Effect of barium sulfate on thermal stability and crystallization properties of poly(ethylene terephthalate)

In order to improve the dispersion and increase the compatibility between barium sulfate (BaSO4) nanoparticles and poly(ethylene terephthalate) (PET) matrix, hydrophobic BaSO4 nanoparticles were successfully prepared. PET/BaSO4 nanocomposites were prepared by in situ polymerization and further investigated properties improvement in PET by incorporating BaSO4 nanoparticles. The results showed the presence of BaSO4 nanoparticles improved the stability of PET matrix and accelerated crystallization process of PET matrix. From TG curves, it was concluded that PET and the samples with different content of BaSO4 nanoparticles presented good thermal stabilities, since no remarkable mass loss occurred up to 360 °C (<0.5%). Moreover, activation energy of nanocomposites during thermal decomposition was calculated by Friedman method. Crystallization kinetics under isothermal conditions was explained by Avrami equation. The activation energy of PET nanocomposites containing BaSO4 nanoparticles was higher than PET, because the presence of BaSO4 nanoparticles inhibited char formation and escape of volatile byproducts during thermal decomposition of PET. The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For PET and PET/BaSO4 nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing BaSO4 content. The change of the n values indicated that the addition of BaSO4 resulted in the increase in the crystallizing growth points. That is a heterogeneous nucleating effect of BaSO4 on crystallization of PET.