Automated Method for Measuring the Thermal Degradation of Polyvinyl Chloride

Abstract

Abstract A system for studying low-temperature degradation of PVC by monitoring HCl evolution is described. The sample is heated in a Du Pont Model 951 Thermogravimetric Analyzer from ambient to 150[ddot]C, and the fractions are collected by means of an AutoAnalyzer® turntable which is synchronized with the TGA instrument. Either air or N2 is used as a sweep gas. This system allows for the precise collection of fractions versus time and temperature. The first fraction contains HCl released from room temperature to 120[ddot]C. Fractions are collected every 5[ddot]C (and 5 minutes) from 120[ddot] to 150[ddot]C, and several additional fractions are collected isothermally at 150[ddot]C. The fractions are then analyzed for chloride with an AutoAnalyzer® connected to a cell containing a chloride specific ion electrode and a fluoride reference electrode. The system is calibrated with standard chloride solutions ranging in concentration from 0.5 to 20 ppm. Samples are analyzed at a rate of 24 per hour. The system is capable of analyzing 60 per hour. Data are given illustrating the precision of both the chloride analysis and the total pyrolysis-analysis system. Also, data are shown comparing an untreated PVC sample to one containing an oxidation inhibitor. As expected, the data show that the inhibitor-containing sample is more stable to 150[ddot]C than the untreated sample. The advantages of this system are: (1) High sensitivity which allows for the detection of HCl evolution at low temperatures. Because of the good sensitivity, the method is very useful for testing the thermal stability of experimental compounds. (2) Ease of operation since the AutoAnalyzer® makes it unnecessary for operator manipulation during pyrolysis and chloride analysis. (3) Precise control of pyrolysis time, temperature, and programming rate.