Study On Preparation Of Polystyrene Grafted Graphene And Properties Of Its Polymer Composites

Graphene is the basic unit of graphite-like materials with an sp2 hybridized structure and a two-dimensional single atomic layer, and it has attracted more and more attention due to its excellent electronic, thermal, mechanical and biorelated properties. Unfortunately, because of high surface area and strong van der Waals forces, the graphene sheets in the polymer matrix are favorable to form severe aggregations, resulting from poor interfacial interaction, which limits their application in polymer nanocomposites. To improve the interfacial interaction between graphene and polymer matrix, modification of graphene is necessary. Graphene oxide (GO), as one of the most important derivatives of graphene, plays an important role in the modification of graphene. Lots of functional groups such as hydroxyl, epoxy, carbonyl, and carboxyl are present in the GO accompanying with the oxidation process. Moreover, GO can be easily reduced to reduced graphene oxide (rGO) by thermal or chemical approaches, therefore GO is regarded as a promising precursor for graphene production. In this research, polystyrene grafted reduced graphene oxide (rGO-PS) was prepared by microemulsion polymerization and subsequent reduction of GO using hydrazine hydrate, and then rGO-PS was incorporated into polystyrene. The grafting density and chain length of rGO-PS were tailored to change the interaction between rGO-PS and PS, and then the effects of interface interaction on the dielectric properties and mechanical properties of the nanocomposites were studied. On the other hand, rGO-PS was introduced into the polyamide 6(PA6)/Acylonitrile Butadiene Styrene (ABS) immiscible blends, and the effect of the localization of rGO-PS at the interface on the microstructure and macro-properties of the blends was studied. The main results are listed as follows:(1) rGO-PS was successfully prepared by microemulsion polymerization and subsequent chemical reduction. Morphology characterization showed that the surface of graphene sheet was coated with PS, which was proved to be linked together by covalent bonds, and the chemical reduction of graphene oxide could still retain some functional groups containing oxygen. In addition, by changing the proportion of monomer and initiator, the rGO-PS was prepared with different grafting density and different chain length, and its structure was studied. The results showed that the increase of PS grafting density and the length of the grafted chain could increase the layer spacing of graphene sheets, and promote the peeling of graphene sheets. The effect of rGO-PS3 on the peeling of graphene sheets is the best.(2) The PS/rGO-PS nanocomposites were prepared by introducing different rGO-PS into PS. It was found that the interfacial interaction between rGO-PS and PS increased gradually with the increase of the grafting density, while the length of the grafted chain showed no positive effect on the improvement of interfacial interaction. The increase of PS grafting density and length of the grafted chain promoted the peeling of graphene sheets, which would promote the dispersion of the graphene sheet. Tensile testing results showed that the increase of the length of the grafted chain made a slight promotion effect on the tensile ductility of the composites, and the increase of grafting density could greatly enhance the modulus, strength and tensile strength of the nanocomposites. The underlying mechanisms for the improvement of mechanical properties were investigated. Firstly, the increase of the chain length and the grafting density could enhance the interfacial interaction between the filler and the matrix. Second, modification of graphene can promote the dispersion of graphene in the polymer matrix. Dielectric testing results showed that the higher the grafting density was, the smaller the percolation threshold was; while the length of the grafted chain had little effects on the dielectric properties of the nanocomposites. With the introduction of 5 wt% rGO-PS, the dielectric properties of the nanocomposites were greatly improved, owing to the interface polarization and the micro-capacitance structure.(3) PA6/ABS/rGO-PS ternary blends were prepared by introducing rGO-PS into PA6/ABS. After the introduction of rGO-PS, the tensile toughness and impact toughness of the blends were improved to a great extent while the modulus and strength were maintained. Compared with the pure PS, the elongation at break and impact toughness increased by 400% and 200% when 0.5 wt% rGO-PS was incorporated into polymer blends, respectively. This was mainly due to the special "amphiphilic" structure of rGO-PS which could interact with ABS and PA6 respectively. As a result, rGO-PS could localize at the interface, and enhance the interfacial adhesion between the two phases, finally leading to toughening of immiscible blends.