Study On Dielectric Properties And PTC Effect Of Nylon 6 Composite

As one of the main products of Nylon,Polyamide 6（PA6）which could be processed into various product by extrusion,injection molding,blow molding,spinning and so on is applied in many fields such as building materials,textile industry,automobile industry.However with the rapid development of economy,PA6 product could take place of wooden ware,steel ware,ceramic ware in daily life and become essential part of electron industry,military industry,high speed train industry,aircraft industry,which shows development trend towards engineering plastic and film membrane manufacture.But PA6 is void of functionality,which do not meet the needs of special fields and prevent the promotion of it.In this article,the PA6 dielectric composites was prepared with titanium dioxide,resins and macromolecule compatilizer.Influence of different resins and compatilizer on dielectric properties and stability of resistivity of PA6 composites in humid and hot environment was investigated.Also carbon fillers and metal fillers was blended with PA6.Affection of different fillers to Positive Temperature Coefficient（PTC）characteristic and thermal conductivity of PA6 composites was investigated.Firstly,four kinds of nylon 6 composites were prepared by dielectric filler Ti O₂,alumina（Al₂O₃）and silica（Si O₂-HL150 and Si O₂-HL200）with different specific surface area.After comparision to others,Ti O₂ was selected as dielectric filler.The influence of Ti O₂ content on dielectric properties,water absorption properties,resisitivity stability and micro-morphology of PA6/Ti O₂ dielectric composites were systematically sudied.The results display that With the increase of Ti O₂ content,the tensile strength,bending strength and bending modulus of nylon6 composite increased,while the impact strength remained almost unchanged.The dielectric constant of the composite material increased significantly with the increase of Ti O₂ content,while the dielectric loss decreased significantly.In a certain extent,The introduction of Ti O₂reduces the water absorption of nylon 6 composites,but with the extension of soaking time,the resistivity of the composites dropped sharply and the resistivity stability is poorer.After 5 hours soak,the PA6/Ti O₂ composites resistivity reduced to 2.1×10¹⁰Ω·cm.Because of the interaction between Ti-O bond and amide group,the interfacial polarization could be generated between titanium dioxide and nylon 6.Ti O₂ is evenly dispersed in the composite material to improve the dielectric constant of the composite material.PA6/Ti O₂composite material is used as the charge barrier layer,which can be polarized when charging the photosensitive drum,effectively maintaining the potential difference on the surface of the photosensitive drum.Strong-polar amido bond in PA6 contributes to strong-water absorption of PA6 product,which is embodied in organic photoconductive drum（OPC）whose print quality deteriorates a lot in a humid environment.In order to solve this problem,PA6 was melt blended with high density polyethylene（HDPE）and polystyrene（PS）,and titanium dioxide was added as a dielectric filler to prepare PA6/HDPE/Ti O₂ and PA6/PS/Ti O₂ two kinds of dielectric composite materials.The results found that the humidity and heat stability of the composite material after adding HDPE is higher than that of the PS system,and the dielectric constant is relatively stable in the alternating electric field.With the increase in the amount of HDPE,the resistivity of the nylon 6 composite material does not change much,maintaining at 3.7×10¹⁴Ω·cm.The water absorption rate of the material is significantly reduced.When HDPE is 20wt%,the water absorption rate after 5 hours of immersion drops to 1.49wt%,and the resistivity stability is significantly improved;but the tensile strength and toughness of the material are Because of the decline,macromolecular compatibilizers were added to improve the interfacial compatibility of the composites.The effects of the types of compatibilizers on the mechanical properties of PA6 composites and the stability of resistivity in a hot and humid environment were systematically studied.Three compatibilizers Ethylene-octene copolymer grafted with maleic anhydride（POE-g-MAH）,ethylene-vinyl acetate copolymer grafted maleic anhydride（EVA-g-MAH）,High-density polyethylene grafted with maleic anhydride（HDPE-g-MAH）can effectively improved the interfacial compatibility of composite materials.The notched impact strength of the material has been greatly improved.Compared with Without addition,the notched impact strength is increased from 8.2 KJ/m² to 91.7KJ/m²,and the tensile strength remains basically unchanged.After adding the compatibilizer,the resistivity of the material does not change much,but the water absorption rate decreases,and the stability of the resistivity is improved.Among them,the addition of EVA-g-MAH The composite material has the highest dielectric constant,while the composite material with POE-g-MAH has the highest dielectric loss.PA6/graphite,PA6/carbon black,PA6/graphite/carbon black were prepared by PA6 with graphite,carbon black,graphite/carbon black（the ratio is 1:1）separately and effect of filler variety and filler content on PTC characteristic and Room temperature resistivity of PA6composites was investigated.Result exhibited that that when the compound filler graphite/carbon black was added,the percolation threshold of the PA6 composite material was10 wt%,which was about 10%lower than the percolation threshold of the PA6 composite with graphite or carbon black;the PTC intensity of the graphite/carbon filler system was higher than the PA6 composite material with single filler.When the filler content was 30 wt%,the PTC intensity of the graphite/carbon filler system was 3.26.The type and amount of filler had almost no effect on the Curie temperature.The Curie temperature（T_c）of the composite material was about 209.2℃.Three low-melting point organic materials,PE wax,POE-g-MAH,and ethylene-vinyl acetate copolymer（EVA）,were introduced into PA6 conductive composite materials.The effect of low-melting point organic materials on the PTC effect and Curie temperature of PA6 composite materials were studied.The results showed that the Curie temperature of the composite material added with EVA was 182.3℃,the PTC strength was 1.5;when the low content of PE wax was added,the Curie temperature of the composite material was 140.0℃,the PTC intensity was 1.45.But the PE wax easily oozed When the content of it was high,which was not conducive to processing.The amount of low-melting organics has almost no effect on the Curie temperature,and its PTC strength decreased with the addition of low-melting organic materials.