Polypropylene Composites Based On Carbon Nanotubes And Flake Graphite:Fabrication?Structure And Properties

Polypropylene(PP)is a commonly used thermoplastic polymer with excellent physical properties.It has been widely applied in electronic,mechanical and auto-manufacturing industries.However,polypropylene material has no functional characteristics such as electrical conductivity and thermal conductivity,so it is difficult to meet the application in some special occasions.Among them,carbon-based fillers have good electrical and thermal conductivity.In this work,nano-scale multi-walled carbon nanotubes(MWNTs)and micro-scale flake graphite(FG)were used to fill polypropylene,PP/MWNTs and PP/FG composites were prepared by melt blending.Then the dispersibility of MWNTs and the thermal conductivity of FG have been further investigated.The main content of this paper are as follows:(1)Research on the physical modification and the dispersibility of MWNTs in PP matrix:PP/MWNTs nanocomposites with excellent toughness and ductility pose significant challenges because of the severe aggregation of MWNTs in non-polar PP matrix due to the incompatibility.In this work,lithium bis(trifloromethanesulfonyl)imide(Li-TFSI)and maleic anhydride grafted polypropylene(MAPP)have been simultaneously introduced to modify MWNTs for the homogenous dispersion in PP matrix.The surface of MWNTs has strong“?-cation”interactions with the Li~+ions of Li-TFSI.At the same time,there are specific interactions between Li-TFSI and MAPP.Therefore,the combination of Li-TFSI/MAPP has been coated onto the MWNTs surface.The Li-TFSI/MAPP modified MWNTs can be dispersed uniformly in the PP.Moreover,the polymer chain of MAPP on the surface of MWNTs could be entangled with PP matrix,which improves the compatibility between PP and MWNTs,thereby further improving the toughness and ductility of PP/MWNTs composites.(2)Investigation on fabrication and thermal conductivity of PP/FG composites.FG is thermally conductive filler with the planar structure and arrangement of the platelets in PP matrix affects the thermal conductivity.At present,few reports have been made to study the orientation effects of platelet-shaped fillers(like flake graphite and boron nitride)on the in-plane and cross-plane thermal conductivity of polymer composites.The article systematically studies the structure and properties of PP/FG composites,mainly include:(a)Study on preparation and properties of PP/FG/MAPP composites:MAPP as a compatibilizer improves the interfacial adhesion between PP and FG,and changes the orientation of FG in PP matrix.It was found that the addition of MAPP enhances the mechanical properties of PP/FG composites.In addition,the addition of MAPP has different effects on the thermal conductivity of PP/FG composites when the total filler content at different contents.For low-filled graphite(such as 30 wt%),the addition of MAPP reduces the vertical thermal conductivity and parallel thermal conductivity of PP/FG composites.While for high-filled graphite(like 50 wt%),the addition of MAPP effectively improves the thermal conductivity of PP/FG composites.Therefore,the effect of thermal conductivity of composites in all direction is related to the total graphite content in the system.So,it is possible to alter the thermal conductivity of the composites by control the content of both MAPP and graphite.(b)Study on preparation and properties of PP/FG/SG composites:Spherical graphite(SG)was used to adjust the packing and orientation of FG to enhance the thermal conductivity.It was found that the addition of 5 wt%SG simultaneously enhances both in-plane and cross-plane thermal conductivity of PP/FG composites when the total filler content is 50 wt%.Moreover,the mechanical properties of the composite at this SG loading are also in its maximum.It is considered that small amount of SG fills the vacancies of FG and induces the denser packing of the fillers in the matrix.At the same time,the addition of SG leads to the anisotropic orientation of the FG in the plane during the hot press.