Heat Treatment Under The Conductivity Of Conductive Polymer Composites And Rheological Behavior,

Nowadays, conductive polymer composites have widely used in many fields such as antistatic materials, pressure sensors, and in particular, the self-regulation heater based on the positive temperature coefficient effect of conductive polymer composites. However, the existence of the negative temperature coefficient (NTC) effect has limited the use of material, and the mechanism of this effect is still controvasial. Using carbon black as the conductive phase, we trace the movement of carbon black in polymer melts, and probe the origin of the NTC mechanism.Simultaneous measurements of rheological and conductive behaviors were conducted on HDPE/CB, PP/CB, PS/CB and PMMA/CB composites during annealing. Thermal-induced dynamic resistance (DR) and moduli (DM) percolation was found in these systems. Influence of annealing temperature and CB content on dynamic percolation was investigated. The DR percolation model was established through introducing a first order kinetics aggregation model to the classical percolation theory. It is found that the resistanc kinetic aggregation constant (K_R) is nearly unchanged with various CB contents, and is a reflection of the terimal relaxation of polymer chains. Similary, The DM percolation model was setup through introducing the first order kinetics aggregation model to mechanical percolation model. The results showed that the modulus kinetic constant (K_G) is insensitive to both the annealing temperatue and CB content. Indeed, increasing the annealing can increase the mobility of polymer chains. At the same time, the aggregation of CB in melts can be accelerated by increasing temperature and the formed bigger aggregation can reduce the mobility of polymer chains. These two controvasial factors can be used to explain the temperature-independent K_G. The resistanc index approaches 2 with increasing temperature and CB content, meaning that the three dimensional and perfect CB conductive networks are formed gradually in the melts. The moduli index approaches 2 with increasing temperature and CB content, suggesting that the contribution of filler phase to the moduli of the composites is dominant gradually. It is suggested that the interfical tension between CB and polymers plays a significant role in driving CB to aggregate.CCA model was use to analysis the experimental data. The DM percolation can be consided as a process that the isolated and small CB particles or aggregates are incorporated into the preexisting CB backbones to form the perfect CB backbones, and this process can be accelerated by increasing annealing temperature, CB content and annealing time.The terminal relaxation behaviors of composites before and after annealing were investigated. It was found that the terminal relaxation times of HDPE/CB and PP/CB composites are nearly unchanged after annealing while they increase significantly in PS/CB and PMMA/CB composites, which means that the aggregation of CB in the former two systems is much slower than the latter ones.Annealing the HDPE/CB composites with a higher CB content at a higher temperature and a longer time, we found that there is a fluid- to solid-like transition in time evolution of moduli and a resistance increase in the time evolution of resistance in the composites, which were resulted from the higher degree of CB aggregation.