Science and technology of graphene-based inks for polymer-composite applications

Advanced materials characterized by a combination of properties, which are not present in conventional materials as metal alloys, ceramics and polymers, are required in technological fields, as aerospace and automotive. For example, the development of materials for structural applications is focused on achieving more than one property, as strength, stiffness and impact resistance. In particular, materials scientists have focused their research on composite materials, due to their wide combination of different properties. Polymer based composites are materials formed by a polymeric matrix, containing one or more fillers, which improve the physical and chemical properties of the matrix. The properties of the polymer based composites can be tailored on-demand depending on the final applications. However, compromises need to be considered for the achievement of the targeted properties. For example, the addition of carbon fibers to a polymer matrix will improve its mechanical strength, but the resulting composite will lose the optical transparency of the pristine material. Nowadays, nanoscale fillers (< 100 nm), as graphene, carbon nanotubes, etc., are proposed as alternative fillers to overcome the limitations provided by the traditional fillers. In detail, graphene is a nanoscale material which possesses a combo of properties, as a high thermal conductivity (5300 W m 1 K 1), outstanding mechanical properties (Young’s modulus ~ 1 TPa, tensile strength ~ 130 GPa) and a remarkable electrical conductivity (up to 108 S m 1). In a graphene polymer composite, the matrix benefits from the presence of graphene as filler, so that the mechanical, thermal, electrical and many other properties are enhanced compared to the bare polymer. However, despite the recent development in the graphene polymer composites, there are several issues that need to be solved in order to obtain the desired properties. For example, the presence of graphene aggregates and a weak interaction between the graphene flakes and the matrix hinder the beneficial effect of graphene itself on the matrix properties. The aim of my PhD work was to enhance the mechanical, thermal, gas barrier and tribological properties of different polymer matrices by exploiting graphene and solving the issues related to factors as the distribution of the graphene in the matrix, for example. Graphene is produced in liquid phase using ultrasonication based exfoliation and the wet jet milling process, tuning the morphological features of graphene, as area and thickness, by means of sedimentation-based separation. Graphene polymer composites are produced using various techniques as solution blending and melt blending and different polymeric matrices, such as acrylonitrile butadiene styrene (ABS), polyamide 6 (PA) and styrene butadiene copolymer (SB). Moreover, the effect of the manufacturing processes on the effect of graphene addition in improving the matrix properties is analysed by using techniques such as 3D printing, injection moulding and compression moulding.