Graphene Nanoplatelets as a Replacement for Carbon Black in Rubber Compounds

In this work, we evaluated the processing and reinforcement characteristics of both carbon black (CB) and graphene nanoplatelets (GNPs) within a nitrile butadiene rubber (NBR) matrix. The aspect ratio of the GNPs was measured using atomic force microscopy (AFM) and related to the dispersion and agglomeration within the NBR matrix, as observed by scanning electron microscopy (SEM). The relationship between GNP aspect ratio and mechanical properties was studied by micromechanical modelling. The tensile and tear properties of NBR after compounding with GNPs were enhanced to a greater extent compared to carbon black, while curing times were smaller and scorch times longer, indicating some of the advantages of using GNPs. Overall, the inherent properties of GNPs along with their geometry led to the production of better-performing rubber compounds that can replace their CB-filled counterparts in applications where flexibility, tear strength and compliance are important. The influence of processing on dispersion, orientation and agglomeration of flakes was also highlighted with respect to the Young’s modulus of the NBR compounds

Realising biaxial reinforcement via orientation-induced anisotropic swelling in graphene-based elastomers

The biaxial mechanical properties constitute another remarkable advantage of graphene, but their evaluation has been overlooked in polymer nanocomposites. Herein, we provided an innovative and practical method to characterise biaxial reinforcement from graphene via swelling of elastomers, where graphene nanoplatelets were controlled to be oriented in-plane. The in-plane-aligned graphene imposed a biaxial constraining force to the elastomer during the swelling process that led to the anisotropic swelling behaviour of the bulk nanocomposites

Mechanisms of mechanical reinforcement by graphene and carbon nanotubes in polymer nanocomposites

Polymer nanocomposites reinforced with carbon-based nanofillers are gaining increasing interest for a number of applications due to their excellent properties. The understanding of the reinforcing mechanisms is, therefore, very important for the maximization of performance. This present review summarizes the current literature status on the mechanical properties of composites reinforced with graphene-related materials (GRMs) and carbon nanotubes (CNTs) and identifies the parameters that clearly affect the mechanical properties of the final materials. It is also shown how Raman spectroscopy can be utilized for the understanding of the stress transfer efficiency from the matrix to the reinforcement and it can even be used to map stress and strain in graphene. Importantly, it is demonstrated clearly that continuum micromechanics that was initially developed for fibre-reinforced composites is still applicable at the nanoscale for both GRMs and CNTs. Finally, current problems and future perspectives are discussed

Anisotropic swelling of elastomers filled with aligned 2D materials

A comprehensive study has been undertaken on the dimensional swelling of graphene-reinforced elastomers in liquids. Anisotropic swelling was observed for samples reinforced with graphene nanoplatelets (GNPs), induced by the in-plane orientation of the GNPs. Upon the addition of the GNPs, the diameter swelling ratio of the nanocomposites was significantly reduced, whereas the thickness swelling ratio increased and was even greater than that of the unfilled elastomers. The swelling phenomenon has been analyzed in terms of a modification of the Flory-Rhener theory. The newly-derived equations proposed herein, can accurately predict the dependence of dimensional swelling (diameter and thickness) on volume swelling, independent of the type of elastomer and solvent. The anisotropic swelling of the samples was also studied in combination with the evaluation of the tensile properties of the filled elastomers. A novel theory that enables the assessment of volume swelling for GNP-reinforced elastomers, based on the filler geometry and volume fraction has been developed. It was found that the swelling of rubber nanocomposites induces a biaxial constraint from the graphene flakes

A New Era in Engineering Plastics: Compatibility and Perspectives of Sustainable Alipharomatic Poly(ethylene terephthalate)/Poly(ethylene 2,5-furandicarboxylate) Blends

The industrialisation of poly(ethylene 2,5-furandicarboxylate) for total replacement of poly(ethylene terephthalate) in the polyester market is under question. Preparation of high-performing polymer blends is a well-established strategy for tuning the properties of certain homopolymers and create tailor-made materials to meet the demands for a number of applications. In this work, the structure, thermal properties and the miscibility of a series of poly(ethylene terephthalate)/poly(ethylene 2,5-furandicarboxylate) (PET/PEF) blends have been studied. A number of thermal treatments were followed in order to examine the thermal transitions, their dynamic state and the miscibility characteristics for each blend composition. Based on their glass transition temperatures and melting behaviour the PET/PEF blends are miscible at high and low poly(ethylene terephthalate) (PET) contents, while partial miscibility was observed at intermediate compositions. The multiple melting was studied and their melting point depression was analysed with the Flory-Huggins theory. In an attempt to further improve miscibility, reactive blending was also investigated

Hybrid poly(ether ether ketone) composites reinforced with a combination of carbon fibres and graphene nanoplatelets

Poly(ether ether ketone) (PEEK), with its superb mechanical properties, excellent chemical resistance and high thermo-oxidative stability is one of the most important engineering thermoplastics for high-end applications. In this work, we investigate the elastic and viscoelastic properties along with the creep mitigation of two sets of samples: PEEK reinforced with graphene nanoplatelets (GNPs) and PEEK reinforced with a hybrid graphene/short carbon fibre (CF) filler. The melt viscosity of the PEEK nanocomposites was found to increase with increasing GNPs content; however, the viscosity of the hybrid CF-GNP samples with the highest filler content was equal to the one of the samples filled only with GNPs at low shear rates. This processability shows the advantage of GNPs over other nano and conventional fillers in the ability to use meaningful loadings. The introduction of GNPs improved significantly the stiffness and the storage modulus of the materials in both PEEK-GNP and PEEK-CF-GNP composites. Moreover, the presence of GNPs within the composites led to a restriction of the mobility of the macromolecular chains of PEEK, which resulted in enhanced creep properties at both room temperature and elevated temperatures. Overall, the nanocomposites produced displayed properties that make them attractive in applications where high stiffness and structural integrity at elevated temperatures are required

The mechanics of reinforcement of polymers by graphene nanoplatelets

A detailed study has been undertaken of the mechanisms of stress transfer in polymeric matrices with different values of Young's modulus, Em, reinforced by graphene nanoplatelets (GNPs). For each material, the Young's modulus of the graphene filler, Ef, has been determined using the rule of mixtures and it is found to scale with the value of Em. Additionally stress-induced Raman bands shifts for the different polymer matrices show different levels of stress transfer from the polymer matrix to the GNPs, which again scale with Em. A theory has been developed to predict the stiffness of the bulk nanocomposites from the mechanics of stress transfer from the matrix to the GNP reinforcement based upon the shear-lag deformation of individual graphene nanoplatelets. Overall it is found that it is only possible to realise the theoretical Young's modulus of graphene of 1.05 TPa for discontinuous nanoplatelets as Em approaches 1 TPa; the effective modulus of the reinforcement will always be less for lower values of Em. For flexible polymeric matrices the level of reinforcement is independent of the graphene Young's modulus and, in general, the best reinforcement will be obtained in nanocomposites with strong graphene-polymer interfaces and aligned nanoplatelets with high aspect ratios

Graphene-Polyurethane Coatings for Deformable Conductors and Electromagnetic Interference Shielding

Electrically conductive, polymeric materials that maintain their conductivity even when under significant mechanical deformation are needed for actuator electrodes, conformable electromagnetic shielding, stretchable tactile sensors, and flexible energy storage. The challenge for these materials is that the percolated, electrically conductive networks tend to separate even at low strains, leading to significant piezoresistance. Herein, deformable conductors are fabricated by spray‐coating a nitrile substrate with a graphene–elastomer solution. The electrical resistance of the coatings shows a decrease after thousands of bending cycles and a slight increase after repeated folding‐unfolding events. The deformable conductors double their electrical resistance at 12% strain and are washable without changing their electrical properties. The conductivity–strain behavior is modeled by considering the nanofiller separation upon deformation. To boost the conductivity at higher strains, the production process is adapted by stretching the nitrile substrate before spraying, after which it is released. This adaption meant that the electrical resistance doubles at 25% strain. The electrical resistance is found sufficiently low to give a 1.9 dB µm−1 shielding in the 8–12 GHz electromagnetic band. The physical and electrical properties, including the electro magnetic screening, of the flexible conductors, are found to deteriorate upon cycling but can be recovered through reheating the coating

Highly stretchable and sensitive self-powered sensors based on the N-Type thermoelectric effect of polyurethane/Na_{x}(Ni-ett)_{n}/graphene oxide composites

The development of stretchable organic thermoelectric materials is prompted by fast evolving application fields like flexible electronic devices, soft robotics, health monitoring and internet-of-things. Stretchability in thermoelectric materials is usually obtained by using an insulating elastomer, either as a substrate or as a matrix in a blend or composite, which, unfortunately, leads to a compromise in thermoelectric performance. Herein, a potential solution is reported exploiting the addition of graphene oxide as a secondary (nano)filler in a polyurethane/poly nickel-ethenetetrathiolates film. Compared with traditional binary blends, our ternary composite shows an increased electrical conductivity (4 times), air-stability (∼20 times after 3 months), and stretchability (38% increase in strain at break). With a gauge factor (GF) of ∼58, this new composite film shows high sensitivity to tensile strain. Thanks to its Seebeck coefficient of ∼ −40 μV K^{−1}, the composite film can generate a thermopower of ∼0.25 pW when subjected to a small temperature difference (30 °C), which could be exploited by self-powered strain sensors. Therefore, the ternary polyurethane/poly nickel-ethenetetrathiolates/graphene oxide composite film can work as a stretchable strain sensor, providing a strategy to reconcile the compromise between thermoelectric performance and stretchability