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- Fall, Andreas, et al.
(författare)
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Shear-stiffening cellulose nanofibre gels with tuneable mechanical characteristics
- 2011
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Ingår i: 241St National Meeting And Exposition Of The American Chemical Society (Acs). - : American Chemical Society (ACS). ; , s. 131--
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Gels have been synthesized from the renewable, strong and low cost cellulose nanofibres; nanofibrillated cellulose (NFC). The gels are shown to exhibit pronounced shear-stiffening properties and large extensibility (above 100%). The stiffening is due to strain induced orientation of the nanofibers, which is enabled by the free rotation at the particle-particle joints. The gels are synthesized from low concn. aq. NFC solns. By decreasing the electrostatic double-layer repulsion between the NFC fibrils, aggregation is initiated and a fluid-gel transition occurs. This transition can be detected within a range of vol. fractions. We characterize the gel microstructures using dynamic light scattering and the mech. properties using a rheometer. The mech. properties of these gels are tuneable; significantly different properties are seen if gels are formed by reducing pH or by increasing ionic strength. It is also obsd. that the properties of the gels depend on the type of counter-ion. [on SciFinder(R)]
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| 5. |
- Köpcke, Viviana, et al.
(författare)
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Study on the feasibility of converting kraft pulps into dissolving pulps : accessibility and reactivity
- 2008
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Konferensbidrag (refereegranskat)abstract
- For the prodn. of cellulose derivs. raw material contg. high cellulose and low hemicellulose content is required and today's industrial state of the art is to use dissolving pulps produced by sulphite process or prehydrolisis kraft. This work, in contrast, focuses on the study of two different paper-grade kraft pulps from hardwood - birch and eucalyptus -- and the possibility to use it as raw material for the prodn. of cellulose derivs. There have been different studies that focus their investigations mainly on the decrease of the hemicellulose content. The aspects of accessibility and reactivity of cellulose towards solvents and reagents, however, are investigated far less although being key parameters when a homogenous substitution is desired for the prodn. of cellulose derivs. of high quality. In order to accomplish the requirements of a com. dissolving pulp, the kraft pulps were subjected to different enzymic treatments using com. enzymes, xylanase and monocomponent endoglucanase. Reactivity (Fock) was notably improved and the hemicellulose content decreased down to com. typical dissolving pulp values. Further on, the structural characteristics of the pulps will be studied by means of 13C-CP/MAS NMR and size exclusion chromatog. (SEC).
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| 6. |
- Larsson, Per A., 1980-, et al.
(författare)
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Ductile cellulose nanocomposite films fabricated from nanofibrillated cellulose after partial conversion to dialcohol cellulose
- 2013
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Konferensbidrag (refereegranskat)abstract
- Ductile nanofibrillar nanocomposite films with a strain at break of 18%, and a tensile strength of 185 MPa, have been fabricated from nanofibrillated bleached kraft fibres partially converted to dialcohol cellulose prior to homogenisation. The conversion to dialcohol cellulose was performed by oxidation with sodium periodate to a degree of oxidation of ca. 30%, followed by reduction with sodium borohydride, and the fabricated films consequentially had one stiff cellulose phase and one flexible dialcohol cellulose phase. The liberated nanofibrils were characterised by AFM, after adsorption onto a silica surface, and imaging in tapping mode showed a blend of elementary fibrils with a width of 5 nm and inter-entangled fibril aggregates with a width of 15-20 nm. Besides good mechanical properties, the films also provided good barrier properties; at 0% RH the oxygen permeability was 2 ml·µm/(m2·d·kPa).
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