The Conductive And Rheological Properties Of Carbon Black/Polymer Composites

Adding conductive particles into insulated polymer matrix to fabricate conductivepolymer composites has attracted considerable attention as the composites exhibit broadapplications in many areas, such as capacitor, sensor and antistatic composite etc. Thereare many types of commonly used conductive fillers. Carbon black (CB) was widelyused due to it is economical and high performance. However, there are still manyscientific matters for us to further research and solve, such as how to improve thedispersion and distribution of CB, lower the conductive percolation threshold of thecomposites, use shear flow field to control the network structure of the conductive fillersto improve the conductive properties of the polymer composites. Moreover, the intrinsicrelationship between the structure and rheological properties of material is also not clearup to now. In this paper, we prepared polypropylene(PP)/poly(styrene-ethylene/butadiene-styrene)(SEBS)/CB composites with ordered parallel stripe structures inducedby the shear flow. The formation of conductive CB network in the immiscible polymerblends was systematically studied. Moreover, the relationship between the conductiveproperties of composites and their rheological properties was also examined. Detailsabout our research works are summarized as follows:1. The ordered parallel CB stripes in the PP/SEBS blends were obtained by theshear-induced self-assembly, which endowed the materials significantly conductiveanisotropy. The formation and the morphological evolvement of the CB stripes under theshear-induced were on-line visualized and analyzed by the shear stage equipped withoptical microscope. Microscope characterization results found CB particles in thecomposites were more affinitive with SEBS phase whether before shearing or aftershearing. The physical mechanism of the formation of stripes induced by shear flow fieldwas also systematically examined. The electrical measurements indicated that theresulting thin film with the well-ordered structures displayed significant anisotropy in conductivity, i.e., the electrical resistivity in the direction parallel to the CB stripes wasalmost8orders of magnitude lower than that perpendicular to the stripes.2. For PP/SEBS/CB composite system, we also investigated the external factors onthe formation of the CB stripes, including shear plate gap, shear rate and CB content.When the gap value was increased from150μm to300μm, the width and conductivity ofthe CB stripes were increased with the gap value. However, the length of the CB stripeswas increased at first, and then was decreased with further increasing the gap value.When the shear rate was increased from0.1s-1to0.2s-1, both the width and conductivityof the CB stripes were almost not changed, but the length of the stripes was increased.When the CB content was increased from1wt%to2.5wt%, the width, length andconductivity of the stripes were increased.3. In order to reveal the inherent physical mechanism that the well-ordered stripestructures formed in the direction vertical to the shear flow, we applied rheologicaltechnique to explore the inner relationship between the formation of stripe structures andthe rheological properties. The results showed that the CB nanoparticles graduallyformed ordered stripes vertical to the shear flow under the shear flow field, and thedifference of the normal stress differences (N) was quickly reduced from a value closeto zero to a negative value, and then fluctuated with time. The experiment proved that theformation of stripe structures was because of the existence of negative first normal stressdifference under the shear flow.