Thermally conductive polymer/graphene-related materials nanocomposites prepared by melt reactive processing

Polymer nanocomposites containing graphene-related materials attracted a wide research interest thanks to the combination of the processability, lightweight and corrosion resistance typical of polymers, with the outstanding properties of graphene-related materials, including mechanical properties, thermal conductivity and electrical conductivity. Nanocomposites exploiting graphene-related materials are indeed showing interesting properties and several industrial applications for such nanomaterials are currently being developed, including structural materials, as well as functional materials, electrodes and conductors in flexible electronics, waste heat management, gas-barrier materials, etc., also taking into advantage of the large European initiative for graphene research, development and application called Graphene Flagship (http://graphene-flagship.eu/). This thesis aims to the preparation of polymer nanocomposites, exploiting graphene-related materials, by the development of industrially viable preparation methods, for the application as heat management materials. These are currently of interest in several application fields, including low temperature heat recovery, heat exchange in highly corrosive environments as well as heat dissipation in electronics and flexible electronics. Beside the thermal conductivity property, this PhD thesis was aimed at the fundamental understanding of phenomena controlling nanoparticle dispersion into the polymer matrix as well as the correlations between structure and properties of the prepared materials, including electrical conductivity, rheological properties and polymer crystallization phenomena. As the availability of graphene (i.e. a single layer of sp2 carbons) nanoflakes remains extremely limited and insufficient for the exploitation in large scale applications embedding graphene in the polymer bulk, different types of graphene-related materials were selected for exploitation in this PhD thesis, namely graphite nanoplatelets (GNP) and reduced graphene oxide (rGO). In particular, different grades of GNP and rGO were selected aiming at the correlation between their quality, mainly in terms of defectiveness and aspect ratio, and the properties of their corresponding polymer nanocomposite. For these reasons, the initial part of this thesis is focused on thorough characterization of nanoflake quality, i.e. defectiveness and aspect ratio, through electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. On the other hand, the second part is focused on the preparation and detailed characterization of nanocomposites prepared by ring opening polymerization of polyester oligomers (CBT) during melt mixing in presence of graphene-related materials. In particular, the effects of the exploitation of different graphene-related materials, of the polymerization during reactive mixing and of the processing parameters (processing temperature, time and shear rate) on the electrical and thermal properties of polymer nanocomposites is addressed. Thorough characterization of the effect of the exploitation of pristine and high temperature-annealed reduced graphene oxide on the nanocomposite properties is also reported, in terms of both of conductivities and modification in the crystallization of the polymer matrix. The results reported in this thesis demonstrate the viability of CBT polymerization during melt mixing with graphene-related materials to produce thermally and electrically conductive polymer nanocomposites aiming at possible industrial applications.