POLYVINYLPYRROLIDONE IN COSMETICS 207 opinion of some users had marked defects. The advantage of polyvinyl- pyrrolidone-based hair sprays appears to lie in the fact that the polymer is soluble both in water and in organic solvents, and the lacquer, therefore, can be applied from a volatile solvent and yet be readily shampooed from the hair when required. When correctly compounded there is no tendency to dust or flake on the hair, and when packing in aerosol cans the compati- bility of polyvinylpyrrolidone with the usual propellants overcomes problems of valve clogging. Polyvinylpyrrolidone hair sprays impart lustre to the hair, and probably owing to its hygroscopic nature improves hair manage- ability this is said to be a marked improvement on the older type lacquers. The hair can be reset, moreover, for several days by using a damp hair brush and comb. It must be admitted that one does not obtain the crisp varnished appearance achieved with some of the older hair lacquers, but although some users think this a disadvantage, one gathers that many prefer the softer and more natural results obtained with polyvinylpyrrolidone. Formulation is basically straightforward, but needs to be varied to meet different climatic conditions and different types of hair. A varied degree of crispness in the finish can also be provided to some extent to meet the needs of the user. All these are functions of the polyvinylpyrroli- done content and the type and quantity of plasticiser used. In a dry climate polyvinylpyrrolidone hair lacquers are said to be somewhat drying on the hair, and it seems to be a common practice 9 in the U.S.A. to incorporate a humectant for this reason. In countries having a damp climate obviously a humectant is undesirable, and indeed in the U.K. a water-repellent plasticiser is used by most producers to make the hair finish reasonably damp-proof. To deal with extreme conditions of moisture i t has been suggested that the waterproofness of the hair spray can be increased still further by including modifying resins such as shellac, polyvinyl formal, etc., although the use of the former does not appear to find general fayour. In deciding the solids content of lacquers it is necessary to consider the type of hair. Fine silky hair calls for lacquers containing as little as 2 per cent poly- vinylpyrrolidone, but such a product would be quite useless on coarse wiry hair, where lacquers containing up to 7 per cent or 8 per cent of poly- vinylpyrrolidone can be used. In commercial practice it seems usual to strike a compromise, and in the U.K. most lacquers appear to contain from about 4 to 6 per cent of polyvinylpyrrolidone. The choice of plasticisers for polyvinylpyrrolidone is largely a matter of individual requirements. If water-repellency.is to be achieved, either an oily plasticiser such as an alcohol-soluble lanolin ,derivative or isopropyl myristate can be used, or alternatively a phthalate plasticiser can be incor- porated together with a small quantity of an alcohol-soluble silicone

208 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Mixtures of plasticisers are also quite common, and are, formulated to get special effects. The crispness of the hair finish is largely a matter of plasticiser content. Using a polyvinylpyrrolidone content of 5 per cent one can use as little as « per cent plasticiser without dusting or flaking and get a relatively crisp finish, but 1 per cent or 2 per cent of plasticiser results in softer and less visible finishes the actual concentration depends to some extent upon the plasticiser used. High plasticiser contents have the advantage of giving increased lustre. The usual solvent is ethyl alcohol, and when packing in aerosol cans this should be substantially anhydrous. For bulk sales and when packing in squeeze bottles many formulators prefer to incorporate a little water as this is said to improve hair manageability, but this is, of course, ruled out when using some plasticiser systems. Iso-propanol also appears to have received some consideration as a solvent, the attraction probably being the absence of duty, the lack of need for denaturants and its ready availability in anhydrous form for aerosol packing. In the past,, I believe that its odour has given rise to some difficulty in perfuming, but it has recently been claimed that this need no longer be regarded as a serious difficulty. Some of the commercial polyvinylpyrrolidone hair lacquers are marketed as combined lacquers/wave sets, but it seems more Usual to formulate wave sets to provide a less permanent, hair finish, their function being, of course, to set the hair into curls after shampooing. Such preparations are now often based on aqueous ethyl alcohol containing'about 2 % of polyvinyl- pyrrolidone together with plasticiser, perfume, etc. Some cosmetic chemists recommend the inclusion of a wetting agent, and indeed this is also done occasionally with hair lacquers intended for use in squeeze bottles which give a rather coarse spray, the idea presumably being to assist the lacquer to spread on the hair. • (ii) Hair Creams Apart from hair lacquers and wave sets primarily intended for use by ladies, considerable interest is being shown, particularly in, America, in the use of polyvinylpyrrolidone in men's hair fixatives. 8 It is generally thought that the market here is larger in tonnage. Such preparation, s can either be similar in formulation to hair lacquers, and such preparations appropriately perfumed are said to be on the American market,, or alternatively they can be made in the form of oily emulsions using polyvinylpyrrolidone in the aqueous phase. ,Such polyvinylpyrrolidone-stabilised creams are fine in texture and• have a,high sur, face gloss in the jar, at the same time imparting a surprising sheen to the.hair without lea,ving it•unduly oily, There appears to be no technical difficulty in the manufacture of such preparations.