The mold was covered with a paper board immediately to control the evaporation rate of acetone. After drying in an oven at 40◦C for 6h, the film was peeled off the mold and stored at constant temperature (23±0.5◦C) and relative humidity (50 ± 5%) for at least 2 days before testing. Films made by casting were reproducible as a result of the controllable variables in operation and environment.