Study On The Properties Of Poly (ethylene Terephthalate)/sio₂ Nanocomposites

Poly(ethylene terephthalate) (PET) is widely used in the fields of the fiber, film and soft drink bottle because of its excellent electrical insulating, resisting heat and chemical resistance properties. However, due to its low surface energy and tendency to block, its application in film and sheet is limited. Usuallly micron-SiO₂ is used as anti-block agent to solve such problems and study on the effect of nano-SiO₂ on the surface tension of PET have seldom reported. Three different surface characteristics nano-SiO₂ were used as additives and the aim of this study on PET/SiO₂ nanocomposite is to further improve PET properties and to exploit novel applications for PET by providing reliable experimental datum.In this thesis, firstly, the PET/SiO₂ nanocomposites were prepared by polymer melt method. PET and three different surface characteristic nano-SiO₂ were mixed in twin-screw extruder. The dispersibilities of three different nano-SiO₂ in PET were examined by scanning electron microscopy (SEM). The nonisothermal crystallization kinetics were studied by differential scanning calorimetry (DSC) method and the rheological behavior of the PET/ nano-SiO₂ blend system was measured by rotary theometer. The mechanical properties of PET/ nano-SiO₂ blend systems and the surface tension and optical performance of the sheets prepared were also primarily studied. The main results were as follow: Firstly, the PET/SiO₂ nanocomposites were prepared by melt method and the dispersibilities of three different surface characteristics of nano-SiO₂ in PET were examined by SEM. The results indicated that both the treated nano-SiO₂ were dispersed uniformly in PET matrix with smaller particles size, ranging from 100nm to 200nm, but the untreated nano-SiO₂ was badly dispersed and aggregated.The non-isothermal crystallization behaviors of PET/SiO₂ nanocomposites were investigated by means of DSC, and the non-isothermal crystallization kinetics were analyzed by Jeziorny equation and Ozawa equation. The results indicated that all the three different surface characteristic nano-SiO₂ improved the crystallization temperature and the crysatllinity, all of which acted as nucleating agents during the crystallization of the PET matrix. The effect of untreated nano-SiO₂ (M-5) on the crystallization of PET was similar with that of nano-SiO₂ grafted with hexa-methydisilazane (TS-530), and the ucleation ability of nano-SiO₂ grafted with dimethyl silicone fluid (TS-720) was higher than those of other two nano-SiO₂. The Jeziorny equation can well describe the non-isothermal crystallization of all the four samples, but the Ozawa equation failed.The rheology behavior of the PET nanocomposites were measured using rotary rhemeter. It is found that the storage modulus, the loss modulus and the complex viscosity of composites increased when the untreated nano-SiO₂ was added, but both the treated nano-SiO₂ decreased these. Compared with nano-SiO₂ grafted with hexamethydisilazane, nano-SiO₂ grafted with dimethyl silicone fluid had a stronger effect.The surface tension of PET/ nano-SiO₂ sheets were measured by the critical surface tension test liquid and calucated by equation in term of the contact angle. The results indicated the untreated nano-SiO₂ improved the surface tension of PET sheets and those containing treated nano-SiO₂ were virtually unchanged.The mechanical property of the PET/SiO₂ nanocomposites and the optical performance of the sheets which prepared by PET/SiO₂ nanocomposites were investigated in the end. The results indicated that both the treated nano-SiO₂ improved the tensile strength of PET while the untreated nano-SiO₂ decreased that of PET; all the three SiO₂ decreased the transparency of PET sheet due to their nucleation effect.