Demonstration of contact sensitizers in resins and products based on phenol-formaldehyde

12 phenol-formaldehyde resins were investigated with regard to the presence of 14 contact sensitizers by using high-pressure liquid chromatography. The allergens consisted of simple methylol phenols, dihydroxydiphenyl methanes, 4,4(1)-dihydroxy-(hydroxymethyl)-diphenyl methanes and 2,4(1)-dihydroxy-(hydroxymethyl)-diphenyl methanes. Four substances, 2,4-dimethylol phenol, 2,6-dimethylol phenol, 4,4(1)-dihydroxydiphenyl methane and 2,4(1)-dihydroxydiphenyl methane, were isolated from a resol resin and identified by mass-spectrometry and nuclear magnetic resonance spectrometry. The highest concentrations (up to 15% w/w) of allergens were noted for methylol phenols in resol resins based on phenol and formaldehyde. The corresponding novolak resins showed a high content of dihydroxydiphenyl methanes. There was great variation in concentration of the sensitizers between the resins. None of these sensitizers were demonstrated in the resin based on paratertiary-butyl phenol. Products based on phenol-formaldehyde resins were also investigated for the presence of allergens. Uncured impregnated paper for laminate production and uncured mineral wool contained the same concentrations of the sensitizers as some of the resins studied. The curing process decreased the content of all the allergens investigated in all products, but the sensitizers did not disappear, and they may thus be present in finished products.