AUTOMATED MICROSCOPIC TECHNIQUE FOR EVALUATING POLY(VINYL CHLORIDE) -PLASTICIZER COMPATIBILITY

An automated microtechnique has been developed that Permits a rapid, r eproducible determination of the Flory-Huggins chi interaction paramet ers for poly (vinyl chloride) plasticizer systems. It is a modificatio n of the Anagnostopoulos method of determining an apparent melting tem perature of a poly(vinyl chloride) (PVC) particle in excess plasticize r. A microscope equipped with a photodiode sensor is used to measure c hanges in the light transmitted through a plasticizer sample containin g a PVC particle as the temperature is increased at a fixed rate, eith er 0.2 or 1.0-degrees-C/min. Data acquisition is done by computer so t hat minimal operator assistance is required. The apparent melting regi on is characterized by a sigmoidal change in the light transmitted thr ough a fixed sample area. This curve allows an accurate, reproducible definition of the apparent melting temperature from which the chi para meter is easily derived. The values obtained for the interaction param eter of PVC with four plasticizers chosen from the phthalate and phosp hate families are in good agreement with general trends of solvent qua lity. Separate experiments demonstrated that the overall transmittance profile reflects changes in both the size and the optical clarity of the PVC particle during heating. This leads to added features in the p rofile that reflect important diffusion and swelling characteristics f or a given system. (C) 1994 John Wiley & Sons, Inc.