iNGREDIENT RELEASE FROM AEROSOL FILMS 671 films were selected based upon their insolubility in water so as to eliminate any effect due to solution of the film in desorbing media. d lkali Resistance The model films were cast from a 5% w/w solution of the film- forming agent and plasticizer. Carboset 525 and Polymid 1155 were dissolved in absolute ethyl alcohol while the Emerez resins were dis- solved in isopropyl alcohol. Twenty milliliters of the solution was potired onto the stirface of mercury contained in a 150- X 20-mm Petri dish which was then covered with an inverted glass funnel. Clearance was provided for the escape of the solvent vapors by raising the base of the funnel just above the resting surface. The hlnnel was an aid in controlling the rate of evaporation of the solvent and redriced the blistering of the surface of the deposited film. The resulting films were removed from the surface of the mercury and stored in a desiccator for 24 hours before they were used. The alkali resistance of the films was determined by suspending the films in a bath containing an alkaline borate buffer solution of pH 9.5 at 37 _+ IøC. The films of approximately 3 x 4 cm size were secured be- tween two 10-mesh stainless steel screens. The screens with the test film were immersed in the bath for an indefinite period of time. The time required by the film to exhibit the first sign of any kind of opalescence was noted as the end point. These results are shown in Tables I and II and represent the average of three determinations carried out on each film. Table I Alkali Resistance of Emerez Fihns Film Appearance of Emerez Plasticizer (%) Opalescence Erosion a Performance,, 1533 Hexadecyl alcohol (10) 49 hours None Fair 1536 ... 25 hours None Fair 1540 Hexadecyl alcohol (10) None None Excellent 1540 Hexadecyl alcohol (20) 5 days None Very good 1540 Hexadecyl alcohol (30) 4 days None Good 1540 Citroflex-4 (10) None None Excellent 1540 Amerchol L-101 (10) None None Excellent • All results reported as "None" were observed for a period of seven days. These results indicate that the films showed no solubility in the desorbing media. * Each film was evaluated physically on the basis of tackiness, flexibility, continuity, and appearance.

672 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Alkali Resistance of Polymid, Carboset, and Ethyl Cellulose Films Appearance of Film Plasticizer (%) Opalescence Erosion Performance Polymid 1155 Hexadecyl alcohol (10) 13 hours 2 days Poor Polymid 1155 Citroflex-4 (10) 13 hours 2 days Poor Polymid 1155 Amerchol L-101 (10) 13 hours 2 days Poor Carbose* 525 a . .. 3 days None Good Ethyl Cellulose N-10 Hexadecyl alcohol (10) None None Excellent Ethyl Cellulose N-10 Hexadecyl alcohol (20) 12 hours None Fair Ethyl Cellulose N-10 Hexadecyl alcohol (30) 12 hours None Fair a Carboset 525 is soluble in alkaline media and therefore the resistance of the film was determined in demineralized water. Film Hardness Film hardness was determined on films which had been cast upon a steel surface. A concentrated solution of the film-forming agent and plasticizer (35-50% w/w depending upon solubility in the alcohol sol- vent) was placed onto a steel plate (4 in. x 12 in.) and by means of a film casting knife* drawn into a thin film having a thickness of approxi- mately 0.0024 in. These plates with the cast film were placed in an oven at 45 _--+- 0.5øC for 3-4 hours. The exact thickness of the film was measured using a magnetic gauge.* Hardness of the applied film was measured as the number of oscilla- tions the Sward Hardness Rocker* completed on the smooth surface of the film compared to 100 oscillations on a polished plate glass. These results are shown in Tables III and IV and represent the average of three determinations for each film. Modulus of Elasticity Following determination of the Sward hardness, R, of the film, the modulus of elasticity, E, was calculated from the following equation: KR • E- * Gardner Film Casting Knife, Model •AG-3820, Gardner Laboratories, Inc., Bethesda. Md. * Elcometer Magnetic Gauge, Model •GG-6270, Gardner Laboratories, Inc., Bethesda, Md. ++ Model •C, Gardner Laboratories, Inc., Bethesda, Md.