Preparation And Characterization Of PET/SiO₂ Nanocomposites

PET/SiO₂ nanocomposites were synthesized via the in-situ and Sol-Gel methods. Bycontrast with the advantages between the different methods, the Sol-Gel method waschoosed to prepare PET/SiO₂ nanocomposites. Firstly, terephthalic acid was reacted withexcess ethylene glycol to form bis(hydroxyethyl) terephthalate(BHET); Second, thetetraethoxysilane(TEOS) was added into the BHET and mixed homogeneously with it,then the TEOS was followed by the Sol-Gel reactions at high temperature to form silicananonetworks concurrent with polycondensation of BHET to produce the PET matrix.The characterization and properties of PET/SiO₂ nanocomposites prepared by Sol-Gelmethod were investigated.The intrinsic viscosity of PET/SiO₂ nanocomposites obviously decreased with theincreasing of silica contents.After burning at high temperature, there was almost nothingleft for pure PET, but there were a lot of white residues for PET/SiO₂ nanocomposites.These white leftover examined by FT-IR showed to be silica, which indicated that silicahad been added into PET matrix. The TEM image showed that the silica particles rangedfrom about several to tens nanometers in diameter. The nanoparticles were dispersed wellin PET matrix and the silica particles and the PET matrix had good compatibility. What'smore, there was no microphase separation between silica particles and PET matrix.The kinetics of thermal oxidative degradation of pure PET and PET/SiO₂ nanocompositeswere investigated by TGA. The results showed that nanosilicas enhanced the activationenergy of different degradation steps except the initial step of degradation, which showedthat nanosilicas made the degradation of PET become difficult at high temperature.The nonisothermal crystallization kinetics of pure PET and PET/SiO₂ nanocompositeswere examined by DSC. The results showed that these silica particles made thecrystallization capability of PET decline. Because the crosslink structure of PET/SiO₂nanocmpsite dramatically restricted the movement of PET chains so as to cause thedecrease of crystallization capability.The flame retardancy was investigated by CONE. Although the initial ignition time ofPET/SiO₂ nanocomposite were shorter than that of pure PET, the heating release rate,peak of heating release rate and its time, total heating release of PET/SiO₂nanocomposites were all lower than those of pure PET. So the silica could retard theburning processes of PET/SiO₂ nanocomposite.The rheological properties were studied by capillary rheometer. The results exhibited thatthe apparent viscosity of PET/SiO₂ nanocomposite melt was higher than that of pure PETmelt at low shear rate, but with the increasing of shear rate the apparent viscosity ofPET/SiO₂ nanocomposite melt decreased more quickly than that of pure PET, socompared with pure PET melt, the PET/SiO₂ nanocomposite melt was more sensitivity toshear rate. The result could improve the fluidity of composites melt when they wereextruded and injected.