Pressed wood products

Pressed Wood Products A group of materials used in building and furniture construction that are made from wood veneers, particles, or fibers bonded together with an adhesive under heat and pressure. 

VOCs are emitted indoors by building materials (e.g., paints, pressed wood products, adhesives, etc.), equipment (photocopying machines, printers, etc.), cleaning products, stored fuels and automotive products, hobby supplies, and combustion activities (cooking, unvented space heating, tobacco smoking, indoor vehicle use). 

Formaldehyde Germicide, pressed-wood products, urea-foimaldehyde foam insulation (UFFI), adhesives, paints, plastics, carpeting, gypsum board, ceiling tiles and panels, wood paneling. 083 2A... 

Xylene Solvent, dyes, insecticides, polyester fibres, adhesives, wallpaper, varnish, carpeting, wet-process photocopying, pressed-wood products, gypsum board, water-based adhesives, grease solvents, paints, carpet adhesives. 2.9 3... 

Synonyms methanal, methylene oxide, oxymethane Formula HCHO MW 30.03 CAS[50-00-0] constitutes about 50% of all aldehydes present in air released in trace quantities from pressed wood products, burning wood, and synthetic polymers and automobiles colorless gas at ambient conditions pungent suffocating odor liquefies at -19.5°C solidifies at -92°C density 1.07 (air = 1) very soluble in water, soluble in organic solvents readily polymerizes flammable, toxic, and carcinogenic (Patnaik, 1992). 

Resins used as bonding agents in pressed wood products Particle board Plywood Paneling... 

The possible sources for the most important chemical compounds identified in the European Audit project are presented in Table 5 [50]. The most important source of VOCs was materials, especially furnishings. The dominant VOCs detected in the majority of the buildings were solvents used in floor or wall coverings and pressed-wood products (carpets, PVC flooring, floor adhesives, wallpaper, particle board, etc.). 

In China, formaldehyde emission of the pressed-wood products sold is generally high. A test showed that the average formaldehyde release rates of four kinds of typical wood-based panels, i.e., particle board, medium-density... 

Although pressed wood products may be a source of formaldehyde in indoor air, there are numerous others. These include permanent press fabrics, fiberglass products, decorative laminates, paper goods, paints, wallpaper, and cosmetics (Kelly et al. 1996). Its presence in indoor air also results from combustion sources, such as stoves, heaters, or burning cigarettes (Matthews et al. 1985 NRC 1981). 

A subpopulation with potentially high exposures to formaldehyde are residents of mobile homes due to the frequent use of pressed wood products and their low rate of air exchange (Wolff 1991). Members of the general population who come in contact with a large amount of unwashed permanent press fabrics treated with formaldehyde-releasing resins may also be exposed to high levels. 

Pressed wood products contribute to indoor formaldehyde levels. Combustion sources and phenol-formaldehyde resin bonded products generally are weak emitters to indoor air. Common indoor combustion sources include gas burners and ovens, kerosene heaters, and cigarettes (Matthews et al. 

Formaldehyde release from pressed wood products is due to latent formaldehyde. During the pressing process, hot steam from moist wood particles transfers heat, formaldehyde, and other volatiles from the surface of the mat to the core of the board where un reacted urea-formaldehyde resin components accumulate. The resulting formaldehyde concentration in the core is approximately twice that of the surface. Release of formaldehyde is diffusion-controlled and gradually decreases over time (Meyer and Hermanns 1985). Formaldehyde can also be produced by hydrolytic cleavage of unreacted hydroxymethyl groups in the formaldehyde resins. Melamine formaldehyde resins generally are more stable, and the amounts of formaldehyde emitted from them are much lower (WHO 1989). 

In the home, fonnaldehyde sources include household chemicals, pressed wood products (especially when new) (EPA 1996), combustion sources (NRC 1986), and some new fabrics (Schorr et al. 1974) and garments. A number of common household products may release formaldehyde to indoor air, including antiseptics, medicines, dish-washing liquids, fabric softeners, shoe-care agents, carpet cleaners, glues, adhesives, and lacquers (Kelly et al. 1996). If children use or play with some of these products, or are present when they are used, additional exposure to formaldehyde may occur. Many cosmetic products contain formaldehyde and some, such as nail polish and nail hardeners, contain high levels (Kelly et al. 1996). If children place these products in their mouth or on their skin, or sniff them, they will be exposed to elevated levels of formaldehyde. 

Formaldehyde is released from many pressed wood products used in the construction of furniture (Konopinski 1983). When placed in a new crib manufactured from these materials, infants may be exposed because of tlieir proximity to the furniture s structural components. Also, small rooms that have new furniture manufactured from pressed wood products installed may have localized, elevated concentrations of fonnaldehyde because of their low total volume. 

Workers in industries where formaldehyde is used or released may receive potentially high exposures. Members of the general population who live in newly constructed homes or homes where pressed wood products have recently been installed may be exposed to high levels of formaldehyde by inhalation for... 

Matthews, T. G. Reed, T. J. Tromberg, B. J. Fung, K. W. Thompson, C. V. Hawthorne, A. R. "Modeling and Testing of Formaldehyde Emission Characteristics of Pressed-Wood Products," Consumer Product Safety Commission, CPSC-IAG-84-1103, 1984. 

Formaldehyde (CH2O) release was measured for seven types of consumer products pressed wood, urea formaldehyde foam materials, clothes, insulation, paper, fabric, and carpet. A modified Japanese Industrial Standard (JIS) desiccator test was used to measure release rate coefficients and to rank 53 products. Ten pressed wood products and five urea formaldehyde foam products showed the highest CH2O releases (1-34 mg m 2.day"b The remainder, representing all product types, had lower releases ranging from 680 yg m 2.day to nondetectable levels. In other studies, CH2O release was measured in a ventilated chamber for single samples of particle board, plywood, insulation, and carpet. 

As measured by the modified JIS desiccator procedure, pressed wood products had the highest release rate coefficients expressed as a function of surface area (Table IIA) of the various sample types tested. Release rate coefficients from urea formaldehyde foam products were comparable to those of pressed wood products (Table IIB). Products labelled substrate (sub 1, sub 2, and sub 6) were experimental foams. The drywall that had been placed next to the foams (Number 1, 2, or 3) for more than 1 week in a configuration similar to that in a building released a moderate amount of formaldehyde. 

Unwashed new clothing samples (Table IIC), fiberglass insulation products with formaldehyde resins (Table IID), paper products (Table HE), fabrics (cotton, nylon, olefin, and blended) (Table HF), and carpets (Table HG), had substantially 3 to > 100 fold) lower formaldehyde release rate coefficients, as measured by this method, than did pressed wood products or urea formaldehyde foams (1, 15). 

Pressed wood products and urea formaldehyde foam products had much higher release rates than those from most of the other products tested. Similar release rates have been observed by others (19). More than half of the products tested had very low release rate coefficients, and this included individual samples from six of seven of the types of products. Products equilibrated at 100% RH prior to the measurement were used to measure formaldehyde release. This equilibration may have removed a variable amount of formaldehyde (8, 14-17). 

The relative ranking for each type of product on the basis of rate of release of formaldehyde per unit surface area was pressed wood products z formaldehyde foam clothes z insulation products z paper products > fabric > carpet. Considering the surface area of each type of product likely to be present in houses and the relative release rate coefficients. 

Based on our and other researchers experience, the minimum air flow across the board should be between 1.5 to 6 meters per minute(11). Current chamber research at the National Bureau of Standards (N.B.S) sponsored by the Consumer Products Safety Commission on formaldehdye emissitivity from pressed wood products is being conducted at 1.5 meters per minute face velocity(12). 

Grot, D. "Plan for Testing Model for Formaldehyde Emissions from Pressed Wood Products" National Bureau of Standards,... 

Matthews, T.G. Daffron, C.R. Corey, M.D. "Formaldehyde Surface Emission Monitor - Protocol I Pressed Wood Products" ORNL/TM—8656, Oak Ridge National Laboratory, June, 1983. 

Figure 2. Safe emission limits for UF-bonded pressed wood products P = perforator value (mg/lOOg) USD = desiccator value (mg/L), after reference 14.

Formaldehyde is directly emitted into the air from vehicles. It is released in trace amounts from pressed wood products such as particleboard and plywood paneling, from old sick bnildings, and from cotton and cotton-polyester fabrics with selected crosslink finishes. Formation of formaldehyde has been observed in some frozen gadoid fish due to enzymic decomposition of the additive trimethylamine oxide (Rehbein 1985). Its concentration can build up during frozen storage of fish (Leblanc and Leblanc 1988 Reece 1985). It occurs in the upper atmosphere, cloud, and fog it also forms in photochemical smog processes. 

A wide range of adhesive types and chemistries are used to bond wood elements to one another (Table 2), but relatively few adhesive types are utilized to form the composites themselves. The vast majority of pressed-wood products use synthetic thermosetting adhesives. In North America the most important wood adhesives are the amino resins (qv), eg, urea-formaldehyde (UF) and melamine-formaldehyde (MF), which account for 60% by volume of adhesives used in wood composite products, followed by the phenolic resins (qv) eg, phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF), which account for 32% of wood composite adhesives (12,13). The remaining 9% consists of cross-linked vinyl (X-PVAc) compounds, thermoplastic poly(vinyl acetates) (PVA), soy-modified casein, and polymeric diphenylmethylene diisocyanate (pMDI). Some products may use various combinations of these adhesives to balance cost with performance. 

Formaldehyde, the simplest aldehyde, is a colorless gas with a pungent odor. An aqueous solution called formalin, which contains 40% formaldehyde, is used as a germicide and to preserve biological specimens. Industrially, it is a reactant in the synthesis of polymers used to make fabrics, insulation materials, carpeting, pressed wood products such as plywood, and plastics for kitchen counters. Exposure to formaldehyde fumes can irritate the eyes, nose, and upper respiratory tract and cause skin rashes, headaches, dizziness, and general fatigue. 

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