Preparation And Study Of Normal Temperature Polymer Based Positive Temperature Coefficient Composite

With the development of technology,the temperature control technology is not only pursuing the accurate and effective temperature control,but also reducing the weight of the temperature control equipment.The positive temperature coefficient(PTC)materials can meet all the requirements as new temperature control materials.However,the Curie temperature of PTC composites is mostly above 50?,and the materials are hard at present,which can not satisfy the condition of temperature control at room temperature.Accordingly,to solve the problem of high Curie temperature point and insufficient flexibility of PTC composites,aiming at the direction of temperature control at normal temperature and low added,polymer based PTC composites with normal temperature Curie point are studied in this paper by introducing low melting point and similar structure organic acid crystals in the polymer support system.First,we studied the preparation method of polymer based PTC composites of EVA/LA/CB/DOP materials,and discussed the main factors.The results showed that the optimum proportion of PTC composites is 6% CB,5% DOP and the mass ratio EVA/LA= 1:3.At this time,the curie temperature is about 37.5?,the room temperature resistivity is about 0.61K?·cm and the PTC strength is about 5.53.The amplitude of resistivity is relatively small before the Curie temperature point and after the peak temperature point,which indicates the composite material is stable.Secondly,we analyzed the microstructure characters of different PTC composites by SEM,and established the mechanism model of PTC effect.It was found that the room temperature resistivity and PTC strength of the composites depend on the lap of fillers and the change of crystal degree.With the optimum proportion,the room temperature resistivity of composites is relatively low,the PTC strength is relatively high and the corresponding microstructure is the best.The conductivity of composite is the result of interaction between tunnel effect and conductive channel theory,and there is a transition process from tunnel effect to conductive channel conduction.The PTC effect is produced by the internal crystal change and the migration of carbon particles.In addition,the thermal characteristics,mechanical properties,stability and temperature rise of the PTC materials with optimum proportion were tested with corresponding test methods.The results showed that the thermal conductivity is about 0.789W/(m*K),the adhesion is 3,the flexibility is 10 mm and the hardness is HB,which ensures that the heat generated can spread to the surrounding area without accumulation,but there is a certain gap of the mechanical properties with the international standard,which needs to be further improved.The PTC properties of composites with optimum proportion are not stable in the first thermal cycle,but after 20 cycles,the properties of the composites are almost stable.But at the same time the PTC strength is smaller and the room temperature resistivity is higher.The simulated heating test of PTC composite material showed that the material can control the temperature rapidly and steadily at Curie temperature.It can be used as a good temperature control material.At last,the research achieves the goal that low Curie temperature,low conductive particle content and certain flexibility.It provides an adaptive temperature control method for electronic components and other components at low temperature working conditions,especially in the period of the need to control the temperature at normal temperature.