Solution Casted 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 of film. Different casting surfaces and humidity during casting are presented in this work, as variables to be considered for cellulose acetate film preparation (CA). Casting surfaces, borosilicate glass, soda-lime glass and Teflon (PTFE) dish are used and their influence on various properties of CA films is assessed. Soda-lime glass was coated with chlorotrimethylsilane because CA is strongly adhered to the neat surface during drying, making the film detachment impossible. The surfaces of glass dishes are smooth, while PTFE surface has a distinctive pattern, which is adopted by casted films upon drying. The resulting patterned morphology of the films is studied using optical profilometry. Patterned films are translucent while smooth surface films are transparent. Apart from the effect of different surface types, 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 compared to films casted in open air; however, wettability of films does not seem to be influenced by this variable, except for a higher hydrophobicity in the patterned films. Due to the specific morphology of the patterned films, change in opacity upon wetting is detected, going from translucent to transparent, while removal of water from the surface restores the translucency. This approach can be used for preparation of patterned films for food packaging application which can serve as humidity sensor.