Particleboard formaldehyde release

Well over 95 percent of the hardwood plywood production in the United States uses urea-formaldehyde as the adhesive bonding agent between veneers for reasons of quality, intended use and economics. In this industry, formaldehyde evolution is a subject of concern because normally all of the adhesive formaldehyde released under elevated temperatures is not tied up in the set glue line. This is an area that is of real concern to the particleboard industry which uses urea-formaldehyde as its binder. 

Roffael E (1993) Formaldehyde release from particleboard and other wood-based panels. 

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. 

HOETJER AND KOERTS Formaldehyde Release from Particleboard... 

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. 

The formaldehyde release of particleboard can, as far as the particleboard is concerned, be described by two characteristic parameters. The equation is ... 

Rybicky, J. Horst, K. Kambanis, S. "Assessment of the 2 Hour Desiccator Test for Formaldehyde Release from Particleboard" Forest Products Journal, Sept., 1983, 33, pp. 50-54. 

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. 

Formaldehyde emission from particleboard has been studied at our laboratory for over 15 years. We search for an answer to the following question Given the fact that amino-resin bonded wood products have the ability to release formaldehyde into indoor air when they are in use, what simple and rapid analysis method can be used at the time of manufacture to predict formaldehyde release under use conditions as quantitatively as possible Obviously, the chosen method needs to be applicable for all types of boards that are available on the market. 

Tannin-Induced Formaldehyde Release Depression in Urea-Formaldehyde Particleboard... 

Roffael E. (1993) Formaldehyde release from particleboard and other wood based panels. Forest Research Institute, Malayan Forest Records No. 37, Maskha Sdn. Bhd., Kuala Lumpur. 

This work describes an optimization procedure for UP resin synthesis, following tin alktiline-acid process, focusing on the conditions of the condensation step. A design of experiments methodology was employed to optimize the 3 selected factors (number of urea additions, time span between urea additions, and condensation pH), in order to produce particleboards with maximum intemtil bond strength and minimum formaldehyde release. 

Comparatively little attention was given to the use of tannin-bonded particleboards for interior use until restrictions on formaldehyde emissions from urea-formaldehyde bonded products became a critical concern (178). Wattle tan-nin/urea-formaldehyde adhesive formulations for interior particleboards do reduce the large, short-term formaldehyde release normally observed soon after pressing, but not the slow emission that is common after extended storage (33). The scavenging effects of wattle tannins are limited to comparatively small amounts of formaldehyde because of the highly condensed nature of the tan-nin/urea-formaldehyde polymer after curing, as was also observed by Marutzky and Dix (136). 

Cameron F A, Pizzi A 1985 Tannin-induced formaldehyde release depression in UF particleboard. Nat Timber Res Inst CSIR Report 247 1-5... 

Marutzky R, Dix B 1984 Formaldehyde release of tannin-bonded particleboards. J Appl Polym Sci Polym Symp 40 49-57... 

Applications. UFs are the primary commodity binder in caul and caulless particleboard processes and medium density fiberboard (MDF). They can be formulated to develop tack and generally are used as a neat liquid. Acid catalysts are frequently used unless the wood species is acidic such as southern pine or oak. Products manufactured with UFs are rated for interior application. Use of MUFs or MFs increases bond durability and imparts water resistance to the bond, speeds cure rate, and reduces potential formaldehyde release. 

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... 

The concentration gradient that exists between the core and the face, leads to a migration of formaldehyde to the surface of the particleboard. From the surface layer it is released to the surrounding air. 

The concentration of formaldehyde in the air of a room containing particleboards, will depend on the content of formaldehyde in the boards and on the rate of its release. The formaldehyde content of a particleboard is determined by the binder used to manufacture the board and a number of production parameters. The release rate is affected by the temperature and the relative humidity of the surrounding air, but also by some of the physical properties of the board. The most important one probably is the diffusion resistance of the surface layer, which may be expressed by means of a mass transfer coefficient. 

A large number of test methods have been introduced for the determination of the tendency of particleboard to release formaldehyde. Some are analytical methods for the content of formaldehyde in the board, some are emission tests, and some are combinations of the two types. It seems to be generally accepted that the emission tests are the more meaningful ones, among other things because most formaldehvde regulations limit the permissible content of formaldehyde in the air rather than in the particleboard. 

Plywood and particleboard, affordable building materials, have been used in many facets of exhibition case design and storage. Unfortunately, these wood products are often bonded together with formaldehyde resins. As the resin cures over time, it will release formaldehyde vapors into the environment. In the presence of moisture, atmospheric formaldehyde will be converted to corrosive formic acid (36). In an attempt to diminish the acidifying effects of wood, coating and varnishes have been applied on the... 

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. 

Methylenebisurea and higher oligomers undergo further condensation with formaldehyde [11] and monomethylolurea [12], behaving like urea. The ability of methylenebisurea to hydrolyze to urea and methylolurea in weak acid solutions (pH 3 to 5) indicates the reversibility of the amidomethylene link and its lability in weak acid moisture. It explains the slow release of formaldehyde over a long time in particleboard and other wood products manufactured with UF resins. 

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