The Effect of Acid-Treatment of Carbon Nanotubes on the Thermal Kinetics of Isotactic Polypropylene

Isotactic polypropylene (iPP)/maleic-anhydride-grafted polypropylene (PP-g-MA)/raw and acid-treated single-walled carbon nanotube (SWCNT) nanocomposites were prepared in an internal mixer. Thermal and crystallization behaviors of these nanocomposites were evaluated. Thermal properties of the iPP and its nanocomposites were estimated using thermo-gravimetric analysis (TGA) under nonisothermal conditions. The kinetics of nonisothermal degradation of iPP and its nanocomposites were studied using the Friedman model based on the single heating rate method. In terms of onset temperature of degradation (T-onset) and activation energy for decomposition (E), it was found that raw and acid-treated SWCNTs provide improved thermal stability to the iPP matrix. The respective activation energy values were determined to be 84, 94, and 96 kJ/mol for iPP, iPP/SWCNT, and iPP/A-SWCNT, respectively. Differential scanning colorimetry (DSC) was used to study the isothermal crystallization kinetics of iPP and its nanocomposites. During isothermal crystallization, relative crystallinity developed with a time dependence described by the Avrami equation, with the exponent n = 3. Further analysis based on the Hoffman-Lauritzen theory revealed that the surface free energy (se) for the nanocomposites was lower than that of iPP.