POLYMER PROPERTIES INFLUENCING CURL RETENTION 867 • ELECTRODE Figure ,3. Schematic diagram o[ transmission apparatus illustrating the electrolytic cell and the polymer/electrode relationship moisture penetrating the film. The particular paper chosen was known to offer no barrier to moisture therefore, the MVTR of the paper/ polymer construction can be considered to be the MVTR of the polymer alone. After drying at 60 øC for two hours, and 15 minutes at 105 øC, and conditioning for 24 hours at 60% RH at 22øC, the test samples were weighed and placed in the high-humidity environment. Weights were taken periodically to determine the rate of water pickup. MVTR is expressed as milligrams of water/square centimeter of polymer film/second/centimeter thickness (mg/em2/see/em). Moisture Transmission (Liquid) Test samples were prepared from a 40% ethanol solution by casting a 0.0038-em wet film on a tin plate. The films were air dried for 16 hours at 22øC, then desiccated for 24 hours. Resistivity measurements were conducted at 22øC. Figure 3 shows a schematic of the transmission apparatus. The upper electrode was connected to a power source* while the lower elec- tode or tin substrate led to an electrometer. t Finally, a recorder, l: activated by the electrometer continuously plotted the change in re- sistivity, which is a measure of the liquid moisture transmission. Tensile Strength and Per Cent Elongation Test specimens were free films deposited from anhydrous ethanol solutions on a paper coated with a silicone release agent. All films * Model #9020~5, Sorer:sen & Co., South Norwalk, Conn. t Model #602, SoF,1 St:t•e Electrometer, Keithley Instruments, Cleveland, Ohio. 2• Model #VO?.l-7). Igau•ch & Lomb, Rochester, N. Y,

868 JOURNAL OF THE SOCIETV OF COSMETIC CHEMISTS .g Figure 4. Strain gauge apparatus were dried slowly and thoroughly to prevent air or solvent entrapment. The dried films were approximately 0.0038 cm in thickness. From these, tensile pieces were cut in 1.26-cm wide strips, conditioned, and tested at 90% RH at 22øC on an Instron Model TM* at a crosshead speed of 0.5 cm/min. Equilibrium Moisture Content The equilibrium moisture content was determined on free films cast from anhydrous ethanol. The films were air dried for 2 hours at 22øC, 2 hours at 60øC, 15 minutes at 105øC, and then stored in a desiccator for 24 hours. The dried films were attached to a hulled pressure transducer or strain gauge (Fig. 4). A pressure transducer will con- vert mechanical motion or strain into electrical current when a stress changes the resistivity of one leg of the transducer circuit. The dry film weight was recorded as millivolts on the readout of a DC-Micro- Volt Aremeter (Model 425At). The film weight was then hulled by the precision potentiometer and the strain gauge assembly was inserted into an atmosphere of 90% RH at 22øC. The increase in weight was * Instron Corp., Springfield, N.J. t Hewlett Packard Corp., Paramus, N. J.