Veneer concentration

The so-called El-emission class describes a wood panel presenting formaldehyde emission which is low enough to prevent any danger, irritation or inflammation of the eyes, nose and mouth mucous membranes. However, it is important that not only the boards themselves, but also the veneering and carpenter s adhesive resins, laquers, varnishes and other sources of formaldehyde are under control, since they also might contribute to the mixture steady state formaldehyde concentration [9]. Table 3 gives an overview on some European regulations. However, it is necessary here to introduce the principal types of composite wood products, especially panels, that are produced in this industry ... 

Chow and coworkers have studied the thermal inactivation of white spruce veneer in detail (61, 62, 63). They were not able to correlate bond quality to the concentration of fatty acids on the veneer surface. They found instead that surface inactivation was a function of time, temperature, and atmosphere. Even extractive-free veneer could be inactivated the presence of extractives did accelerate the inactivation. The infrared spectra of the veneer... 

Figure 1 The estimated composition of the silicate portion of the Earth as a function of condensation temperature normalized to Cl values in Anders and Grevesse (1989). Open circles lithophile elements shaded squares chalcophile elements shaded triangles moderately siderophile elements solid diamonds highly siderophile elements. The spread in concentration for a given temperature is thought to be due to core formation. The highly siderophile element abundances may reflect a volatile depleted late veneer. Condensation temperatures are from Newsom (1995).

The amount of nitrogen in the upper mantle is therefore 1.6 X 10 ° g, which is only 3% that in the crust and atmosphere. The MORE flux is equivalent to a flux of 5.0 X 10 °molyr or 9% of the surface N2 over 4.5 Ga. Note that Javoy (1998) argued that nitrogen is relatively compatible, with an upper-mantle concentration of up to 40 ppm (Cartigny et ai, 2001). However, this is from mass balance calculations based upon model assumptions that volatiles in the upper mantle and on the surface are a mixture of enstatite chondrites and a late veneer of Cl chondrites, and such a model has not been widely adopted. 

Knotwood. From the outerwood of older trees, lumber, veneer, or chips can be cut without the inclusion of natural wood defects called knots. Knots are residual, embedded portions of branches, or more specifically, branch bases. Although knots are usually concentrated in wood near the pith, i.e., in crown-formed wood, they are characteristic of wood in any stem region that is manufactured while in the proximity of branches (Figure 35A). 

For deeper samples, collected in the form of snow and ice cores, contamination is more or less always present. In this respect, decontamination of the snow and ice cores is of paramount importance in order to give reliable results. Decontamination consists of eliminating the contaminated outside concentric layers and recovering the presumably uncontaminated inner core. This really important operation has to be carried out in strict accordance to clean room protocols (2, 6, 27, 29, 34, 35). Usually, the ice core to be decontaminated is fixed horizontally on a LDPE speed lathe under a high purity air laminar flux, in a cold room at -15°C (6, 34). Beginning from the outside and moving towards the center of the core, successive veneers of ice are chiseled by a series of ultra-clean plastic or stainless steel knives depending on the hardness of the snow or ice the material obtained is collected in ultra-clean LDPE bottles and then analyzed to quantify the trace element content. Usually, three-four outer layers and one inner ice core can be obtained. 

Figure 9 illustrates the effect of veneering on formaldehyde emission of particleboard. For the veneering the same type of resin was used as in the production of the particleboard. Pressing conditions are not comparable. Veneering has increased the equilibrium value a little, from 0.48 to 0.56 mg/m. The mass transfer coefficient however, decreased very much. The mass transfer resistance shows an increase from 2,400 sec/m to 11,000 sec/m. In the case at issue, the formaldehyde concentration, at a loading factor of 1 m /m of the veneered particleboard, is below that of the bare particleboard, only at a ventilation rate in excess of 0.2 per hour. 

If the mass transfer coefficient is sufficiently low, the emission will be so slow that the ventilation can manage to remove the formaldehyde at almost the same rate as it is liberated, resulting in a very low formaldehyde concentration in the air. This presentation deals with what can be achieved in terms of reduced mass transfer coefficient and emission rate by applying some sort of diffusion barrier to the surface of the particleboard. The diffusion barriers studied comprise overlays or surface finishes commonly applied when particleboard is used as a building material, such as wall paper, painting and floor covering, but even overlays that are used by the furniture and joinery industries, such as veneers, melamine facing and resin saturated paper foils (finish foils). 

In contrast, benthic community structure and processes in the NEPAP region are likely to be both extremely sensitive to, and have very little resistance to, physical perturbations (e.g. mining disturbance). This is because the natural ecosystem is relatively very stable (compared to virtually all other ecosystems), most animals are small and/or very delicately constructed, and critical habitat structure for the entire benthic fauna is concentrated within a few centimeters of the sediment-water interface. Thus, it would require very little physical energy to disrupt the animals and the thin veneer of surface sediments that define this ecosystem. The extremely low sediment accumulation rates, biotur-bation rates, nodule growth rates and macrofaunal recolonization rates of the NEPAP seafloor ecosystem, compared to other seafloor habitats (Smith Demopoulos, 2003), suggest that recovery from physical disturbance is likely to be extremely slow relative to other ecosystems. 

Figure 1.9-1. Concentration vs time profile for the emission of DEGME from a water-based lacquer system for furniture coating. The substrate was particle board covered with oak veneer. Test chamber conditions 23 °C, 45 % rel. humidity, 1 h air exchange, Im /m loading (Fuhrmann and Salthammer, 1998).

Mixed borate salts are very effective as a treatment for the preservation of wood products against fungi and most insects. However, the boron salts, which become localized in high concentration on the veneer surface, tend to gel the phenol resin before it can reach the wood surface and bond to it. However, very dilute aqueous solutions of borates (i.e.,... 

The experimental data were interpreted in terms of the equilibrium between the water content in the water-solvent mixture held in the wood pores and that in the surrounding solvent at the end of the extraction phase. A comparison of these two concentrations based on a simple mass balance indicates how far the displacement process has proceeded during the treatment time used. Figure 18.4 presents representative data for veneer sampies treated for different periods from 0.5 to 2 hours at a solvent-to-wood mass ratio of 4. It... 

Figure 18.4 Concentration of water in the water-solvent mixture at the end of the extraction phase of green veneer. (From Pajunen et al., 1988.)...

Figure 17. Case Cl. Images of the interior surface. The fracture origin is an internal crack (large arrows) that started entirely in the outer veneer and then propagated into both porcelain layers in steps creating concentric arrest lines.

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