Evolution of dispersion in the melt compounding of a model polymer nanocomposite system
A multi-scale study
Hugo Gaspar (University of Minho)
Raquel Santos (University of Minho)
Paulo Teixeira (University of Minho)
Loic Hilliou (University of Minho)
Michael P. Weir (University of Sheffield)
CP Duif (TU Delft - RST/Technici Pool, TU Delft - RID/TS/Technici Pool)
Wim Bouwman (TU Delft - RST/Neutron and Positron Methods in Materials)
S.R. Parnell (TU Delft - RST/Fundamental Aspects of Materials and Energy)
Stephen M. King (Rutherford Appleton Laboratory)
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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.