Structure, properties, and processing of graphene reinforced thermoplastic polymer composites formed in-situ by a high-shear process

Critical needs for weight reduction and fuel efficiency in the transportation industry call for new materials with enhanced or comparable capabilities at lower specific weights. Graphene-polymer matrix composites present an attractive opportunity to meet this need. Graphene has emerged as a subject of substantial scientific interest due to its exceptional electrical, mechanical, and thermal properties. When incorporated into a polymer matrix, these thin carbon sheets can provide significant property improvements, such as increased fracture toughness, increased Young’s modulus, increased electrical conductivity, and gas barrier resistance, over those properties of the host polymer--even at low loading levels. However, several major obstacles prevent the widespread use of these materials including poor dispersion of graphene within the polymer, high cost and low yield of current graphene production technologies, poor graphene-matrix interaction, and a lack of scalable composite production techniques. This work explores a new, scalable method of delaminating graphite to a variety of component elements, including graphene, using an in-situ molten polymer high-shear process to generate polymer composites reinforced at least in part with graphene. Delamination results from a five-step process of comminution, stack separation, debonding of plates, formation of aggregates, and separation of the aggregates to form single- and multi-layer graphene. Combined Mode III shearing and tensile forces applied to the particles from the adhesive molten polymer drive the latter delamination steps to produce graphene. The structure and properties of these composites show well-mixed and well-dispersed graphite delamination products (GDPs) in the matrix, with excellent engineering mechanical properties including elastic moduli 197 – 539% of expected rule-of-mixtures values. To achieve load transfer from the matrix to the GDPs, some level of bonding is required. This research suggests that secondary bonding via polar interaction are most important, from weak pi-pi interactions (~10 kJ/mole) to strong ion-dipole bonds (~60 kJ/mole), in generating this connection. Polymer chemistry, graphene pi-bond character, and graphene defects are key elements as described in this thesis. Covalent bonding may also occur where free-radicals are generated, principally on torn graphene edges and to a lesser degree on graphene basal plane defect structures, but this subject was not formally studied in this work.Ph.D.Includes bibliographical reference