In the case of PBTI, which contains the higher content of dimethyl isophthalate (DMI) having substituent on the meta position of the main chain benzene ring, such melt viscosities and shear sensitivities behavior may be due to the fact that in the lower shear rate region the polymer has higher resistance to flow, hence it shows higher melt viscosities.
But, taking the report (18) that carbon black has some affinity for aromatic solvent into consideration, PBTI also have possibility to wet carbon black easily from the point of interaction.
So, the shear stress on carbon black agglomerate is directly proportional to the matrix viscosity and PBTI has the highest one.
In the case of PBTI, it broke up carbon black agglomerate so effectively among three dispersing agents that it enlarged carbon black inter-aggregates distances, then PBTI/carbon black masterbatch got high volume resistivity.
Capillary rheometer test shows that PBTI containing the highest content of aromatic group has the highest viscosity and shear sensitivity among the three agents.