14. Cellulose Under Extreme Pressure

Efficient routes for controlled modification of the wood-pulp fibre cell wall structure are attractive for obtaining increased accessibility to the fibre interior and enabling functionalisation such as controlled drug delivery, interpenetrated networks, and selective removal of metal ions from aqueous mixtures to mention a few examples. By changing the physical state of water, it should be possible to significantly alter the structure of the wet fibre wall, providing the possibility to perform cell wall modifications under extreme conditions. To address this challenge, we have investigated the structural development of the wet softwood kraft pulp fibre wall under high pressure and high temperature (HPHT) conditions (up to 2 GPa and 100 °C). Characterisation has been performed to clarify the effects on the porosity and the accessibility of the fibre wall, before and after the HPHT treatment. Furthermore, changes in the crystalline structure have been identified, including in-situ X-ray diffraction measurements at high pressures performed at the P02.2 Extreme Conditions Beamline at the DESY/Petra III synchrotron in Hamburg. These measurements have been complemented with Electron microscopy, X-ray diffraction, Small and wide-angle X-ray scattering, and Cross-polarized/magic angle spinning 13C-NMR. Key findings from the experiments show that extreme conditions cause changes in crystallinity, specific surface area, bound water content and surface morphology.