Thermochimica Acta 510 (2010) 103–112 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Non-isothermal crystallization kinetic of poly(ethylene terephthalate)/fumed silica (PET/SiO 2 ) prepared by in situ polymerization G. Antoniadis a , K.M. Paraskevopoulos a , D. Bikiaris b , K. Chrissafis a,∗ a School of Physics, Solid State Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece b Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece article info Article history: Received 27 April 2010 Received in revised form 1 July 2010 Accepted 2 July 2010 Available online 29 July 2010 Keywords: Poly(ethylene terephthalate) Fumed silica Activation energy Nanocomposites Crystallization abstract A number of poly(ethylene terephthalate) (PET) nanocomposites were prepared by in situ polymerization using different amounts (0.5, 1, 2, 3 and 4 wt%) of fumed silica (SiO 2 ). The polymerization of PET was carried out by the two-stage melt polycondensation method. From DSC studies it was found that the melting point of the nanocomposites was shifted slightly to higher temperatures by the addition of SiO 2 till 3 wt% while for PET–4 wt% SiO 2 nanocomposite the melting point was reduced. As the amount of SiO 2 was increased the crystallization became faster, and there was, also, a shifting of the temperature of the crystallization peak to higher values, this being evidence that SiO 2 can act as nucleating agent. At higher content (3 and 4 wt%) the temperature of the crystallization peak is lower than that of PET–2 wt% SiO 2 due to the formation of crosslinked macromolecules. The activation energy is calculated with the Friedman’s method. PET/SiO 2 samples present lower activation energy compared to that of neat PET, except those of PET–4% SiO 2 , in which the activation energy have a maximum value for ˛ = 0.8 probably due to the second crystallization peak. Extensive crystallization studies by using Avrami, Ozawa and Malek methods verified that PET and its nanocomposites must be crystallized by two mechanisms with different activation energies taking place in different degrees of crystallization. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The investigation of the kinetics of polymer crystallization is sig- nificant both from the theoretical and practical point of view. The mechanism of the formation of fine structure during polymer crys- tallization has practical importance and it arises from the effect of crystallinity on both physical and chemical properties of polymer. Poly(ethylene terephthalate) (PET) is a linear semi-crystalline thermoplastic polyester with excellent mechanical, physical, and chemical properties, including very good heat resistance, high stiff- ness and strength, and good dimensional stability. These properties make PET an attractive high performance polymer for engineering plastic applications in areas of electronics, transportation, con- struction, and consumer products. However, PET application as an engineering plastic for injection moulding is rather limited, due to its slow crystallization rate and large cycle time [1]. The first studies on the non-isothermal crystallization of PET were carried out in 1971 when Ozawa [2] proposed a new method to analyze data for the solidification of semi-crystalline polymers cooled at a constant cooling rate. ∗ Corresponding author. Tel.: +30 2310 998188; fax: +30 2310 998188. E-mail address: hrisafis@physics.auth.gr (K. Chrissafis). Crystallization process of PET has recently been reexamined due to the increasing theoretical and technological interest. Valev and Betchev [3] studied the crystallization thermodynamics and kinet- ics of amorphous PET fibers subjected to simultaneous thermal and mechanical treatments. They found that the Ozawa’s model can be used for the qualitative description of the amorphous PET fibers crystallization. In order to increase its performance, during last years, nanocom- posites were prepared and studied, especially that containing silica nanoparticles (SiO 2 ). Fumed silica is a non-crystalline, fine-grain, low density and high surface area silica. Zheng and Wu [4] in their study have shown that nanosilica do not behave as a nucleat- ing agent but rather retard the appearance of the microcrystalline phase that enhances spinnability. Liu et al. [5] have found that the addition of nanoparticles increases the crystallization temperature and the melting point of the polymer. Additionally, nanoparti- cles do not affect very much the process of pure PET synthesis. Yang et al. [6] demonstrated that it is possible to control the crystallization behavior of PET by inorganic nanoparticles. Wang et al. [7] studied the non-isothermal crystallization behavior of pristine PET and PET/clay nanocomposites with a differential scan- ning calorimeter (DSC), and found that the introduction of clay into PET matrix weakens the dependence of the non-isothermal crystallization exotherm peak temperatures on the cooling rates. Additionally, they verified that the absolute value of activation 0040-6031/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2010.07.003