Evolution of dispersion in the melt compounding of a model polymer nanocomposite system

A multi-scale study

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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.