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Lahti J.,Christian Doppler Laboratory | Schmied F.,Mondi Uncoated Fine and Kraft Paper GmbH | Bauer W.,University of Graz
Nordic Pulp and Paper Research Journal | Year: 2014

Extensibility is an important property for papers undergoing large deformations in converting or end use application (e.g. industrial bags). Industrially, high extensibility is created by compacting the moist paper web in machine direction (MD) using an extensible unit such as the Clupak or Expanda methods. In this study, a method was developed to produce extensible paper on the laboratory scale. The Clupak unit was simulated using a purpose-built MD compaction apparatus. A paper sheet is placed between two stretched rubbers which are recoiled under perpendicular pressure to create sufficient friction between paper and rubber.The laboratory method for producing extensible paper sufficiently corresponds to the industrial process, i.e. strain increased while tensile stiffness index and tensile index decreased. Increased solids content during rubber recoiling enhanced the sigmoidal shape of the specific stress versus strain curves whereas tensile index remained unchanged. The reproducibility of the method is at a good level and thus the developed method offers a feasible way to study the production of extensible paper on the laboratory scale. Source

Fischer W.J.,University of Graz | Zankel A.,University of Graz | Ganser C.,University of Leoben | Ganser C.,University of Graz | And 7 more authors.
Cellulose | Year: 2014

Besides the determination of the force and the energy needed to break individual fibre to fibre joints, the investigation of the formerly bonded area (FBA) is of essential importance to learn more about the failure mechanisms of fibre-fibre bonds in general. In this study the surfaces of paper fibres and the FBA of fibre-fibre joints after the determination of the breaking force as well as the bonding energy were analysed by means of low voltage scanning electron microscopy and atomic force microscopy. A comparison between the contact zone of fibres broken at different loading rates as well as under cyclic loading showed that there seems to be no significant difference in the appearance of the FBA in these cases. Only minor delamination of the cell wall could be found in the bonding zone, which indicates no mechanical interlocking of fibrils in the bonding zone. Furthermore, it is shown that some glues used for specimen preparation of fibre-fibre bond strength measurement are forming a glue film on the fiber surface and migrate into the bonding region. © 2013 Springer Science+Business Media Dordrecht. Source

Korntner P.,University of Natural Resources and Life Sciences, Vienna | Hosoya T.,University of Natural Resources and Life Sciences, Vienna | Dietz T.,Evonik Industries | Eibinger K.,Zellstoff Pols AG | And 12 more authors.
Cellulose | Year: 2015

The chromophore release and identification method isolates well-defined chromophoric substances from different cellulosic matrices, such as highly bleached pulps, cotton linters, bacterial cellulose, viscose or lyocell fibers, and cellulose acetates. The chromophores are present only in extremely low (ppm to ppb) concentrations. The concept of primary and secondary chromophores is introduced, with primary chromophores arising only from the polysaccharides inherent to cellulosic materials. Secondary chromophores also include atoms from the chemicals used to process the cellulose. Most primary chromophores belong to one of three compound classes: hydroxy-[1,4]-benzoquinones, hydroxy-[1,4]-naphthoquinones, and hydroxyacetophenones. Among them, three individual compounds dominate: 2,5-dihydroxy-[1,4]-benzoquinone, 5,8-hydroxy-[1,4]-naphthoquinone, and 2,5-dihydroxyacetophenones, amounting to more than 80 % of the total isolated chromophores in most cases. In lignin-free cellulosics, these three compounds can thus be regarded as key chromophores. The prevalence of these molecules is due to both exceptionally strong resonance stabilization, as reflected in delocalized double bonds, and their ready reformation from carbohydrate degradation products by recondensation reactions. The findings that (a) most chromophores in lignin-free cellulosic materials belong to only three compound classes and that (b) three chromophore compounds make up the bulk of the chromophore mixtures are foundational for future bleaching research: Based on this knowledge, specific searches for optimized bleaching conditions can now concentrate on these compounds and still cover the vast majority of chromophores. © 2015, Springer Science+Business Media Dordrecht. Source

Ehmann H.M.A.,University of Graz | Werzer O.,University of Graz | Pachmajer S.,University of Graz | Mohan T.,University of Graz | And 8 more authors.
ACS Macro Letters | Year: 2015

The supramolecular rearrangements of biopolymers have remained difficult to discern. Here, we present a versatile approach that allows for an in situ investigation of two major types of rearrangements typically observed with cellulose, the most abundant biopolymer on earth. Model thin films were employed to study time-resolved pore size changes using in situ grazing incidence small-angle X-ray scattering (GISAXS) during regeneration and drying. (Figure Presented). © 2015 American Chemical Society. Source

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