Isothermal crystallization kinetics and melting behaviors of nanocomposites of poly(trimethylene terephthalate) filled with Nano-CaCO3

The isothermal crystallization and subsequent melting behavior of poly(trimethylene terephthalate) (PTT) composites filled with nano-CaCO3 were investigated at designated temperatures with differential scanning calorimetry. The Avrami equation was used to fit the isothermal crystallization. The Avrami exponents were determined to be 2-3 for the neat PTT and PTT/CaCO3 composites. The particles of nano-CaCO3, acting as nucleating agents in the composites, accelerated the crystallization rate, with the half-time of crystallization decreasing or the growth rate constant (involving both nucleation and growth rate parameters) increasing. The crystallization activation energy calculated from the Arrhenius formula was reduced as the nano-CaCO3 content increased from 0 to 2%, and this suggested that nano-CaCO3 made the molecular chains of PTT easier to crystallize during the isothermal crystallization process. Subsequent melting scans of the isothermally crystallized composites exhibited triple or double melting endotherms: the greater the content was of nano-CaCO3, the lower the temperature was of the melting peak. The degree of crystallization deduced from the melt enthalpy of composites with the proper concentration of nano-CaCO3 was higher than that of pure PTT, but it was lower when the nano-CaC03 concentration was more than 2%. The transmission electron microscopy pictures suggested that the dispersion state of nano-CaCO3 particles in the polymer matrix was even when its concentration was no more than 2%, whereas some agglomeration occurred when its concentration was 4%. Polarized microscopy pictures showed that much smaller or less perfect crystals formed in the composites because of the interaction between the molecular chains and nano-CaCO3 particles. (C) 2007 Wiley Periodicals, Inc.