Rethinking fibreboards Irle, Mark
Wood Based Panels International,
06/2015
Trade Publication Article
Plywood, OSB and particleboard are all multi-layer products by design. The multi-layer aspect gives manufacturers some control over the mechanical and physical properties of their products. Wood ...based fibreboards, such as MDF and hardboard, on the other hand, are almost invariably made as single-layer products. Elena Tikhonova, E, LECOURT, M and Mark Irle, MA (2014). The potential of partial substitution of the wood fibre in hardboards with reject fibres from the paper recycling industry. European Journal of Wood and Wood Products Volume 72, Issue 2 (2014), Page 177. (Online First DOI 10.1007/s00107013-0765-5). There are some exceptions: some hardboard manufacturers apply a thin layer of finely ground pulp to the top surface to help achieve a dense and smooth face; some softboards (low density fibreboards) are made with a thin layer of bleached pulp to give a white face; and some MDF manufacturers are making three layer panels because they wish to use dry fibre blending for the core layer. In the first two exceptions, the additional layer is thin relative to the bulk of the panel, while in the MDF exception, the fibres in the core and surface layers are, essentially, identical.
A question of fibre Irle, Mark
Wood Based Panels International,
02/2015
Trade Publication Article
The thermo-mechanical pulping process (TMP) is the most common method for producing the fibres needed within the sector. The process generates a wide range of fibre sizes. This is partially caused by ...the different cells which make up wood, but is mainly because not all the fibres are completely separated during refining. Consequently, many of the fibres used to make board products are actually bundles of cells still stuck together, but, because they are rather small and long compared to their thickness, they are termed fibres within the industry. The fibres are, of course, small and this makes the preparation of a test sample time consuming, fiddly and prone to errors. Our approach is to use two drops of superglue to fix a fibre to a paper support that is nearly cut in two. The paper support makes it possible to position the fibre in the test machine. Once there, we cut the remaining part of the paper support so that the fibre is the only connection between the two halves of paper (see Figure 1).
In the zone Irle, Mark
Wood Based Panels International,
12/2014
Trade Publication Article
Eventually the log is rounded and a continuous ribbon of veneer is cut. The quality of veneer changes as the bolt diameter is reduced. Initially, the veneer is clear, ie knot-free, and this veneer ...can be used for the faces of a plywood panel. Further into the bolt, knots tend to be more frequent as the tree was much younger, and therefore shorter, so the wood was formed near the crown, where the branches are. The knottier veneer can be used as face veneers for lower quality plywoods or for the inner veneers.
It is already known by the scientific and industrial communities that lignocellulosic substrates are, to a certain extent, inhibitors of the hydration reaction of cement. The extent to which and how ...they influence such reactions is still a matter of debate. Several techniques, such as calorimetry, i.e., the measurement of the heat evolved or obtaining temperature profiles during the hydration, the determination of extractive contents of lignocellulosic substrates and their relation with the characteristics of the hydration curves, or even testing of the mechanical properties of the wood-cement composites, have been used in previous research. This study complements past research using two techniques that have been used in the analysis of cement hydration but are not usually applied to lignocellulose-cement mixes, namely X-ray diffraction (XRD) and differential thermal analysis (DTA). The raw materials for this study were three lignocellulosic materials of Portuguese origin: cork (the bark of Quercus suber L.), blue gum (Eucalyptus globulus Labill.), and maritime pine (Pinus pinaster Ait); and Portland cement. The two techniques allowed tracking of the evolution of the main cement constituents during hydration. It was found that all the lignocellulosic substrates had detrimental effects on cement hydration. The blue gum exhibited the fastest hydration kinetics in the initial stage of reaction, but was then overtaken by cork, which at the end gave the highest hydration conversion amongst the three lignocellulosic substrates. Although pine caused the slowest initial hydration kinetics, with the passage of time its effect approached that of blue gum. At the end of the hydration period, specimens containing either species had similar quantities of hydration reaction products. The DTA and XRD results were consistent and are in good agreement with the temperature profiles and compatibility indexes reported in a previous work.
The objective of the present study was to develop a simple and direct screening method to assess antimicrobial activities of wood material. Wood samples consisted of sawdust and wood discs cut in ...transversal (RT) and tangential (LT) direction, from four different wood species which were tested against four important bacteria in hospital hygiene. Area of inhibition was observed around sawdust embedded wells and wooden discs placed on agar. This study showed that wood disc diffusion can be used to easily and rapidly screen antimicrobial properties of untreated wood, while sawdust diffusion needs further work to do this.
VOCs explained Irle, Mark
Wood Based Panels International,
04/2014, Letnik:
34, Številka:
2
Magazine Article, Trade Publication Article
I have mentioned VOCs (volatile organic compounds) in several articles for WBPI in the past, but I have never really explained what these are. I am sure that many readers will have an immediate and ...negative reflection about VOCs because of all the 'bad press' about such compounds. If one understands what VOCs are, it immediately becomes obvious that not all VOCs are dangerous. To state the obvious somewhat, a VOC is an organic compound, ie one that contains carbon atoms and one that is volatile at room temperature. Various official definitions of VOCs exist. The World Health Organisation (WHO) defines a VOC as "an organic compound that has a boiling point of 50 to 250°C". Other organic compounds with lower boiling points are considered VVOCs, or very volatile organic compounds - things like butane and propane.
This study evaluates the feasibility of incorporating reject fibres from paper recycling into wet process fibreboards as a partial replacement for virgin wood fibres. The rejects were obtained from ...newspaper and magazine paper recycling in the form of sludges. Three sludges were obtained from the process steps: coarse screening, fine screening, and flotation. Fibre size and inorganic contents of these fibres are presented. Incorporating rejects into a single layer panel has a negative impact on the visual appearance of the panels. Therefore, a method of making multi-layer fibreboards which permits the inclusion of rejects in the core layer was developed. The board performances were assessed according to EN 310, EN 317 and EN 319. The results indicate that the quantity of rejects incorporated into the panels must be limited. The maximum amount of the rejects, which do not significantly affect board performance, is estimated to be 10 %.
The mechanisms which cause an improvement in the dimensional stability of particleboards made from steam pretreated particles were investigated from the aspects of potential thickness recoveries of ...densified wood particles and the breakage of the adhesive bond network in particleboards. Since the latter would depend on the balance between bond strengths and stresses imposed on the adhesive bond, the effects of steaming temperature (160 to 220°C) on bond quality, recovery stress of compressed wood and in-plane swelling stress were investigated. Steam pretreatment was found: 1) to reduce thickness recoveries of densified wood particles, steaming temperatures above 190°C are especially effective, 2) not to cause a significant reduction in bond strength when steaming below 210°C or if relatively high press pressures of 1.5MPa are employed, 3) to reduce recovery stress of compressed wood, which is mainly caused by the increase in wood compressibility, 4) to reduce in-plane swelling stress of particles, which was found to correlate with reductions in both hygroscopicity and elasticity.
This study evaluates the feasibility of incorporating reject fibres from paper recycling into wet process fibreboards as a partial replacement for virgin wood fibres. The rejects were obtained from ...newspaper and magazine paper recycling in the form of sludges. Three sludges were obtained from the process steps: coarse screening, fine screening, and flotation. Fibre size and inorganic contents of these fibres are presented. Incorporating rejects into a single layer panel has a negative impact on the visual appearance of the panels. Therefore, a method of making multi-layer fibreboards which permits the inclusion of rejects in the core layer was developed. The board performances were assessed according to EN 310, EN 317 and EN 319. The results indicate that the quantity of rejects incorporated into the panels must be limited. The maximum amount of the rejects, which do not significantly affect board performance, is estimated to be 10 %.
Chemically modified wood composites were obtained via the compression moulding of thermoplasticised Aspen (Populus tremula) sawdust. This sawdust was previously prepared by esterification with maleic ...anhydride (MA) and subsequent oligoesterification with maleic anhydride and glycidyl methacrylate (GMA). The thermoplastic properties of the chemically modified wood resulting from different modification procedures were confirmed and compared by compression-moulding experiments leading to preliminary and final products. An SEM study of the resulting products clearly showed that the oligoesterified wood had partially melted under pressure and temperature, such that the overlapping and surface melting of particles ensured adhesive bonding between those particles. A new type of wood/thermoplastic-wood composite was obtained. In these composites, the melted part of the modified wood plays the role of the cohesive matrix whilst none-melted wood remains as a fibrous reinforcing material. FTIR spectra suggested that changes in the chemical structure of the modified wood are possible during the thermal forming process (e.g. polymerisation of C=C double bonds). The final composites were yellowish-brown, glossy, plastic-like products that showed interesting physical, mechanical and biological properties. They are water-resistant and dimensionally stable and display good electrical insulating behaviour. Their mechanical properties (bending strength of ca. 64 MPa and tensile strength of ca. 36 MPa) are in the typical range for plastics and conventional wood-fibre/plastic composites, and are superior to common wood products such as fibreboards and particleboards. Furthermore, the outstandingly high internal bond (ca. 3.0 MPa) highlights the totally different adhesion mechanism operating in these new types of composites. Although the novel composites are much more resistant to decay than the original unmodified wood, they remain ultimately biodegradable plastic-like composites.
