Graham Ormondroyd

The water vapour sorption behaviour of acetylated birch wood: how acetylation affects the sorption isotherm and accessible hydroxyl content

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.

What is the role of the accessibility of wood hydroxyl groups in controlling moisture content

It has often been claimed that the equilibrium moisture content (EMC) of wood is controlled by the available hydroxyl group content and their accessibility, but this has not been proven. In the present study, the accessibility of the hydroxyl groups were analysed by deuterium exchange in a dynamic vapour sorption apparatus, and generally poor correlation with the EMC and hydroxyl group accessibility was found. Therefore, the role of the accessibility of wood hydroxyl groups in relation to exerting sole influence on the EMC is disputable. It is concluded that there has to be an additional mechanism to exercise control over the EMC in addition to hydroxyl group accessibility.

Ocean warming, more than acidification, reduces shell strength in a commercial shellfish species during food limitation.

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day−1). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO3 saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.

Decay resistance of anhydride-modified Corsican pine sapwood exposed to the brown rot fungus Coniophora puteana

Abstract Corsican pine (Pinus nigra) sapwood was chemically modified with acetic or hexanoic anhydride to a variety of weight gains. The modified wood was exposed to the brown rot fungus Coniophora puteana, and the relationship between weight loss due to decay and weight percentage gain, or degree of hydroxyl substitution, was determined in a 16-week exposure test. The effect of exposure time and the strain of C. puteana upon the decay protection threshold of acetylated Corsican pine was also examined.

Dimensional changes in Corsican pine (Pinus nigra Arnold) modified with acetic anhydride measured using a helium pycnometer

Abstract Helium pycnometry was used to determine the changes in volume of wood samples of Corsican pine following modification with acetic anhydride. Results were compared with changes in volume determined from external dimensions only. Percentage change in volume, as determined from external dimensions of the sample, showed a non-linear relationship with weight percentage gain as a result of acetylation; whereas percentage volume change determined by helium pycnometry showed a linear relationship. The difference in volume as determined by the two methods is explained by considering volume change of the lumens as level of cell wall substitution increases. Results obtained in this study show that volume increases due to chemical modification, when determined by measurement of external dimensions, should not be used to evaluate changes in cell wall volume.

A rapid method for investigating the absorption of formaldehyde from air by wool

Formaldehyde emitted from household products, such as furniture produced with medium density fibreboards, has been reported as causing health concerns in both domestic and business environments, these concerns being generally known as ‘sick building syndrome’. A number of differing approaches to removing formaldehyde from the atmosphere have been investigated. It is known that formaldehyde binds to wool fibres when the formaldehyde is in the liquid phase. However, few investigations into the sorption potential of wool for vapour phase formaldehyde have been made. This article details a rapid, novel method to directly measure the uptake of formaldehyde by wool and by inference, other materials. The data detailed in this article also demonstrates the significant ability of wool to sorb formaldehyde in the vapour state.

Changes in the cell wall volume of a number of wood species due to reaction with acetic anhydride

Abstract A number of softwoods and hardwoods (beech, rubberwood, Corsican pine, Korean pine) were reacted with acetic anhydride to a variety of weight percentage gain (WPG) values and the volume change due to reaction was determined both by measurement of the external dimensions and by helium pycnometry. The volume change due to modification determined by helium pycnometry was found to be equal to that calculated, except for Corsican pine. The volume change as determined by the external dimensions was not a reliable method for determining cell-wall volume changes. The molar volume of the acetyl group in the cell wall was calculated over a range of WPG values, with volumes ranging from approximately 32 to 42 cm3 mol-1, depending on the wood species studied. The differences in acetyl molar volume observed between most wood species were significant.

Water sorption, surface structure and surface energy characteristics of wood composite fibres refined at different pressures

ABSTRACT During fibre processing, wood fibres are subjected to a range of physical and chemical conditions sufficient to slightly alter their chemical composition and hence their ultimate performance when used in the manufacture of wood fibre-based composites. In order to better understand the effects of refiner conditions on material performance, wood fibres were subjected to processing at different refiner pressures (4, 6, 8 and 10 bar) and subsequently dried in a flash drier. The fibres were analysed for changes in surface area, surface energy, surface structure and water vapour sorption characteristics. The methods applied were nitrogen adsorption utilising the Brunauer–Emmett–Teller theory, inverse gas chromatography, scanning electron microscopy and dynamic vapour sorption. It was found that increasing refiner pressure resulted in fibres of lower surface area, accompanied by increasing dispersive surface energies up to operating refiner pressures of 8 bar. It was found with fibres refined at different pressures that as the refiner pressure increased the equilibrium moisture content of the fibre decreased at the set relative humidities. However, it was also noted that the hysteresis was not significantly different between each of the refiner pressures. The results suggest that different refiner pressures can be used to tune the surface characteristics which may be beneficial to product development and the improvement of the environmental profile of the wood fibre composites.

Assessment of health implications related to processing and use of natural wool insulation products

This paper discusses possible health implications related to dust particles released during the manufacture of sheeps wool-based non-woven insulation material. Such insulation may replace traditional synthetic insulation products used in roofs, wall cavities, etc. A review of the literature concerning organic dusts in general and sheeps wool fiber summarizes dust exposure patterns, toxicological pathways and the hazards imposed by inhalation and explosion risk. This paper highlights a need for more research in order to refrain from overgeneralizing potential pulmonary and carcinogenic risks across the industries. Variables existing between industries such as the use of different wool types, processes, and additives are shown to have varying health effects. Within the final section of the paper, the health issues raised are compared with those that have been extensively documented for the rock and glass wool industries.

The Opportunities and Challenges for Re-use and Recycling of Timber and Wood Products Within the Construction Sector

This chapter addresses the many factors which have influenced the re-use and recycling of wood in the UK over approximately a 20 year period to 2015. Drawing on a wide range of reports and data for the sector, the main trends are described. These include early adoption of standards for the quality of recycled wood in the particleboard industry, clear segregation of waste wood by origin and level of expected contamination, and more recently, the development of the biomass energy market. The construction sector presents several challenges when reclaiming, re-using or recycling timber, however, significant progress has been made by the introduced legislation, and through initiatives, best practice and the development of waste transfer stations and businesses utilising waste wood. Further avenues of research and emerging technologies are also discussed.