On the influence of binder content in particleboards bonded with resins of high and low molar ratio on the formaldehyde release measured by the perforator method

A comprehensive literature survey and the results of investigations clearly show that the influence of resin level in particleboards on the perforator value (EN 120) depends on the molar ratio of the resin used as a binder. In case of high molar ratio resins (F:U 1.6:1) increasing the binder content in the boards leads to an increase in the perforator value of the boards. In contrast, boards bonded with very low molar ratio aminoplastic resins with molar ratio F:U of 1:1 (F:NH₂ 0.5:1) or even lower do not show any noticeable increase in the perforator value on raising the binder level. On the contrary, the measured perforator values may sometimes decline due to increase in the resin content in the boards. The perforator test seems to include two main processes taking place alongside each other: the physical extraction of free formaldehyde and the chemical hydrolysis process of the resin itself, induced by the moisture content of the boards. In case of low molar ratio resins, particularly at very low molar ratios (F:U 1:1 or even lower), free urea may also be present in the resin or added to the resin as a scavenger. Urea seems to react with extracted formaldehyde at high temperature during the extraction process. This lowers the perforator value without necessarily decreasing the emission at ambient conditions. Insofar, inextricably intertwined chemical processes seem to unfold during the extraction process. Additionally, the results show that subtle differences in the perforator value in the very low formaldehyde emission region may remain without noticeable impact on the emission measured by the chamber method (EN 717-1).