Formaldehyde emission extract

To shed additional light on the emission mechanism and the contribution of resin hydrolysis to formaldehyde emission, my recent experiments have examined the liberation or extraction of formaldehyde from particleboards, from wood containing sorbed formaldehyde, and from cured resins. Here, I present results from particleboard and formaldehyde-sorbed wood experiments in which rates of formaldehyde removal were measured by three different procedures (see Appendix 1 for experimental details). 

Particleboard-Determination of Formaldehyde Content-Extraction Method Called Perforator Method, European Standard EN-120-1982, European Committee for Standardization, Brussels, 1982. "Particleboards - Determination of Formaldehyde Under Specified Conditions. Method Called Formaldehyde Emission Method, European Committee for Standardization, CEN Situation Report N 76 E, Brussels, 1984. 

No wax emulsion was added to the board to avoid the introduction of another factor that could have limited formaldehyde emission. To this glue mix were added 2 %, 5 % and 10 % UF resin solids by mass of commercial mimosa (wattle, Acacia mearnsii formerly mollissima) bark extract, a commercial flavonoid-type tannin extract. 

More interesting are the cases in which the tannin extract was added to the chips rather than to the glue mix. The effect here is also a depressed formaldehyde emission. The effect appears also to last much longer due to the higher amount of tannin added. (It must be borne in mind that pure tannin-formaldehyde commercial boards... 

Table I. Formaldehyde Emission Results of Boards "Spiked with Tannin Extract...

Work in South Africa and in South America has resulted in development of adhesives based largely or entirely on tannins. Tannins, which like lignins are renewable natural products, have the advantage of affording adhesives with low or no formaldehyde emissions, but tannin-based adhesives tend to be brittle. A useful tannin-based particleboard adhesive was reported using tannin extract... 

The emission of formaldehyde fumes from particleboard manufactured using urea-formaldehyde resins, and its decrease, have now been topics of interest in the timber and wood adhesives industry for a long time. Many solutions, some very effective, to this problem have already been advanced by many authors. In this brief article we do not pretend to present yet another successful or less successful method to control HCHO emission but to show the decrease in the amount of formaldehyde emitted by UF-bonded particleboard, over a period of time, to which tannin extract has been added in small amounts. Tannin extract is an inexpensive commodity in Southern Africa as well as in many other countries in the southern emisphere such as Brazil, Argentina and New Zealand. The method presented, if not completely effective may be an inexpensive system of control of HCHO emission over a limited period of time. 

During the manufacture (hot pressing) of the particleboard the formaldehyde is concentrated in the core of the board. Tests run on laboratory made particleboard with the same binder level throughout the board, have shown about 75% higher content of extract-able formaldehyde in the core than in the face ( ). Emission tests indicate an even greater difference between the two layers of the board. 

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