The effects of temperature and humidity on formaldehyde emission from UF-bonded boards : a literature critique

An analysis has been conducted on available data related to temperature and humidity effects on formaldehyde concentrations that are produced by emission from particleboard and hardwood plywood paneling. Temperature changes are described by an exponential relation while a linear relation suffices for humidity effects. Large variations exist in the results from different investigators on different boards for the exponential temperature coefficients B (– 5620° to 12,480°K-1) and for the linear humidity coefficients s (0.005% to 0.038%-1). The variations appear to be caused by experimental errors, procedural differences between laboratories, board-to-board differences, and board aging. Statistical treatment of all chamber test data as a composite set (normalized to unity at 25°C) yields a composite B of – 8930°K-1, with a 95 percent confidence interval from – 8390° to – 9470°K-1 (± 6% relative error). Using this composite B, calculated correction factors, c (25°C)/ c(T), varied from 4.89 at 10°C to 0.152 at 45°C. The statistical analysis also indicates that significant board-to-board and laboratory-to-laboratory variations occurred. Assuming this composite coefficient is indeed valid for a particular board or dwelling, it can be used to make temperature corrections to standard temperature with, for example, relative errors (95% confidence) in correction factors being ± 7 percent for a ± 10°C temperature difference. In the absence of knowledge about the specific applicability of a particular temperature coefficient, however, temperature corrections should probably be restricted to a 5°C range, except for general engineering or planning purposes. A similar composite analysis of all the humidity data (normalized to unity at 50% relative humidity (RH)) yields a composite s of 0.0195%-1 with a 95 percent confidence interval from 0.014 to 0.025 (± 28% relative error). The corresponding correction factors, c (50%)/ c (RH), vary from 2.41 at 20 percent RH to 0.56 at 90 percent RH. Very large variations between investigators, and between boards, lead to poor confidence in such composite universal humidity correction factors, however, and no clear recommendation can be made regarding correction factors to convert formaldehyde concentrations to a standard humidity. Small humidity changes (~10% RH), however, probably can be neglected since they may be masked by rather minor temperature changes (± 1° to 2°C). Much more information is needed to clarify the reasons for the large variability and to increase confidence in temperature and humidity correction factors. This is the fourth in a planned series of six critical reviews of the literature on different aspects of the problem of formaldehyde emission from adhesively bonded wood products. The series was initiated because of the need expressed by industry representatives for an independent evaluation and summation of data from a wide variety of studies. The six aspects being reviewed are concerned with effects of 1) formaldehyde-to-urea mole ratio (25), 2) ventilation rate and loading (26), 3) additions to wood furnish (28), 4) temperature and humidity, 5) post-manufacture treatments of boards, and 6) hydrolysis. This paper analyzes the available data on effects of changing temperature or humidity (RH) on formaldehyde emission from particleboard and hardwood plywood paneling. As with the first three reviews (25, 26, 28), it is based upon a bibliography (27) derived from several sources (25), in this case covering the period from 1960 through May 1984.1 The author is a Chemist, USDA Forest Serv., Forest Prod. Lab., One Gifford Pinchot Dr., Madison, WI 53705. This work was partially funded by the Formaldehyde Institute. Aid was provided by the FPL library staff in literature search and procurement, and by the staff of the Systems and ADP group in establishing and manipulating a computer literature file. The efforts of Carol Link were indispensabe in the statistical analysis. This paper was received for publication in October 1984. Forest Products Research Society 1985. Forest Prod. J. 35(9):20-31.