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Specifications of wood adhesives must be in correlation with the requirements for the corresponding wood products, for which they will be used. Formaldehyde emission of wood products bonded with urea-formaldehyde resin based
adhesives is strictly regulated by standards and there is a compromise is between formaldehyde emission and performance, such as strength, or water resistance. Since values of formaldehyde emission depend on the test method used,
in Europe urea-formaldehyde resins for adhesives may generally be classified according to HCHO emission in the particleboard rating of Emission 0 to Emission I class (E-0 to E-1). According to DIN EN 120, particleboard quality E1
emits <6.5 mg/100 g dry article determined with the perforator method. Although a great number of factors effect the formaldehyde emission of the cured products, such as the hardener system, the type of wood etc., the emission of
formaldehyde is in strict correlation with the free formaldehyde content of the resin before the curing process. E1 emission class can be achieved, if the free formaldehyde content of the resin is lower than 0.2% by mass.
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This information was referenced from The Technical University of Budapest, at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10526993&dopt=Abstract
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