THE INTERFERENCE OF NONIONIC EMULSIFIERS WITH PRESERVATIVES IX By JOHANNA POPRZAN AND MAISON G. DENAVARRE* Presented September l, 1960, Munich, Congress of IFSCC A vREV•OVS STVD¾ (1) has indicated that some polyols, e.g., hexylene glycol, commercial propylene glycol, and 1,3-propanediol are effective in low concentration for purposes of preserving nonionic surfactant solutions. Propylene glycol is known to possess antimicrobial properties being used as a preservative in the food, pharmaceutical, and cosmetic industries. Because propylene glycol is so widely used as a humectant in cosmetic and pharmaceutical products, it may account for the fact that many nonionic surfactant type emulsions on the market are free from spoilage. These products may be preserved by the dual action of the polyol and the com- monly used preservative. The present study will evaluate the effectiveness of other common polyols and alcohols, both as preservatives and as synergists in nonionic emulsions. The disinfectant activity of the simple aliphatic alcohols is well known. Some polyols have shown synergistic antimicrobial activity in non- ionic surfactant solutions, the alcohols then seem to be in a logical position to produce possibly better results. EXPER•4•NTAL A 2 per cent solution of the nonionic G-3720 [polyoxyethylene (20) stearyl alcohol] was used throughout this work for reasons of convenience. This nonionic solution was prepared in either nutrient broth (for bacterial tests), or in Czapek Dox broth (for mold tests). The various polyols or alcohols were then added to the nonionic solutions in concentrations re- quired by the test. Methyl p-hydroxybenzoate, if required for the test. was added prior to sterilization at 15 pounds pressure for twenty minutes The addition of the alcohols and polyols after sterilization was done sepa- rately to test the effect of sterilization on these substances. Essentially, the same results were obtained, which proved that sterilization had no ill effect on these particular materials. * Cosmetic Laboratories, Inc., Detroit 7, Mich. 280

THE INTERFERENCE OF NONIONIC EMULSIFIERS 281 To twelve and one half ml. of the sterilized solutions in test tubes (25 X 200 mm.) was added 0.1 ml. of A/spergillus niger spore suspension in sterile distilled water or 0.1 ml. of a forty-eight hour nutrient broth sus- pension of Pseudomonas aeruginosa or Bacillus subtills. All inoculations were made in duplicate. The tubes were stored at room temperature (25øC.) for at least two months and some for as long as one year. Po LYO LS The polyols used in this study were dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2,6--hexanetriol, and 1,$-pentanediol in appropriate nutri- ent. The effect of 5 per cent polyot on a 2 per cent solution of G-3720 with no addition of methyl p-hydroxybenzoate, is summarized in Table 1. All five polyols supported the growth of the three micro6rganisms at a 5 per cent concentration. Previous work has shown that hexylene glycol and 1,3-propanediol inhibited the growth only of A/spergi//us niger at the $ per cent level while commercial propylene glycol was ineffective at this concentration. Table 2 shows the effect of the addition of 0.2 per cent methyl p-hydroxy- benzoate to the polyol-nonionic medium. Examination of Table 2 shows that the growth of z/. niger is inhibited in all tests, but the bacteria continued to grow. Only 5 per cent 1,5-pentane- diol plus 0.2 per cent methyl p-hydroxybenzoate was a completely effective combination it inhibited the growth of all three microiSrganisms under test. It is apparent from these data that an additive effect is obtained with the polyols and methyl p-hydroxybenzoate in preventing mold growth in particular in media containing a nonionic. Further investigation shows the effect of 10 per cent polyol on a nonionic surfactant solution. 1,3-butanediol and 1,5-pentanediol at a 10 per cent concentration, with- out any preservative, were capable of inhibiting the growth of the three micro6rganisms under test. In the previous work, hexylene glycol and 1,3-propanediol were equally as effective while commercial propylene glycol required a concentration of 15 per cent or higher to inhibit growth. When 0.2 per cent methyl p-hydroxybenzoate was added to this system, the results in Table 4 were obtained. With the addition of the preservative, all the 10 per cent polyol com- binations except dipropylene glycol, were effective in preserving a non- ionic surfactant solution. These results also indicate a synergism or additive effective. Molecular weight or position of hydroxyl groups does not seem to have a bearing on the efficiency of the polyols among those tested. The hydroxyl groups seem to be the only chemical grouping in common with these compounds which can be responsible for this activity.