Llandegfan, United Kingdom
Llandegfan, United Kingdom

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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 | Year: 2015

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.


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 | Year: 2011

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.


Popescu C.-M.,Petru Poni Institute of Macromolecular Chemistry | Hill C.A.S.,Norsk Institutt for Skog Og Landskap | Hill C.A.S.,JCH Industrial Ecology Ltd | Anthony R.,Bangor University | And 2 more authors.
Polymer Degradation and Stability | Year: 2015

The water vapour sorption properties of biochar derived from apple wood (Malus sp.) have been studied. The biochar used in the study were formed from wood samples taken from different parts of the trunk and they exhibited different cell wall densities and surface area values when charred under identical conditions. The water vapour adsorption and desorption characteristics of the biochar were investigated over the relative pressure range P/Po = 0-0.95 in a dynamic vapour sorption apparatus and the kinetics was analysed in terms of the parallel exponential kinetics (PEK) model. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The fast process is attributed to a linear driving force mass transfer diffusion model, while the slow process is attributed to a relaxation-limited kinetic process. Markedly different sorption behaviour was found between the biochar samples, which had been produced under identical conditions. © 2014 Elsevier Ltd.


Popescu C.-M.,Petru Poni Institute of Macromolecular Chemistry | Hill C.A.S.,Norsk Institutt for Skog og Landskap | Hill C.A.S.,JCH Industrial Ecology Ltd | Curling S.,Bangor University | And 2 more authors.
Journal of Materials Science | Year: 2014

The water vapour sorption isotherms and sorption kinetics of birch (Betula pendula L) acetylated to different levels have been determined using a dynamic vapour sorption (DVS) apparatus. A DVS instrument was also used to determine the accessible hydroxyl content in the wood samples using deuterium exchange. The results are reported in terms of the reduced equilibrium moisture content (EMCR), in which the moisture content per unit mass of wood substance is used for the calculation. As the level of acetylation of the wood samples increased there was a corresponding reduction in EMCR of the wood samples, which was accompanied by a decrease in hysteresis in the same order. The sorption kinetics were also determined using the DVS and analysed using the parallel exponential kinetics model, in which the sorption kinetics curve is composed of two processes (labelled fast and slow). Using this analysis, it is possible to calculate two pseudo-isotherms associated with the two processes. The sorption isotherm is a composite of the sorption isotherms associated with the fast process water and the slow process water and there are significant differences in behaviour between the two. It is suggested in this paper that the fast process is related to diffusion limited kinetics, whereas the slow process is a relaxation-limited phenomenon. The reduction in accessible OH content due to acetylation was well correlated with the weight gain due to acetylation, although the relationship did not exactly correspond with that theoretically determined. © Springer Science+Business Media New York 2013.


Hill C.A.S.,Napier University | Hill C.A.S.,JCH Industrial Ecology Ltd. | Xie Y.,Northeast Forestry University
Journal of Materials Science | Year: 2011

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.


Nemeth R.,University of West Hungary | Hill C.A.S.,JCH Industrial Ecology Ltd | Takats P.,University of West Hungary | Tolvaj L.,University of West Hungary
Wood Material Science and Engineering | Year: 2014

Black locust, poplar and spruce samples were steamed at 80°C and 120°C for 48 hours. IR difference spectra and the CIE Lab colour coordinates were measured for determining the chemical changes caused by the steaming. Steaming at 80°C caused only small changes in both IR spectra and colour. But steaming at 120°C produced intensive colour change and well-visible changes in IR spectra. The guaiacyl lignin in hardwoods underwent slight degradation but in spruce suffered substantial degradation during steaming at 120°C. The syringyl lignin absorbing around 1600 cm−1 did not show any changes, indicating that it is more stable to steaming than guaiacyl lignin. The absorption decrease at 1175 cm−1 indicated the cleavage of ether linkage in cellulose and hemicelluloses at both steaming temperatures. © 2014 Taylor & Francis


Rautkari L.,Aalto University | Honkanen J.,Aalto University | Hill C.A.S.,431 As | Hill C.A.S.,JCH Industrial Ecology Ltd | And 2 more authors.
European Journal of Wood and Wood Products | Year: 2014

Scots pine sapwood and heartwood were thermally modified under saturated steam at 120, 150 and 180°C in a high pressure reactor. Mechanical properties such as dynamic and static modulus of elasticity (MOE), static modulus of rupture (MOR), Brinell hardness and impact toughness were evaluated. The static MOE for sapwood did not decrease substantially (approximately 1 %), not even with a high mass loss of more than 12 %, when the wood was modified at 180°C. Static MOE of the wood increased approximately 14 %, when modified at 150°C. Surprisingly, MOR increased by 15 %, when modified at 150°C with mass loss of 2.3 %. Whereas impact strength and hardness decreased somewhat, when modified at 180°C. Moreover, high anti-swelling efficiency values were obtained (60 % for sapwood and 52 % for heartwood) when modified at 180°C. © 2013 Springer-Verlag Berlin Heidelberg.


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
Holzforschung | Year: 2015

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.


Rautkari L.,Aalto University | Hill C.A.S.,N 1431 As | Hill C.A.S.,JCH Industrial Ecology Ltd.
Holzforschung | Year: 2014

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.

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