross-linked with polyvinyl alcohol (PVA) to create a self-standing matrix architecture. The matrix is operational in the challenging submerged conditions and outperforms existing alginate-based solutions in terms of wet strength, long-term cell fitness, and stability. Based on rheological investigations, the critical strength of wet TCNF matrices is three times higher than in the existing immobilization matrices of alginate cross-linked with Ca2+. This is due to the rigid nature of the colloidal nanofiber network and the strong cross-linking with PVA, as opposed to polymeric alginate with reversible ionic Ca2+ bonds. The porous and hygroscopic nanofiber network also shields the cyanobacterial cells from environmental stress, maintaining photosynthetic activity during partial drying of films, and when submerged in the nutrient medium for long-term cultivation. Finally, TCNF matrices allow the ethylene-producing Synechocystis sp. PCC 6803 cells to operate in submerged conditions under high inorganic carbon loads (200 mM NaHCO3), where Ca2+-alginate matrices fail. The latter show severe cell leakage due to matrix disintegration already within 20 min of NaHCO3 supplementation. In contrast, TCNF-based matrices prevent cell leakage to the medium and restrict culture growth, leading to improved ethylene production yields. Furthermore, the operational capacity of the self-standing TNCF cell factory can be maintained long-term by periodically refreshing the nutrient medium. All in all, the results showcase the versatility and potential of cell immobilization with the never-dried colloidal TCNF matrix, paving the way towards novel biotechnological pathways using solid-state cell factories designed for efficient and sustainable production of e.g., monomers and fuels.