Preparation And Properties Of Polypropylene-Based Dielectric Composite

Dielectric material plays a significant role in the power electronics industry, information functional, military and other fields. All kinds of electrical and electronic equipment tend to the miniaturization and integration with the rapid development of science and technology. Material with high dielectric properties have become a focus of academic research. Application of pure polypropylene(PP) in insulation materials field is limited. It has important significance to research PP-based composite with high dielectric constant, low loss factor. In this paper, a series of PP-based composite materials was prepared through an advanced method of micro-nano polymer multilayer co-extrusion technology, which structure and performance was studied. It should offer reference for prepare and properties study of polymer-based dielectric composites.(1) PP as the matrix, multi-walled carbon nanotubes(MWCNTs) as filler, MWCNTs/PP single-layer composite, multi-layer composite and(MWCNTs/PP)/PP alternative-multilayer composite material were prepared by a micro-nano multilayer co-extrusion extruder, which structure and properties were studied. It is found that MWCNTs agglomeration both happened in the three composites. But the single-layer composite material MWCNTs reunion is more serious, and with the MWCNTs content increased, the aggregate increase; while in multilayer and alternating multilayer composites,due to the function of laminating-multiplying element, MWCNTs agglomeration yet, but clusters is smaller, and it's volume would not increase with the MWCNTs content increases. Alternating multilayer composite has obvious layer structure. Uniform dispersion of MWCNTs and alternating multilayer structure make composite higher dielectric constant. When the MWCNTs content of 2wt%, alternating multilayer composite dielectric constant is 3.57(1MHz, room-temperature), which is 1.9 times to pure PP, and 1.7 times to single-layer composite, 1.4 times multi-layer composite material, at the same MWCNTs content.(2) PP as the matrix, the carbon nanotube conductive fillers for plastics(CB-CNTs: CNTs/Carbon Black Chezacarb B(40/60) blends) as dispersed phase.(CBCNTs/PP)/PP alternating multilayer composite was prepared through the micro-nano multilayer co-extrusion extruder. CB-CNTs dispersion similar to the MWCNTs in(MWCNTs/PP)/PP composite. The dielectric constant of the(CB-CNTs/PP)/PP alternating multilayer composite increased with the increase of the CB-CNTs content, but still low.(3) PP as the matrix, polyamide 11(PA11) as the dispersed phase. In situ microfiber PA11/PP composite was prepared through the micro-nano multilayer coextrusion extruder. PA11 form fine micro-fiber in PP matrix, and obviously oriented along the extrusion direction. The dielectric constant of the PA11/PP composite increased with the increase of the PA11 content, but still low.(4) TNPP(Polypropylene/multi-walled carbon nanotube(MWCNTs) composite masterbatch) as filler, PP as matrix,(TNPP/PP)/PP alternating multilayer composites was prepared the micro-nano multilayer co-extrusion extruder. MWCNTs dispersion is very uniform, almost micro-nano level in the PP matrix. Obvious structure of alternative multilayer for composite can be seen. The uniform dispersion of MWCNTs and its heterogeneous nucleation effect for PP, make the crystallization temperature and crystallinity of(TNPP/PP)/PP composites were increased with the content of MWCNTs increasing. Because of well-dispersed, even the content of MWCNTs reach up to 5wt%, also can improve crystallization temperature of composite. TNPP added improve the tensile strength of the composite significantly. At the same frequency and the same content of carbon nanotubes,(TNPP/PP)/PP composites dielectric constant higher than direct addition of MWCNTs or CB-CNTs. When the content of MWCNTs is 5wt%, percolation phenomenon happened to(TNPP/PP)/PP composites apparently, which have a high dielectric constant of 47.45(room-temperature, 100Hz), low tan? of 0.61, and low conductivity of 1.62 × 10-7(S/m).(5) TNPA6(polyamide 6 / multi-walled carbon nanotube(MWCNTs) composite masterbatch) as disperse phase, PP as matrix,(TNPA6/PP)/PP alternating multilayer composites was prepared by the micro-nano multilayer co-extrusion extruder. Instead of achieving micro-nano level uniform dispersed in blend system, MWCNTs priority dispersed in PA6 form PA6/MWCNTs composite particle, and than dispersed in PP matrix. MWCNTs can not play the role of heterogeneous nucleation for matrix, composite particle can not, yet. Due to the large size, it would obstruct segment movement of PP molecular chain so that the crystallization temperature and crystallinity of composite declining to some extent. Therefore, the tensile strength of(TNPA6/PP)/PP composites decrease with the content of TNPA6 increased obviously. However, the existence of composite particle enlarge inner material interface which is very helpful to improve the dielectric properties of composite. When the content of MWCNTs is 5wt%(TNPA6 content is about 33wt%), dielectric constant(roomtemperature, 100Hz) of(TNPA6/PP)/PP composite reach up to 127.34, the conductivity just 9 × 10-5(S/m).