| Conductive behavior for carbon black (CB) filled polypropylene/(ethylene-propylene-diene terpolymer) (PP/EPDM/CB) composites was studied. Resistivity dependence on the uniaxial pressure and ambient temperature were investigated. The effects of the filler volume fraction and crystallization were also discussed.The relationship between resistivity and filler weight fraction for PP/EPDM/CB composites was analyzed. The composites exhibited typical percolation characteristic. The conductive behavior in PP/EPDM/CB composites followed the prediction of mean-field theory.Results revealed that resistance of PP/EPDM/CB conductive composites strongly depends on uniaxial pressure, showing marked piezoresistivity behavior. In general, above the percolation threshold, resistance exhibits a negative pressure coefficient of resistance (NPCR) effect and positive pressure coefficient of resistance (PPCR) effect could hardly be observed. The reversibility and stability of piezoresistance increase with CB concentration. It is found that the piezoresistive stability could considerably be improved through repeated compression with the same level of maximum stress. The resistance of the composites also demonstrates the creep and relaxation behaviors similar to strain and stress do.Furthermore, conductive behavior of PP/EPDM/CB composites undergoing thermal cycles was investigated. It can be found that with increasing CB content, the intensity of both negative temperature coefficient (NTC) and positive temperature coefficient (PTC) effects decrease during the heating processes. However, degree of resistance change is almost independent of CB content during the cooling processes. Besides, the melt and crystallization of the composites were preliminarily studied in the thesis. It is found that there exist some notable affect of melt and crystallization on the conductive behavior. |
