Data are presented on the effects that cork, blue gum, or maritime pine, all grown in Portugal, have on cement setting. These materials were mixed with cement either without any treatment or after ...being extracted previously with a range of solvents (ranging from nonpolar to very polar). Other experiments were carried out in which extractives or calcium chloride were added to the cement paste. All lignocellulosic substrates have detrimental effects on cement setting, which is mostly seen by a delay in attaining the maximum temperature in the process. However, the addition of calcium chloride was able to overcome this disadvantage. Extraction of the substrates with some polar extraction agents before addition to the cement paste only slightly improved compatibility, and the addition of water-based extractives to a cement paste affects the setting much less than the lignocellulosic material by itself. Several thermal compatibility indices, including a new index proposed in this article, were calculated from data taken from temperature profiles, and conclusions are presented on the performance of the setting systems, as compared with a neat cement paste. In addition, comments are expressed on the level of accuracy offered by the indices applied in this study, and how such accuracy can be checked or improved by matching them to the physical properties of the wood-cement composites.
COST AND COLOUR Irle, Mark
Wood Based Panels International,
04/2017
Trade Publication Article
...this demonstrates the popularity of using wood and wood products in construction. The omnipresence of spores was brought home to me recently when I received some samples from New Zealand that I ...had requested for an experiment on the release of formaldehyde from solid wood.
DENSITY Irle, Mark
Wood Based Panels International,
10/2016
Trade Publication Article
A panel that has been recently hot pressed will have a relatively low moisture content, typically between 4 and 7%. ...the weight of most panels increases with conditioning due the adsorption of ...water. Since the density of water is 1000 kg/m3 the density of the panels tends to increase too.
HOW TO CLEAN WOOD Irle, Mark
Wood Based Panels International,
02/2016
Trade Publication Article
Secondly, and possibly more importantly, recovered wood is dryer than virgin wood and so less energy is required at the drying stage of the manufacturing process. On average, recovered wood has been ...found to have a mean moisture content of around 25%. This is significantly lower than virgin wood, which can have moisture contents as high as 200%, but is typically in the range of 60-100%. The drying step in the manufacture of particleboard is the most energy-intensive part of the process as it typically requires 60% or more of the total energy needed to make the product. Therefore, using a drier raw material can have a marked impact on the profitability of particleboard manufacture. Some use EN 14778, Solid biofuels -sampling, to obtain a representative sample of a large stock pile. The methods contained in the standard are based on experience obtained when sampling coal stock piles. The large size of the stock piles, and the variable particle size, often causes the resultant primary sample to weigh several tens of kilograms. Even so, the sample is a very small percentage of the weight of the original stock pile, so there is still a chance For significant error. The primary sample must be ground into a fine powder with particles with a maximum dimension of 500pm. Grinding is required to homogenise the sample and to help ensure that any heavy metals or halogens can be separated from the wood. It is not practical to grind all the primary sample into a fine flour as it would be too time-consuming and expensive; a method of sub-sampling must be applied and this is where there is less regulation as it is often done by companies, and/or the laboratory, using a proprietary method. Where sub-sampling is deemed necessary, then some form of particle size reduction should be applied before the sub-sample is taken. Then one must make sure that the sample is thoroughly mixed before subsampling in order to ensure that the chipping process has not created 'layers' of particles with different contaminant levels.
The thermal conductivity of solid wood across the grain is dependent on the density of the species and ranges from about 0.05 to 0.17W/mK. Still, dry air has a thermal conductivity of about 0.025W/mK ...- much less than wood. However, in the real world, air is rarely dry, or stilt. There is a research project in France called ECOMATFIB which aims to optimise existing wood fibre insulation products and potentially to develop new ones. The approach being taken is to make a detailed study of the product's structure and, in particular, the interaction between the wood and synthetic fibres in the product. In low density products, such as insulation panels, there are large air gaps between fibres (see Figure 1 and Figure 2) and so longer synthetic fibres are incorporated in order to provide a net, to hold the wood fibres and to bond them together.
The application of water-based finishes to wood surfaces is known to increase surface roughness by raising the grain. This phenomenon is detrimental in the appearance of the finished wood surface. To ...eliminate it, light denibbing is needed prior to applying the second coat of finish. The objective of this study is to optimize wood machining to minimize raised grain caused by water-based coatings and to avoid, or at least, to minimize the sanding operation between each coat of finish. Experiments were done on beech samples. Complete experimental design was defined to generate several surface qualities from “smooth” to “rough” which are linked to the average thickness of the removed chips. The planing parameters were the cutting mode, cutting direction, feed speed, and rotation speed. To compare with existing practices in joinery industries, specimens were also sanded. Two layers of water based coating were applied. Half of the samples were sanded after the first coat and the other half were not. Following each coat, surface roughness was measured and raised grain was evaluated through tactile tests. Results show that sanding operation is responsible for more raised grain than planing. Whereas for planing, high chip removal thickness gives more raised grain after coating application. The effects of the other parameters on raised grain occurence are not found to be statistically significant. The average roughness (
Sa
), quadratic mean roughness (
Sq
), reduced peak height (
Spk
) and the material volume of the peak section (
Vmp
) are the roughness parameters best correlated with tactile evaluation of grain raising, but the correlations are weak.
New ways to recycle Irle, Mark
Wood Based Panels International,
10/2015
Trade Publication Article
The particleboard industry is the biggest user of recovered wood, although the energy sector is growing year by year. According to the latest EPF Annual Report, 32% of the raw wood used by the ...European particleboard manufacturing sector in 2014 came from recovered wood sources. This equates to just under six million tons per annum, which is a small fraction of the recovered wood available, so there is room for expansion. Recycling particleboard into new particleboard can and is being done. Breaking-up the particleboard generates dust that cannot be recycled and is normally burned to provide energy for the manufacturing process. Since some of the wood is 'lost' with each cycle, a particleboard cannot be recycled ad infinitum. In addition, the average particle size must fall with each cycle and this will affect the physical and mechanical properties of the resultant particleboard.
Size matters Irle, Mark
Wood Based Panels International,
08/2015
Trade Publication Article
It is almost impossible to recreate the conditions found inside a commercial mattress during hot pressing using a laboratory press. You can use the same particles, glue mix, press temperatures and ...moisture contents and so on, but the particles inside will not experience the same temperature and moisture history found in a commercial press. This is for two main reasons: Laboratory presses rarely close as quickly as commercial presses; and, more importantly in my opinion, the size of the mattress does not allow the generation of the same steam pressures inside the mattress. Much higher steam pressures are possible in a large mattress compared to a small one because the steam escape path is longer. The steam pressure determines the temperature inside a mattress (see WBPI 33(5):58 and 33(6): 58) which, in tum, will determine the temperature and moisture content of the particles or fibres in the mattress.
A question of age Irle, Mark
Wood Based Panels International,
06/2015
Trade Publication Article
The cells in the lighter coloured part of the growth ring have relatively thin cell walls and large lumina (the void in the centre of the cell) and are called early wood or spring wood. Conversely, ...the darker wood, known as late wood or summer wood, has thick walls and relatively small lumina. Hardwoods can be classified into ringporous, semi-ring porous and diffuse porous. In the first two groups, the vessels tend to have larger diameters and/or be more numerous in the early wood compared to the late wood, so the growth rings are generally clearly defined. The growth rings of diffuse porous hardwoods are sometimes more difficult to see because the vessel diameter does not really change. However, the end of the growing season can be marked by a ring of late wood tracheids and fibres, creating a thin line.
