Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

In situ preparation of transparent polyimide nanocomposite with a small load of graphene oxide

Polyimide (PI) nanocomposites with 4,4′‐bisphenol A dianhydride, 4,4′‐oxydiphthalic anhydride, and diaminodiphenyl methane (MDA) as comonomers and functionalized with graphene oxide (GO), were prepared by in situ polymerization. Only a small amount of GO (0.03–0.12 wt %) is added to improve the mechanical properties of PI and to avoid a substantial decrease of PI transparence. The nanocomposites are characterized by FTIR, X‐ray diffraction, thermogravimetric analysis, transmission electron microscope, tensile test, and UV‐vis spectroscopy. It is demonstrated that the PI/GO composite films possess transmittance of above 80% at wavelengths of 500–800 nm when the GO content is under 0.12 wt %, while the stress intensity and Young's modulus are improved by 29 and 25%, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

In situ Synthesis and mechanical,thermal properties of polyimide nanocomposite film by addition of functionalized graphene oxide

Polyimide (PI) and chemical modified graphene oxide nanocomposite films are prepared by in situ polymerization from solutions of pyromellitic dianhydride and 4,4′‐oxydianiline with various amount (0.5–2 wt%) of 3‐aminopropyltriethoxysilane (APTS) functionalized graphene oxide (GO) sheets in dimethylacetamide. The APTS functionalized GO (GO‐APTS) is a versatile platform for polymer grafting, improving excellent dispersion of GO in the PI matrix, and forming strong interaction with the PI matrix. The GO‐APTS/PI nanocomposites exhibited improvement in mechanical and thermal properties by addition of a small amount of GO‐APTS. With the addition of a small amount of GO‐APTS (1.5 wt%) to PI matrix, mechanical properties with the tensile strength and Young's modulus improved by 45% and 15%, respectively. The thermal analysis showed that the thermal stability of PI was slightly enhanced by the incorporation of GO‐APTS (1.5 wt%). This approach provides a strategy for developing high performance functionalized GO‐polymer composite materials. POLYM. COMPOS., 37:907–914, 2016. © 2014 Society of Plastics Engineers     

Thermal and mechanical properties of liquid silicone rubber composites filled with functionalized graphene oxide

To improve the thermal and mechanical properties of liquid silicone rubber (LSR) for application, the graphene oxide (GO) was proposed to reinforce the LSR. The GO was functionalized with triethoxyvinylsilane (TEVS) by dehydration reaction to improve the dispersion and compatibility in the matrix. The structure of the functionalized graphene oxide (TEVS‐GO) was evaluated by Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD), and energy dispersive X‐ray spectroscopy (EDX). It was found that the TEVS was successfully grafted on the surface of GO. The TEVS‐GO/LSR composites were prepared via in situ polymerization. The structure of the composites was verified by FTIR, XRD, and scanning electron microscopy (SEM). The thermal properties of the composites were characterized by TGA and thermal conductivity. The results showed that the 10% weight loss temperature (T₁₀) increased 16.0°C with only 0.3 wt % addition of TEVS‐GO and the thermal conductivity possessed a two‐fold increase, compared to the pure LSR. Furthermore, the mechanical properties were studied and results revealed that the TEVS‐GO/LSR composites with 0.3 wt % TEVS‐GO displayed a 2.3‐fold increase in tensile strength, a 2.79‐fold enhancement in tear strength, and a 1.97‐fold reinforcement in shear strength compared with the neat LSR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42582.     

Effect of octa(aminopropyl) polyhedral oligomeric silsesquioxane (OapPOSS) functionalized graphene oxide on the mechanical,thermal, and hydrophobic properties of waterborne polyurethane composites

A novel graphene nanomaterial functionalized by octa(aminopropyl) polyhedral oligomeric silsesquioxane (OapPOSS) was synthesized and then confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM EDX), atomic force microscopy, and X‐ray diffraction. The obtained functionalized graphene (OapPOSS‐GO) was used to reinforce waterborne polyurethane (WPU) to obtain OapPOSS‐GO/WPU nanocomposites by in situ polymerization. The thermal, mechanical, and hydrophobic properties of nanocomposites as well as the dispersion behavior of OapPOSS‐GO in the polymer were investigated by TGA, a tensile testing machine, water contact angle tests, and field emission SEM, respectively. Compared with GO/WPU and OapPOSS/WPU composites, the strong interfacial interaction between OapPOSS‐GO and the WPU matrix facilitates a much better dispersion and load transfer from the WPU matrix to the OapPOSS‐GO. It was found that the tensile strength of the OapPOSS‐GO/WPU composite film with 0.20 wt % OapPOSS‐GO exhibited a 2.5‐fold increase in tensile strength, compared with neat WPU. Better thermal stability and hydrophobicity of nanocomposites were also achieved by the addition of OapPOSS‐GO. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44440.     

In situ polymerization of bio‐based thermosetting polyurethane/graphene oxide nanocomposites

Novel bio‐based polyurethane/graphene oxide (GO) nanocomposites have been successfully synthesized from biorenewable epoxidized soybean‐castor oil fatty acid‐based polyols with considerable improvement in mechanical and thermal properties. The GO was synthesized via a modified pressurized oxidation method, and was investigated using Raman spectra, AFM and XPS, respectively. The toughening mechanism of GO in the bio‐based polyurethane matrix was explored. The elongation at break and toughness of polyurethane were increased by 1.3 and 0.8 times with incorporation of 0.4 wt % GO, respectively. However, insignificant changes in both mechanical strength and modulus were observed by adding GO. The results from thermal analysis indicated that the GO acts as new secondary soft segments in the polyurethane which lead to a considerable decrease in the glass transition temperature and crosslink density. The SEM morphology of the fracture surface after tensile testing showed a considerable aggregation of graphene oxide at concentrations above 0.4 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41751.     

Properties and application of polyimide‐based composites by blending surface functionalized boron nitride nanoplates

Ball milling was used to decrease the particle size of boron nitride (BN) nanoplates and to form more silylated functionalization of their surface. Such functionalized BN nanoplates enhanced their homogeneous dispersion in polyimide (PI) matrix. Thermal conductivities, thermal stabilities, and dielectric properties were characterized to investigate the particular effects on the performance of PI‐based composites with functionalized BN nanoplates. When the concentration of functionalized BN nanoplates increased to 50 wt %, thermal conductivity of the composite increased up to 1.583 W m^?1 K^?1, and the temperature of final thermal decomposition was improved to 600°C. An increasing trend was found in the dielectric constant of the composites while the dielectric loss decreased with the increase in the fraction. An appropriate fraction of functionalized BN nanoplates in PI‐based composites were necessary to meet the requirement of withstanding drilling forces for the interconnecting through holes of flexible circuits. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41889.     

Performance enhancement of polylactide by nanoblending with POSS and graphene oxide

We report the effect of filler modification on the properties of polylactide (PLA)‐based nanocomposites, where graphene oxide (GO) nanosheets and polyhedral oligomeric silsesquioxane (POSS) nanocages are employed as nanofillers. The organically treated nanofillers are termed as GO‐functionalized and POSS‐functionalized. The synthesis of the nanocomposites was carried out via in situ ring‐opening polymerization of lactic acid (LA). The following four naocomposite systems were prepared, characterized, and compared to achieve a better understanding of structure‐property relationship (1) PLA/GO‐functionalized, (2) PLA/POSS‐functionalized, (3) PLA/physical mixture of GO‐functionalized and POSS‐functionalized, and (4) PLA/GO‐graft‐POSS (with eight hydroxyl groups). As revealed by the thermal and mechanical (nanoindendation) characterization, that the nanocomposites having a combination of GO and POSS as nanofiller, either as physical mixture of GO‐functionalized and POSS‐functionalized or as GO‐graft‐POSS, is far more superior as compared with the nanocomposites having individually dispersed nanofillers in the PLA matrix. Observed enhancement is attributing to the synergistic effect of the nanofillers as well as better dispersion of the modified‐fillers in the matrix. POLYM. COMPOS., 35:118–126, 2014. © 2013 Society of Plastics Engineers     

Preparation and properties of functionalized graphene/waterborne polyurethane composites with highly hydrophobic

The long‐chain functionalized graphene nanoplatelets (FGN) were functionalized by isophorone diisocyanate and then octadecylamine, the graphene functionalized/waterborne polyurethane (WPU) composites were prepared by solution mixture. The results showed that the FGN achieved good dispersion with exfoliated and intercalated nanostructure and strong interfacial adhesion with WPU, which made the nano–composites have a significant enhancement of thermal stability and mechanical properties at low FGN loadings. With 1.5% of FGN added, the tensile strength of the composites reached the maximum of 17 MPa, which improved by 41.6%, the water absorption of the composites is only 6.7%. With the incorporation of 2 wt % FGN, and the static contact angle of the composites reached to about 120°, showing the high hydrophobicity. At the same time, the volume resistivity of the composites was changed from 2.34 × 10¹² Ω·cm to 3.77 × 10⁹ Ω·cm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42005.     

Morphology,thermal, mechanical,and barrier properties of graphene oxide/poly(lactic acid) nanocomposite films

To improve the physical and gas barrier properties of biodegradable poly(lactic acid) (PLA) film, two graphene nanosheets of highly functionalized graphene oxide (0.3 wt% to 0.7 wt%) and low-functionalized graphene oxide (0.5 wt%) were incorporated into PLA resin via solution blending method. Subsequently, we investigated the effects of material parameters such as loading level and degree of functionalization for the graphene nanosheets on the morphology and properties of the resultant nanocomposites. The highly functionalized graphene oxide (GO) caused more exfoliation and homogeneous dispersion in PLA matrix as well as more sustainable suspensions in THF, compared to low-functionalized graphene oxide (LFGO). When loaded with GO from 0.3 wt% to 0.7 wt%, the glass transition temperature, degree of crystallinity, tensile strength and modulus increased steadily. The GO gave rise to more pronounced effect in the thermal and mechanical reinforcement, relative to LFGO. In addition, the preparation of fairly transparent PLA-based nanocomposite film with noticeably improved barrier performance achieved only when incorporated with GO up to 0.7wt%. As a result, GO may be more compatible with hydrophilic PLA resin, compared to LFGO, resulting in more prominent enhancement of nanocomposites properties.     

Effect of graphene loading on thermomechanical properties of poly(vinyl alcohol)/starch blend

Polymer nanocomposites based on poly(vinyl alcohol) (PVA)/starch blend and graphene were prepared by solution mixing and casting. Glycerol was used as a plasticizer and added in the starch dispersion. The uniform dispersion of graphene in water was achieved by using an Ultrasonicator Probe. The composites were characterized by FTIR, tensile properties, X‐ray diffraction (XRD), thermal analysis, and FE‐SEM studies. FTIR studies indicated probable hydrogen bonding interaction between the oxygen containing groups on graphene surface and the –OH groups in PVA and starch. Mechanical properties results showed that the optimum loading of graphene was 0.5 wt % in the blend. XRD studies indicated uniform dispersion of graphene in PVA/starch matrix upto 0.5 wt % loadings and further increase caused agglomeration. Thermal studies showed that the thermal stability of PVA increased and the crystallinity decreased in the presence of starch and graphene. FE‐SEM studies showed that incorporation of graphene increased the ductility of the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41827.     

Preparation and characterization of graphene oxide reinforced PVA film with boric acid as crosslinker

PVA films were prepared through aqueous solution method, and boric acid (BA) as well as graphene oxide (GO) was added to improve the mechanical and thermal properties. It was found that 5 wt % BA could increase the tensile strength threefold (from 23.3 to 67.7 MPa), and the incorporation of 0.2 wt % GO would provide additional percentage growth of 30% (from 67.7 to 88.5 MPa). Moreover, an enhancement of thermal stability of PVA film was found when BA or GO filler was added. The reinforcement mechanisms of both BA and GO were investigated, and a competitive phenomenon that the addition of BA would influence the reinforcement effect of GO sheets was found. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42000.     

Properties and structural characterization of oxide starch/chitosan/graphene oxide biodegradable nanocomposites

Novel chitosan (CS)/oxidized starch (OST)/graphene oxide (GO) nanocomposites (COST/GO‐n) films are prepared in a casting and solvent evaporation method. Fourier transform infrared spectroscopy, X‐ray diffractions, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, tensile testing, and moisture uptake are used to study the structure and properties of these nanocomposites. To indicate the effect of carboxyl groups of OST, some results of the properties of CS/starch/GO nanocomposite (CST/GO‐n) were selected for control experimentation. Compared with the control CST/GO‐n series, COST/GO‐n films, which have the same component ration showed higher tensile strength (σ_b) and lower elongation at break (ε_b). Additionally, in the COST/GO‐n series, the σ_b increased with an increase of GO loading. However, higher proportion of GO could result in aggregations of GO nanosheets and deterioration of the film properties. Compared with the COST/GO‐0, the values of σ_b and water resistance of the COST/GO‐4 containing 2.0 wt % of GO were improved by 57.7 and 20.1%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and mechanical behavior of poly(vinyl butyral)‐modified novolac epoxy/multiwalled carbon nanotube nanocomposites

The effects of poly(vinyl butyral) (PVB) and acid‐functionalized multiwalled carbon nanotube modification on the thermal and mechanical properties of novolac epoxy nanocomposites were investigated. The nanocomposite containing 1.5 wt % PVB and 0.1 wt % functionalized carbon nanotubes showed an increment of about 15°C in the peak degradation temperature compared to the neat novolac epoxy. The glass‐transition temperature of the novolac epoxy decreased with increasing PVB content but increased with an increase in the functionalized carbon nanotube concentration. The nanocomposites showed a lower tensile strength compared to the neat novolac epoxy; however, the elongation at break improved gradually with increasing PVB content. Maximum elongation and impact strength values of 7.4% and 17.0 kJ/m² were achieved in the nanocomposite containing 1.5 wt % PVB and 0.25 wt % functionalized carbon nanotubes. The fractured surface morphology was examined with field emission scanning electron microscopy, and correlated with the mechanical properties. The functionalized carbon nanotubes showed preferential accumulation in the PVB phase beyond 0.25 wt % loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43333.     

Enhanced thermal conductivity and dimensional stability of flexible polyimide nanocomposite film by addition of functionalized graphene oxide

Polyimide (PI) nanocomposites with both enhanced thermal conductivity and dimensional stability were achieved by incorporating glycidyl methacrylate‐grafted graphene oxide (g‐GO) in the PI matrix. The PI/g‐GO nanocomposites exhibited linear enhancement in thermal conductivity when the amount of incorporated g‐GO was less than 10 wt%. With the addition of 10 wt% of g‐GO to PI (PI/g‐GO‐10), the thermal conductivity increased to 0.81 W m^?1 K^?1 compared to 0.13 W m^?1 K^?1 for pure PI. Moreover, the PI/g‐GO‐10 composite exhibited a low coefficient of thermal expansion (CTE) of 29 ppm °C^?1. The values of CTE and thermal conductivity continuously decreased and increased, respectively, as the g‐GO content increased to 20 wt%. Combined with excellent thermal stability and high mechanical strength, the highly thermally conducting PI/g‐GO‐10 nanocomposite is a potential substrate material for modern flexible printed circuits requiring efficient heat transfer capability.     

SiO2-covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO2) nanocomposites with superior mechanical and tribological properties

The modified Hummer technique was used in the preparation of graphene oxide (GO) nanosheets, and then SiO₂ decorated GO [GO(SiO₂)] nanosheets were synthesized via the sol–gel method. Then, ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites loaded with 0.5, 1, 1.5, and 2 wt % of GO(SiO₂) were prepared using magnesium ethoxide/GO(SiO₂)-supported Ziegler–Natta catalysts via the in situ polymerization. Morphological study of the prepared polymer powders was assessed using field-emission scanning electron microscopy, which showed that GO(SiO₂) nanohybrids have been uniformly dispersed and distributed into the UHMWPE matrix. Also, the neat UHMWPE and its nanocomposites were evaluated with different analyses, including viscosity-average molecular weight measurement, differential scanning calorimetry, thermogravimetric analysis, tensile test, scratch hardness, and pin-on-disk test. The characterization of the UHMWPE nanocomposites indicated that many characterizations, including the mechanical, thermal, and tribological properties of UHMWPE, were significantly improved by incorporation of these new nanosheets in spite of the molecular weight reduction of the polymeric matrix and the improved flowability and processability of the produced nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47796.     

Effects of graphene nanosheets on the dielectric,mechanical, thermal properties,and rheological behaviors of poly(arylene ether nitriles)

Poly(arylene ether nitriles) (PEN) containing various contents of graphene nanosheets (GNs) was prepared via solution‐casting method and investigated for their dielectric, mechanical, thermal, and rheological properties. For PEN/GNs nanocomposite with 5 wt % GNs, the dielectric constant was increased to 9.0 compared with that of neat PEN (3.1) and dielectric losses of all nanocomposites were in the range of 0.019–0.023 at 1 kHz. The tensile modulus and strength were increased about 6 and 14% with 0.5% GNs, respectively. The fracture surfaces of the all PEN/GNs nanocomposites revealed that GNs had good adhesion to PEN matrix. The thermal properties of the nanocomposites showed significant increase with increasing GN loading. For 5 wt % GNs‐reinforced PEN nanocomposite, the temperatures corresponding to a weight loss of 5 wt % (T_d5%) and 30 wt % (T_d30%) increased by about 20 and 13°C, respectively. Rheological properties of the PEN nanocomposites showed a sudden change with the GN fraction and the percolation threshold was about 1 wt % of GNs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Chitosan–graphene oxide nanocomposites: Effect of graphene oxide nanosheets and glycerol plasticizer on thermal and mechanical properties

In this study, graphite oxide (GO) is synthesized from natural graphite flakes by the modified Hummers method. Characterization by Fourier transform infrared, X‐ray photoelectron, Raman and ultraviolet‐visible spectroscopies, X‐ray diffraction, and thermogravimetric analysis is conducted on GO to confirm the oxidation of graphite. Unplasticized and glycerol plasticized chitosan/graphene oxide (CS/GO) nanosheets nanocomposites with different GO loadings are prepared by solution casting. The combined effect of GO and glycerol on structure, thermal and mechanical properties of nanocomposite films is studied. GO nanosheets are well dispersed throughout the CS matrix due to the hydrogen bonding and electrostatic interactions between CS and GO nanosheets. The incorporation of GO within the CS matrix results in a decrease of the crystallinity, an improvement of thermal stability, and a significant enhancement of the stiffness and tensile strength that is emphasized by the glycerol. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45092.     

Synthesis and properties of click coupled graphene oxide sheets with three‐dimensional macromolecules

A facile click chemistry approach to the functionalization of three‐dimensional hyperbranched polyurethane (HPU) to graphene oxide (GO) nanosheets is presented. HPU‐functionalized GO samples of various compositions were synthesized by reacting alkyne‐functionalized HPU with azide‐functionalized GO sheets. The morphological characterization of the HPU‐functionalized GO was performed using transmission electron microscopy and its chemical characterization was carried out using Fourier transform‐infrared spectroscopy, nuclear magnetic resonance spectroscopy, and X‐ray photoelectron spectroscopy. The graphene sheet surfaces were highly functionalized, leading to improved solubility in organic solvents, and consequently, enhanced mechanical, thermal, and thermoresponsive and photothermal shape memory properties. The strategy reported herein provides a very efficient method for regulating composite properties and producing high performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43358.     

Enhanced interfacial interaction of epoxy nanocomposites with activated graphene nanosheets

The interfacial properties of epoxy nanocomposites reinforced by thermally exfoliated graphene nanosheets (TEG) and activated thermally exfoliated graphene nanosheets (a‐TEG) were compared. The specific surface area (SSA) of a‐TEG with well‐defined micro‐mesopore size distribution was 1000 m²/g, which was much higher that of TEG (550 m²/g). The interfacial interaction between a‐TEG and epoxy was stronger than that of TEG/epoxy owing to their higher SSA and pore size which was proved by dynamic mechanical analysis. As a result, the tensile strength of a‐TEG/epoxy was increased compared with that of TEG/epoxy for all concentrations. In particular, the tensile and flexural strength of a‐TEG/epoxy was increased up to 20 and 50% in comparison to that of TEG/epoxy at 0.05 wt % graphene, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41164.