Optimization of simultaneous thermal analysis for fast screening of polycondensation catalysts

Abstract

Dynamic simultaneous thermal analysis was optimized to screen activity of different catalysts for polycondensation of bis-hydroxy ethylene terephthalate (BHET) to polyethylene terephthalate. Reactions were performed by heating BHET to 300 °C at a linear heating rate in 50 μl thermal analysis crucibles under inert gas purging. A sensitive and reproducible screening method was obtained after overcoming of critical problems such as monomer evaporation, catalytic activity of crucible material, and optimization of gas purging, monomer amount in the crucible and heating rate. Under the applied conditions mass transport limitations were absent and the reaction was controlled solely by chemistry. The temperature at which maximum reaction rate occurs was used as an index of catalytic activity. It was obtained from maximum differential scanning calorimetry signal together with the maximum derivative of thermogravimetry signal. Temperature at which the reaction starts was also applied as an activity index. It was obtained from the onset of mass loss. The value of these three indices was smaller for more active catalysts. The optimized method was applied to study the activity of a new polycondensation heterogeneous catalyst based on hydrotalcite. This new catalyst was shown to be much more active than the conventional antimony catalyst under the applied conditions.