ANALYSIS OF DSC RESULTS BY INTEGRATION

The integration of data from differential scanning calorimetry to obtain enthalpy vs. time or temperature curves can be performed easily and painlessly with modern thermoanalytical instruments interfaced with computers. This paper reviews old techniques and develops new ones for determining proper thermodynamic quantities and temperatures, and degrees of conversion from the integrated curves. Methods for using the isothermal baseline rather than the transient one for minimizing the displacement from it during a constant heating rate experiment and for calibrating the isothermal temperature are described. Integration avoids errors due to kinetics effects and changes in interfacial resistance in the determination of heat capacity. The thermodynamic or ''fictive'' glass transition temperature and change in specific heat at the glass transition are determined more easily and in a correct manner by the integration method. The analysis of both sharp and diffuse first order transitions are discussed. Thermodynamically correct temperatures and heats of transition and reaction are obtained through integration. Application of the lever rule to isothermal ''tie lines'' is used to obtain the correct ''fraction reacted'' during transitions, and methods for compensating for weight loss and heat of evaporation are discussed. Purity determination by the stepwise isothermal method is briefly reviewed.