DALE B. EDWARDS, ANAND R. SHAH, DONALD E. DUVALL
Papers # 2014 Chicago
Differential scanning calorimetry (DSC) has been used to study the processing of PVC pipes. This work has been largely embodied in ISO 18373-1-2007, Rigid PVC Pipes –differential scanning calorimetry (DSC) method – Part 1: Measurement of the processing temperature and Part 2: Measurement of the enthalpy of fusion for crystallites. Part 2 of the ISO method allows for a measurement of the enthalpy for the lower of two endotherms (“A”) that are observed in a typical PVC DSC trace. A measurement procedure for obtaining the enthalpy for the second endotherm (“B”) is not included in the standard.
The processing temperature measurement (ISO 18373 Part 1) has been used on many different PVC pipes with great success, as well as the enthalpy measurement of the lower “A” endotherm. There have been several papers that describe a procedure for calculating the “percent gelation” of the PVC pipe material by using measurements of the enthalpy of both the lower and upper endotherms (“A” and “B”), even though measurement of the upper endotherm is not included in the ISO standard. Attempts have been made using these extensions of Part 2 and other published material to utilize these types of measurements in order to determine whether a particular PVC pipe was “processed correctly”. This paper investigates the precision of these measurements of both processing temperature and the percent gelation measurements in order to ascertain whether the measurements are indeed meaningful. The paper will report measurements of the processing temperature and “percent gelation”, based on DSC experiments from multiple PVC pipes and will include information with respect to the effect of sample location on the results.