Solution Casting of Cellulose Acetate films. Influence of Surface Substrate and Humidity on Wettability, Morphology and Optical Properties

Variations on the processing conditions of conventional methods for polymeric film preparation may allow tuning certain properties. In this work, different casting surfaces and humidity are presented as variables to consider for cellulose acetate (CA) film preparation using conventional solution casting method. Specifically, borosilicate glass (BS), soda-lime glass (SL) and Teflon (PTFE) dishes have been used for casting and their influence on various properties on CA films assessed. The surfaces of glass dishes are smooth, while PTFE surface has a pattern constituted by concentric channels of micro dimensions (as seen by optical microscope), which is adopted by cast films upon drying. The resulting patterned films are translucent while smooth surface films are transparent. Apart from different surface of the substrate for casting, humidity influence on CA films is evaluated in terms of conditions during the evaporation of solvent from solution (35 %, 55 % and 75 % humidity). The increase of the humidity produces smoother surfaces and higher film crystallinity as shown by XRD and DSC; however, wettability of films does not seem to be influenced by this variable. Due to the specific morphology of the patterned films, change in opacity upon wetting is detected, from translucent to transparent, while removal of water from the surface restores the translucency. This approach can be used for micropatterning of films that can serve as humidity sensor.