MEASURING PROPERTIES OF INDUSTRIAL POLYMER-FILMS USING INTERFERENCE-FRINGES IN THE INFRARED REGION

A study about the interference fringes caused in the infrared region by polymer films and their applications to the evaluation of some properties is reported. Interference fringes, a sinusoidal waveform superimposed on the baseline, arise from reinforcement and destructive interference of various wavelengths of radiation reflected from the internal surfaces of the film when the IR spectrum is carried out. An optical interference method is proposed for measuring the thickness and the refractive index, both within an accuracy better than 1%, and for evaluating the surface texture of polymer films. Each one of these procedures is explained by its application for polypropylene, polystyrene and polyethylene films, respectively, three commercially available industrial films widely used for packing and membranes. These methods can easily be extended to any fair thin film of transparent or weakly absorbing solid materials.