Preparartion,Structure and Properties of Graphene/Poly (Methyl Methacrylate) Composites

Author:Shang Yu Dong

Supervisor:li tie hu

Database:Doctor

Degree Year:2017

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Pages:125

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Since was found in 2004,academic community has always concerned graphene.Due to the outstanding physical and chemical qualities of it such as large specific surface area,the development tendency of graphene in composite field is rapid,and graphene is expected to improve performance of the composite materials as the new nano-filler.However,some elements always restrict the application of graphene in composites field such as high cost of the high quality graphene preparation and the low dispersity in matrix.For evenly dispersed,researchers common tried to explore new preparation methods or modify graphene in the past research,but few one tried to achieve this purpose via improving or modifying the graphene application methods.Based on the traditional preparation methods of graphene and composites,effect of preparation method and processing mode on the structure and performance of graphene/poly(methyl methacrylate)composites were studied.The raw Multi-walled carbon nanotubes(MWCNTs)were treated by mixed concentrated acid(V H2SO4:VH3PO4=6:1)for removing the amorphous carbon and residual metal catalyst from the raw MWCNTs.Then,MWCNTs were oxidized by potassium permanganate(KMnO4)to form graphene oxide nano ribbons(GONRs),and which would be reduced in hydrogen atmosphere via thermal treated process in next step.With the addition of KMnO4,the tubular structure of MWCNTs was disappeared to form GONRs.In addition,when the oxidation temperature was excess or the dosage of KMnO4 over 700wt.%,the surface of GONRs was broken,and the GONRs edge gradually blurred.Through several comparing experiments,the optimum dosage of KMnO4 is 600wt.%via three-step method(Raito 3:2:1),70℃of oxidation temperature,the reduction temperature is to 600℃.By Raman and XRD analysis showed that the defect density(R=ID/IG)is ca.0.995,the interlamellar spacing of graphene layers is ca.0.81nm.It is indicated that through this three-step method,we could prepare neat GONRs with complete layer structure.Via in-situ polymerization,GNRs were synthesized with MMA to form GNRs/PMMA composites.Through the microstructure analysis and mechanical,thermal stability,electromagnetic shielding effectiveness test found that,compared with PMMA matrix and MWCNTs/PMMA composites,the temperature of maximum pyrolysis rate of GNRs/PMMA respectively improved 24℃and 8℃,and the flexural strength of it increased 21.0%and 18.0%respectively,and the flexural modulus increased 25.0%and 26.0%respectively.Because of the effect of Van der Waals force,GNRs prone to reunite,and failed to fully dispersed in the matrix to form effective conductive network,electromagnetic shielding effectiveness just only increased to 6.1dB from 0.9dB of original matrix.While GNRs loadings up to 6wt.%,thermal stability and flexural strength reached the maximum value respectively,the temperature of maximum pyrolysis rate and flexural strength at 387℃and 77.4MPa respectively.And with increasing filler amount,GNRs network gradually improved within the matrix,result in raising the electromagnetic shielding effectiveness to 11.8dB in loadings 8wt.%.Graphene oxide(GO)prepared by Hummers method.Because of containing lots of oxygen functional groups,GO could form homodisperse solution with MMA monomer by stirring and ultrasonic processing,and the GO/PMMA composites prepared by in situ polymerization method.Then,by the Low-temperature thermal reduction process(LTPR),GO was reduced within the matrix to prepare IG/PMMA composites.With oxygen functional groups thermal decomposition,more and more CO2 gas serve as“jack”separate graphene layers to generate single or few layered graphene within viscous state matrix,result in IG homodisperse.When the LTPR process conditions was 260℃and 4MPa,graphene was generated with high structural integrity lower residual rate of oxygen containing functional groups,and this result was similar with the residual rate of oxygen containing functional groups of graphene which reduced by traditional thermal reduction at 1000℃(G-1000).Comparing IG/PMMA with G-1000/PMMA,the electromagnetic shielding effectiveness(SE)of IG/PMMA composites was particularly prominent.The SE of G-1000/PMMA showed5.28dB with G-1000 loadings 2wt.%,and the SE of IG/PMMA showed 24.06dB with GO loadings 2wt.%.It explained that the LTPR processing helps graphene evenly dispersed in matrix with forming crosslinking network structure.With the increase of IG content in composites,the SE of IG/PMMA shows 55dB with GO loadings 8wt.%.Moreover,the flexural modulus of it increased in a straight line,showed 4192.3MPa with GO loadings8wt.%.It is obvious that composite gradually by ductile material to brittle material.Furthermore,the temperature of maximum pyrolysis rate and flexural strength showed 392℃with GO loadings 8wt.%,and 91.38MPa with GO loadings 6wt.%,respectively.In addition,used lanthanum nitrate modified GO to prepare lanthanum(La)doped graphene oxide(La-GO),and La-Graphene/PMMA composites were prepared by in-situ polymerization and LTPR process.Confirmed by EDS,XRD and FT-IR characterization,GO has been doped by La.However,the doping of La leaded to loss of oxygen functional groups in doping process.Hence,composing with IG/PMMA,the dispersity of nano-fillers,mechanical property,thermal stability and electromagnetic shielding effectiveness of it was lower than before doping,the flexural strength and flexural modulus showed 68.48MPa and2133.9MPa,and the electromagnetic shielding levels significantly lower,but peak value showed ca.30dB at 12.2 GHz.