THE CHOICE OF PERFUMES FOR PRESSURIZED PRODUCTS 389 SOME FACTORS RELATING TO THE CHOICE OF PERFUMES FOR PRESSURIZED PRODUCTS R. E. ECKTON, M.A.* Presented at the Symposium on "Aerosols", organised by the Society, at Southport, Lancs., on 24th April 1963. The average consumer is rapidly becoming more odour-conscious and effective perfuming is one of the most important aspects of sales appeal. Since perfumes are complex chemical mixtures, they are capable of enter- ing into a variety of reactions in aerosol systems, and other factors not previously encountered have to be taken into account. It is essential, therefore, that per/runes for aerosols are compounded specifically and that they are thoroughly tested under proposed conditions of use. THE IMPORT^NCE of odour in toilet preparations and household products of all types is now very clearly recognised. Effective perfuming or re- odorising represents a major aspect of sales appeal. Exploitation of this is producing an increasingly odour-conscious public this trend goes forward hand in hand with our ability, by virtue of the production of new materials and accumulated experience, to meet the technical and economic require- ments of perfuming an ever-widening range of products. Aerosol products (which in this paper are taken to include wet sprays, foams, etc.) are expected to measure up to the same standards. The greater convenience in use of push-button packaging does not compensate for any inferiority in other respects. Perfume compounds are complex mixtures from both natural and syn- thetic sources of organic chemicals, including alcohols, esters, aldehydes, ketones, acetals, lactones, ethers, hydrocarbons, acids, phenols, etc. It is hardly surprising, therefore, that many new problems have arisen in the application of these materials to aerosol systems. So many writers have described their experiences and contributed to our progress in this field that it is possible to draxv attention only to some •'5. Thus, when producing or selecting a perfume for an aerosol, it is necessary to give careful consideration to many factors affecting performance and stability some of these are involved in the perfuming of non-pressurized products, others are peculiar to the aerosol. *Givaudan & Co. Ltd., Whyteleafe, Surrey.

390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS AESTHETICISM The first desirable requirement is for the odour of the product to be acceptable immediately on release from the container. This involves adequate masking of the odour of the propellants, solvents or other ingredients. DiGiacomo 6 has drawn attention to the way in which the perfume in certain aerosol products is presented to the nose in entirety rather than progressively from top note onwards as with conventional products. He also pointed out the effect of particle size, which depends on internal pressure and valve characteristics. The perfume should be evanescent or persistent, according to the product, and must continue to mask any residual odour of the medium. No staleness or unpleasant effect as a result of successive apphcations should develop. IRRITATION This factor is always weighed seriously in the practice of perfumery but there are additional considerations in the case of perfumes for aerosols, especially where fine sprays are involved. New situations are created and unexpected effects of irritation of the nasal and other membranes can arise. The case of benzyl benzoate which, although widely used in dermatological preparations, gives rise to sternutatory effects in some aerosols ilhIstrates this point 6. SOLUBILITY In most conventional products, incomplete solubility of perfume would most certainly be undesirable, as it would be uneconomical and could result in an unsightly appearance of the preparation, but in the case of pressurized products it can be responsible also for malfunctioning of the dispenser owing to valve blockage. The normally used halogenated hydrocarbon propellants are not the best of solvents for many perfumery materials. In some aerosol formulations, other ingredients such as alcohols and glycols exert a favourable influence, whereas hydrocarbons and water for example. can aggravate the situation. Insolubility is not always obvious at once precipitation of gummy or other residues can be progressive as the system reaches equilibrium. It is possible to process some natural products and to develop special synthetics with solubility in mind, so that the restrictions are not an embarrassing limitation. CORROSION AND OTHER ACTION ON CONTAINERS AND COMPONENTS Apart from the action of certain organic acids and alcohols on some metals, the part played by perfumery materials in container corrosion is incompletely understood. It is certain, however, that their presence in a given system can exert an influence on the degree of corrosion resulting.