Particleboard equilibrium concentration

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. 

It is important to distinguish between those emission tests that measure the emission in a closed, or unventilated, system and those that measure in a ventilated system. If a particleboard is kept in an unventilated system, the formaldehyde concentration will increase until it levels off at an equilibrium concentration which will depend on the formaldehyde content of the board under test, the temperature and the relative humidity. The particleboard loading, on the other hand, will not influence the equilibrium concentration, just the time it takes to reach it. The time to reach the equilibrium concentration is also influenced by the mass... 

In a ventilated system the exhaust air will remove some of the emitted formaldehyde, and a steady state concentration will be established. The steady state concentration will be lower than the equilibrium concentration. How much lower, will depend on the ventilation rate, the particleboard loading and the mass transfer coefficient. 

The project plan involved the use of the Bell method to determine the equilibrium concentration and mass transfer coefficient for a number of particleboard samples with different surface finishes and overlays. 

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. 

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. 

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. 

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