Processing of Composites of Polymers and Nanoparticles

T. McNally
University of Warwick, UK

Keywords: composites, polymers, nanoparticles

Summary:

Despite more than two decades of intense research activity with regard composites of carbon nanoparticles and polymers, their widespread commercial exploitation has yet to be fully realised. This in the main is a consequence of the combined challenges of achieving effective dispersion and distribution of nanoparticles in polymer melts and of fully characterizing and modelling the interface between particle and polymer across the length scales. An appreciation of the parameters which govern nanoparticle dispersion during melt mixing has only been studied intensively for a small number of polymer/CNT systems, much less so for composites of polymers and graphene(GO). CNT dispersion in polymer melts follows three distinct mechanisms; infiltration of the polymer melt into CNT primary agglomerates, agglomerate rupture, and erosion of CNTs from agglomerate surfaces [1], all governed by the melt temperature and the shear and other forces acting on the melt during mixing. Typically, the relationship between varying processing parameters, including screw speed, residence time, melt temperature and screw configuration with nanoparticle dispersion is investigated using a combination of microscopic techniques and the extent of nanoparticle dispersion interpreted by assessing nanoparticle network formation studied using electrical and rheological techniques [1-5]. Processing variables as well as thermodynamic considerations also play a key role in the localization of CNTs in immiscible polymer blends [6]. While the majority of the published literature reports on studies which have focused on understanding the factors which govern nanoparticle dispersion during mixing, the as-compounded polymer/CNT composite can then experience a second thermo-mechanical cycle, as in injection moulding. Moreover, secondary processing in the solid state and quasi-solid state, as in thermoforming and blow moulding, of these composites has largely been ignored to date [7]. Indeed, irrespective of the level of nanoparticle dispersion achieved during initial melt mixing, the final properties of the composite material are determined by the extent of deformation and any subsequent strain induced crystallization and re-localisation of nanoparticles. This invited presentation will provide an overview of melt processing of composites and blends of polymers and carbon based nanoparticles, with a particular focus on carbon nanotubes.