Thermal Stability, Crystallization, and Melting Behaviours of Iodine Doped Semiconducting Polyethylene Terephthalate (PET) Thin Films

The influence of iodine doping on the thermal stability, degradation kinetics, and the melting and crystallization behaviors of polyethylene terephthalate (PET) films were investigated. Iodine doping was performed by immersing PET films in 0.4 M I2/l toluene. The thermal stability and degradation kinetics of PET and the semi-conducting PET/iodine complex films were studied using the thermogravimetric analysis-derivative thermogravimetric analysis (TGA-DTGA) studies and the differential scanning calorimetry (DSC). It was found that iodine incorporation accelerated the thermal degradation and weight loss through increased chain mobility owing to the imperfections formed by doping. Both pure and doped films exhibited appreciable thermal stability with the peak degradation temperature above 400 degrees C. DSC thermograms of the pristine PET and the PET/iodine films in the crystallization regions were recorded during the cooling scan and the significant parameters were studied. The peak crystallization temperature of PET increased from 192 to 209 degrees C after iodination. Doping initiated crystallization at an early stage of cooling with an increase in the rate of crystallization and smaller crystallization half time. Iodine catalyzed crystallization and acted as a nucleating agent. DSC scans were also used to study the melting characteristics of the polymer samples. The peak melting temperature was lower and the absolute crystallinity reduced for the iodine doped PET films.