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Llandegfan, United Kingdom

Rautkari L.,Aalto University | Hill C.A.S.,N 1431 As | Hill C.A.S.,JCH Industrial Ecology Ltd

The effects of initial moisture content (MC) on anti-swelling efficiency (ASE), mass loss (ML), and equilibrium MC (EMC) at 65% relative humidity of thermally modified Scots pine sapwood under saturated steam (TMSA) has been investigated. ML during the TMSA process was higher with the specimens containing moisture before modification compared with initially dry specimens. Surprisingly, the EMC of the modified specimens with initial moisture was higher than that observed with the modified wood that was initially dry before the modification process. Higher initial MC before thermal modification results in a lower ASE. Source

Hughes M.,Aalto University | Hill C.,JCH Industrial Ecology Ltd | Hill C.,Norsk Institutt for Skog Og Landksap | Pfriem A.,Eberswalde University Of Applied Sciences

The mechanical properties of thermally modified wood are discussed with regard to toughness. The molecular origins of the mechanical properties and, in particular, the role of the hemicelluloses are considered. The important role of water and its interaction with the cell wall components is also examined. The properties are discussed from the point of view of composite theory, with the three main macromolecular components acting as reinforcement, matrix and interfacial coupling agent. The important role that hemicelluloses play as a coupling agent between the cellulosic microfibril reinforcement and the lignin-rich matrix is highlighted. Destruction of the hemicelluloses during the thermal modification process has a profound effect upon the mechanical behaviour. © 2015 by De Gruyter. Source

Hill C.A.S.,Napier University | Hill C.A.S.,JCH Industrial Ecology Ltd | Xie Y.,Northeast Forestry University
Journal of Materials Science

In a previous article, the sorption kinetics' properties of a range of natural fibres were reported. Analysis of the sorption kinetics was made using the parallel exponential kinetics (PEK) model, and it was argued that the rate limiting step of the sorption process was determined by substrate swelling rather than being diffusion limited. The PEK model divides the sorption kinetics curve into two first-order kinetics processes (fast and slow) but there is as yet no generally accepted explanation of what these two processes represent. In this article, the PEK parameters for sorption have been further evaluated in terms of two Kelvin-Voigt elements arranged in series. The force constant in the spring of each Kelvin-Voigt elements determines the equilibrium moisture content for each of the processes, whereas the viscosity of the dashpot is represented by the time constant for each process. Determination of interfibrillar matrix modulus using the Kelvin-Voigt model gives values that are in line with what would be predicted, giving credence to this interpretation of the sorption kinetics. Possible interpretations of the fast and slow kinetics processes are discussed. © 2011 Springer Science+Business Media, LLC. Source

Xie Y.,Northeast Forestry University | Hill C.A.S.,Napier University | Hill C.A.S.,JCH Industrial Ecology Ltd | Jalaludin Z.,Napier University | And 5 more authors.
Journal of Materials Science

Hygroscopic behaviour is an inherent characteristic of natural fibres which can influence their applications as textile fabrics and composite reinforcements. In this study, the water vapour sorption kinetic properties of cotton, filter paper, flax, hemp, jute, and sisal fibres were determined using a dynamic vapour sorption apparatus and the results were analyzed by use of a parallel exponential kinetics (PEK) model. With all of the fibres tested, the magnitude of the sorption hysteresis observed varied, but it was always greatest at the higher end of the hygroscopic range. Flax and sisal fibres displayed the lowest and highest total hysteresis, respectively. The PEK model, which is comprised of fast and slow sorption components, exhibited hysteresis in terms of mass for both processes between the adsorption and desorption isotherm. The hysteresis derived from the slow sorption process was less than from the fast process for all tested fibres. The fast processes for cotton and filter paper dominated the isotherm process; however, the hemp and sisal fibres displayed a dominant slow process in the isotherm run. The characteristic time for the fast sorption process did not vary between adsorption and desorption, except at the top end of the hygroscopic range. The characteristic time for the slow process was invariably larger for the desorption process. The physical interpretation of the PEK model is discussed. © 2010 Springer Science+Business Media, LLC. Source

Hill C.A.S.,Norsk Institutt for Skog og Landskapp | Hill C.A.S.,Bangor University | Hill C.A.S.,JCH Industrial Ecology Ltd | Ramsay J.,Highfield Forestry Ltd. | Gardiner B.,French National Institute for Agricultural Research
International Wood Products Journal

The objective of this study was to investigate the influence of the earlywood and latewood of different annual rings of kiln dried Japanese larch wood upon the water vapour sorption properties. Samples of earlywood and latewood from different lateral positions in the tree at 1.5 m height were exposed to water vapour over a range of different relative humidities to obtain sorption isotherms. A difference was found between the behaviour of the earlywood and latewood and this became more pronounced as the distance from the pith increased. The results indicated that there was residual water trapped in the cell wall of the latewood of the more recent annual rings after the first drying curve was completed. However, when the latewood was exposed to a second sorption cycle much of the residual trapped water was no longer present. Nonetheless, there were still differences in the EMC between the earlywood and latewood. © 2015 IWSc. Source

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