Optical monitoring of the solidification process of polyester and vinyl resins

Abstract

Ultrasonic waves were generated and detected by laser light in solidifying polyester and vinyl resins, allowing an evaluation of the extent of reaction by a non-contact method. Commercial polyester and vinyl resin samples were prepared following the standard procedure under room conditions. A liquid adjacent to the sample was irradiated by a pulsed Nd:YAG laser beam. The resulting ultrasonic wave was detected in the sample at two distances from the source by the deflection of an HeNe laser probe beam. The displacements of the probe beam were detected by a position-sensitive photodiode. Arrival times of the ultrasonic pulses at various times during the solidification were measured and the corresponding propagation velocities calculated. The method is aimed at monitoring the final part of the solidification, after the gelation has taken place, and will allow the investigation of the influence of various parameters of the course of the reaction and on the final properties of the material.