Nanostructures based on carbon allotropes – graphites, fullerenes and graphene – have attracted scientific and technological interest due to their potentially remarkable mechanical reinforcement effects and electrical conductivity. A common drawback of the graphitic network is its chemical inertness and tendency to agglomerate, which hinders their thorough dispersion in polymer matrices. From the point of view of the preparation and processing of these materials, it is important to understand their dispersion and eventual re-agglomeration mechanisms during melt mixing with polymers. This study focus on graphene nanoplatelets – polypropylene composites.
A flow cell consisting of a sequence of five converging/diverging channels (8:1 and 1:8 ratios), followed by a relaxation chamber and another sequence of converging/diverging channels (two different ratios were tested) was attached to a capillary rheometer. The set-up allows for sample collection along the axis of the mixer. Pre-mixed composites containing 2% and 10% w/w of xGnP® Grade C were processed at 200ºC and different ram speeds, corresponding to distinct average shear rates. Samples were characterized in terms of their morphology (namely number and size of agglomerates per unit area) and volume resistivity. Thus, the evolution of dispersion and eventual agglomeration upon mixing could be detected and related to processing conditions.
