Characterization of polymer-based materials using fluorescence method and fractal analysis

On the basis of multiple valuable properties polymer materials are widely used in our life today. There is no industrial field in which polymers will not be applied. Based on high molecular organic compounds rubbers, fibres, plastics, films and coatings will be fabricated. Important topic is thereby the study of aging mechanisms and stability of polymers against external load or influences. Especially desired is to establish non-destructive methods avoiding destruction of polymers occurring for example by widely used breaking stress and tensile test, measurement of friction coefficient or definition of water vapour permeability. Current work is based on using of fluorescence measurements for evaluation of aging state of polymer-based materials, especially adhesives and medical polymers. The evaluation of the time dependent fluorescence signals has been performed supposing fractal behaviour of the fluorophores molecules with an algebraic decay of the fluorescence intensity in a certain time interval. This allow to estimate the parameter of fractal dimension DF. To characterize the polymer state two more parameters are taken into consideration; the maximum of the fluorescence intensity after short Laser pulse excitation and the fluorescence decay parameter. The fluorescence measurements were performed by the help of a special device for the fractal analysis of the time-time-correlation in the fluorescence decay, developed at Fraunhofer IKTS for other purpose. In this paper we report on measurements of three kinds of adhesives used in electronic industry before and after stress as well as several kinds of medical polymers before and after sterilization by means of different sterilization technique. With the help of reference methods - infrared and Raman spectroscopy - it was previously defined if the polymer structures were changed or not. Collecting a large number of time resolved fluorescence data a suitable statistical analysis of measured results could be performed. The presented results of the new approach characterizing polymer materials offer a promising method for non-destructive evaluation of the polymer status, however, this approach requires further trials and has to be validated by that.