Particleboard concentration

Philippou, J.L., Johns, W.E. and Nguyen, T. (1982). Bonding wood by graft polymerisation. The effect of hydrogen peroxide concentration on the bonding and properties of particleboard. Holzforschung, 36(1), 37-42. 

Wolkoff, 1998 Haghighat and de Beilis, 1998). Table 15.7, for example, shows the effects of temperature and relative humidity on the emissions of particular compounds associated with carpet, PVC flooring, sealants, varnish, and wall paint (Wolkoff, 1998). Interestingly, exposure of these samples to N2 rather than air also increased the emissions in some cases. However, using increased temperatures to bake-out buildings and hence lower the concentrations of indoor VOCs does not appear to be particularly effective. For example, Bayer (1991) reports that the total VOC concentrations from particleboard are about the same after as before a 5-day bake-out at 88°C. Similarly, significant levels of HCHO have been observed in a mobile home even after 20 years of use in a hot ambient air environment (Pitts et al., 1989 see later). 

In this chapter, the development of a thermosetting adhesive from soda bagasse lignin is described. The research has concentrated on the development of interior-grade adhesives for particleboard. The local market for exterior boards is smaller than that for the interior panels, and adhesives for exterior boards are already covered by an excellent range of tannin-based adhesives. 

Now consider a nonreactive pollutant having a constant source, no appreciable sink, and a negligible concentration in outside air. Such pollutants may be emitted by building materials and furniture components, such as adhesives and particleboard (Godish, 1989). To estimate the pollutant concentration inside the building at steady state [i.e., d(Cinside)/dt Vbuilding equals zero], Eq. [4-14] can be simplified to... 

The curing conditions are equally important for reducing formaldehyde emission. The curing process is not yet fully understood. In fact, there is even still some question about the nature of the reactive resin. The latter subject is described in a later chapter by Johns. Appropriate resin cure conditions must take into account the wood moisture content and wood acidity, as well as resin concentration, temperature gradients, and press duration. In excessively cured UF bonded wood products, and in products that are stacked while still hot from the press, UFR can hydrolyse so strongly that particleboard loses internal bond strength. 

If we consider as an example a relative air humidity of 50% and a temperature of 25 l, the wood moisture content would be 9.2 wt% (3. If we further consider that the product manufacturing process leaves about 1 wt% of the formaldehyde content of the UF resin as unreacted formaldehyde, we obtain for particleboard or medium density fiberboard (MDF), where UF-resin makes up 6-10 wt%, an approximate formaldehyde concentration of 0.2 M in the S-2 cell of the wood. 

Guideline for the Use of Particleboards with Respect to the Avoidance of Unacceptable Formaldehyde Concentration in Room Air Commission for Uniform Technical Building Specifications, Beuth Publishers Berlin, April 1980. 

When we place a piece of particleboard with a surface area of A in an enclosed space with a volume of V m, in which at time zero no formaldehyde gas is present in the air (Figure 1), it is known that the particle board will release formaldehyde into the air and that, viewed over a period of time, the rate of release will not be constant but decreases as the formaldehyde concentration Cg in the environment increases, until a certain maximum concentration... 

Three situations are shown. In each of them the concentration of formaldehyde in the exit air has been measured for four rates of airflow. The equilibrium value of the examined particleboard sample has been determined as well (1.06 mg/m ). 

From the results it can be concluded that the formaldehyde concentrations in the exit air in situation 2 differ from those in situations 1 and 3, which are almost the same. The reason is that in situation 2 the exchange of formaldehyde between the particleboard and the air concerned, was not complete. So the measurements in situation 2 do not fit in with the equilibrium determined. 

Out of the results of the intersection should follow an equilibrium concentration of 0.35 mg/m, which is not in accordance with the determined equilibrium value. So this experimental set up is a case of a situation which is not well defined and therefore not suitable for measurement of the relevant formaldehyde release parameters of the particleboard. 

To explain this, it can be argued that a not inconsiderable increase in resistance to mass transfer has been set up in the gas phase, which in fact may vary from situation to situation. Such situations are indeed normal in everyday practice. This explains why in practice, especially at low ventilation rates, much lower concentrations are found, than would follow from measurements done in climate chambers with good circulation. Such intensive circulations remain absolutely necessary if determination of the characteristic particleboard parameters is wanted, independant of the test environment. 

The effect on particleboard of an ammonia treatment can also be shown using this testing method. In figure 8 again the ideal mixing model is applied. Notice that the line with the lowest emission is the one on the top. The reason is that the reciprocal values and not the steady state formaldehyde concentrations as such, are plotted. Here the slope is different as well. 

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. 

After a few hours of circulating, different steady state concentrations are in fact found in the two burettes. In other words, one particleboard continually absorbs formaldehyde from the other. In this case particleboard 1 absorbs formaldehyde from particleboard 2. Table VIII shows the formaldehyde emission parameters of the two boards. Especially the equilibrium values are different, the mass transfer coefficients do not differ much. 

The expected concentrations when both the particleboards are placed in the same environment, are given in Table IX. 

Neither the simple sum of the concentrations nor the worst particleboard is decisive. 

Table VIII presents chamber data on underlayment particleboard, mobile decking particleboard, and industrial particleboard obtained from four different chambers identified A, B, C and D. A particleboard "set" is a specific production run of a particleboard type. The observed concentration is the formaldehyde level actually determined in the chamber for a specific loading and air change rate. "N" represents the air change rate (number per hour). The column labeled "L" is the loading (m2/m3) that the test was conducted. The column "N/L" ( m/hr) is the ratio of air change rate to the loading. Finally, the column labeled "Normalized Chamber Concentration" is the actual chamber concentration (first column) normalized to 0.3 ppm at N/L = 1.16. The 0.3 ppm chamber...

Table IX presents chamber data obtained in only one large test chamber identified as A on medium density fiberboard made at one plant. A medium density fiberboard "set" is a specific production run. The columns are labeled the same as the particleboard Table VIII described above. The "Normalized Chamber Concentration" is based on a 0.6 ppm formaldehyde concentration at an N/L ratio of 0.96. The choice of 0.6 ppm concentration is purely arbitrary. Figure 8 graphically represents the normalized formaldehyde chamber concentrations to loadings at air changes of 0.5, 1.0 and 1.5. The points which define the curves are averages of the normalized concentrations.

In addition, the effect of ventilation rate on chamber concentration is different for each wood product type, i.e. particleboard, medium density fiberboard, hardwood plywood paneling. 

Figure 7. Effect of air change rate and loading on chamber formaldehyde concentration - particleboard.

Table VIII. Particleboard - Loading and Air Exchange Rate Effects on Chamber Concentration...

The H.U.D. formaldehyde standards of 0.2 ppm and 0.3 ppm for hardwood plywood paneling and particleboard, respectively, were chosen because the combination of these products at their specific loadings and air change rate would result in a chamber concentration of less than 0.4 ppm. This assumption was based on four studies. 

Upon completion of the chamber test, the hardwood plywood paneling or particleboard is removed and 12 each 7.00cm x 12.7 cm specimens are randomly cut from each board loaded into the chamber. For the surface monitor (FSEM) and the small scale test chamber(SSTC), one 30.5cm X 30.5cm board is cut from each board loaded in the chamber. These samples are immediately tested by the Equilibrium Jar for particleboard or the Two Hour Desiccator or FSEM or SSTC for all wood product types. The values obtained from each test are averaged and are then compared to the chamber concentration observed for that loading and air change rate. 

The purpose of this study was to evaluate laboratory formaldehyde release test methods for predicting real-life formaldehyde air concentrations human exposure levels, and health risk. Three test methods were investigated the European perforator test, the gas analysis method at 60 C and 3% RH, and the gas analysis method at 23 C and 55% RH. Different types of particleboard bonded with urea-formaldehyde and urea-melamine-formaldehyde resins were tested. The results were used to rank boards as a function of test method, conditioning, short-term humidity, and temperature variations during storage. Additional experiments were conducted in small experimental houses at a Dutch research institute. Our conclusions are that relative ranking of products is influenced by the test method and by change in relative humidity. The relationship between test method and release in real-life situations is not clear. In fact, it seems impossible to use laboratory measurements to predict real-life product performance of board if the board is not fully in equilibrium with the atmosphere. 

During the manufacture (hot pressing) of the particleboard the formaldehyde is concentrated in the core of the board. Tests run on laboratory made particleboard with the same binder level throughout the board, have shown about 75% higher content of extract-able formaldehyde in the core than in the face ( ). Emission tests indicate an even greater difference between the two layers of the board. 

---