Research On Properties Of LDPE/CB/Inorganic Particles PTC Composites With Irradiation Crosslinked

Polyolefin PTC composites were widely used in heating and insulation of civil,industrial, oil and other fields, because of its low production cost, easy processing,low room-temperature resistance, etc. However, its application is still prevented byits shortcoming, such as unstable performance, existence of NTC effect, shortlifespan, and so on. Based on practical application, LDPE/CB system was modifiedby inorganic particles(Al2O3, SiO2, MgO, TiO2and BaTiO3), to improve the overallperformance of composites and expand the applications.In this paper, LDPE/CB composites were irradiation crocsslinked by γ60Coirradiation technology with different irradiation doses. Performance changed ofcomposites was studied and the results showed that, with increased of irradiationdoses, room-temperature resistivity increased gradually, PTC intensity increasedgradually and NTC effect weakened gradually. The optimal irradiation dose wasdetermined by thermal prolongation test, which was300kGy. And crystallinity ofcomposites was reduced, reproducibility was improved when composites wereirradiation crosslinked. The result of SEM analysis showed that agglomeration of CBparticles was weakened which due to thermal cycles when the composites wereirradiation crosslinked. On this basis, a series of LDPE/CB/inorganic particlescomposites were systematically studied, the result showed that crystallinity ofcomposites increased to7.51%,5.60%,5.43%,5.94%or5.46%respectively form4.82%when Al2O3, SiO2, MgO, TiO2or BaTiO3was added into. The result of SEManalysis showed that, there was a positive influence on dispersion of CB particleswhen Al2O3, MgO or TiO2was added into, while SiO2or BaTiO3wasn’t. Whencontent of Al2O3was0.6g (others’ amount was50g), LDPE/CB/Al2O3compositeshad the highest PTC intensity (reached to7.7) and the best reproducibility, resistivity-temperature curves were almost coincident after the second thermal cycle.The result of SEM analysis showed that, the addition of Al2O3played an inhibitionrole to CB particles’ agglomeration due to thermal cycles, especially, agglomerationwas stable basically after the second thermal cycle. Exploratory research on thermalconductivity showed that, thermal conductivity had some correlation with PTCperformance and reproducibility, lower thermal conductivity played a positive role toreproducibility. The contents of CB and Al2O3of LDPE/CB/Al2O3composites wereoptimized by uniform design and the results showed that, PTC performance andreproducibility of composites were decided collaboratively by CB’s content andAl2O3’s content, and the influence of Al2O3’s content was more significant. Theoptimizing formula of LDPE/CB/Al2O3composites was obtained: LDPE, CB,antioxidant and Al2O3was used for35g,8.52g,6.25g and0.53g respectively.