How Mole Ratio of UF Resin Affects Formaldehyde Emission and Other Properties: A Literature Critique

A critical review was made of the literature concerned with how the formaldehyde to urea mole ratio (F/U) affects formaldehyde emission from particleboard and plywood bonded with urea-formalde hyde (UF) adhesives, and how this ratio affects certain other adhesive and board properties. It is difficult to quantify the dependence of various properties on mole ratio or determine lower limits of mole ratio for a particular property because of the range in resin, board, and testing parameters used in the cited studies. However, the available data do at least suggest the following limitations on F/U in conventional UF particleboard systems for maintenance of acceptable properties: 1) F/U < 1.2 or even < 1.1 to meet the German El emission standard, 2) F/U < 1.3 or possibly < 1.2 to meet the tentative NPA emission standard for U.S. mobile homes, 3) F/U equal or less than 1.2 for bending strength and modulus of rupture, 4) F/U >1.1 or possibly >1.2 for internal bond, 5) F/U >1.2 or possibly equal or less than 1.3 for 24-hour thickness swell. These conflicting limitations strongly indicate that problems exist in depending solely on mole ratio reductions to produce low emission UF particleboard with acceptable physical properties.

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