The Preparation, Creep And Recovery Behaviors Of Graphene-filled-polymer Nanocomposites

Due to the excellent properties, such as electrical, thermal and unique structure, graphene became a hotspots in the field of material science for preparing the high-performance and multi-functional polymer nanocomposites. Considerable previous studies have shown that a small amount addition of graphene or graphene oxide can significantly improve the strength, fracture toughness and fatigue properties of the polymer materials, and even endow other multi-functionalization including excellent electrical and thermal conductivities. In particular, graphene should be also idea nanofillers to improve the intrinsic creep deformation,and has an important impact on the life(creep and recovery properties) of polymer materials. Therefore, studies on creep and recovery behavior of graphene-filled-polymer nanocomposites without loss in the static mechanical properties of materials will be helpful to promoting the practical application of the advanced graphene-based nanocomposites, and has important theoretical and engineering application value.In this thesis, we prepared the graphene/polymer nanocomposites by using different fabricating processing methods and aimed to improve creep and recovery performance of polymer materials including two kinds of different polymer systems(thermoplastic polystyrene and silicone elastomer). We systematically investigated creep and recovery behaviors of the graphene/composites under different stress and temperature conditions, explored the complicated interaction mechanism between polymer chains and graphene, and thus analyzed the viscoelastic behavior and microstructure-property relationship of the composites. Resistance to time-dependent plastic deformation of polymer composites is a crucial requirement in their application for long-term durability and reliability. We firstly investigated the effect of different carbon nano-fillers including carbon black(CB), carbon nanotubes(CNTs) and chemically reduced graphene oxide(CRGO) on the creep and recovery behaviors of polystyrene(PS) composites. The results revealed that both the CB/PS and CNT/PS systems present worse efficiencies in reducing the creep and unrecovered response. The CRGO sheets with corrugated structures possess higher specific surface area and display better dispersion in the PS matrix compared to the CB or CNT nano-additives, which should produce strong sheet/matrix interfacial interaction to restrict the mobility of polymer chains. Based on the above results, we further investigated the creep and recovery behaviors of PS composites filled with various loadings of CRGO at different stress levels and environment temperatures. As expected, incorporation of CRGO into PS polymer increases the thermal stability, glass transition temperature and elastic modulus, although the tensile strength of the composite has a slight decrease. Reduced creep deformation and strain rate and improved recovered strain of PS polymer were with decreasing temperature and with increasing loading of CRGO. Based on the analytical modelings(Burger’s model and Weibull distribution function) and experimental results, the role of CRGO on improving the creep and recovery performance of thermoplastics was proposed and discussed.In addition, we also studied the effect of different fabricating methods(mechanical mixing, solution blending and ball-mill procedure) on the mechanical, electrical, creep and recovery behaviors of CRGO-filled silicone rubber composites. The different methods resulted in different distribution states of CRGO in silicone rubber, and thus produced different impacts on improving the related properties. The composites prepared by solution blending showed lowest percolation threshold among all three composite systems. It should be also noted that compared to other methods the ball-mill procedure can yield high shear stress to disperse and exfoliate the graphene sheets in the matrix. It is favorable to enhance the interfacial interaction between the sheet and the matrix, and consequently provided the improved creep and recovery properties of the graphene-based composites under low stress levels.