8 Mechanisms of Formaldehyde Release from Bonded Wood Products George E. Myers
Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: August 8, 1986 | doi: 10.1021/bk-1986-0316.ch008
U.S. Department of Agriculture, Forest Products Laboratory, One Gifford Pinchot Drive, Madison,WI53705-2398
Published studies on wood systems and my recent research on the influence of urea-formaldehyde (UF) resin hydrolysis on formaldehyde emission from UF-bonded wood products indicate that (a) in an acid-catalyzed UF board, formaldehyde can exist in a wide variety of states, including dissolved methylene glycol monomer and oligomers, paraform, hexa, chemically bonded UF resin states, chemically bonded UF-wood states, cellulose hemiformals and formals. Each of those states is a potential source of formaldehyde emission by evaporation (methylene glycol) or initial hydrolysis. We cannot now quantify the relative contributions of these states over time; (b) in a base-catalyzed phenol-formaldehyde (PF) board, formaldehyde states may include methylene glycol monomer and oligomer, chemically bonded PF resin states, chemically bonded PF-wood states, cellulose hemiformals. Emission sources apparently include methylene glycol, cellulose hemiformals, and possibly phenolic methylols; and (c) diffusion processes very likely exert a major influence on panel emission rates and may involve movement of methylene glycol in the wood's moisture or of gaseous formaldehyde within the board or within the board-air interface. Over the past decade or so, great progress has been made in reducing formaldehyde emission from wood products such as particleboard, hardwood plywood paneling, and medium density fiberboard (1~3). Beneficial steps include reducing the formaldehyde-to-urea (F/U) mole ratio (4), impregnating the wood furnish (substrate) with a formaldehyde scavenger having hindered access to the urea-formaldehyde (UF) adhesive (5), and treating boards with formaldehyde scavengers and/or barrier coatings after manufacture (6). Many plants in Europe now produce particleboard, for example, that meets the German E-l standard recommending large test chamber formaldehyde levels of This chapter not subject to U.S. copyright. Published 1986, American Chemical Society
In Formaldehyde Release from Wood Products; Meyer, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: August 8, 1986 | doi: 10.1021/bk-1986-0316.ch008
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F O R M A L D E H Y D E RELEASE F R O M WOOD PRODUCTS
