| Ethylene-vinyl acetate copolymer(EVA)/ternary polyamide(t PA)blends and composites are novel materials that have great potential to be used in insulation,and heat-or oil-resistant materials for electrical cable,construction,and automotive applications.However,the applications of EVA/t PA blends are limited due to their low tensile strength,thermal stability,and thermal conductivity.To overcome these deficiencies,the electron beam(ebeam)irradiation of the blends in the presence of co-agents and the addition of functional fillers into the blends were used.Furthermore,the fillers were modified to maximize the application of the novel EVA/t PA blend in electronic devices by improving its thermal conductivity.The present work aims to develop high-performance EVA/t PA blends with high tensile strength,storage modulus,thermal stability,oil-resistance,and thermal conductivity.In the first part,EVA/t PA blend was mixed with trimethylolpropane trimethacrylate(TMPTMA),and triallyl isocyanurate(TAIC)as co-agents,and the effect of e-beam irradiation over a dose range from 50 to 500 k Gy on the blend was studied.The gel content and tensile strength of EVA/t PA/TMPTMA(70/30/3)blend increased by about 207% and 177% at 500 k Gy.The thermal degradation behavior of EVA/t PA blends was investigated by thermogravimetric analysis(TGA)and kinetics models,including Kissinger,Flynn–Wall–Ozawa,and Friedman methods and linear mixing rule.After irradiation at 500 k Gy,the EVA/t PA/TMPTMA(TAIC)blends exhibited significant improvement in thermal stability at 5% weight loss with a difference of temperature 50 °C.Moreover,the kinetics study showed that the activation energy of the EVA/t PA/TAIC blend significantly increased by irradiation.After irradiation,the oil resistance of the EVA/t PA/TMPTMA(70/30/3)blend was also improved.EVA/t PA blends based on EVA with different VA content were prepared with TMPMTA and TAIC co-agents and irradiated by e-beam over a dose range of 50 to 300 k Gy.With the increase in VA content,the tensile strength of EVA/t PA/TMPTMA blends increased,while the tensile strength of EVA/t PA/TAIC blends decreased.Nevertheless,after e-beam irradiation,the tensile strength of the EVA/t PA/TMPTMA(TAIC)blends increased,and the elongation at break and the crystallinities decreased.When the VA content of EVA was 33%,the tensile strength of EVA/t PA/TMPTMA blend reached to the maximum value of 26 MPa after irradiation at 300 k Gy.The thermal stability of un-irradiated EVA/t PA blends became poor with increasing VA content but got better after e-beam irradiation.The results of scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR)showed that with increasing VA content,the compatibility of EVA/t PA was improved,which could be better after e-beam irradiation.The crosslinking of EVA/t PA induced by e-beam irradiation was carried out over a dose range from 50 to 250 k Gy with different multifunctional monomers,including tripropylene glycol diacrylate(TPGDA),pentaerythritol tetraacrylate(PETA),dipentaerythritol hexaacrylate(DPEHA),and TMPTMA as crosslinking co-agents.The gel content of EVA/t PA with 3 phr TPGDA showed optimum value of 81% at 250 k Gy dose.The tensile strength of the EVA/t PA/TPGDA(70/30/3)also increased by about 340% at 250 k Gy.The irradiated EVA/t PA/TPGDA(70/30/3)blend showed better oil resistance than EVA/t PA blend.The addition of TPGDA and the irradiation dose are two crucial factors affecting the mechanical properties of the EVA/t PA blend.Sepiolite(SP)as an inorganic filler was modified with vinyltriethoxysilane(VTES)to enhance its dispersion and compatibility in EVA/t PA blend.The crosslinking of EVA/t PA induced by e-beam irradiation was carried out over a range of dose from 50 to 250 k Gy.The tensile strength and storage modulus of irradiated EVA/t PA/VTES-g-SP5 composite significantly increased due to the increase in crosslinking.The modification of sepiolite with VTES also helped to reduce the oil swelling of composite.The results suggested the possible application of the EVA/t PA/SP composite as an oil pipeline material.EVA/t PA/multi-walled carbon nanotube(MWCNT)composites with different MWCNT loading were prepared for increasing thermal conductivity,and e-beam irradiation was used to maintain the tensile strength of composites.SEM images showed a better dispersion and compatibility of MWCNT into EVA/t PA blend,which further increased after irradiation at 250 k Gy.The thermal conductivity of EVA/t PA/MWCNT(70/30/5)composite increased 188% compared to EVA/t PA blend because of higher thermal conductivity of MWCNT filler.A novel filler,EVA-g-halloysite nanotubes(HNT)was prepared and mixed with EVA/t PA to obtain a composite.The novel filler has better dispersion and compatibility in the EVA/t PA/EVA-g-HNT composite.The EVA/t PA/EVA-g-HNT(70/30/3)composite had high tensile strength and tear strength due to a better reinforcing effect of EVA-g-HNT filler.The improvement of mechanical properties can be attributed to the well dispersion of EVA-g-HNT in the EVA/t PA matrix.A coupling agent,3-aminopropyl-triethoxysillene(APTES),was used to modify Al2O3 filler.The modified Al2O3 and EVA grafted with maleic anhydride(EVA-g-MAH)were mixed with EVA/t PA blend.The thermal conductivity of the EVA/t PA composite was increased by 130%,with the addition of 40wt% EVA-g-MAH/APTES-g-treated Al2O3.Surface morphology observation showed a strong interfacial adhesion when using the EVAg-MAH/APTES-g-Al2O3 into the EVA/t PA matrix.The tensile strength of EVA/t PA composite increased by 66% after addition 30 wt% of EVA-g-MAH/APTES-g-Al2O3.The residual content at 500 °C of EVA/t PA composites increased by more than 33% with the addition of alumina.These results suggest that the e-beam irradiation and functionalization of fillers with silane coupling agents have great potential to improve the mechanical and thermal properties of EVA/t PA blends that can be used as oil pipelines and electronics devices material,respectively. |
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