Evaluation of formaldehyde emission of pine and wattle tannin-based adhesives by gas chromatography

Formaldehyde emissions from wood particleboards bonded with pine and wattle tannin-based adhesives, using hardeners paraformaldehyde, hexamethylenetetramine and TN (tris(hydroxyl)nitromethan), were measured by the perforator method (DIN EN 120-European Committee For Standardization 1991). All particleboards made using the wattle tannin systems with the three different hardeners were satisfied grade E₁, while in the case of pine tannin only the use of the hexamine hardener led to grade E₁ being satisfied. This tendency was attributed to the curing mechanism of the hardener, the reactivity of the tannin molecule toward formaldehyde and the fast reactivity toward formaldehyde of pine tannin, due to the inclusion of phloroglucinolic A-rings within its molecular structure. Hexamine was effective at reducing formaldehyde emission in tannin-based adhesives when used as the hardener. Being a more sensitive and advanced method, it was also used. The samples used for gas chromatography were gathered during the perforator method. The formaldehyde emission levels obtained from gas chromatography were similar to those obtained from the perforator method.