206 JOURNAL OF THE SOCIETY CF COSMETIC CHEMISTS (b) Hair Preparations (i) Hair Lacquers and Wave Sets The first cosmetic products based on polyvinylpyrrolidone to reach large- scale commercial production in the U.S.A. and Europe have been hair lacquers, wav• sets and other allied hair sprays.' It has been stated 8 that in the U.S.A. in 1955 somewhere between thirty-five and thirty-eight million aerosol cans of polyvinylpyrrolidone-based hair spray were sold, and at the time this information was published it was claimed that sales were still increasing rapidly. These sales, in fact, accounted for something in the region of 70 per cent of the total U.S. output of hair sprays in that year. Hair lacquers have, of course, been known for many years, but the older type materials were usually based on shellac and other resins, and in the •*' ..-.•.: •.' •- ::•. •:.-'•?•.-•:•-.-,g• .. *: -•:-• ..• .... :::•. :•'• . •: • ::•'- .--••.•:• •'- -:-:-:':. ':: • "::.• • ." .:? :':...f'e•: •':" .::. :• ? . ....... . .... •.... :..•..:...:• :.%... •..:..-• ..• :.. ( -.. • ...................... ?... .., .,...::.....- :• ,.. • .... ....?:- :• ...... :: •':•:.•t'-":..- '..' •.I'•.•'-'..'. '•, • ........ .•:'•' ..... "' ...... ..&? •. ..... • .... . •.. . ,: :....:-.:"• ,.. .--...:::. •' ...: ...-,......-.-,•....,......:.--,.: ,.: ß :z ....... -. •..' .. •-. ..:. •? :•:.•..•".. ....... * ."* :•.--....:...:.:.:...:'.-- .½• ...¾ : *-* ::'•'•"•.' •. ':* : * '•*•*•":"*' '-*..':2' :?:"':: .* ...... ..' '*' * ::-. ..... •,, ... •.:-...-..?-•,.: ..? .. ,. •. .:..:. .... ..............-. ß .•. --. . ..... . •...•-.• •.... I--.,. ... . .:. . ,.: •,-... :. ...•',• .:.::. :::..:- ':'-'- .:-.... -•...•....:. ... x ..:. •.*m ,:..•:' ß: .& •.., .: ',?:, ".----, .......... ..... ....:..:? ...::.•::..:....: •,.. •½ :1:• '...:'"'"'.::,.:' • ,•., •. :•' '.,::.:?:•?...• .-:....: ,:,: ::?.': •: •, '. .: i• • ' '... ::::::::::::::::::::::::::::1....::'""••-:•{•,:%?'%}2:::?...'*• .. .... .. ....... ..... ..•} :-'..•. .... .. 2 ....... :':" ":".•'-•-- .:') ,-: '*..'-.... .,:... .. ' ::•'.: ::.. ...::..• ,,...... ....:? ..... ....... .:.:.:. ., : ,¾• • .,½::' ,..': .-' . )..?r..:... . :•:.:. Fig. I0o Another view of the spray dryer f•r the final recovery of solid polyvinylpyrrolidone.

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