Synthsis Of Dispersants For Graphene Or Graphene Oxide Reinforced Epoxy Composites And The Properties Of Generated Composites

Epoxy resins have been widely applied in adhesions,coatings,insulation,composites,and so on,because they exhibited the excellent mechanical properties,thermal stability,insulativity,corrosion resistance and bonding.However,the inherent brittleness has limited their applications in the field of many high-performance materials,owing to the high crosslinking density of thermosetting epoxy resin.Introduction of graphene(GR)into epoxy resin is a facile way to improve the various properties.However,homodispersion of GR nanosheets in epoxy resin matrix is still a large challenge now,because of the great differenc between GR and epoxy resin in chemical properties.In this work,through the non-covalent functionalization manner,GR can form?-?interaction among GR sheets and pyrene functional groups within the as-prepared Py-PEG-Py dispersant,making GR nanosheets uniformly disperse in epoxy resin.The the flexural strength and the fracture toughness greatly increased since the reinforced effects caused by GR nano sheets.Firstly,pyrene functionalized polyethylene glycol(Py-PEG-Py)with different molecular weights were synthesized via the esterification reaction of pyrene butyric acid and polyethylene glycol(PEG).The formed Py-PEG-Py was further used as the dispersant for GR nano sheets.Nuclear magnetic resonance spectroscopy(~1H NMR and ¹³C NMR),Fourier transform infrared spectroscopy(FT-IR)spectra,and Gel permeation chromatography(GPC)analyses were applied to characterize the chemical structure of Py-PEG-Py.Ultraviolet-Visible(UV–Vis)spectroscopy and dynamic laser light scattering(DLS)measurements were utilized to prove the homodispersion of GR nanosheets in epoxy resin matrix and to confirm the?-?interaction among GR/GO sheets and pyrene functional groups.As 3.0 wt%of Py-PEG_6k-Py were incorporated in epoxy resin,the resulted composites exhibited the highest storage modulus(3.77 GPa),exhibiting the improvement of 52.2%,compared with that of cured epoxy resin.As the loading of graphene was 0.04 wt%,the flexural strength and K_IC value of the as-obtained composite reached maximum,108.36±1.90MPa(about 70.5%)and 2.15±0.02 MPa m^1/2(around 72.0%),respectively.Secondly,the hyperbranched polyethylene glycols(HPGs)were facilely synthesized via ring-opening reaction.Then,the hyperbranched polyethylene glycol-block-polycaprolactones(HPG-PCL)with different molecular weights were synthesized via the subsequent ring-opening reaction of?-caprolactone(?-CL)with the feeding reatio(m _HPGs:m_?-CL)of 1:1.5,1:2 and 1:3,respectively.Finally,HPG-PCLs were fuctionalized with pyrene butyric acid via the esterification to generate the dispersants(HPG-PCL-Pys).~1H NMR,¹³C NMR,FT-IR and GPC measurements were used to characterize the structures of the products.Differential scanning calorimetry(DSC)analyses were used to evaluate the compatibility of HPG-PCL-Pys with epoxy resin.Dynamic mechanic analysis(DMA)was carried out on a Q800(TA Instruments)to determine their properties of composites reinforced by GR sheets.As 4.0 wt%of HPG₁-PCL-Py were incorporated in epoxy resin,the resulted composites exhibited the highest storage modulus(3.90 GPa),exhibiting the improvement of 56.6%,compared with those of cured neat epoxy resin.As the feeding of 0.04 wt%graphene and 5.0 wt%of HPG₁-PCL₂-Py were added in,the flexural strength and K_IC value of the as-obtained composites reached maximum,94.13±7.75 MPa(about 48.1%)and 3.03±0.08 MPa m^1/2(around 142.0%),respectively.Thirdly,the pyrene groups functionalized hyperbranched polyesters-block-polycaprolactones(HPER-PCL-Py),using as the dispersant for GR,were easily synthesized via the similar stratergy.Their chemical structures were characterized by the ~1H NMR,¹³C NMR,FT-IR and GPC measurements.According to the results of DMA measurements,the highest storage modulus and the maxmum glass-transition temperature(T_g)of formed composites were 3.40 GPa and 173.2°C,respectively,as the loading of HPER₁-PCL₂-Py was 5.0 wt%.As the feeding of 0.04 wt%graphene and 2.0 wt%of HPG₁-PCL₃-Py were added in,the flexural strength and K_IC value of the composites reached maximum,109.33±0.90 MPa(about 72.0%)and 2.33±0.11 MPa m^1/2(around 85.6%),respectively.Finally,the aziridine group functinalized polyethylene glycols(Az-PEG-Azs)were easily synthesized via the addition of 1-aziridinyl ethanol and isocyanate group.The aziridine group can smoothly react with the carboxyl groups from graphene oxide(GO)sheets,making GO sheets be well dispersed in epoxy resin.The ~1H NMR and FT-IR measurements were applied to characterized their chemical structures.The addition between aziridine group located on the end of PEG chain and carboxyl groups from GO sheets was proved through the FT-IR,Raman,XRD,TGA and SEM measurements,respectively.As 0.2 wt%of Az-PEG-Azs and 0.024 wt%of GO sheets were incorporated in epoxy resin,the resulted composites exhibited the greatest K_IC value,exhibiting the improvement of 71.2%,compared with that of neat epoxy resin.