Contact allergy to phenoplastics

Abstract

The phenoplastic in the ICDRG series is ptertiary butylphenol-formaldehyde. This is often used in glues and is then often not completely hardened to an insoluble network. However, there are many other phenols and aldehydes used in phenoplastics. Furthermore, the processing procedure provides different types. Phenols commonly used are phenol, cresols, xylenol, resorcinol, alkylphenols (p-tert. butyl-, diisoethyl-, cardanol, etc.), bisphenol A, pphenylphenol, etc. Aldehydes used are mainly formaldehyde and furfural.Different types can be manufactured: Resols are formed when formaldehyde is in excess to phenol in alkaline environment. These are, for example, used for impregnation of paper in laminates. Novolaks ("new shellak") are formed when phenol is in excess to formaldehyde in an acid environment. These are used for casting "bakelite" objects. First, methylol compounds are formed. Particularly in resols these can be stable for months. When the semi-cured resols or novolaks are hardened (polycondensated), the end product is a network, i.e. an insoluble resit. For polycondensation novolaks need the addition of formaldehyde or a formaldehyde releaser, e.g. hexamethylenetetramine, paraform. Resols can polycondensate by the presence of free methylol groups. Varnishes made of phenoplastics are made of alkyl-/arylphenols (p-tert. butyl-, p-octyl-, p-nonyl-, etc.) or are modified by the addition of colophony, fatty acids, terpenes. Then also glycerol, pentaery thritol or ethyl glycol are added to complete the esterification. Furthermore, there are alkyl-and epoxy-copolymers. Phenoxyplastics are made of epichlorhydrin and Bisphenol A but do not contain epoxide groups.Because of the great variety, it is necessary to patch test with the resins used by the patient. The reactions among our patients illustrate this. Of 5628 routine patch tested subjects, 94 (1.7 %) gave positive reaction; 49 subjects were additionally tested with a resol (5 % pet.) and a novolak (5 % pet.) because they had reacted to p.tert.-nutylphenolformaldehyde resin in the routine series or were known to have been in contact with noncondensated phenoplastics. Twenty-eight reacted to p-tert.-butylphenol-formaldehyde resin, 10 simultaneously to resol and three both to the resol and the novolak; 21 were negative to p-tert.-butylphenol-formaldehyde resin but all were positive to the resol. Ten of these reacted simultaneously to the novolak. Of the 31 resolpositive cases, 25 worked at the same plastic factory, where both resols and novolaks were used. All the novolak-positive subjects also worked there.In this material of 49 cases of contact allergy to phenol-formaldehyde resin, 21 cases would never have been traced if only routine patch testing had been performed.The simultaneous reactions among the three different resins can hardly be evaluated at this stage. Both for diagnostic and preventive purposes it is necessary to isolate and identify the sensitizers in different phenol-formaldehyde resins. This has been carried out in the case of p-tert.-butylph...

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