Study On Functionallized Graphene Sheets And Orientated Distribution In Isotactic Polypropylene Matrix

Graphene, an atomically thin layer of carbon, is theoretically a robust two-dimensional (2D) sp2 -hybridized hexagonal honeycomb attice plane carbon material with excellent thermal, mechanical, optical, electrical and other properties. Thus, it is widely used in the field of materials science. The introduction of graphene in polymer is currently one of the major research focus, scientists from various countries in the field made a lot of impressive results.However, there are many problems when graphene blends with polymers to be solved; such as the dispersion and orientation of graphene in polymer matrix,the interfacial interaction between the graphene and the polymer matrix. In this article, we improved its dispersion and interaction in polymer via surface functionalized treatment on graphene. On this basis, we have prepared a series of polypropylene (PP)/functionalized graphene sheets (FGs) nanocomposites via efficient melt-blending. The PP/FGs composites were prepared by a shear-induced orientation extrusion technology (SIOE). In addition, the self-assembled design oriented laboratory extrusion equipment is applied to prepare oriented distribution of PP/FGs composites.(1) The FGs was prepared by graphene oxide (GO), which originated from flake graphite, by Hummers method and reacted with stearic acid under the existence of 4,4-diphenyl methane diisocyanate (MDI). The structure and properties of the FGs were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM). The results showed that the stearic acid is successfully covalently grafted by MDI to the surface of the graphene oxide, to obtain FGs, which are well compatible with the organic solvent and had a good compatibility with isotactic polypropylene (iPP). The interlayer distance of the functionalized graphene particles increased, and thermal stability compared with the graphene oxide also had very significant improvement.(2) The isotactic polypropylene/functionalized graphene (iPP/FGs) composites with different amounts of functionalized graphene particles were prepared by melt blending method. The X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and universal tensile test were used to analyze the structure and properties of iPP/FGs composites. Experimental results indicated that FGs particles could preferably disperse in the polypropylene matrix, while there was a strong interfacial interaction between them. Comparing with polypropylene/flake graphite composites, the crystallinity, thermal stability and mechanical properties of the polypropylene composites were obviously improved.(3) The SIOE system with orientation elements (OEs) was self designed in our laborotary. The shear stress can be controlled by adding the different number of OEs. The iPP and FGs were firstly pelleted by a two-screw extruder to prepare a master batch, and then used the SIOE system for the preparation of the orientated iPP/FGs composites.The X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), the two-dimensional wide-angle X-ray diffraction (2D-WAXD), gas transmission rate tester (GPT) and mechanical universal tensile tests were carried out to characterize the structure, morphology and properties of the composites. The results showed that the FGs had a significant alignment along the flow direction in SIOE system. With increasing the number of OEs, the FGs dispersed more uniformly and orientation in iPP matrix, even with higher orientation of iPP crystals. Because of the FGs, the composites had good mechanical and barrier properties. These results had significance for the development of high-performance mechanics and barrier polymer materials.