| Polymer based with conductive additive composite PTC (Positive Temperature Coefficient ) material which have some properties such as temperature-sensitive . This property arose material scientist' s widely attention and be applied in many field. This thesis use polypropylene^ high density polyethylene^ low density Polyethylene as based material, and take the lead in using graphite replace carbon black as conductive filler material, succeed prepared polymer based composite conductive material with distinct Positive Temperature Coefficient. The relationship of the material PTC effect, change temperature (Tc) and other properties with the prescription, processing were studied. The study result proved that PE/graphite composite material which use certain diameter graphite particles as conductive additive have distinct PTC effect , eletricity- heat performance and better properties for application.The experimentation show that LDPE/graphite PTC material sensitivity temperature between 40-110℃, the resistivity increase above 5 magnitude. At first, Positive Temperature Coefficient increasing along with temperature raising. The max Positive Temperature Coefficient occurrence when temperature attain 80℃ commonly. When the temperature reached this material melting point(115℃), the Negative Temperature Coefficient will appeared. This material temperature sensitive range is different as the graphite content change. On the whole, along with the graphite content increasing, the begin point of the temperature-sensitive range raise also. The rule is consistent with this material Tg. Due to graphite' s density higher than cb, the PE/ graphite composite material need more graphite to attend the same Positive Temperature Coefficient.The graphite weight reached 30% could obtain obviously Positive Temperature Coefficient commonly. The graphite weight reached 35% could obtain max Positive Temperature Coefficient. Anneal is a very important measure for repeat and stability of the material preparation. The study result proved that anneal temperature near Tm is a better choice. After anneal, the low temperature resistivity will raise commonly. Consider conductive additive interphase property is very important for material' s resistivity, so pretreatment measure is needed for graphite powder. Particular, when conductive additive through organic solvent cleanout. This measure could make the resistivity reduce 1 magnitude in the low temperature.For the HDPE/graphite system, due to HDPE s crystallization and Tm higher than LDPE, this material PTC sensitivity temperature between 90-130℃. The material' s resistivity intensity could attain 5 magnitude. Before 100℃, the Positive Temperature Coefficient increase relatively slowly. But after 105℃, it increase faster. After 130℃, Negative Temperature Coefficient appeared. Compare with LDPE/ graphite system, HDPE/graphite system could attend max Positive Temperature Coefficient in 25% graphite weigh content. HDPE/graphite system have more resistivity intensity in temperature-sensitive range, and the temperature range more narrow than LDPE/ graphite system. This system PTC temperature-sensitive range behind 30℃ than former system.Polypropylene(PP) have more branch , and the crystallization is lower. The PP/ graphite system' s Positive Temperature Coefficient isn' t very obviously, only have 2 magnitude. PTC temperature-sensitive range is strongly affect by the graphite' s content, and the PTC intensity is lower than other system.In this thesis , the relationship of the heating power / temperature were determined by the experiment equipment which designed by ourself.The study result proved LDPE/ graphite system self-controlled temperature around 60℃, this system fit for low temperature self-controlled heater material. HDPE/ graphite system self-controlled temperature around 90℃, this system fit for higher temperature self-controlled heater material. This study result is consistent with the former test which we obtained in correlation system study.In conclusion, The experimental results show that the HDPE, LDPE/ graphite system have development future , better application foreground . The former test which we obtained in correlation system study result proved this system have good property of self-controlled temperature (bellow 100℃ ). It is a good ground for the farther industrialized application.
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