Formaldehyde concentration loading

Reduced sample loadings in the dynamic chamber led to decreased formaldehyde concentrations in the chamber as noted or predicted previously by others (17, 20-22). This resulted in increased release rate coefficients (yg m 2 day"b. Samples analyzed at 1.4 and 1.6 m2 of product surface area/m of chamber volume chamber loadings had formaldehyde chamber concentrations of 28-32% of the calculated equilibrium air concentrations of formaldehyde (17), suggesting better relative ventilation than that at higher chamber loadings. 

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. 

The GEM method is based upon the assumption that the size and shape of the testing chamber does not influence the emission. During the testing the formaldehyde concentration in the chamber will rise and stabilize at a steady state concentration. At constant climate the steady-state concentration or emission rate from the test object depends on the relation between the loading factor and the air change rate. Good air circulation in the chamber is also essential ( ). 

Formaldehdye generation and recovery studies 3.) Air exchange measurement techniques 4.) Preconditioning of test boards 5.) Temperature effect on chamber formaldehyde concentrations 6.) Relationship of popular quality control test methods to the large chamber 7.) Loading, air exchange rate, and wood product combination effects on chamber formaldehyde concentrations 8.) Chamber Round Robin studies between Georgia-Pacific s chamber and other outside lab chambers 9.) Chamber concentrations and its relationship to actual field measurements. 

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.

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

Effects of loading and air exchange rates on chamber formaldehyde concentrations can be predicted. 

Myers, G. "Effect of Ventilation Rate and Board Loading on Formaldehyde Concentration A Critical Review of the Literature" Forest Products Journal, 1984, 34, pp. 59-68. 

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... 

The formaldehyde concentration in the gel depends on the length of the electrophoretic run short runs (high voltage) require less formaldehyde (1.2%), whereas overnight runs may require 7% denaturant. It has even been reported that formaldehyde can be eliminated from the gel without affecting electrophoretic separation or subsequent transfer if runs are shorter than 3 h (only formaldehyde/formamide in loading buffer) (Liu and Chou, 1990). We generally use 1.2% (= 0.41 M) formaldehyde, to decrease the level of toxic vapors in the gel. 

A limited number of sink effect studies have been conducted in full-sized environments. Tichenor et al. [20] showed the effect of sinks on indoor concentrations of total VOCs in a test house from the use of a wood stain. Sparks et al. [50] reported on test house studies of several indoor VOC sources (i.e., p-dichlorobenzene moth cakes, clothes dry-cleaned with perchloroethylene, and aerosol perchloroethylene spot remover) and they were compared with computer model simulations. These test house studies indicated that small-chamber-derived sink parameters and kj) may not be applicable to full-scale, complex environments. The re-emission rate (kj) appeared to be much slower in the test house. This result was also reported by other investigators in a later study [51]. New estimates of and were provided,including estimates of fca (or deposition velocity) based on the diffusivity of the VOC molecule [50]. In a test house study reported by Guo et al. [52], ethylbenzene vapor was injected at a constant rate for 72 h to load the sinks. Re-emissions from the sinks were determined over a 50-day period using a mass-balance approach. When compared with concentrations that would have occurred by simple dilution without sinks, the indoor concentrations of ethylbenzene were almost 300 times higher after 2 days and 7 times higher after 50 days. Studies of building bake-out have also included sink evaluations. Offermann et al. [53] reported that formaldehyde and VOC levels were reduced only temporarily by bake-out. They hypothesized that the sinks were depleted by the bake-out and then returned to equilibrium after the post-bake-out ventilation period. Finally, a test house study of latex paint emissions and sink effects again showed that... 

In dynamic (ventilated) chambers, release rate coefficients were increased by a factor of 4.4 for particle board and 2.2 for plywood at loadings of 1.4-1.6 m /m over values at loadings of 9-11 m2/m3 (Table IV). Increased pressure of formaldehyde in the chamber was associated with reduced release of formaldehyde from wood products, as indicated by comparing equilibrium concentrations of formaldehyde (H). 

This vapor acts as a driving force for formaldehyde diffusion from the wood cel I towards the product surface, and for emission from the finished wood product. An internal vapor pressure of 20 Torr would approximately correspond to a formaj ehyde air concentration of about 1 ppm at 25 t, a load factor of I m and a ventilation rate of 1 ach. However, as emission continues and depletes the methylene glycol concentration in the wood moisture, the dissociation of hemiacetals will set in and add to the formaldehyde source. The bottleneck in the formaldehyde transport will be diffusion through the product towards the product surface. This process depends on the permeability of the product which, in turn, depends on diffusion... 

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...

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