A Study Of Structure And Properties In Ethylene-Tetrafluoroethylene Copolymer Composites

Ethylene-tetrafluoroethylene alternating copolymers(ETFE)is a semi-crystalline polymer which consists of equal content of ethylene(E)and tetrafluoroethylene(TFE).It exhibits more excellent properties than other fluoropolymer due to the presence of TFE component,such as corrosion resistance,weather resistance,high temperature resistance,aging resistance and radiation resistance.ETFE can be processed into coating,film,foil and cushion for various applications due to its lightweight,high transparency,and environment-friendly characteristics.However,the poor processing properties and low yield strength limit the use of ETFE.Therefore,:in the present dissertation,Poly(vinylidene fluoride)(PVDF)is added into ETFE matrix in order to optimize the processing properties of ETFE.The phase structure,compatibility,rheological properties,thermal and mechanical properties of ETFE/PVDF blends were detailedly characterized.Thus,the corresponding relationship between the microstructure and macro-performance of the ETFE/PVDF blends was investigated.Furthermore,ETFE/PVDF blends were modified with electron beam(EB)or adding Montmorillonite(MMT)nanoparticles for optimize the properties of the blends.In this study,the main contents and conclusions are as follows:1.The thermal stability,rheological and mechanical properties of ETFE/PVDF blends were investigated by thermogravimetric analysis(TGA),rheometer and tensile tests.TGA results indicate that blends have better thermal oxidation resistance than pure ETFE.Particularly,the initial thermal decomposition temperature(Td0)and the temperature at maximum decomposition rate(Tdmax)of ETFE/PVDF(90/10 wt%)blends are 374.49? and 480 ? respectively,which are 52.6 ? and 34 ? higher than those of pure ETFE.The activation energy of thermal degradation(Ed)of ETFE is 66 kJ/mol,while ETFE/PVDF(90/10 wt%)blends exhibit a higher Ed,about 187 kJ/mol.Furthermore,rheological measurements demonstrate that the shear-thinning tendency of blends become stronger with increasing PVDF content.PVDF/ETFE(10/90 wt%)blends have slightly lower mechanical properties than ETFE,which was still high enough for various applications.The incorporation of PVDF provide an efficient method to extend the application area of ETFE.2.ETFE/PVDF blends containing different kinds of sensitizing agent were prepared by melting extrusion process and then modified with electron beam irradiation.Those sensitizing agents are Triallyl Isocyanurate(TAIC),Trimethylolpropane Trimethacrylate(TMPTMA)and Trially trimellitate,respectively.Thermal stability,mechanical properties,chemical structure,rheology properties and crystallization behavior of irradiated samples were investigated.X-ray photoelectron spectroscopy(XPS)results demonstrate that the composite system underwent crosslinking and degradation reactions due to HF elimination and the formation of unsaturated structures and hydroperoxide species.Besides,XPS results also prove that the induce effect of TAIC is better than other sensitizing agents and the best addition content is 5 wt%.Rheological results demonstrate that the melt property of irradiated samples changes from liquid-like behavior to pseudo-solid-like behavior.The yield strength and Young's modulus of irradiated samples have obvious improvement at the range of 0-50 kGy and decrease with further increase of the irradiation dose.In general,the test results suggest that the modification of PVDF/ETFE blends with electron beam irradiation provides a way to improve their thermal and mechanical properties for various challenging applications.3.The MMT nanoparticle was modified by Tetraphenylphosphonium bromide(TPB)through ion-exchange reaction which exhibits better thermal stability and larger layer space.ETFE/PVDF/OMMT three phase nanocomposites were prepared by melt extrusion process.The morphology,rheology properties,thermal and mechanical properties of nanocomposites were investigated.Rheological results demonstrate that the incorporation of OMMT nanoparticles improves the storange modulus and complex viscosity of ETFE/PVDF,because of the physical entanglement of chain segments.DSC results indicate that OMMT nanoparticles change the crystallization behaviors of PVDF and ETFE.Moreover,ETFE/PVDF/OMMT nanocomposites exhibit better Young's modulus comparing with ETFE/PVDF,which means that this material has better deformation resistance.4.The thermal stable MMT was prepared based on multiple organics modification,which has large interlayer spacing and reactive groups on its surface.Susequently,MMT was grafted with Dodecafluoroheptyl methacrylate(DFMA)and denoted as PDFMA-g-OMMT.PVDF/ETFE/PDFMA-g-OMMT nanocomposites were prepared via melt compounding using a twin-screw extruder.XPS results demonstrate that MMT is coated with DFMA long chains formed by self-polymerization of monomers.SEM results show that PDFMA-g-OMMT disperses at the interface of PVDF/ETFE blends and thus improves the compatibility between PVDF and ETFE.DMA and DSC results also indicate that the addition of PDFMA-g-OMMT nanoparticles into ETFE/PVDF blends is beneficial to improve the physical entanglement of two phase chain segments.Furthermore,the mechanical tests indicate that both tensile strength and yield strength obviously increase with increasing PDFMA-g-OMMT contents(0-2 wt%).However,the elongation at break decrease with increasing PDFMA-g-OMMT contents.In all,PDFMA-g-OMMT nanoparticles prepared in this study are effective for improving mechanical properties of ETFE/PVDF blends.