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.     

Electrical and mechanical properties of expanded graphite/high density polyethylene nanocomposites

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5–7 μm (EG5) and 40–55 μm (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young’s modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites.     

Improving the flexural and thermomechanical properties of amino-functionalized carbon nanotube/epoxy composites by using a pre-curing treatment

A prior thermal (pre-curing) treatment of mixtures of epoxy monomer and amino-functionalized carbon nanotubes (CNTs) was used to promote a chemical reaction between the matrix and the reinforcement, favouring the formation of a strong interface. Samples of epoxy resin and different weight percentages of amino-functionalized multi-walled CNTs were prepared with and without the pre-curing treatment (150 °C, 1 h). The degree of dispersion of the nanofiller was better when this pre-curing treatment was used. This allowed a higher CNT content while keeping a high sample homogeneity. Without the pre-curing step, the addition of CNTs increases both the flexural strength and strain to failure by 45%. Moreover, with the pre-curing step, the nanocomposite with 0.25 wt.% CNTs presents an increase of flexural strength by 58% and strain to failure by 68% regard to neat epoxy resin.     

Elastomeric epoxy nanocomposites: Nanostructure and properties

In polymer layered silicate nanocomposites, significant differences have been reported between the effects of the nano-reinforcement on rigid and elastomeric nanocomposites. In this paper, we have studied elastomeric nanocomposites based upon DGEBA epoxy resin filled with montmorillonite (MMT) and cured with a long-chain polyoxypropylene diamine, for comparison with analogous rigid nanocomposites. Ultrasonic mixing was used to disperse the MMT in the matrix to improve homogeneity and decrease the agglomerate size. Two different methods of nanocomposite preparation were used in which the MMT was first swollen with either the curing agent or the epoxy before the addition of, respectively, DGEBA or diamine. A better dispersion of the nanoclay in the matrix and a greater amount of intercalation occurred when the MMT was first swollen with the diamine. The effect of MMT concentrations up to 8 wt.% on the mechanical behaviour of the epoxy/MMT nanocomposites was investigated. It was found that the addition of MMT increased the tensile strength and modulus, although SAXS and TEM indicated that a significant fraction of the clay layers were not exfoliated. Nevertheless, the addition of the clay resulted in changes in the fracture surfaces, as indicated by SEM, consistent with the tensile results and indicative of toughening.     

The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.     

Electrical and dielectric properties of polypropylene nanocomposites based on carbon nanotubes and barium titanate nanoparticles

Functional polypropylene (PP) nanocomposites were prepared by melt compounding with multiwalled carbon nanotubes (MWNT) as the electrically conductive component and barium titanate (BT) spherical nanoparticles as the ferroelectric component. To make PP electrically conductive, more than 3 wt.% MWNT is required. Surface modification of either MWNT or BT with titanate coupling agent further improves the electrical conductivity of the PP/MWNT/BT ternary nanocomposites. Interestingly, by modifying both MWNT and BT, 2 wt.% MWNT are sufficient to make the ternary nanocomposite electrically conductive. In addition, the incorporation of MWNT greatly increases the dielectric permittivity of PP/BT nanocomposites. However, to retain a low dielectric loss, the MWNT loading should be slightly less than the percolation threshold of the nanocomposites. The improved electrical conductivity and dielectric properties make the ternary nanocomposites attractive in practical applications.     

Effects of grafted chain length on mechanical and electrical properties of nanocomposites containing polylactide-grafted carbon nanotubes

We herein report the effects of interfacial reinforcement on mechanical and electrical properties of nanocomposites based on polylactide (PLA) and multi-walled carbon nanotube (MWCNT). For this purpose, a series of MWCNTs grafted with PLA chains of various lengths (MWCNT-g-PLAs) were prepared by ring-opening polymerization of l-lactide with carboxylic acid-functionalized MWCNT (MWCNT-COOH). MWCNT-g-PLAs were then mixed with commercial PLA to obtain PLA/MWCNT-g-PLA nanocomposites with 1.0 wt.% MWCNT content. It was revealed that morphological, mechanical, and electrical properties of PLA/MWCNT-g-PLA nanocomposites were strongly dependent on the PLA chain length of MWCNT-g-PLAs. FE-SEM images exhibited that the nanocomposites containing MWCNT-g-PLA with longer PLA chain length exhibited better dispersion of MWCNTs in the PLA matrix. Initial moduli and tensile strengths of PLA/MWCNT-g-PLA composites increased with the increment of chain length of PLA grafted on MWCNTs, which attributes to the improved interfacial adhesion between the grafted PLA chains of MWCNT-g-PLA and the PLA matrix. As a result, the experimental initial modulus (2775 ± 193 MPa) of the nanocomposite including MWCNT-g-PLA with PLA chains of average molecular weight of 530 g/mol was quite close to the theoretical value (2911 MPa) predicted for the nanocomposite with perfect interfacial adhesion. Unexpectedly, electrical resistivities of PLA/MWCNT-g-PLA nanocomposites were found to increase from ∼10⁴ to ∼10¹² Ω/sq with increasing the PLA chain length of MWCNT-g-PLA, which is due to the fact that the PLA chains grafted on MWCNTs prevent the formation of the electrical conduction path of MWCNTs in the PLA matrix.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

High performance natural rubber/thermally reduced graphite oxide nanocomposites by latex technology

The latex technology is an innovative alternative for the preparation of composites of natural rubber (NR) and thermally reduced graphite oxide (TRGO). To achieve an improvement of material properties is indispensable to prepare stable suspensions of TRGO. In this work the influence of two surfactants, such as sodium dodecyl sulfate (SDS), as ionic, and Pluronic F 127 as non-ionic surfactant, on the dispersion of TRGO in NR latex and the mechanical and physical properties of the composites were studied. The results showed that the SDS surfactant is ideal for preparing latex NR/TRGO nanocomposite. An optimum dispersion of the nanoparticles in the polymer matrix was achieved in the presence of SDS, as reflected in a considerable improvement of the physical and mechanical properties of the material. Thus, the nanocomposites with 3 phr of TRGO exhibited an improvement of nearly 400% in the maximum strength and an electrical percolation threshold with values around 10⁻⁶ S/cm, above the static limit.     

The preparation of high performance and conductive poly (vinyl alcohol)/graphene nanocomposite via reducing graphite oxide with sodium hydrosulfite

Sodium hydrosulfite is used to reduce graphite oxide in current study. The preparation of poly (vinyl alcohol) (PVA)/graphene nanocomposites is realized using two simple steps: the synthesis of PVA/graphite oxide (GO) nanocomposites film and immersion of such a film in the reducing agent aqueous solution. This method prohibits the agglomeration of GO during direct reduction in PVA/GO aqueous solution, and opens a new way to scale up the production of graphene nanocomposites using a simple reducing agent. A 40% increase in tensile strength and 70% improvement in elongation at break have been obtained with only the addition of 0.7 wt.% of reduced graphite oxide. Furthermore, a good level of conductivity and a variation in the surface property of the prepared films have been observed for the composites containing graphene.     

The role of epoxy matrix occlusions within BaTiO3 nanoparticles on the dielectric properties of functionalized BaTiO3/epoxy nanocomposites

In this work, the effects of controlled nanoparticles aggregations of barium titanate (BaTiO₃) on the dielectric properties of epoxy nanocomposites are investigated in detail with respect to different experimental parameters like frequency, ceramic content and temperature. Dispersing silanized BaTiO₃ nanopowder under ultrasonic and stir, nanocomposites of epoxy-amine matrix with different morphologies are obtained. The nanoparticles silane functionalization containing amine end groups effectively improve the compatibility of the nano-BaTiO₃ and the epoxy matrix. Storage modulus, glass transition temperature, tensile and flexural properties of nanocomposites and dielectric properties are increased until 10% by weight of nano-BaTiO₃ loading, well dispersed in the matrix. Above 10 wt.% of nano-BaTiO₃, scanning electronic microscopy and thermal analysis showed that agglomeration of nanoparticles occurs. Rheological and mechanical nanocomposites properties were evaluated and matrix occlusion behaviors were identified. In light of the specific behavior of the occluded polymer, the dielectric properties, especially dielectric loss are discussed.     

Structural characterization, thermal and mechanical properties of polyurethane/CoAl layered double hydroxide nanocomposites prepared via in situ polymerization

Dodecyl sulfate (DS), one kind of sulfate anion, was intercalated in the interlayer space between CoAl layered double hydroxide (CoAl-LDH) layers, and then polyurethane (PU) based nanocomposites were prepared by in situ intercalation polymerization with different amounts of the organo-modified CoAl-LDH. An exfoliated dispersion of CoAl-LDH layers in PU matrix was verified by the disappearance of the (0 0 3) reflection of the XRD results when the LDH loading was less than 2.0 wt%. Tensile testing indicated that excellent mechanical properties of PU/LDH nanocomposites were achieved. The weak alkaline catalysis of DS to polyurethane chains, combined with the dehydration and structural degradation of the LDH below 300 °C, accounted for the process of proceeded degradation as shown in TGA results. The real-time FTIR revealed that the as-prepared nanocomposites had a slower thermo-oxidative rate than neat PU from 160 °C to 340 °C, probably due to the barrier effect of LDH layers. These results suggested potential applications of CoAl-LDH as a promising flame retardant in PUs.     

Influence of hexamethylene diamine functionalized graphene oxide on the melt crystallization and properties of polypropylene nanocomposites

Hexamethylene diamine was chemically grafted to the graphene oxide (GO) surface via two type of reactions viz. (i) amidation reaction between amine groups and carboxylic acid sites of GO and (ii) nucleophilic substitution reactions between amine and epoxy groups on surface. Successful grafting of HMDA on GO surface was confirmed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric results (TGA). These chemically modified GO (AGO) with varying loading amount were incorporated in polypropylene matrix in the presence of maleic anhydride-g-polypropylene (PP-g-MA) compatibilizer through melt processing technique. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies revealed that the loading of AGO resulted in the improvement in crystallization characteristics of polypropylene. Owing to the strong interfacial interactions between AGO and polymer, significant enhancement in mechanical and electrical properties was observed, when compared to pristine GO filled polypropylene composites.     

Synthesis and properties of sandwiched films of epoxy resin and graphene/cellulose nanowhiskers paper

Graphene (GN)-based composite paper containing 10 wt.% cellulose nanowhiskers (CNWs) exhibiting a tensile strength of 31.3 MPa and electrical conductivity of 16 800 S/m was prepared by ultrasonicating commercial GN powders in aqueous CNWs suspension. GN/CNWs freestanding paper was applied to prepare the sandwiched films by dip coating method. The sandwiched films showed enhanced tensile strength by over two times higher than the neat resins. The moduli of the sandwiched films were around 300 times of the pure resins due to the high content of GN/CNWs paper. The glass transition temperature of the sandwiched films increased from 51.2 °C to 57.1 °C for pure epoxy (E888) and SF (E888), and 49.8 °C to 64.8 °C for pure epoxy (650) and SF (650), respectively. The bare conductive GN/CNWs paper was well protected by the epoxy resin coating, which is promising in the application as anti-static materials, electromagnetic interference (EMI) shielding materials.     

Effect of multi-walled carbon nanotubes on mechanical,thermal and electrical properties of phenolic foam via in-situ polymerization

In this study, phenolic foam (PF)/multi-walled carbon nanotubes (MWCNTs) composites were fabricated by in-situ polymerization, and carbonized foams based on these PF foams were prepared and the electrical property was investigated. TEM results indicated excellent dispersion of MWCNTs in the phenolic resin matrix. Scanning electron microscope results indicated that PF composites exhibited smaller cell size, thicker cell wall thickness, and higher cell density, compared with pure PF. The incorporating of MWCNTs significantly improved the mechanical properties of PF. All PF composites showed a lower thermal conductivity versus pure PF. Moreover, the carbonized pure and composites PF exhibited open-cell three-dimensional skeleton carbon structure and the MWCNTs were well-dispersed on the surface of the skeletons. It is noteworthy that the introduction of MWCNTs significantly improved the electrical performances of foams and carbonized foams by construction of conductive MWCNTs network.     

In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.     

The effect of graphene presence in flame retarded epoxy resin matrix on the mechanical and flammability properties of glass fiber-reinforced composites

The effect of adding graphene in epoxy containing either an additive (MP) or reactive-type (DOPO) flame retardant on the thermal, mechanical and flammability properties of glass fiber-reinforced epoxy composites was investigated using thermal analysis; flexural, impact, tensile tests; cone calorimetry and UL-94 techniques. The addition of MP or DOPO to epoxy had a thermal destabilization effect below 400 °C, but led to higher char yield at higher temperatures. The inclusion of 10 wt% flame retardants slightly decreased the mechanical behavior, which was attributed to the poor interfacial interactions in case of MP or the decreased cross-linking density in case of DOPO flame retarded resin. The additional graphene presence increased flexural and impact properties, but slightly decreased tensile performance. Adding graphene further decreased the PHRR, THR and burning rate due to its good barrier effect. The improved fire retardancy was mainly attributed to the reduced release of the combustible gas products.     

Specific rheological and electrical features of carbon nanotube dispersions in an epoxy matrix

The rheological analysis of epoxy pre-polymer/MWCNT dispersions indicates that a physical network is formed. This is destroyed with an imposed shear, giving a viscoplastic and shear thinning behavior. Such destruction is not reflected in dynamic viscoelastic experiments, due to the very rapid recovery of the MWCNT network in the pre-polymer matrix. This responds to the observed lower electrical than rheological percolation threshold. Electrical conductivity results fulfill electron hopping/tunnelling mechanism, which implies a tube–tube distance close to 5 nm. However, rheological percolation requires nanotubes should touch each other, since no polymer chains are implied in the network.     

Morphology,thermal and mechanical properties of PVC/MMT nanocomposites prepared by solution blending and solution blending + melt compounding

Two types of montmorillonite (MMT), natural sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT), in different amounts of 1, 2, 5, 10 and 25 phr (parts per hundred resin), were dispersed in rigid poly (vinyl chloride) by two different methods: solution blending and solution blending + melt compounding. The effects on morphology, thermal and mechanical properties of the PVC/MMT nanocomposites were studied by varying the amount of Na-MMT and OMMT in both methods. SEM and XRD analysis revealed that possible intercalated and exfoliated structures were obtained in all of the PVC/MMT nanocomposites. Thermogravimetric analysis revealed that PVC/Na-MMT nanocomposites have better thermal stability than PVC/OMMT nanocomposites and PVC. In general, PVC/MMT nanocomposites prepared by solution blending + melt compounding revealed improved thermal properties compared to PVC/MMT nanocomposites prepared by solution blending. Vicat tests revealed a significant decrease in Vicat softening temperature of PVC/MMT nanocomposites prepared by solution blending + melt compounding compared to unfilled PVC.