Study On Properties Of Mechanical, Flame Retardancy And Electrical Conductivity Of MWCNTs/PS Composites

Since their discovery, as a new type of nanomatreial, carbon nanotubes (CNTs) have attracted scientists' extensive attention all over the world for their extraordinary physical and chemical properties, which make them possess widely potential applications in many aspects. The application of carbon nanotubes in improving properties of mechanical, electrical conductivity and flame retardation in polymer/carbon nanotubes composites has extensively been paid attention. The composites composed of polystyrene (PS) ethylene-propylene- diene terpolymer (EPDM), multiwalled carbon nanotubes (MWCNTs), and nanometer TiO₂ (nano-TiO₂) were prepared in this paper. The properties of mechanical, flame retardation, electrical conductivity of the MWCNTs/PS composites were investigated. The influences of filling nano-TiO₂ on the mechanical property, flame retardation, electrical conductivity of MWCNTs/PS composites were studied.The mechanical property of EPDM/PS blends and MWCNTs/PS composites were measured through mechanical testing method. The structure of EPDM-g-PS chemical grafting blends and surface treatment MWCNTs were investigated by Fourier infrared spectrum (FTIR). The results showed that the mechanical property of EPDM-g-PS blend was optimal with the proportion of (60:40) EPDM/PS. And chemical grafting modified PS by filling 3.0Wt% of AlCl₃ with EPDM demonstrated the optimal property. The tensile strength and the elongation at break of the MWCNTs/PS composites were obtained by filling 1.0Wt% of MWCNTs. The mechanical property of PS with using surface modified MWCNTs was better than that unmodified MWCNTs. For the mechanical property of nano-TiO₂/MWCNTs/PS composite, the optimal compounds' proportion of nano-TiO₂ and MWCNTs was 5:1.The flame retardation property of PS was modified by MWCNTs, surface modified MWCNTs and blends of MWCNTs and nano-TiO₂. Flame retardation and thermal stability were studied through limit oxygen index (LOI) and thermogravity (TG). The micro morphology and structure of composites were studied by SEM and FTIR. The results demonstrated that a small quantity of MWCNTs improved the property of flame retardancy of PS, and the flame retardant effect with using surface modified MWCNTs was better than using unmodified MWCNTs. With increasing the content of MWCNTs to 3.0Wt%, the LOI of the composite was 22. And MWCNTs decreased combustion drippage efficiently. The LOI of composites composed of MWCNTs (1.0 Wt%)/nano-TiO₂ (5.0 Wt%)/PS composite was 23, MWCNTs and nano-TiO₂ showed a flame retardation synergism. And the synergism of flame retardant effect with modified nano-TiO₂ with titanate coupling agent NDZ-311 was better than that without modifying.MWCNTs were surface modified by HNO₃, H₂SO₄, H₂O₂ and dodecanesulfonic acid sodium salt (SDS) with micro-wave dispersion. The dried MWCNTs were then mixed with PS to prepare MWCNTs/PS composites. And some of the composites were treated by heat treatment. The structures of MWCNTs were analyzed by FTIR. The conductivity and behavior of MWCNTs/PS composites were researched through conductivity properties testing in different way of treatment and at different temperature. The fracture surface of the composites was characterized by SEM. Results indicated that some of polar groups were introduced on MWCNTs, such as -OH,-HSO₃, which were confirmed by FTIR spectra. SDS surface modified MWCNTs improved the electrical conductivity of MWCNTs/PS composites, but (HNO₃ + H₂SO₄> H2SO4 + H₂O₂) purified MWCNTs decreased the volume resistivity of composite slightly. The volume resistivity of MWCNTs(10.0Wt%)/PS composite with heat treatment at 120℃was lower 1 magnitude than that without heat treatment. With increasing the content of MWCNTs, the volume resistivity of MWCNTs/PS composite was decreased. When the content of MWCNTs was between 0.5Wt% and 5.0Wt%, the volume resistivity of MWCNTs/PS composite decreased slowly, but lower than 0.5Wt% and higher than 5.0Wt% it decreased rapidly with the addition of MWCNTs increased. When the content of MWCNTs was 8.0Wt%, the value decreased to 2 magnitudes. PTC effect of 10.0Wt% MWCNTs/PS composites of 1-3 connectivity was not obvious, but PTC effect of 5.0Wt%MWCNTs/PS composite was more obvious than former. Over 150℃, NTC effect was emerged, since the "interactional filled effect"(IFE).