Effects of Post Manufacture Board Treatments on Formaldehyde Emission: A Literature Review (1960-1984)

This paper reviews the literature dealing with the many post-manufacture board treatments used to reduce formaldehyde emission from urea-formaldehyde bonded boards. Such treatments have almost solely used one or more of five chemical or physical principles: formaldehyde reaction with NH3, formaldehyde reaction with oxygenated sulfur compounds, formaldehyde reaction with organic -NH functionality, pH adjustment, and physical barrier. I have categorized the available reports according to four primary board treatment methods that use the five principles in different ways. The four primary treatment methods are: Application of scavengers as solids or aqueous solutions: Ammonium bicarbonate and carbonate have been used as solid powders, while the solutions involved a varie of ammonium salts, ammonium and alkali metal salts with sulfur-containing anions, and urea and other compounds having -NH functionality. Exposure to scavengers as gases: NH3 is the primary reactant here, with minor effort using S02. Application of coatings: A variety of polymeric formulations have been examined as physical barriers, often supplemented by incorporating a scavenger such as urea. Lamination with barrier materials: Barrier materials have included polymer films, metal films, and impregnated papers, the last also incorporating scavengers. Firm, detailed conclusions or recommendations about the effectiveness of these methods are difficult to make due to lack of information, the wide variety of materials and processes employed, and the importance and variety of economic and processing considerations required in selecting among options for a manufacturing process. Clearly, however, major reductions in initial formaldehyde emission can be achieved by each of the four treatment methods; most reported improvements are by at least a factor of 2 and many exceed a factor of 10. Often, the barrier properties of coatings or laminates can be supplemented by scavengers. There is a strong need for additional aging studies to verify the long-term reliability of these treatments. At present I suggest that impregnation of boards with aqueous solutions is likely to be the most reliable because it should permit the use of a large scavenger excess ands also allow neutralization of board acidity to reduce resin hydrolysis.

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