Study On The Positive Temperature Coefficient Effect Of Polyethylene/Carbon Black Composite

Polyethylene/carbon black (HDPE/CB) PTC ( positive temperature coefficient ) materials have a wide applications due to its lower room temperature resistivity, higher PTC intensity, adjustability of resistivity and PTC intensity, the feasibility of restraining NTC ( negative temperature coefficient ) effect by some modification, easiness for processing and lower production cost.Further applications of HDPE/CB PTC materials are limited for some disadvantages, such as the difficulties to simultaneously obtain lower room temperature resistivity and higher PTC intensity, and poor stability of PTC effect.In this paper, some factors influencing room temperature resistivity, PTC intensity and NTC effect were firstly studied, including carbon black content, properties of carbon black, dispersion of cabon black, mixing with other inorganic filler, chain structure of matrix, melt fluidity of matrix, crystallinity of matrix, etc.Through gamma ray irradiation, the PTC intensity and the stability of PTC effect could be improved and the NTC effect is weakened. The main factor to improve PTC property is the gel content, some polyfunctional monomers have been used to increase gel content of HDPE/CB composite.The effect of EVA with different VA content on HDPE/CB composite was also researched. The phase separation of HDPE and EVA, and thetendency for carbon black to concentrate in EVA phase make HDPE/EVA/CB composite have a lower percolation threshold, a higher PTC intensity and the NTC effect is avoided.Through irradiation of HDPE and ozonization of carbon black, the compatibility between HDPE and CB are improved. Irradiated HDPE/ ozonized carbon black composite has a higher PTC intensity and good stability of PTC effect when the CB content is high.Blending with one kind of high melt point polymer (HMP), the migration and agglomeration of carbon black in HDPE matrix is restricted. The NTC effect of HDPE/HMP/CB composite are restrained, the PTC intensity and the stability of PTC effect are improved.