Particleboard emission

For VOCs, control options are multiple. Source reduction or removal includes product substitution or reformulation. Particleboard or pressed w ood has been developed and used extensively in building materials for cabinet bases and subflooring and in furniture manufacturing for frames. If the product is not properly manufactured and cured prior to use as a building material, VOCs can outgas into the interior of the residence or building. Other sources of VOCs may be paints, cleaning solutions, fabrics, binders, and adhesives. Proper use of household products will lower volatile emissions. 

Wood particle and fiber driers are used to dry the raw material for particleboard and similar products (20). Just as with the veneer for plywood, the parhcles must be dried before being mixed with the resins and formed into board. Drying is accomplished in a gas-fired drier, a direct wood-fired drier, or steam coil driers. Many different types of driers are used in the industry. Emissions are fine particles and condensible hydrocarbons, which produce... 

Only a small amount of work has been done up to now concerning the prediction of bond strengths and other properties based on the results of the analysis of the resin. Ferg et al. [59] worked out correlation equations evaluating the chemical structures in various UF-resins with different F/U molar ratios and different types of preparation on the one hand and the achievable internal bond as well as the subsequent formaldehyde emission on the other hand. These equations are valid only for well defined series of resins. The basic aim of such experiments is the prediction of the properties of the wood-based panels based on the composition and the properties of the resins used. For this purpose various structural components are determined by means of - C NMR and their ratios related to board results. Various papers in the chemical literature describe examples of such correlations, in particular for UF, MF, MUF and PF resins [59-62]. For example one type of equation correlating the dry internal bond (IB) strength (tensile strength perpendicular to the plane of the panel) of a particleboard bonded with PF adhesive resins is as follows [17]... 

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). 

Baumann, M.G.D., Batterman, S.A. and Zhang, G.-Z. (1999) Terpene emissions from particleboard and medium-density fiberboard products. Forest Products Journal, 49 (1), 49-56. 

Leovic (1996) reported that the combined emissions of VOCs as ketones, ethers and aldehydes were generally much in excess of formaldehyde emissions for veneered particleboards. Koontz and Hoag (1995) had a similar folding for unfinished and veneered particleboard and MDF. They idenhfied the major VOCs... 

Brown (1999b) reported formaldehyde and VOC emissions from new, unfinished particleboard and MDF (both using urea formaldehyde resins) in Ausbalia. Formaldehyde emissions over the first three weeks exhibited first-order decay behavior that predicted little to no formaldehyde emission after 6 months. However, further emission measurements at 8 months showed the products sbll emitted formaldehyde at approximately one-half the new product rate (also further unpublished measurement at 2 years showed the same emission rate as at 8 months). It was concluded that the wood-based panels emitted formaldehyde by a double-exponen-ttal model, the early- to late-term emissions including the free formaldehyde in the products but the long-term emissions consisbng of only the formaldehyde... 

Lower formaldehyde emissions were found for the plywoods (all exterior grades) than for particleboard and MDF, but organic acid emissions still occurred, especially for the hardwood-based plywood (black butt) since such woods are... 

Koontz, M.D. and Hoag, M.L. (1995) Volatile organic compound emissions from particleboard and medium density fiberboard. Measuring and Controlling Volatile Organic Compounds and Particle Emissions from Wood-Processing Operations and Wood-Based Products, Proceedings No. 7301, Forest Products Society, WI, pp. 76-87. 

Nelms, L.H., Mason, M.A. andTichenor, B.A. (1986) The effects of ventilation rates and product loading on organic emission rates from particleboard. Proceedings of IAQ 86 Managing Indoor Air for Health and Energy Conservation, ASHRAE, Atlanta, pp. 469-85. 

The phenoloxidase-lignin-bonded particleboards are free of any emission. 

Formaldehyde emission JIS A 5908 Particleboards 5.9 Formaldehyde emission test... 

Zinn TW, Cline D, Lehmann WF. 1990. Long-term study of formaldehyde emission decay from particleboard. For Prod J 40 15-18. 

Particleboard and other products made with isocyanates emit only little formaldehyde (IJ, but these adhesives are expensive and require expensive manufacturing procedures. In contrast, phenolic soft wood plywood is a well established product that is predominantly used for exter i or appIi cat i ons. It conta i ns forma Idehyde i n chemically strongly bonded form and also emits little formaldehyde, as shown in a later chapter in this book. In fact, under almost all common use conditions this type of board contributes not much more formaldehyde than is already present in ambient air in many urban areas. The same is true for waferboard, which has recently become popular for replacing plywood. Likewise, phenolic particleboard emits little forma Idehyde, unIess the phenoIi c res in is bIended w i th UFR. Normally, the products with highest potential for formaldehyde emission are those bonded with UFR. During the past year, approximately 300,000 metric tons of UFR have been used for panel manufacturing in the U.S. 

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. 

When particleboard was first introduced, the risk of consumer exposure to formaldehyde emission was comparatively small as long as only moderate quantities of products were used in consumer applications. This situation changed when particleboard became popular and when its production reached millions of tons per year. This popularity caused different types of formaIdehydic products, such a wall panelling, flooring, tables, cabinet work and furniture to accumulate in homes and offices, yielding load ratios of I m of product surface area per 1 m indoor air space. 

Product tests. Clearly, the best product test is full-scale testing of finished panels under actual use conditions. This has been done (27,38) but is expensive, because several full-sized panels of each product must be pre-conditioned at constant temperature and humidity for at least a week. The next best approach is to test product samples in air chambers under standardized conditions. A summary of such methods is contained in Table I. A very large effort has been made over the last three decades world-wide to develop quick, reliable and meaningful product tests. Wittmann (16), Zartl (20), Plath (17), Verbestel (1, Neusser (21,22), Roffael (25), HUD, the U.S. Forest Products Industry (39,40), many standaraization organizations (41-43) and others have published many viable methods, but the testing involves a combination of complex factors and there is simply no single test that fulfills everybody s specific needs. Table I list some of the currently accepted test methods for formaldehyde emission from particleboard, plywood and medium density fiberboard. 

Large Scale Test Method for Determining Formaldehyde Emission from Wood Products Air Chamber Method, FTM-2" National Particleboard Assocaiton, Hardwood Plywood Association, U.S. Department of Housing and Urban Development, Federal Register, 1982, 48, 37169. 

Particleboard-Determination of Formaldehyde Emission under Specified Conditions Method Called Formaldehyde Emission Method," European Standard Situation Report EN-N76E-1983, European Committee for Standardization, Brussels, 1983... 

Hardwood plywood products are decorative in nature and are designed for interior use. Over 95X of all hardwood plywood is made with urea-formaldehyde adhesives. Responding to concerns about formaldehyde and certain wood products, test methods for measuring surface emissions were developed in the early 1980 s. Emissions from most hardwood plywood and particleboard products have decreased 65% to 95% in recent years primarily by use of low emitting UF adhesives and/or scavengers. Good correlation has been demonstrated between product test methods and indoor levels of formaldehyde in experimental manufactured homes. Decorative surface finishes can act to either increase or decrease surface emissions, depending on the nature of the finish and the substrate. 

Reduction in the emission characteristics of unfinished hardwood plywood is currently being achieved primarily by the use of low formaldehyde to urea molar ratio formulations. For the manufacture of hardwood plywood and particleboard, formaldehyde to urea molar ratios have been reduced to a range of 1.15/1 to 1.3/1. An important caveat low F/U ratios perhaps should be considered a proxy for the potential to reduce emissions through improved urea-formaldehyde adhesive technology rather than the exclusive means for improvement. Reducing the F/U ratio is not always the most effective way of reducing emissions in consideration of the variety of hardwood plywood constructions, products, and thicknesses. ... 

In-plant quality control and routine acceptance testing by property verification organizations such as the Hardwood Plywood Manufacturers Association and the National Particleboard Association require a method more efficient than the chamber for routinely monitoring trends in emission characteristics of products. The relationship between chamber and the small scale desiccator test observations is illustrated by a series of 76 tests accomplished during the past year on hardwood plywood wall panel products at a chamber loading rate of 0.29 sq ft per cu ft ... 

National Particleboard Association, Hardwood Plywood Manufacturers Association, October 10, 1983. Large scale test method for determining formaldehyde emissions from wood products, large chamber method, FTM 2, Reston, VA. 

G. Gramp, W. Groah. "Evaluation of the relationship between formaldehyde emission from particleboard mobile home decking and hardwood plywood wall paneling as determined by product test methods and formaldehyde levels in experimental mobile homes." U.S. Dept. of Housing and Urban Development, 1982. 

Although formaldehyde emissions from some products glued with urea formaldehyde adhesives can cause indoor air quality problems under certain conditions, such problems have not been associated with phenol formaldehyde-bonded (phenolic) products. Unfortunately, however the commonplace usage of the generic terms particleboard and plywood has failed to distinguish between product types and has led to a great deal of confusion among consumers. 

Roffael (15) measured formaldehyde emissions from a phenolic particleboard using the WKI-Method which involves suspending small samples over 50 cm of distilled water in tightly closed polyethylene bottles and measuring formaldehyde levels in the water after varying times. Temperatures were maintained at 42 C. This work indicated that formaldehyde release from the phenolic particleboards ceased after a relatively short reaction period (approximately 96 hours). This finding is consistent with the resin stability considerations discussed previously under theoretical considerations. 

Large-Scale Test Method For Determining Formaldehyde Emissions From Wood Products — Large Chamber Method, FTM 2-1983 National Particleboard Association Gaithersburg, MD, 1983. 

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