Agglomeration Of Carbon Black Particles In Polymer Matrix

Carbon black (CB)-filled conductive polymer composites have been widely used in anti-static, electromagnetic shielding, heating tapes with automatic temperature control and various sensors. However, many researches, such as how to quantitatively describe the effect of the processing history on conductivity and how to make the conductive properties associated with the viscoelastic properties of the polymer matrix in theory which involved in conductive polymer materials for controllable preparation, remains to be further explored. The conductive properties reflect the agglomeration of CB particles, and it is very helpful to understand the micro-rheological behaviors and the microstructural evolution in processing of the CB-filled composites by studying the agglomerated behaviors of CB in polymer matrix.The agglomeration behaviors of four kinds of CB in high-density polyethylene(HDPE) were analyzed by resistivity at room temperature, dynamic percolation effect and Payne effect. The agglomeration of CB in HDPE was found to be related with the oxygen content on the CB surface. On contrary to carbon particles-filled polar polymer composites, CB with higher surface oxygen content was easier to agglomerate and form networks in HDPE, and the effect that CB particles were confined by HDPE chains becomes weak with increasing the surface oxygen content of CB. The dynamic agglomeration equations were used to analyze the mobility of CB, and the retardation time for percolation of HDPE/CB composites with higher CB surface oxygen content was lower at the same annealing temperature.The process of HDPE chains relaxation and CB particles agglomeration was also analyzed by creep-recovery test in linear deformation condition. The retardation time of percolation and the terminal relaxation time of confined HDPE molecular chains were compared, and the relation between the viscoelasticity and the dynamic percolation effect of HDPE/CB composites was investigated. The terminal relaxation time determined by creep-recovery test increases with increasing the CB content, while the retardation time of percolation remains constant. It was demonstrated that the retardation time of percolation is indeed represents the terminal relaxation time of HDPE matrix because the terminal relaxation time of HDPE filled with about 8 wt% CB particles determined by the two methods were comparable.The difference of CB agglomeration behaviors in oil-based polycarbonate(PC) and bio-based PC was analyzed by resistivity at room temperature, the initial dispersion state, dynamic percolation effect and dynamic rheological properties. CB particles agglomerate to form conductive networks more easily in bio-based PC, which was ascribed to a weaker interaction between bio-based PC and CB. The relation between the electrical conductivity and the dynamic rheological properties was analyzed The flocculation index, A, which reflects the conductive networks density of interparticles could be used to corelate the conductivity with the relative storage modulus in the percolation transition region. The fractal agglomeration model was used to fit the dynamic percolation curves. The effect of CB content and annealing temperature on the fractal dimension was found negligible, clarifying that van der waals force dominates the process of carbon black agglomeration and the agglomeration structure of CB developed in the conductive chains.