Evolution of dispersion in the melt compounding of a model polymer nanocomposite system: a multi-scale study

Abstract

We investigate the morphological development of polystyrene (PS)-C-60 nanocomposites along the length of a prototype co-rotating twin-screw extruder with sampling capabilities. The effects of C-60 concentration and output on the morphological evolution along the extruder are studied employing a suite of characterization techniques covering a wide range of length-scales, thereby shedding new light on the dispersion mechanism in this model system. We show that the relatively new spin-echo small-angle neutron scattering (SESANS) technique is well suited to probe both the distribution and the dispersion of C-60. SESANS complements optical microscopy (OM) data as it covers sampling areas several orders of magnitude larger than OM. The multi-scale morphological information conveyed by OM, SESANS, SANS and rheological data shows that for larger outputs, C-60 agglomerates are eroded as they travel along the extruder, resulting in C-60 dispersion and distribution at both molecular and micrometric levels. The picture is more complex when smaller feed rates are used, as the evolution of C-60 dispersion depends on the C-60 loading. For larger C-60 contents, agglomeration develops along the extruder, whereas dispersion is improved for smaller C-60 contents. Overall, it is concluded that an over-high feed rate in extrusion does not necessarily result in a bigger size of the nanoparticle agglomerates because of the complex interplay between stresses and residence time.