THEORY AND PRACTICE OF THE PREPARATION OF LOW FORMALDEHYDE EMISSION UF ADHESIVES

The resin manufacturing parameters which need to be manipulated to produce urea-formaldehyde (UF) resins capable of producing low formaldehyde emission particleboards of class E1 are presented and discussed. Several E1 UF resin formulations are presented and discussed, each achieving the wanted goals of strength and low formaldehyde emission by different approaches but still satisfying the required balance of preparation parameters. The different approaches were explained on the basis of the relative proportions of the chemical species produced analyzed by C-13 NMR. Resins preparation and structural parameters and relative proportions of the chemical species present in the final resin were compared and related. Both the manufacturing procedures and the laboratory and industrial boards results produced using these formulations are presented, underlying a common denominator in all these types of formulations. At laboratory level even formulations of urea: formaldehyde molar ratio as low as 1. : 0.7 gave an acceptable balance of results, while industrially the optimum balance of properties appeared to be reached in the molar ratio range of 1 : 0.9 to 1 : 1.0 but particularly at around 1 : 0.96. El emission levels of 5mg/100g board and lower (by perforator test) were achieved with ease.