| Based on the excellent properties and low-priced,PET has became a highly competitive engineering plastics,which get a lot of attention by scholars.Rencently,the preparation of high-performance PET materials to satisfy the development of key engineering fields such as automotive,marine and aerospace has became the focus of researchers.With the development of nanotechnoligy,the nanocomposite method has became an important aspect of research which involves improve PET properties and perparation of multifunctional materials.Nano-SiO2 is considered to be one of the most promising nano-fillers due to its high rigidity,strong heat resistance,no pollution and wide range of sources.But the agglomeration behavior and the poor interfacial interaction of nano-SiO2 in PET matrix severely restricts its strengthening effect on PET performance.Currently,these problems could be solved by surface modification of nano-SiO2.Neverthless,there are several disadvantages of traditional modified method,such as complex process,high-cost and pollute the environment.In view of this,this paper focuses on an efficent and simple nano-SiO2 surface funtionalization method suitable for commercial process,and studied the strengthening mechanism and law of nanoparticle functionalization on PET/SiO2 nanocomposites.Firstly,the functionalized nano-SiO2 grafted with PET molecular chains prepared by simple melt blending and high-speed centrifugation process using pristine nano-SiO2 and PET.The functionalization effect of nano-SiO2 and mechanism of covalent grafting PET molecular chains were studied by thermogravimetric analysis,transmission electron microscopy,contact angle tester,Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.The result indicat:(1)During the melt blending process,high temperature and strong shear force induce chemical reaction between PET and nano-SiO2 surface silanol,and then PET molecular chains are covalently grafted onto the surface of nano-SiO2;(2)Short-time(5 min)melt blending process can obtain functionalized nano-SiO2 with excellent grafting effect,and the grafting rate reaches 39.4%;(3)The reaction mechanism of PET covalent grafting of nano-SiO2 is mainly through transesterification reaction of the silanol groups on the surface of with the ester groups in the PET molecular chain,and the condensation reaction and esterification reaction occurred between the surface silicon hydroxyl of nano-SiO2 and degraded PET molecular chain which have hydroxyl or carboxyl groups at the end.Secondly,the PET/SiO2 nanocomposites were prepared by injection molding with different contents of pristine nano-SiO2 and functionalized nano-SiO2.The effects of unmodified nano-Si02 and functionalized nano-SiO2 on the mechanical properties,crystallization properties and thermal stability of composites were investigated by scanning electron microscope,electronic universal testing machine,dynamic mechanical,differential scanning calorimeter and thermogravimetric analyzer.The conclusions as follows:(1)Low content(0.5 wt%)of functionalized nano-SiO2 exhibits the best dispersibility and interfacial compatibility in PET matrix,while significantly enhanced the tensile strengh and elongation at break of PET.(2)Due to the immobilization of nano-SiO2 on the molecular chain of PET,especially the physical entanglement between the functionalized nano-SiO2 surface grafted PET molecular chains and the PET matrix molecular chains,the storage modulus of PET is significantly improved;(3)Functionalized nano-SiO2 acts as a heterogeneous nucleation in the PET matrix,effectively increasing the crystallization rate and crystallinity of PET;(4)A small amount(0.5 wt%)of functionalized nano-SiO2 can effectively improve the thermal stability of PET,The kinetic results show that functionalized nano-SiO2 can greatly improve the thermal degradation activation energy of PET. |
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