Preparation And Properties Of Graphene/Polyolefin Nanocomposites

Polyolefin are used widely in industrial production because of its good comprehensive performance,low cost and easy processing.Graphene has excellent mechanical properties,outstanding electrical conductivity,thermal conductivity,high specific surface area and excellent adsorption performance.When the graphene is used as the reinforcement phase of polyolefin,it can improve effectively the common shortcomings of the polymer such as low mechanical strength,poor thermal resistance,bad barrier property and flame retardant,expanding the scope of the polyolefin applications.In this thesis,graphene oxide was used as a precursor,the functional modification of GO has been completed and reduced into graphene,then the graphene/polyolefin nanocomposites were prapared by different methods,and their structures and preperties were studied through a series of characterization.The main results are as follows:1.The controllable reduction and structural characterizations of graphene oxide.Hydrazine hydrate and ammonia were used as combined reducing agents,and the effect of the reduction time on the structure of the graphene oxide were studied systematically.The results inhibited that the oxygen-containing groups in GO were reduced and the UV absorption peak showed a gradual red-shifted with the increase of reductive degree.Moreover,the intensity ratio of D band and G band increased observably,and the distance between layers of graphene was decreased,and the thermal stability and electrical conductivity were improved notably.The molecular morphology was observed by transmission electron microscope(TEM),scanning electron microscope(SEM)and atom force microscope(AFM).Compared with those of graphene oxide,reduced graphene possessed more crumples and thicker layer,and these results were "pretty confident" of X-ray diffraction(XRD)analysis and thermogravimetric analysis(TGA).This work provides an experimental basis to control the reducted degree of the functionalized graphene oxide,which establishs the theoretical base for the subsequent preparation of graphene/polyolefin nanocomposites.2.Graphene/ethylene-vinyl alcohol copolymer(EVOH)nanocomposites.Water and isopropanol were adopted as mixed solvents to dissolve EVOH and graphene/EVOH nanocomposites were prepared by solution mixing method.The experimental results showed that the graphene could disperse homogeneously in the EVOH matrix.The addition of graphene into matrix could improve the EVOH crystallinity and made crystal perfect.Compared to the matrix resin,the glass transition temperature,thermal decomposition temperature and tensile strength of RGO/EVOH composites are raised markedly,and the water absorption of the film is decreased.In summary,the addition of graphene has improved greatly barrier property,thermal performance and mechanical strength of EVOH,making up the inherent defect of EVOH as the packaging material,and the RGO/EVOH composites have great potential applications in the fields of food preservation and drug packaging.3.Trimethoxysilane-functionalized graphene/polypropylene(PP)nanocomposites.Functionalized reduced graphene oxide(RGO)was obtained by reaction of graphene oxide with dodecyl(12C),octyl(8C)and propyl(3C)trimethoxysilane and subsequent reduction using hydrazine hydrate.FTIR and TGA demonstrated that these alkyltrimethoxysilane have been grafted successfully on the surface of RGO nanosheets,and the contents of the alkyl groups incorporation onto RGO-12C,RGO-8C and RGO-3C are approximate 35%,25.5%and 17.5%,respectively.The PP/graphene nanocomposites also exhibited an improved thermal stability with the increasing contents of RGO due to the barrier role of two-dimensional structures.For example,the maximum degradation temperature were enhanced by 16.7℃ by incorporating only 3 wt%RGO-C12 into PP.Comparing the mechanical properties of the nanocomposite by addition of 0.5 wt%RGO with that of neat PP,the tensile strength(30.41 MPa),the Young’s modulus(1.15 GPa)and the elongation at break(270%)of the composites increased up to by 19.7%,16.5%and 26.8%,respectively.Our work provides a facile and promising method to fabricate high-strength and high-toughness PP/graphene nanocomposites.4.Alkylamine-functionalized graphene/low density polyethylene(LDPE)nanocomposites.Functionalized reduced graphene oxide(RGO)was synthesized by modification of graphene oxide(GO)with octadecylamine(ODA),dodecylamine(DDA)and octylamine(OTA)and subsequent reduced by hydrazine hydrate.The successful grafting of alkylamine onto the RGO surface was confirmed by fourier-transform infrared spectroscopy(FTIR)and them ograv im etric analysis(TGA),and the structure of alkylamine-functionalized graphene was characterized by means of XRD and Raman spectroscopy.The contents of alkyl groups incorporated on the RGO-OTA,RGO-DDA and RGO-ODA comprise about 14.2%,23.27%and 33.7%,respectively.UV-vis spectra showed that the solubility of RGO-DDA and RGO-ODA are equivalent in organic solvents,which is higher than that of RGO-OTA owing to the different alkyl chains bonded on the graphene nanosheets.Besides,RGO-DDA/LDPE nanocomposites exhibited higher mechanical properties and thermal stability at the same content of alkylated graphene compared with the RGO-ODA/LDPE nanocomposites.Our work provides a new horizon to choose a compatilizer with appropriate alkyl chain lengths in the development of graphene/polyolefin nanocomposites.5.Isothermal and non-isothermal crystallization kinetics of graphene/Polyolefin nanocomposites.The Avrami equation could depict pefectly the isothermal crystallization of pure PP and RGO/PP nanocomposites;RGO/PP nanocomposites have higher crystallization rate and lower crystallization activation energy than those of neat PP,which imply that RGO has promoted the crystallization of PP.The Avrami theory modified by Ozawa’s method and Mo’s method was suitable to depict the non-isothermal crystallization kinetics for neat PP and RGO/PP nanocomposites.The polarization microscope(POM)showed that the size of the spherulites became smaller by the addition of RGO into neat PP,suggesting that RGO can.serve as an efficient nucleating agent and promote crystallization of neat PP.