Synthesis Of PET/TiO₂ Composite Via In-Situ Polymerization And Study On Its Structure And Performance

In this paper, a series of PET/nano-TiO₂ composites were prepared by in-situ blending of nano-TiO₂ with the polymerization system of poly(ethylene terephthalate). The crystallization characteristics, dynamic rheological behavior, thermal stability, UV resistance and mechanical properties of the samples were studied.Firstly, a TiO₂/EG dispersion system was obtained from substituting water in an aqueous colloid with ethylene glycol. Light scattering test showed that TiO₂ particles dispersed in nano-scale. Then the dispersion system was mixed with dimethyl terephthalate and the polymerization was carried out. Again the TiO₂ would maintain uniform dispersion when its content was less than 0.5%.DSC analysis showed that the crystallization from melt would happen at a higher temperature for nano-TiO₂ modified PET, namely the super-cooling degree decreased. However, the melting point of the composites was showed higher than that of pure PET. The results of isothermal crystallization kinetics analyses (198-213℃) showed that crystallization rate increased with increasing content of TiO₂ until the content of TiO₂ reached 3 wt%. In fact the crystallization rate of the sample with 3wt% TiO₂ was almost as same as that of the one with 2wt% TiO₂; The Avrami exponent and the super-cooling degree of the composites decreased with increasing content of TiO₂, indicating that TiO₂ had acted as a heterogeneous nucleation. XRD results proved that the crystalline structure formed in composites was the same as that in pure PET. Moreover, the sample containing 2wt% nano-TiO₂ showed the sharpest diffraction peaks and the highest crystallinity.Melting rheological behaviors of the samples were studied systematically by a rotary rheometer. The results showed that the composite melt appeared the more homogeneous phase structure than PET, and loss modulus G",loss factor tgδdecreased with increasing content of TiO₂. The mechanical properties, heat stability and UV absorption were also investigated. It was found that the tensile strength and the elongation at break increased first and then decreased with the increasing content of TiO₂, and it seemed that 0.5-1.0% TiO₂ load was help to the improvement of mechanical properties. Meanwhile, it was noticed that PET/TiO₂ nano-composites showed good UV absorption, and the absorption intensity became higher with the increasement of TiO₂, showing a better UV resistance than pure PET. With the time of ultraviolet irradiation increased, some hollow space appeared in the surface of samples and the intrinsic viscosity and density of the aged samples decreased. After the ultraviolet aging, the thermal decomposition rate became slow and decomposition activation energy together with reaction order increased, which demonstrated the decomposition started firstly from the oligomer in the composites.