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  • 51.
    Larsson, Per A.
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Riazanova, Anastasiia
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Ciftci, Goksu Cinar
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Rojas, Ramiro
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Ovrebo, Hans Henrik
    Wågberg, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Berglund, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Towards optimised size distribution in commercial microfibrillated cellulose: a fractionation approach2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 3, s. 1565-1575Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For the successful commercialisation of microfibrillated cellulose (MFC) it is of utmost importance to carefully characterise the constituent cellulose particles. This could for instance lead to the development of MFC grades with size distributions tailored for specific applications. Characterization of MFC is challenging due to the heterogeneous chemical and structural nature of MFC. This study describes a fractionation approach that combines two steps of physical sieving of larger particles and a final centrifugation step to separate out the smallest, colloidally stable particles, resulting in four distinctly different size fractions. The properties, such as size and charge, of each fraction were studied, as well as MFC filtration time, film formation, and film properties (mechanical and optical). It was found that virtually all surface charges, determined by polyelectrolyte adsorption, are located in the colloidally stable fraction of the MFC. In addition, the amount of available surface charges can be used as an estimate of the degree of fibrillation of the MFC. The partly fibrillated particles frequently displayed a branching, fringed morphology. Mechanical testing of films from the different fractions revealed that the removal of large particles may be more important for strength than achieving full fibrillation. Overall, this study demonstrates that by controlling the size distribution in MFC grades, property profiles including dewatering time to make films by filtration, rheology, film strength and optical transmittance could be optimised. [GRAPHICS] .

  • 52.
    Larsson, Per A.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Diffusion-induced dimensional changes in papers and fibrillar films: influence of hydrophobicity and fibre-wall cross-linking2010Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 17, nr 5, s. 891-901Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial dimensional stability of paper measured as hydroexpansion, i.e. when paper is exposed to liquid water, has been considerably improved by combining a periodate-oxidation-induced cross-linking of the fibre wall with the subsequent adsorption of a hydrophobic polyelectrolyte multilayer consisting of three layers of poly(allylamine hydrochloride) and two layers of poly(acrylic acid). This reduced the rate of diffusion of water into the fibre wall at the same time as the diffusion distance was increased, i.e. the water has to diffuse all the way from the top of the sheet and not only from the individual fibre surfaces since capillary absorption was prevented. However, as a consequence, the hydrophobic sheets present a greater expansion maximum before contraction. It is suggested that this may be due to a higher moisture content in the top fibre layers of the hydrophobically modified papers than in the hydrophilic sheets, since all the water is concentrated to the top fibre layers of the hydrophobic papers. Sheets made from bleached kraft pulp or thermo-mechanical pulp as well as model sheets made from microfibrillated cellulose (MFC) were studied. The MFC-sheets were intended as a model of the fibre wall, i.e. a sheet without any fibre joints. The behaviour of the MFC-sheets was similar to that of ordinary sheets when subjected to water, which indicates that the properties of the fibre joints do not affect the hydroexpansion to any great content and that the expansion of the paper is directly linked to the expansion of the fibre wall.

  • 53.
    Larsson, Per A.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Influence of fibre-fibre joint properties on the dimensional stability of paper2008Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 15, nr 4, s. 515-525Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements have been performed to clarify the connection between fibre-fibre joint properties and dimensional stability using laboratory sheets prepared from never-dried fibres, from heavily hornified fibres having a low molecular contact area between the fibres, and from both hornified and never-dried fibres treated with a polyelectrolyte multilayer (PEM) technique to increase the molecular contact area in the fibre-fibre joint. The influence of the drying mode, i.e. whether the sheets are dried freely or under restraint, was also evaluated. The results showed that neither paper strength nor fibre-fibre joint contact area had any significant influence on the dimensional stability of sheets dried under restraint. On the other hand, when the sheets were dried freely, the PEM-treated sheets expanded to the same extent as, or to an even greater extent than the non-PEM-treated sheets, even though they adsorbed less water for a given change in relative humidity. There was also a correlation between drying shrinkage and dimensional stability, where greater shrinkage was associated with a greater hygroexpansion in the freely dried sheets.

  • 54.
    Larsson, Per Tomas
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Svensson, Anna
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls2013Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, nr 2, s. 623-631Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state.

  • 55.
    Le Normand, Myriam
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Träkemi och massateknologi.
    Moriana, Rosana
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Träkemi och massateknologi.
    Ek, Monica
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Träkemi och massateknologi.
    The bark biorefinery: a side-stream of the forest industry converted into nanocomposites with high oxygen-barrier properties2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 6, s. 4583-4594Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of the bark biorefinery concept is to upgrade the different constituents present in bark to multiple value-added bio-based products. Non-cellulosic polysaccharides (NCP) and cellulose nanocrystals (CNC) sequentially isolated from the inner bark of Norway spruce were used as raw materials for the formulation of renewable nanocomposites. The film formation abilities of NCP/CNC formulations prepared with different proportions of CNC were studied. Homogeneous transparent films with a glossy appearance were obtained when more than 30 wt% CNC was incorporated. The influence of the CNC content on the NCP/CNC films was assessed in terms of structural, thermal, mechanical and oxygen-barrier properties. All the films showed better performances with increasing CNC content, which was explained by the strong interactions between the two components. The effect on the film performances of adding sorbitol as a plasticizer was also evaluated. The presence of sorbitol decreased the thermal stability, the stiffness and the oxygen permeability of the films at 80 % RH. However, the addition of sorbitol enhanced the elongation of the films and further improved their oxygen-barrier properties at 50 % RH. The composite properties could thus be tailored by adding different amounts of sorbitol and CNC, resulting in all-carbohydrate materials with performances similar to or even better than the conventional barrier materials used in packaging.

  • 56.
    Lindh, Erik L.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Salmén, Lennart
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Surface accessibility of cellulose fibrils studied by hydrogen-deuterium exchange with water2016Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 1, s. 21-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A problem with cellulose-based materials is that they are highly influenced by moisture, leading to reduced strength properties with increasing moisture content. By achieving a more detailed understanding of the water–cellulose interactions, the usage of cellulose-based materials could be better optimized. Two different exchange processes of cellulose hydroxyl/deuteroxyl groups have been monitored by transmission FT-IR spectroscopy. By using line-shape-assisted deconvolution of the changing intensities, we have been able to follow the exchange kinetics in a very detailed and controlled manner. The findings reveal a hydrogen exchange that mainly is located at two different kinds of fibril surfaces, where the differences arise from the water accessibility of that specific surface. The slowly accessible regions are proposed to be located between the fibrils inside of the aggregates, and the readily accessible regions are suggested to be at the surfaces of the fibril aggregates. It was also possible to identify the ratio of slowly and readily accessible surfaces, which indicated that the average aggregate of cotton cellulose is built up by approximately three fibrils with an assumed average size of 12 × 12 cellulose chains. Additionally, the experimental setup enabled visualizing and discussing the implications of some of the deviating spectral features that are pronounced when recording FT-IR spectra of deuterium-exchanging cellulose: the insufficient red shift of the stretching vibrations and the vastly decreasing line widths.

  • 57.
    Lindström, Stefan
    et al.
    Linköping University, Sweden.
    Karabulut, Erdem
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Sehaqui, Houssine
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Mechanosorptive creep in nanocellulose materials2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 3, s. 809-819Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate, it is shown that mechanosorptive creep is not significantly affected by the through-thickness moisture gradient. It is also shown that cellulose nanofibril aerogels with high porosity display the same accelerated creep as films. Microstructures larger than the fibril diameter thus appear to be of secondary importance to mechanosorptive creep in nanocellulose materials, suggesting that the governing mechanism is found between molecular scales and the length-scales of the fibril diameter.

  • 58. Liu, Jun
    et al.
    Korpinen, Risto
    Mikkonen, Kirsi S.
    Willfor, Stefan
    Xu, Chunlin
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. Process Chemistry Centre, c/o Laboratory Wood and Paper Chemistry, Åbo Akademi University, Finland.
    Nanofibrillated cellulose originated from birch sawdust after sequential extractions: a promising polymeric material from waste to films2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 4, s. 2587-2598Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The residual cellulose of wood processing waste, sawdust, which was leftover after sequential hot-water extraction processes to isolate hemicelluloses and lignin in a novel forest biorefinery concept, was explored as the starting material for preparation of a highly value-added polymeric material, nanofibrillated cellulose (NFC) also widely termed as cellulose nanofiber, which has provided an alternative efficient way to upgrade sawdust waste. The residual cellulose in sawdust was converted to a transparent NFC suspension in water through the 2,2,6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaBr oxidization approach. The resultant NFC with a dimension of ca. 5 nm in width and hundreds of nanometers in length were further processed into NFC films. The morphological features of the NFC suspension and its films were assessed by transmission electron microscopy and scanning electron microscopy. Highly even dispersion of NFC fibrils in the films originated from sawdust feasibly contributes to the outstanding mechanical performance of the films. NFC suspension with higher carboxylate content and its resultant NFC films were found to show higher transmission of light.

  • 59.
    Liu, Yingxin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. Stockholm Univ, Sweden.
    Gordeyeva, Korneliya
    Bergstrom, Lennart
    Steady-shear and viscoelastic properties of cellulose nanofibril-nanoclay dispersions2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 4, s. 1815-1824Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the steady-shear and viscoelastic properties of composite dispersions of cellulose nanofibrils (CNFs) with medium or high charge density and two different nanoclays, viz. rodlike sepiolite or plate-like bentonite. Aqueous dispersions of CNFs with medium charge density displayed significantly lower steady-state viscosity and storage modulus but higher gelation threshold compared with CNFs with high charge density. Dynamic light scattering (DLS) results showed that the apparent hydrodynamic radius of bentonite particles increased when CNFs were added, implying that CNFs adsorbed onto the amphoteric edges of the plate-like bentonite particles. The sepiolite network in CNF-sepiolite dispersions was relatively unaffected by addition of small amounts of CNFs, and DLS showed that the hydrodynamic radius of sepiolite did not change when CNFs were added. Addition of CNFs at concentrations above the gelation threshold resulted in drastic decrease of the steady-shear viscosity of the sepiolite dispersion, suggesting that the sepiolite network disintegrates and the rod-like clay particles are aligned also at low shear rate. The relative change in the rheological properties of the clay-based dispersions was always greater on addition of CNFs with high compared with medium charge density. This study provides insight into how the rheology of CNF-nanoclay dispersions depends on both the nanoclay morphology and the interactions between the nanoclay and nanocellulose particles, being of relevance to processing of nanocellulose-clay composites.

  • 60.
    López Durán, Vernica
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Larsson, Per A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    On the relationship between fibre composition and material properties following periodate oxidation and borohydride reduction of lignocellulosic fibres2016Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 23, nr 6, s. 3495-3510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Periodate oxidation followed by borohydride reduction was performed on four structurally different pulp fibres to clarify the effect of chemical composition on the structural and mechanical properties of sheets made from these fibres. The main purpose was to explore the possibility of extending the use of lignocellulose fibres in novel applications. The degree of oxidation, morphological changes, chemical and physical structure of the fibres, the supramolecular ordering of the cellulose and the mechanical performance of handsheets made from the fibres were studied. The results showed that both periodate oxidation and borohydride reduction are more reactive towards the carbohydrates of the fibres and as a result, there is an improvement in the tensile properties of the sheets. If the carbohydrates of the fibres are only periodate oxidised to produce dialdehydes, inter- and intra-fibre crosslinks can be formed, leading to paper with increase strength and higher stiffness. The borohydride reduction results in fibres and papers with a greater strength and ductility. It was also found that the characteristic ductility of these modified papers, emanating from the dialcohol cellulose produced, is limited with lignin-rich fibres.

  • 61.
    Magnusson, Mikael S.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Östlund, Sören
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Numerical evaluation of interfibre joint strength measurements in terms of three-dimensional resultant forces and moments2013Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, nr 4, s. 1691-1710Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interfibre joint is one of the key elements in creating the strength of self-binding fibrous materials such as paper and board. In order evaluate the strength properties of interfibre joints using direct measurements, a greater understanding on how the mode of loading influences the results is desirable. The methods reported in the literature do not in general distinguish between the contributions of normal and shear stresses in the bonded region. This paper presents a numerical analysis procedure, based on the finite element method, for evaluating interfibre joint strength measurements in terms of the normal, shear, and moment loading components during testing. The target is to estimate the resultant forces and moments, that acts in the interfibre joint region at rupture, of Kraft pulp interfibre joints tested under two principally different modes of loading. The results show that for a typical interfibre joint test, modes of loading other than pure shear cannot, in general, be neglected, and are strongly dependent on the structural geometry of the fibre-fibre crosses. In addition, the resultant forces and moments were scaled in terms of the interface area and the twisting and bending resistance of the interface approximated as an ellipse to account for differences in interface area between the measurements. These scaled resultants were used to quantify how the mode of loading influences the relation between the amount of normal stress and the amount of shear stress that develop in the interfibre joint.

  • 62.
    Marais, Andrew
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Magnusson, Mikael S.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Joffre, Thomas
    Wernersson, Erik L. G.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    New insights into the mechanisms behind the strengthening of lignocellulosic fibrous networks with polyamines2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 6, s. 3941-3950Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyelectrolytes have been used extensively in the papermaking industry for various purposes. Although recent studies have shown that polyamines can be efficient dry-strength additives, the mechanism governing the strength enhancement of paper materials following the adsorption of polyamines onto pulp fibres is still not well understood. In this study, the effect of the adsorption of polyallylamine hydrochloride (PAH) onto the surface of unbleached kraft pulp fibres was investigated on both the fibre and the network scale. Isolated fibre crosses were mechanically tested to evaluate the impact of the chemical additive on the interfibre joint strength on the microscopic scale and the effect was compared with that previously observed on the paper sheet scale. X-ray microtomography was used to understand structural changes in the fibrous network following the adsorption of a polyamine such as PAH. Using image analysis methods, it was possible to determine the number of interfibre contacts (or joints) per unit length of fibre as well as the average interfibre joint contact area. The results showed that the median interfibre joint strength increased by 18 % upon adsorption of PAH. This can be achieved both by a larger molecular contact area in the contact zones and by a stronger molecular adhesion. The addition of the polymer also increased the number of efficient interfibre contacts per sheet volume. This combination of effects is the reason why polyamines such as PAH can increase the dry tensile strength of paper materials.

  • 63.
    Marais, Andrew
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    The use of polymeric amines to enhance the mechanical properties of lignocellulosic fibrous networks2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 4, s. 1437-1447Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cationic polyelectrolytes (polyallylamine and polyvinylamine with different molecular masses) were adsorbed onto lignocellulosic fibres from unbleached and unbeaten spruce chemical fibres with different kappa numbers to investigate the effects on the mechanical properties of the final paper materials. Adsorption isotherms were first established to determine the maximum quantity of polymer that could be adsorbed onto each type of fibre. Paper sheets were then made with different amounts of added polyelectrolyte, and the structural and mechanical properties of the sheets were investigated, as well as the effect of an extra heating. The use of fibres with different kappa numbers led to different responses in terms of adsorption, and thus to differences in the mechanical properties of the resulting sheets. The tensile strength index was significantly increased (almost 50 % improvement in the best case) as a consequence of this polyelectrolyte adsorption onto the fibres, even at as low an adsorption level as 2 mg/g. The heating of paper sheets for 10 min at 160 A degrees C was also shown to improve the tensile strength index by about 10 % for pulps with high kappa number.

  • 64. Martinez-Sanz, Marta
    et al.
    Olsson, Richard T.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Lopez-Rubio, Amparo
    Lagaron, Jose M.
    Development of electrospun EVOH fibres reinforced with bacterial cellulose nanowhiskers. Part I: Characterization and method optimization2011Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 18, nr 2, s. 335-347Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, hybrid electrospun EVOH fibres reinforced with bacterial cellulose nanowhiskers (BCNW) were developed and characterized. The nanowhiskers, obtained by sulphuric acid digestion of native bacterial cellulose mats generated by Gluconacetobacter xylinum, were morphologically characterized by SEM and optical microscopy with polarized light and revealed a highly crystalline structure of nanofibrils aggregates. XRD analyses suggested a crystalline structure corresponding to the cellulose I allomorph. It was also confirmed by means of FT-IR spectroscopy that amorphous regions were preferentially digested by the acid treatment, whereas TGA analyses showed a decrease in the thermal stability of the nanowhiskers most likely due to incorporation of sulphate groups and the inherent acidity remaining in the filler even after extensive washing cycles. A method was developed for improving the incorporation of BCNW within the EVOH electrospun fibres, consisting on the addition of the BCNW in the form of a centrifuged precipitate, versus the most conventionally employed freeze-dried nanowhiskers. DSC analyses showed a significant increase in the glass transition temperature of the composites during the second heating run, which may be related to the acidic character of the nanofiller. Finally, sonication was seen to enhance interfacial interaction but to reduce the incorporation of the filler in the matrix in the case of the centrifuged material.

  • 65. Mikkonen, K. S.
    et al.
    Mathew, A. P.
    Pirkkalainen, K.
    Serimaa, R.
    Xu, Chunlin
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap. Åbo Akademi University.
    Willför, S.
    Oksman, K.
    Tenkanen, M.
    Glucomannan composite films with cellulose nanowhiskers2010Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 17, nr 1, s. 69-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spruce galactoglucomannans (GGM) and konjac glucomannan (KGM) were mixed with cellulose nanowhiskers (CNW) to form composite films. Remarkable effects of CNW on the appearance of the films were detected when viewed with regular and polarizing optical microscopes and with a scanning electron microscope. Addition of CNW to KGM-based films induced the formation of fiberlike structures with lengths of several millimeters. In GGM-based films, rodlike structures with lengths of several tens of micrometers were formed. The degree of crystallinity of mannan in the plasticized KGM-based films increased slightly when CNW were added, from 25 to 30%. The tensile strength of the KGM-based films not containing glycerol increased with increasing CNW content from 57 to 74 MPa, but that of glycerol-plasticized KGM and GGM films was not affected. Interestingly, the notable differences in the film structure did not appear to be related to the thermal properties of the films.

  • 66. Moberg, Tobias
    et al.
    Sahlin, Karin
    Yao, Kun
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Geng, Shiyu
    Westman, Gunnar
    Zhou, Qi
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Oksman, Kristiina
    Rigdahl, Mikael
    Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 6, s. 2499-2510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.

  • 67.
    Moriana, Rosana
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Träkemi och massateknologi.
    Vilaplana, Francisco
    Ek, Monica
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Träkemi och massateknologi.
    Forest residues as renewable resources for bio-based polymeric materials and bioenergy: chemical composition, structure and thermal properties2015Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, nr 5, s. 3409-3423Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential of three different logging residues (woody chips, branches and pine needles) as renewable resources to produce environmentally friendly polymeric materials and/or biofuel has been critically evaluated in terms of their structure, chemical composition and thermal properties. Woody chips constitute the most attractive forest residue to be processed into polymeric materials in terms of their highest cellulose content, crystallinity and thermal stability. In contrast, pine needles and branches offer higher heating values and optimum product distribution for solid fuel applications due to their higher lignin content. In general, forest residual biomass has great potential for conversion into new added value products, such as composites or solid biofuel, thus constituting a sustainable waste management procedure from a biorefinery perspective. The correlation between the chemical and structural properties with the thermal/pyrolytic behavior of residual biomass offers valuable insights to assess their sustainable exploitation.

  • 68.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). Graz Univ Technol, CD Lab Fiber Swelling & Paper Performance, Inffeldgasse 23, A-8010 Graz, Austria.
    Halilovic, Armin
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). Graz Univ Technol, CD Lab Fiber Swelling & Paper Performance, Inffeldgasse 23, A-8010 Graz, Austria.
    Mechanisms of strength and stiffness improvement of paper after PFI refining with a focus on the effect of fines2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 6, s. 4099-4124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Refining (i.e., mechanical beating of pulp) is a common procedure that is used in paper-making to improve the mechanical properties of the final product. The improvements caused by refining are mainly attributed to increased density and to a better bonding between fibers. In this work, we study how various mechanisms that can be triggered by refining affect the tensile behavior of the sheets. Consequently, we use direct numerical simulations of fiber networks. We relate our finding to the experimental measurements that we conducted on handsheets. We have found that fibrillar fines with size distributions below the resolution of modern state-of-the art pulp characterization tools have a substantial contribution to the increased strength and stiffness of the sheets.

  • 69.
    Naderi, Ali
    et al.
    Innventia AB, Drottning Kristinasv 61, S-11486 Stockholm, Sweden..
    Larsson, Per Tomas
    Innventia AB, Drottning Kristinasv 61, S-11486 Stockholm, Sweden..
    Stevanic, Jasna S.
    Innventia AB, Drottning Kristinasv 61, S-11486 Stockholm, Sweden..
    Lindström, Tom
    Innventia AB, Drottning Kristinasv 61, S-11486 Stockholm, Sweden..
    Erlandsson, Johan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Effect of the size of the charged group on the properties of alkoxylated NFCs2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 3, s. 1307-1317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impact of the size of the charged group on the properties of alkoxylated NFC was studied by two chloroalkyl acid reagents. It was found that the employment of the larger 2-chloropropionic acid reagent leads to improved properties, e.g. higher fraction of nano-sized materials, and significantly better redispersion as compared to when the smaller monochloroacetic acid was employed. The differences in the impacts of the different reagents were hypothesized to be due to a more efficient disruption of the cohesion between the nanofibrils when a larger charged group was employed.

  • 70. Naderi, Ali
    et al.
    Lindstrom, Tom
    Pettersson, Torbjorn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    The state of carboxymethylated nanofibrils after homogenization-aided dilution from concentrated suspensions: a rheological perspective2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 4, s. 2357-2368Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological properties of a carboxymethylated (D. S. & 0.1) nanofibrillated cellulose (NFC) were investigated at different solid contents. The critical overlap concentration was determined to be in the range between 0.04 and 0.07 % (w/w) using shear stress versus shear rate measurements. From the critical overlap concentration using the simple Mason excluded volume formalism, the apparent aspect ratio was estimated to be 75 [ at a critical overlap concentration of 0.04 % (w/w)]. The aspect ratio of the NFC system was also estimated by using the EinsteinSimha equation together with the intrinsic viscosity value of the system (corrected for the electroviscous effects). The obtained value was found to be around 80, which is in good agreement with the value obtained from the excluded volume calculation. Further, by combining oscillatory measurements and the equation of Shankar et al. the apparent fibril length was determined to be 4 mu m. As the production of NFC through homogenization occurs at concentrations far above the critical overlap concentration an NFC-gel is constituted by a severely entangled structure. The disentanglement of the fibrils is therefore difficult and the employed dilution method was found not to lead to fully liberated nanofibrils, which was also indicated by atomic force microscopy-imaging.

  • 71. Naderi, Ali
    et al.
    Lindström, Tom
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Centrum för Biofibermaterial, BiMaC.
    Sundstrom, Jonas
    Carboxymethylated nanofibrillated cellulose: rheological studies2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 3, s. 1561-1571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological properties of carboxymethylated nanofibrillated cellulose (NFC), investigated with controlled shear rate- and oscillatory measurements, are reported for the first time. It was shown that the rheological properties of the studied system are similar to those reported for other NFC systems. The carboxymethylated NFC systems showed among other things high elasticity and a shear thinning behaviour when subjected to increasing shear rates. Further, the shear viscosity and storage modulus of the system displayed power-law relations with respect to the dry content of the NFC suspension. The exponential values, 2 and 2.4 respectively, were found to be in good agreement with both theoretical predictions and published experimental work. Furthermore, it was found that the pulp consistency at which NFC is produced affects the properties of the system. The rheological studies imply that there exists a critical pulp concentration below which the efficiency of the delamination process diminishes; the same adverse effect is also observed when the critical concentration is significantly exceeded due to a lower energy input during delamination.

  • 72. Naderi, Ali
    et al.
    Lindström, Tom
    Sundström, Jonas
    Pettersson, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Flodberg, Göran
    Erlandsson, Johan
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Microfluidized carboxymethyl cellulose modified pulp: a nanofibrillated cellulose system with some attractive properties2015Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, nr 2, s. 1159-1173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method (Ankerfors and Lindstrom in Method for providing nanocellulose comprising modified cellulose fibers, 2009) was employed to physically attach anionic carboxymethyl cellulose (CMC) chains onto wood pulp, upon which it was fibrillated by a microfluidizer-type homogenizer at high applied pressures and at dilute conditions [< 3 % (w/w)]. It was found that the CMC-modified pulp can be fibrillated at the same consistencies as many of the commercially available NFC products. The NFC manufacturing process was also deemed to be energy efficient, as it lacked the need for mechanical pre-treatment, which is often a prerequisite for the production of many existing NFC systems. The CMC-based NFC was studied with respect to the rheological characteristics, and was also characterized using AFM-imaging. Further, The NFC was made into films, and its tensile strength was determined together with its barrier properties. In general, the rheological characteristics (viscosity and storage modulus) together with the tensile strength and oxygen barrier properties of the films were improved with increasing the number of passes through the microfluidizer. The fibrillated CMC-modified pulp was found to be as efficient as other NFC systems when employed as dry strength additive. The employment of the investigated material, which can be produced at acceptable costs and through environmentally benign and industrially relevant processes can, hence, potentially lead to significant future savings in the energy consumption levels in the paper and cardboard manufacturing processes, which have been recognized as major application areas of NFC products.

  • 73.
    Nilsson, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Galland, Sylvain
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Biokompositer. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Larsson, Per Tomas
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Gamstedt, E. Kristofer
    Uppsala University.
    Iversen, Tommy
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Compression molded wood pulp biocomposites: A study of hemicellulose influence on cellulose supramolecular structure and material properties2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 3, s. 751-760Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.

  • 74.
    Nyström, Gustav
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Fall, Andreas
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Carlsson, Linn
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Aligned Cellulose Nanocrystals and Directed Nanoscale Deposition of Colloidal Spheres2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 3, s. 1591-1599Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose nanocrystals are aligned in wrinkled polydimethylsiloxane templates and transferred to polyethyleneimine-coated silica surfaces in a printing process similar to microcontact printing. The highly aligned nanorods were deposited onto the surfaces with a line-to-line distance of 225-600 nm without loss of alignment. It was also possible to repeat the transfer process on the same surface at a 90-degree angle to create a network structure. This demonstrates the versatility of the technique and creates more options for advanced multilayering of materials. To demonstrate that the surface properties of the anionic cellulose nanorods were unaffected by the transfer process and to prove the concept of functionalizing transferred particles, cationic latex particles were electrostatically self-assembled onto the cellulose nanorods. The directed deposition of these particles resulted in excellent site specificity and the highest resolution to date for controlled deposition of colloids on an electrostatically patterned surface.

  • 75.
    Ottenhall, Anna
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Träkemi och massateknologi.
    Seppänen, Tiinamari
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Ek, Monica
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Water-stable cellulose fiber foam with antimicrobial properties for bio based low-density materials2016Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 5, s. 2599-2613Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New bio-based packaging materials are highly interesting for replacing conventional fossil based products for a more sustainable society. Water-stable cellulose fiber foams have been produced in a simple one-batch foam-forming process with drying under ambient conditions. The cellulose fiber foams have a low density (33–66 kg/m3) and can inhibit microbial growth; two highly valuable features for insulating packaging materials, especially in combination with stability in water. Cationic chitosan and/or polyvinylamine have been added during the foam-forming process to give the foams water-stability and antimicrobial properties. The structural and mechanical properties of the cellulose fiber foams have been studied and the antimicrobial properties have been evaluated with respect to both Escherichia coli, a common model bacteria and Aspergillus brasiliensis, a sporulating mold. The cellulose foams containing chitosan had both good water-stability and good antibacterial and antifungal properties, while the foams containing PVAm did disintegrate in water and did not inhibit fungal growth when nutrients were added to the foam, showing that it is possible to produce a bio-based foam material with the desired characters. This can be an interesting low-density packaging material for protection from both mechanical and microbial damage without using any toxic compounds.

  • 76.
    Ottenhall, Anna
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Seppänen, Tiinamari
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Ek, Monica
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Water-stable cellulose fiber foam with antimicrobial properties for bio based low-density materials2018Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, nr 4, s. 2599-2613Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New bio-based packaging materials are highly interesting for replacing conventional fossil based products for a more sustainable society. Water-stable cellulose fiber foams have been produced in a simple one-batch foam-forming process with drying under ambient conditions. The cellulose fiber foams have a low density (33–66 kg/m3) and can inhibit microbial growth; two highly valuable features for insulating packaging materials, especially in combination with stability in water. Cationic chitosan and/or polyvinylamine have been added during the foam-forming process to give the foams water-stability and antimicrobial properties. The structural and mechanical properties of the cellulose fiber foams have been studied and the antimicrobial properties have been evaluated with respect to both Escherichia coli, a common model bacteria and Aspergillus brasiliensis, a sporulating mold. The cellulose foams containing chitosan had both good water-stability and good antibacterial and antifungal properties, while the foams containing PVAm did disintegrate in water and did not inhibit fungal growth when nutrients were added to the foam, showing that it is possible to produce a bio-based foam material with the desired characters. This can be an interesting low-density packaging material for protection from both mechanical and microbial damage without using any toxic compounds.

  • 77.
    Ottesen, Vegar
    et al.
    NTNU, Dept Chem Engn, Trondheim, Norway..
    Larsson, Per Tomas
    KTH.
    Chinga-Carrasco, Gary
    Rise PFI, Trondheim, Norway..
    Syverud, Kristin
    NTNU, Dept Chem Engn, Trondheim, Norway.;Rise PFI, Trondheim, Norway..
    Gregersen, Oyvind Weiby
    NTNU, Fac Nat Sci, Trondheim, Norway..
    Mechanical properties of cellulose nanofibril films: effects of crystallinity and its modification by treatment with liquid anhydrous ammonia2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 11, s. 6615-6627Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of cellulose crystallinity on mechanical properties of cellulose nano-fibrils (CNF) was investigated. Degree of crystallinity (DoC) was modified using liquid anhydrous ammonia. Such treatment changes crystal allomorph from cellulose I to cellulose III, a change which was reversed by subsequent boiling in water. DoC was measured using solid state nuclear magnetic resonance (NMR). Crystalline index (CI) was also measured using wide angle X-ray scattering (WAXS). Cotton linters were used as the raw material. The cotton linter was ammonia treated prior to fibrillation. Reduced DoC is seen to associate with an increased yield point and decreased Young modulus. Young modulus is here defined as the maximal slope of the stress-strain curves. The association between DoC and Young modulus or DoC and yield point are both statistically significant. We cannot conclude there has been an effect on strainability. While mechanical properties were affected, we found no indication that ammonia treatment affected degree of fibrillation. CNF was also studied in air and liquid using atomic force microscopy (AFM). Swelling of the nanofibers was observed, with a mean diameter increase of 48.9%.

  • 78. Peciulyte, A.
    et al.
    Kiskis, J.
    Larsson, Per Tomas
    Innventia AB, Sweden.
    Olsson, L.
    Enejder, A.
    Visualization of structural changes in cellulosic substrates during enzymatic hydrolysis using multimodal nonlinear microscopy2016Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 23, nr 3, s. 1521-1536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Enzymatic hydrolysis of cellulose provides a renewable source of monosaccharides for production of variety of biochemicals and biopolymers. Unfortunately, the enzymatic hydrolysis of cellulose is often incomplete, and the reasons are not fully understood. We have monitored enzymatic hydrolysis in terms of molecular density, ordering and autofluorescence of cellulose structures in real time using simultaneous CARS, SHG and MPEF microscopy with the aim of contributing to the understanding and optimization of the enzymatic hydrolysis of cellulose. Three cellulose-rich substrates with different supramolecular structures, pulp fibre, acid-treated pulp fibre and Avicel, were studied at microscopic level. The microscopy studies revealed that before enzymatic hydrolysis Avicel had the greatest carbon-hydrogen density, while pulp fibre and acid-treated fibre had similar density. Monitoring of the substrates during enzymatic hydrolysis revealed the double exponential SHG decay for pulp fibre and acid-treated fibre indicating two phases of the process. Acid-treated fibre was hydrolysed most rapidly and the hydrolysis of pulp fibre was spatially non-uniform leading to fractioning of the particles, while the hydrolysis of Avicel was more than an order of magnitude slower than that of both fibres.

  • 79.
    Pettersson, Torbjörn
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Hellwig, Johannes
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Gustafsson, Per-Johan
    Stenstrom, Stig
    Measurement of the flexibility of wet cellulose fibres using atomic force microscopy2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 10, s. 4139-4149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Flexibility and modulus of elasticity data for two types of wet cellulose fibres using a direct force-displacement method by means of AFM are reported for never dried wet fibres immersed in water. The flexibilities for the bleached softwood kraft pulp (BSW) fibres are in the range of 4-38 x 10(12) N-1 m(-2) while the flexibilities for the thermomechanical pulp (TMP) fibres are about one order of magnitude lower. For BSW the modulus of elasticity ranges from 1 to 12 MPa and for TMP between 15-190 MPa. These data are lower than most other available pulp fibre data and comparable to a soft rubber band. Reasons for the difference can be that our measurements with a direct method were performed using never dried fibres immersed in water while other groups have employed indirect methods using pulp with different treatments.

  • 80. Rueda, L.
    et al.
    Saralegi, A.
    Fernandez-d'Arlas, B.
    Zhou, Qi
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Alonso-Varona, A.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Mondragon, I.
    Corcuera, M. A.
    Eceiza, A.
    In situ polymerization and characterization of elastomeric polyurethane-cellulose nanocrystal nanocomposites. Cell response evaluation2013Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, nr 4, s. 1819-1828Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyurethane/Cellulose nanocrystal (CNC) nanocomposites have been prepared by means of in situ polymerization using CNCs as precursors of polyurethane chains. Thermal, mechanical and morphological characterization has been analyzed to study the effect of CNC on the micro/nanostructure, which consisted of individualized nanocellulose crystallites covalently bonded to hard and soft segments of polyurethane. The incorporation of low CNC content led to a tough material whereas higher amount of CNC provoked an increase in soft and hard segments crystallization phenomenon. Moreover, from the viewpoint of polyurethane and polyurethane nanocomposites applications focused on biomedical devices, biocompatibility studies can be considered necessary to evaluate the influence of CNC on the biological behaviour. SEM micrographs obtained from cells seeded on top of the materials showed that L-929 fibroblasts massively colonized the materials surface giving rise to good substrates for cell adhesion and proliferation and useful as potential materials for biomedical applications.

  • 81. Rundlof, M.
    et al.
    Eriksson, M.
    Strom, H.
    Wågberg, Lars
    Effect of Mannanase and Lipase on the properties of colloidal wood extractives and their interaction with mechanical pulp fines2002Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 9, nr 2, s. 127-137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of enzymatic treatments of dissolved and colloidal substances (DCS) released from thermomechanical pulp (TMP) have been investigated. A model dispersion of DCS was made by leaching several portions of TMP in distilled water and separating the fibrous material. Some samples were enriched in colloidal particles by removing dissolved substances using ultra-filtration. The DCS, which had been subjected to different enzymatic treatments, were added in a fixed quantity to TMP fines that had been made cationic, and were subsequently used to form handsheets. All DCS additions increased the content of lipophilic extractives in the sheets. Lipase gave a complete hydrolysation of triglycerides into free fatty acids. The untreated DCS gave no significant decrease in tensile strength, because of the relatively small addition. A treatment of the DCS with Lipase gave a higher extractives content and a tensile strength on the same level as the reference. A Mannanase treatment gave a decrease in strength compared with the reference at the same amount of extractives in the sheet. A combined treatment with Mannanase and Lipase gave a more pronounced decrease in tensile strength. Two possible reasons for the differences in strength at a given amount of extractives were suggested: (i) the destabilisation of the colloidal wood extractives due to the Mannanase could affect the distribution of the colloid in the sheet, making it more detrimental to sheet strength compared with the stable colloid. This would account for the observation that Lipase did not affect sheet strength as such, but the combination with Mannanase gave the lowest tensile strength; (ii) the decomposition of galactoglucomannans in aqueous solution would diminish their positive effect on tensile strength and/or affect the adsorption of the colloid. A reflectometry technique was used to quantify the adsorption of the differently treated DCS onto a model surface of the cationic fines. Colloidal wood extractives were identified on the surfaces after adsorption using staining and light microscopy. No variations in adsorbed amounts were found that could explain the differences in sheet strength, which indirectly suggests that the distribution of the colloid over the surface was affecting the ability of a strong bonded joint to be formed between two such surfaces.

  • 82.
    Sjöstedt, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Larsson, Per Tomas
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. Innventia AB, Sweden.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Structural changes during swelling of highly charged cellulose fibres2015Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, nr 5, s. 2943-2953Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural changes of fibrils and fibril aggregates in the fibre wall were studied after oxidation of the cellulose by 2,2,6,6-tetramethyl-1-piperidinyloxy to high charge densities (highest charge density: 1300 mu eq/g). The increase in pore volume was measured by mini-WRV at two different pH levels, and the supramolecular structure in the fibre wall in terms of aggregate size, specific surface area and average pore size was measured by solid state NMR, DVS desorption and BET N-2 gas adsorption. A structural change in the arrangement of the fibrils inside the fibril aggregates was observed although the oxidation did not lead to a complete liberation of individual fibrils, i.e. they still exist as an aggregated structure after oxidation. Theoretical estimates suggest that the electrostatic repulsion energy connected with the increase in surface charge of the fibrils can be sufficient to gradually separate the fibrils enough to expose all fibril surfaces to oxidation chemicals.

  • 83.
    Srinivasa, Prashanth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Aulin, C.
    Experimental characterisation of nanofibrillated cellulose foams2015Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882XArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a growing interest in applications for nanofibrillated cellulose based materials owing to their exceptional mechanical properties. Nanofibrillated cellulose (NFC) foam is one such derivative which has potential applications in a wide array of fields. Here, we characterise the mechanical properties of two particular high porosity NFC foams (98.13 and 98.96 %) prepared by a freeze drying process. We evaluate their behaviour in uni-axial and bi-axial compression with cyclic loading. The secondary loading cycles reveal complete irreversible damage of the microstructure, with the secondary loading path being characterised by near zero plateau stress. In force controlled tests, negligible hysteresis corroborates the idea that there is no energy dissipation owing to near complete microstructural damage. Furthermore, we observe no indications of preferential orientation of the microstructure in these tests. The stress responses in mutually perpendicular directions are seen to be identical, within statistical considerations. We then utilise the “pseudo-elastic” model developed and adopt it to the case of highly compressible Ogden strain energy formulation with a modified neo-Hookean for the unloading, with a view of fitting a continuum hyperelastic model to the experimental data. The material parameters obtained from uni-axial data are seen to be insufficient to describe the more general bi-axial deformation. The parameters obtained from the bi-axial test describe uni-axial deformation up to stretches of 0.5 but overestimate the stress levels beyond that point.

  • 84.
    Srinivasa, Prashanth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Karlberg, Filip
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Material properties of the cell walls in nanofibrillar cellulose foams from finite element modelling of tomography scans2017Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, nr 24, s. 519-533Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical properties of the nanofibrillar cellulose foam depend on the microstructure of the foam and on the constituent solid properties. The latter are hard to extract experimentally due to difficulties in performing the experiments on the micro-scale. The aim of this work is to provide methodology for doing it indirectly using extracted geometry of the microstructure. X-ray computed tomography scans are used to reconstruct the microstructure of a nanofibrillar cellulose foam sample. By varying the levels of thresholding, structure of differing porosities of the same foam structure are obtained and their macroscopic properties of the uni-axial compression are computed by finite element simulations. A power law relation, equivalent to classical foam scaling laws, are fit to the data obtained from simulation at different relative densities for the same structure. The relation thus obtained, is used to determine the cell wall material properties, viz. elastic modulus and yield strength, by extrapolating it to the experimental porosity and using the measured response at this porosity. The simulations also provide qualitative insights into the nature of irreversible deformations, not only corroborating the experimental results, but also providing possible explanation to the mechanisms responsible for crushable behaviour of the nanofibrillar cellulose foams in compression.

  • 85.
    Stevanic Srndovic, Jasna
    et al.
    STFI-Packforsk, Swedish Pulp and Paper Research Institute.
    Salmén, Lennart
    STFI-Packforsk, Swedish Pulp and Paper Research Institute.
    Characterizing wood polymers in the primary cell wall of Norway spruce (Picea abies (L.) Karst.) using dynamic FT-IR spectroscopy2008Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 15, nr 2, s. 285-295Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dynamic Fourier Transform Infra-Red (FT-IR) spectroscopy was used to examine the interactions among cellulose, xyloglucan, pectin, protein and lignin in the outer fibre wall layers of spruce wood tracheids. Knowledge regarding these interactions is fundamental for understanding the fibre separation in a mechanical pulping process. Sheets made from an enriched primary cell wall material were used for studying the viscoelastic response of the polymers. The results indicated that strong interactions exist among lignin, protein, pectin, xyloglucan and cellulose in the primary cell wall. This signified a closely linked network structure of the components on the fibre surface. This ultrastructural arrangement in the primary cell wall and the relatively high content of lignin, pectin and protein in it, means that the primary cell wall is more submissive to selective chemical attacks, when compared to the secondary cell wall. A low ratio of cellulose I alpha to cellulose I beta in the primary cell wall was also found.

  • 86.
    Träger, Andrea
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Klein, Gregor
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Carrick, Christopher
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Pettersson, Torbjörn
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Johansson, Mats
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Wågberg, Lars
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Pendergraph, Samuel A.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Carlmark, Anna
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. RISE Research Institutes of SwedenStockholmSweden.
    Macroscopic cellulose probes for the measurement of polymer grafted surfaces2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 3, s. 1467-1477Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A synthesis protocol was identified to produce covalent grafting of poly(dimethyl siloxane) from cellulose, based on prior studies of analogous ring opening polymerizations. Following this polymer modification of cellulose, the contact adhesion was anticipated to be modified and varied as a function of the polymer molecular mass. The synthetic details were optimized for a filter paper surface before grafting the polymer from bulk cellulose spheres. The adhesion of the unmodified and grafted, bulk cellulose spheres were evaluated using the Johnson-Kendall-Roberts (JKR) theory with a custom build contact adhesion testing setup. We report the first example of grafting poly(dimethyl siloxane) directly from bulk cellulose using ring opening polymerization. For short grafting lengths, both the JKR work of adhesion and the adhesion energy at the critical energy release rate (G(c)) were comparable to unmodified cellulose beads. When polymer grafting lengths were extended sufficiently where chain entanglements occur, both the JKR work of adhesion and G(c) were increased by as much as 190%. Given the multitude of options available to graft polymers from cellulose, this study shows the potential to use this type of cellulose spheres to study the interaction between different polymer surfaces in a controlled manner. [GRAPHICS] .

  • 87. Vanderfleet, O. M.
    et al.
    Reid, Michael S.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi.
    Bras, J.
    Heux, L.
    Godoy-Vargas, J.
    Panga, M. K. R.
    Cranston, E. D.
    Insight into thermal stability of cellulose nanocrystals from new hydrolysis methods with acid blends2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 1, s. 507-528Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract: This study provides insight into the thermal degradation of cotton cellulose nanocrystals (CNCs) by tuning their physico-chemical properties through acid hydrolysis using blends of phosphoric and sulfuric acid. CNCs isolated by sulfuric acid hydrolysis are known to degrade at lower temperatures than CNCs hydrolyzed with phosphoric acid; however, the reason for this change is unclear. Although all CNCs are inherently relatively thermally stable, their application in polymer composites and liquid formulations designed to function at high temperatures could be extended if thermal stability was improved. Herein, thermogravimetric analysis was carried out on six types of CNCs (in both acid and sodium form) with different surface chemistry, surface charge density, dimensions, crystallinity and degree of polymerization (DP) to identify the key properties that influence thermal stability of nanocellulose. In acid form, CNC surface charge density was found to be the determining factor in thermal stability due to de-esterification and acid-catalyzed degradation. Conversely, in sodium form, surface chemistry and charge density had a negligible effect on the onset of thermal degradation, however, the DP of the cellulose polymer chains highly influenced stability. The presence of more reducing ends in lower DP nanocrystals is inferred to facilitate thermally-induced depolymerization and degradation. Degree of crystallinity did not significantly affect CNC thermal stability. Studying CNCs produced from single or blends of acids (and changing the counterion) elucidated the thermal behavior of cellulose and furthermore demonstrated new routes to tailor CNCs thermal and colloidal stability. Graphical abstract: [Figure not available: see fulltext.].

  • 88. Voiges, Kristin
    et al.
    Adden, Roland
    Rinken, Marian
    Mischnick, Petra
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Polymera material.
    Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 3, s. 993-1004Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.

  • 89. Werner, Oskar
    et al.
    Quan, Can
    Turner, Charlotta
    Pettersson, Bert
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Properties of superhydrophobic paper treated with rapid expansion of supercritical CO2 containing a crystallizing wax2010Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 17, nr 1, s. 187-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Paper samples were rendered superhydrophobic with Alkyl Ketene Dimer using (1) Airblasting with cryo ground micro particles, (2) crystallizing from organic solvents and (3) spraying with Rapid Expansion of Supercritical Solutions (RESS) technique. The papers were characterized using Scanning Electron Microscopy, contact angle to water measurements and X-ray Photoelectron Spectroscopy (XPS). Advancing contact angles were in the region of 150A degrees-160A degrees and receding contact angles were in the region of 110A degrees-130A degrees. Diagrams showing the drop base diameter vs. the contact angle when water is pumped into, and then withdrawn from, a sessile drop show that a stick slip pattern is present in the advancing phase for a non coated internally sized paper. Papers rendered superhydrophobic with the RESS technique showed a much less pronounced stick slip pattern in the advancing phase but still a stick slip pattern in the receding phase.

  • 90.
    Wetterling, Jonas
    et al.
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Sahlin, Karin
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Mattsson, Tuve
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Westman, Gunnar
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Theliander, Hans
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Electroosmotic dewatering of cellulose nanocrystals2018Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, nr 4, s. 2321-2329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the main challenges for industrial production of cellulose nanocrystals is the high energy demand during the dewatering of dilute aqueous suspensions. It is addressed in this study by utilising electroosmotic dewatering to increase the solid content of suspensions of cellulose nanocrystals. The solid content was increased from 2.3 up to 15.3 wt%, i.e. removal of more than 85% of all the water present in the system, at a much lower energy demand than that of thermal drying. Increasing the strength of the electric field increased not only the dewatering rate but also the specific energy demand of the dewatering operation: the electric field strength used in potential industrial applications is thus a trade-off between the rate of dewatering and the energy demand. Additionally, it was found that high local current intensity had the potential of degrading cellulose nanocrystals in contact with the anode. The maximum strength of the electric field applied should therefore be limited depending on the equipment design and the suspension conditions.

  • 91. Wickholm, K.
    et al.
    Hult, E. -L
    Larsson, P. T.
    Iversen, T.
    Lennholm, Helena
    KTH, Tidigare Institutioner (före 2005), Pappers- och massateknik.
    Quantification of cellulose forms in complex cellulose materials: A chemometric model2001Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 8, nr 2, s. 139-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS C-13-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.

  • 92.
    Wohlert, Jakob
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Bergenstråhle-Wohlert, Malin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Deformation of cellulose nanocrystals: entropy, internal energy and temperature dependence2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 6, s. 1821-1836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An in-depth analysis was performed of the molecular deformation mechanisms in cellulose during axial stretching. For the first time, it was demonstrated that entropy affects the stiffness of cellulose nanocrystals significantly. This was achieved through Molecular Dynamics simulations of model nanocrystals subject to constant stress in the axial direction, for nanocrystals of varying lateral dimensions and at different temperatures. The simulations were analyzed in terms of Young's modulus E, which is a measure of the elastic response to applied stress. A weak but significant temperature dependence was shown, with partial derivative E/partial derivative T = -0.05 Gpa K-1 at room temperature, in agreement with experimental numbers. In order to analyze the respective contributions from internal energy and entropy, a decomposition of the total response of the free energy with respect to strain was made. It was shown that the decrease in E with increasing T is due to entropy, and that the magnitude of the decrease is 6-9 % at room temperature compared to the value at 0 K. This was also shown independently by a direct calculation of the vibrational entropy of the cellulose crystal. Finally, it was found that internal hydrogen bonds are contributing to the stiffness by 20 %, mainly by stabilizing the cellulose internal structure.

  • 93.
    Zhang, Qiong
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512). KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Bulone, Vincent
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512). KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Tu, Yaoquan
    A molecular dynamics study of the thermal response of crystalline cellulose I beta2011Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 18, nr 2, s. 207-221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations were performed to better understand the atomic details of thermal induced transitions in cellulose I beta. The latest version of the GLYCAM force field series (GLYCAM06) was used for the simulations. The unit cell parameters, density, torsion angles and hydrogen-bonding network of the crystalline polymer were carefully analyzed. The simulated data were validated against the experimental results obtained by X-ray diffraction for the crystal structure of cellulose I beta at room and high temperatures, as well as against the temperature-dependent IR measurements describing the variation of hydrogen bonding patterns. Distinct low and high temperature structures were identified, with a phase transition temperature of 475-500 K. In the high-temperature structure, all the origin chains rotated around the helix axis by about 30A degrees and the conformation of all hydroxymethyl groups changed from tg to either gt on origin chains or gg on center chains. The hydrogen-bonding network was reorganized along with the phase transition. Compared to the previously employed GROMOS 45a4 force field, GLYCAM06 yields data in much better agreement with experimental observations, which reflects that a cautious parameterization of the nonbonded interaction terms in a force field is critical for the correct prediction of the thermal response in cellulose crystals.

  • 94.
    Zhao, Yadong
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Li, Jiebing
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Excellent chemical and material cellulose from tunicates: diversity in cellulose production yield and chemical and morphological structures from different tunicate species2014Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 21, nr 5, s. 3427-3441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The high crystallinity and the high microfibrils aspect ratio of tunicate cellulose (TC) indicate TC's excellent chemical and material applications. However, its quantity and quality from different species have never been systematically reported and compared. In this study, the tunics of Ciona intestinalis (CI), Ascidia sp. (AS), Halocynthia roretzi (HR) and Styela plicata (SP) were processed to TC after an identical prehydrolysis-kraft cooking-bleaching sequence, while the tunicate fibrils were chemically and structurally characterized in situ and during the sequence. All tunics studied were composed of crystalline cellulose embedded with protein, lipids, sulfated glycans and mucopolysaccharides. The native composite structures are all very compact. However, the tunics from Phlebobranchia order (CI and AS) are soft, while those from Stolidobranchia, HR and SP, are hard. Fibrous cellulose could be prepared after removing the lipids, sulfated glycans and mucopolysaccharides through prehydrolysis, protein removal through kraft cooking and a final purification by bleaching. The final product is similar to 100 % pure cellulose which is in large molecular masses, composed of highly crystalline I-beta crystals, in elementary microfibrils form, with high specific surface area and thermal stability. There were lower TC yields from the soft tunics than from the hard ones. The cellulose fibrils had a section shape of lozenges with higher crystallinity. This study demonstrates that TC could be obtained in different yields and exhibited different chemical and morphological structures depending on the species. There is a great potential of tunicate resources for preparing excellent chemical and material cellulose.

  • 95.
    Zhou, Qi
    et al.
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Rutland, Mark W
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Teeri, Tuula T.
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Brumer, Harry
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Xyloglucan in cellulose modification2007Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 14, nr 6, s. 625-641Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Xyloglucans are the principal polysaccharides coating and crosslinking cellulose microfibrills in the majority of land plants. This review summarizes current knowledge of xyloglucan structures, solution properties, and the mechanism of interaction of xyloglucans with cellulose. This knowledge base forms the platform for new biomimetic methods of cellulose surface modification with applications within the fields of textile manufacture, papermaking, and materials science. Recent advances using the enzyme xyloglucan endo-transglycosylase (XET, EC 2.4.1.207) to introduce varied chemical functionality onto cellulose surfaces are highlighted.

  • 96. Östlund, Åsa
    et al.
    Idström, Alexander
    Olsson, Carina
    Larsson, Per Tomas
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Nordstierna, Lars
    Modification of crystallinity and pore size distribution in coagulated cellulose films2013Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, nr 4, s. 1657-1667Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study the effects of altering the coagulation medium during regeneration of cellulose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate, were investigated using solid-state NMR spectroscopy and NMR cryoporometry. In addition, the influence of drying procedure on the structure of regenerated cellulose was studied. Complete conversion of the starting material into regenerated cellulose was seen regardless of the choice of coagulation medium. Coagulation in water predominantly formed cellulose II, whereas coagulation in alcohols mainly generated non-crystalline structures. Subsequent drying of the regenerated cellulose films, induced hornification effects in the form of irreversible aggregation. This was indicated by solid-state NMR as an increase in signal intensity originating from crystalline structures accompanied by a decrease of signal intensity originating from cellulose surfaces. This phenomenon was observed for all used coagulants in this study, but to various degrees with regard to the polarity of the coagulant. From NMR cryoporometry, it was concluded that drying induced hornification generates an increase of nano-sized pores. A bimodal pore size distribution with pore radius maxima of a few nanometers was observed, and this pattern increased as a function of drying. Additionally, cyclic drying and rewetting generated a narrow monomodal pore size pattern. This study implies that the porosity and crystallinity of regenerated cellulose can be manipulated by the choice of drying condition.

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