Improving the thermal and mechanical properties of polysulfone by incorporation of graphene oxide

Nanocomposites of polysulfone (PSF)-graphene oxide (GO) were prepared by classical phase inversion method. The structural and surface features and the mechanical and thermal performances of the prepared materials were investigated in detail. TEM and X-ray diffraction analysis indicated a good compatibility and excellent dispersability with PSF matrix for the low GO content (0.25, 0.5 and 1 wt.%) composites. It was observed that GO dispersion was reasonably homogeneous for the composite with 2 wt.% GO. The mechanical properties of the prepared materials were found to be greatly enhanced by the addition of GO for some compositions. The thermogravimetrical investigation demonstrated considerable improvements in thermal stability for the composite with low GO content. This novel material offers a feasible candidate for practical membrane application.     

Facile preparation and characterization of free-standing stiff carbon-based composite films with excellent performance

Novel free-standing stiff all carbon films based on multi-walled carbon nanotube (MWNT)/glassy carbon (GC) with excellent performance were fabricated. MWNTs, as excellent reinforcing materials, were successfully dispersed in polyimide (PI) matrix by in situ polymerization. The resultant MWNT/PI nanocomoposite films were used as precursors and underwent carbonization process. As a result, all carbon constituted MWNT/GC composite films were obtained. Mechanical results showed the maximum 3-point bending strength and modulus reached 575.5 MPa and 7.7 GPa respectively, improved by 54% and 78% compared to those of neat GC films. This method is simple, and the free-standing composite films can be prepared in large scales, which hold great potential in many applications.     

Free-standing functional graphene reinforced carbon films with excellent mechanical properties and superhydrophobic characteristic

In this work, we reported a simple method to fabricate novel free-standing stiff carbon-based composite films with excellent mechanical properties and superhydrophobic behaviors. The free-standing stiff carbon composite films based on reduced graphene oxide/glassy carbon (rGO/GC) were prepared by the combination of in-situ polymerization and carbonization process. The obtained composite films exhibited excellent mechanical properties by the addition of rGO nanosheets. It was found that incorporating 0.5 wt.% of rGO sheets in GC precursors resulted in enhancements of 99% in strength (202.6 MPa) and 184% in modulus (33.8 GPa), respectively. More interestingly, carbon nanoarrays were uniformly grown on the surface of composite films by the incorporation of rGO sheets. Superhydrophobic surfaces of carbon films were subsequently formed through functionalizing carbon nanoarrays with Trichloro(1H, 1H, 2H, 2H-perfluorodecyl)silane. Contact angle (CA) analysis suggested that superhydrophobic surfaces with a CA as high as 155° could be formed through optimizing the fabrication process.     

Study on the phase change thermal storage performance of palmitic acid/carbon nanotubes composites

After oxidization with the mixed acid of H₂SO₄ and HNO₃, carbon nanotubes (CNTs) were further grafted by γ-(2,3-epoxypropoxy)propyltrimethoxysilane. Then, CNTs, oxidized CNTs and grafted CNTs were respectively dispersed into palmitic acid (PA) matrix to prepare phase change composites at a mass ratio of 1/100. According to the comparative analysis results of the FT-IR spectra, morphology, dispersion and latent heat of the three composites, it is discovered that the composite with grafted CNTs showed the greatest dispersion and tube–matrix adhesion, and thus gained the highest latent heat. It is worth mentioning that the composite with grafted CNTs demonstrated a more favorable latent heat and a 34.1% enhancement of thermal conductivity in comparison with PA. Moreover, the composite with grafted CNTs kept homogeneous after 100 times of melting and freezing, and the retention rate of latent heat can be as high as 98.5%.     

Synthesis and characterization of novel hyperbranched polyimides/attapulgite nanocomposites

Novel hyperbranched polyimides/attapulgite (HBPI/AT) nanocomposites were successfully synthesized by in situ polymerization. HBPI derived from novel 2,4,6-tri[3-(4-aminophenoxy)phenyl]pyridine (TAPP) and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA). 4,4′-diphenylmethane diisocyanate (MDI) modified AT copolymerized with HBPI and the nanocomposites formed multilinked network. Chemical structure, morphology, thermal behavior, and mechanical properties of nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing et.al. Results indicated that modified AT was homogeneously dispersed in matrix and resulted in an improvement of thermal stability, mechanical properties and water resistance of HBPI/AT nanocomposites.     

Facile preparation,characterization and performance of noncovalently functionalized graphene/epoxy nanocomposites with poly(sodium 4-styrenesulfonate)

Graphene was noncovalently functionalized with poly(sodium 4-styrenesulfonate) (PSS) and then successfully incorporated into the epoxy resin via in situ polymerization to form functional and structural nanocomposites. The morphology and structure of PSS modified graphene (PSS-g) were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The effects of PSS-g additions on tensile, electrical and thermal properties of the epoxy/graphene nanocomposites were studied. Noncovalent functionalization improved interfacial bonding between the epoxy matrix and graphene, leading to enhanced tensile strength and modulus of resultant nanocomposites. The PSS-g additions also enhanced electrical properties of the epoxy/PSS-g nanocomposites, resulting in a lower percolation threshold of 1.2 wt%. Thermogravimetric and differential scanning calorimetric results showed the occurrence of a two-step decomposition process for the epoxy/PSS-g nanocomposites.     

Enhanced mechanical,thermal and flame retardant properties by combining graphene nanosheets and metal hydroxide nanorods for Acrylonitrile–Butadiene–Styrene copolymer composite

Three metal hydroxide nanorods (MHR) with uniform diameters were synthesized, and then combined with graphene nanosheets (GNS) to prepare acrylonitrile–butadiene–styrene (ABS) copolymer composites. An excellent dispersion of exfoliated two-dimensional (2-D) GNS and 1-D MHR in the ABS matrix was achieved. The effects of combined GNS and MHR on the mechanical, thermal and flame retardant properties of the ABS composites were investigated. With the addition of 2 wt% GNS and 4 wt% Co(OH)₂, the tensile strength, bending strength and storage modulus of the ABS composites were increased by 45.1%, 40.5% and 42.3% respectively. The ABS/GNS/Co(OH)₂ ternary composite shows the lowest maximum weight loss rate and highest residue yield. Noticeable reduction in the flammability was achieved with the addition of GNS and Co(OH)₂, due to the formation of more continuous and compact charred layers that retarded the mass and heat transfer between the flame and the polymer matrix.     

Fabrication of multi-walled carbon nanotube–carbon fiber hybrid material via electrophoretic deposition followed by pyrolysis process

An integrated multi-walled carbon nanotube (MWCNT)–carbon fiber (CF) hybrid material has been fabricated by electrophoretic deposition of acid-functionalized MWCNTs on CF surface followed by soaking in a 10% solution of petroleum pitch in toluene, followed by pyrolysis in a nitrogen atmosphere. It has been revealed that MWCNTs entirely covered the CF surface. Mechanical properties of composites reinforced by MWCNT–CF hybrids were considerably enhanced (up to 120% in tensile strength and 100% in elastic modulus) compared to composites reinforce by as-received CFs. According to fractography observations, robust interlocking occurred between epoxy matrix and MWCNT–CF hybrids.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

Repair of shear-deficient normal weight concrete beams damaged by thermal shock using advanced composite materials

The use of advanced composite materials such as Fiber Reinforced Polymers (FRPs) in repairing and strengthening reinforced concrete structural elements has been increased in the last two decades. Repairing and strengthening damage structures is a relatively new technique. The aims of this study was to investigate the efficiency and effectiveness of using Carbon Fiber Reinforced Polymer (CFRP) to regain shear capacity of shear-deficient normal weight high strength RC beams after being damaged by thermal shock. Sixteen high strength normal weight RC beams (100 × 150 × 1400 mm) were cast, heated at 500 °C for 2 h and then cooled rapidly by immersion in water, repaired, and then tested under four-point loading until failure. The composite materials used are carbon fiber reinforced polymer plates and sheets. The experimental results indicated that upon heating then cooling rapidly, the reinforced concrete (RC) beams exhibited extensive map cracking without spalling. Load carrying capacity and stiffness of RC beams decreased about 68% and 64%, respectively, as compared with reference beams. Repairing the thermal damaged RC beams allowed recovering the original load carrying without achieving the original stiffness. Repaired beams with CFRP plates with 90° and 45° regained from 90% to 99% of the original load capacity with a corresponding stiffness from 79% to 95%, whereas those repaired with CFRP sheet on the web sides and a combination of CFRP plates and sheet regained from 102% to 107% of the original load capacity with a corresponding stiffness from 81% to 93%, respectively. Finally, finite element analysis model is developed and validated with the experimental results. The finite element analysis showed good agreement as compared with the experimental results in terms of load–deflection and load–CFRP strain curves.     

Enhanced thermal resistance of GO/C/phenolic nanocomposite by introducing ZrB2 nanoparticles

The effectiveness of different additives on improving the thermal stabilities of phenolic composite was investigated by incorporating of graphene oxide sheets (GO) into the carbon/phenolic (PR), and then the ZrB₂ nanoparticles into the GO/PR composite. The GOs dissipate heat throughout the sample thereby reducing thermal gradients and the intensity of heating at the surface exposed to flame. Also, at higher exposure time, the resistance to oxidation of the nanocomposite begins taking advantage of the ongoing formation of an oxide coating layer (ZrO₂) on the exposed face. This protected the underlying unoxidized material from the structural damage caused by thermal shocks and high shear forces.     

Electroactive behavior of graphene nanoplatelets loaded cellulose composite actuators

In this study, graphene nanoplatelets (0.10, 0.25, and 0.50 wt.%) were loaded into cellulose matrix to improve electroactive performance of cellulose-based composite actuators. Firstly, cellulosic films were produced by dissolving microcrystalline cellulose in 1-butyl-3-methylimidazolium chloride. Afterwards, graphene loaded cellulosic films were fabricated and gold leaf was coated on both surfaces of graphene loaded cellulose-based films. The changes in crystallographic properties and chemical functional groups of cellulose were investigated by X-ray diffraction and Fourier transform infrared analyses, respectively. Besides, thermal stability, electrical conductivity, and morphological properties of the films were examined by thermogravimetric analysis, electrical conductivity measurement, and scanning electron microscopy, respectively. The tensile strength and the Young's modulus of the films and actuators were also determined by tensile tests. The electroactive characteristics were analyzed under DC excitation voltages of 3 V, 5 V and 7 V. The time responses were evaluated via proposed experimental data based model. The performances of the actuators were compared in terms of maximum tip displacement, minimum tip displacement and time constant.     

Mechanical,thermal and morphological characterization of cellulose fiber-reinforced phenolic foams

In this work, the compressive mechanical properties, thermal stability and morphology of cellulose fiber-reinforced phenolic foams were studied. The cellulose fiber-reinforced phenolic foam showed the greatest compressive mechanical properties by incorporating 2 wt.% of the reinforcement. The compressive modulus and strength of 2 wt.% cellulose fiber-reinforced phenolic foam were increased by 21% and 18%, respectively, relative to the unreinforced material. The addition of the cellulose fibers to the phenolic foam slightly decreased the thermal stability of the material. The study on the morphology of the cellulose-reinforced phenolic foams via Scanning electron microscopy (SEM) indicated a strong bonding between the fibers and phenolic matrix. In addition, the incorporation of the cellulose fibers into the foam resulted in a decreased cell size and increased cell density of the material. The incorporation of 2 wt.% of cellulose fibers into the phenolic foam led to obtain the material with the best features.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Functional shape memory composite nanofibers with graphene oxide filler

In the present study, we prepared a series of graphene oxide (GO) filled shape memory polyurethane (SMPU) nanofibers and systematically investigated the morphological, thermal and mechanical properties, surface wettability, and the shape memory effect (SME) followed by the proposed programming model. The results show that GO can be well dispersed within the SMPU matrix, and the introduction of GO significantly improves the mechanical strength, surface wettability, and thermal stability of the SMPU. Compared with pristine SMPU nanofibrous mats, the prepared SMPU/GO nanofibrous mats have better SME and lower thermal shrinkage. When the loading amount of GO increased to 4.0 wt%, the thermal shrinkage ratio (R_ts) of composite nanofibrous mats could be as low as 4.7 ± 0.3%, while the average fixation ratio (R_f) and recovery ratio (R_r) could be as high as 92.1% and 96.5%, respectively. The study indicates that GO is a desirable reinforcing filler for preparing shape memory nanofibers with improved properties.     

Advanced biomaterials in hip joint arthroplasty. A review on polymer and ceramics composites as alternative bearings

Wear of total hip prosthesis is a significant clinical problem that nowadays involves a growing number of patients. To acquire further knowledge on the tribological phenomena that involve hip prosthesis, wear tests are conducted on new biomaterials to increase materials life in orthopaedic implants. Advances in biomaterials for biomedical purposes have enhanced in the last years evolving in new improved ceramic and polymeric materials producing the so-called composite materials.This paper aims to review the evolution and the current state of the art of the ceramics composites and polymers commonly used in orthopaedic field as hip joint implants. This is specified through a schematic overview by describing, in particular, the evolution of various composites materials. The authors propose commentary on the evolution and current use of biomaterials for orthopaedic application on the evolution and actually used biomaterials for orthopaedic applications.     

Evaluation of thermal,mechanical, and electrical properties of PVDF/GNP binary and PVDF/PMMA/GNP ternary nanocomposites

Graphene nanoplatelet (GNP) was incorporated into poly(vinylidene fluoride) (PVDF) and PVDF/poly(methyl methacrylate) (PMMA) blend to achieve binary and ternary nanocomposites. GNP was more randomly dispersed in binary composites compared with ternary composites. GNP exhibited higher nucleation efficiency for PVDF crystallization in ternary composites than in binary composites. GNP addition induced PVDF crystals with higher stability; however, PMMA imparted opposite effect. The binary composite exhibited lower thermal expansion value than PVDF; the value further declined (up to 28.5% drop) in the ternary composites. The storage modulus of binary and ternary composites increased to 23.1% and 53.9% (at 25 °C), respectively, compared with PVDF. Electrical percolation threshold between 1 phr and 2 phr GNP loading was identified for the two composite systems; the ternary composites exhibited lower electrical resistivity at identical GNP loadings. Rheological data confirmed that the formation of GNP (pseudo)network structure was assisted in the ternary system.     

Starch/polylactide sustainable composites: Interface tailoring with graphene oxide

The high production cost of polylactide (PLA) can be effectively reduced by simply mixing with starch, unfortunately a trade-off of its mechanical properties. In this paper, we reported a new strategy in which graphene oxide (GO) was used as a compatibilizer to bridge PLA and starch. The native starch was first cationized and then encapsulated with GO by electrostatic force between the negatively charged GO and the positively charged cationic starch. The encapsulating GO was reduced by the quaternary ammonium ions on the cationic starch, which converted the surface of the starch from hydrophilic to hydrophobic. Due to the amphipathicity approximation between PLA and starch, a good dispersion as well as a strong interfacial adhesion was achieved. The PLA composite reinforced with GO encapsulated starch exhibited much higher yield strength than that of pure PLA, increasing from 36.64 MPa up to 41.40 MPa.     

Mechanical characterization of hierarchical carbon fiber/nanofiber composite laminates

Susceptibility to matrix driven failure is one of the major weaknesses of continuous-fiber composites. In this study, helical-ribbon carbon nanofibers (CNF) were dispersed in the matrix phase of a continuous carbon fiber-reinforced composite. Along with an unreinforced control, the resulting hierarchical composites were tested to failure in several modes of quasi-static testing designed to assess matrix-dominated mechanical properties and fracture characteristics. Results indicated CNF addition offered simultaneous increases in tensile stiffness, strength and toughness while also enhancing both compressive and flexural strengths. Short-beam strength testing resulted in no apparent improvement while the fracture energy required for the onset of mode I interlaminar delamination was enhanced by 35%. Extrinsic toughening mechanisms, e.g., intralaminar fiber bridging and trans-ply cracking, significantly affected steady-state crack propagation values. Scanning electron microscopy of delaminated fracture surfaces revealed improved primary fiber–matrix adhesion and indications of CNF-induced matrix toughening.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.