Document rBnRNvwMZ5Zy9ojEnw3a9XV7e

30,264 540,012 l&sifcation of the occupation tnd are for men aged 45-64 >mposed. F. Holt and Sonia G. id F. M. Troisi. field Cooper, f Occupational Health. i. Knowles and M. D. ince of Joan Bedford. , , BY D. KENWIN HARRIS From Imperial Chemical Industries Ltd., Plastics Division (received for publication JUNE 8. 1953) :i j The increasing variety of plastic materials Formaldehyde Products /f produced during the last few years is due mainly The thermosetting types in this group are those 1 to the ability of the modern chemist to synthesize the formed by the condensation of phenol, cresol, urea, chemical compounds from which plastics are made. or melamine with formaldehyde. In the manufacture ( The basis of most plastics today is the synthetic and use of resins, glues, and moulding powders of j polymer and its introduction has made available this type free formaldehyde may be liberated under 1 many substances hitherto unknown in industry. certain circumstances, the amount depending on 1 Modern plastics are manufactured to serve specific such factors as the ratio of the ingredients, the degree purposes so that the synthetic polymers cam no of condensation, and the addition of other chemicals longer be regarded as substitutes for those found such as hexamethylenetetramine. For the sake of naturally as cellulose, rubber, and proteins. A wide simplicity these products are discussed below in two range of materials can be made from them and so separate sections depending upon whether they designed as to meet the actual properties required mainly affect the human body externally or internally. for any particular application. In addition to the polymer, synthetic plastic Effects on the Skin.--Formaldehyde and hexamine | materials contain varying amounts of other chemicals are well known as primary irritants of the skin and ; as catalysts, accelerators, stabilizers, hardeners, mucous membranes and many factories handling j pigments, and so on, which are added to assist resin glues have had cases of dermatitis at some and regulate polymerization or to influence the time or another (Factory Department, 1943). properties of the final material, such as colour and Schwartz, Peck, and Dunn (1943) mention a factory flexibility. Most polymers are chemically inert and of 800 employees where 600 cases of glue dermatitis under ordinary circumstances the final plastic occurred during the first six months of operation. In material should be comparatively harmless. Jt is a small leather factory the incidence of dermatitis admittedly difficult, however, in practice to effect was highest (28%) in the section where " notorious complete polymerization and traces of free monomer sensitisers such as formaldehyde, lacquer and or other chemicals may be present which can Bismarck Brown were used " (Squire, Cruickshank, sometimes produce pathological conditions such as and Topley, 1950). It has been stated that the dermatitis. actual substance responsible for hexamine and Polymerized chemicals may be broadly divided formaldehyde dermatitis is formic acid (Schwartz, into two groups, condensation and addition poly Tulipan, and Peck, 1947). mers. They may also be divided into thermoplastic There is another factor that should be considered or thermosetting types depending upon whether the in assessing the predominant cause of dermatitis as polymer is softened or hardened by heating. The the result of handling some of these products. change that takes place on heating the thermosetting In their usual commercial form, for example, these materials is irreversible. formaldehyde glues and resins will adhere to the skin and rapidly harden on contact with it, and Little CONDENSATION POLYMER PLASTICS (1950) considers this to be the primary cause of the Condensation polymers are usually formed by the more serious outbreaks of dermatitis from them. linkage of molecules with the elimination of water or Mayen and Silverburg (1936) stress the great some other compounds. variation in the length of time ranging from a few 255 w