STUDY ON CORRELATION BETWEEN RHEOLOGICAL AND CONDUCTIVE BEHAVIOR THROUGH SIMULTANEOUS MEASUREMENTS DURING ISOTHERMAL CRYSTALLIZATION FOR CARBON BLACK FILLED ISOTACTIC POLYPROPYLENE

The kinetics of isothermal crystallization for isotactic polypropylene (iPP) containing different volume fraction (phi(CB)) of carbon black (CB) was evaluated by using differential scanning calorimetry (DSC) at 137.5 degrees C, 139.5 degrees C and 141.5 degrees C with moderate rates of crystallization. Simultaneous measurements of rheological and conduction behaviors were performed to probe the process of isothermal crystallization in dynamic and static modes. It was found that when CB volume fraction phi(CB) was 0.09, the characteristic time for sharp resistance variation was comparable to those for shape changes in storage modulus (G') or normal force (F-N). At phi(CB) of 0.13 and 0.17 above the upper limit of percolation transition, however, the characteristic time resulted from resistance was much less than those from G' or F-N, which could be explained by the formation of the percolation network during the induction period of crystallization. On the other hand, for all phi(CB) and crystallization temperatures, the characteristic time from dynamical method was less than that from the static one, which indicated that the dynamical method was more sensitive to the structural transformation than the static one. It was suggested that rheological and electrical simultaneous measurements endowed us a novel approach to probe the formation of percolation network involving in crystallization of polymer matrix.