Silicone Composites with CNT/Graphene Hybrid Fillers: A Review

Graphene-Based Hybrid Fillers for Rubber Composites

Graphene and its derivatives have been confirmed to be among the best fillers for rubber due to their excellent properties, such as high mechanical strength, improved interface interaction, and strain-induced crystallization capabilities. Graphene rubber materials can be widely used in tires, shoes, high-barrier conductive seals, electromagnetic shielding seals, shock absorbers, etc. In order to reduce the graphene loading and endow more desirable functions to rubber materials, graphene-based hybrid fillers are extensively employed, which can effectively enhance the performance of rubber composites. This review briefly summarizes the recent research on rubber composites with graphene-based hybrid fillers consisting of carbon black, silica, carbon nanotubes, metal oxide, and one-dimensional nanowires. The preparation methods, performance improvements, and applications of different graphene-based hybrid fillers/rubber composites have been investigated. This study also focuses on methods that can ensure the effectiveness of graphene hybrid fillers in reinforcing rubber composites. Furthermore, the enhanced mechanism of graphene- and graphene derivative-based hybrid fillers in rubber composites is investigated to provide a foundation for future studies.

Elastomer Nanocomposites: Effect of Filler-Matrix and Filler-Filler Interactions

The reinforcement of elastomers is essential in the rubber industry in order to obtain the properties required for commercial applications. The addition of active fillers in an elastomer usually leads to an improvement in the mechanical properties such as the elastic modulus and the rupture properties. Filled rubbers are also characterized by two specific behaviors related to energy dissipation known as the Payne and the Mullins effects. The Payne effect is related to non-linear viscoelastic behavior of the storage modulus while the Mullins or stress-softening effect is characterized by a lowering in the stress when the vulcanizate is extended a second time. Both effects are shown to strongly depend on the interfacial adhesion and filler dispersion. The basic mechanisms of reinforcement are first discussed in the case of conventional rubber composites filled with carbon black or silica usually present in the host matrix in the form of aggregates and agglomerates. The use of nanoscale fillers with isotropic or anisotropic morphologies is expected to yield much more improvement than that imparted by micron-scale fillers owing to the very large polymer-filler interface. This work reports some results obtained with three types of nanoparticles that can reinforce rubbery matrices: spherical, rod-shaped and layered fillers. Each type of particle is shown to impart to the host medium a specific reinforcement on account of its own structure and geometry. The novelty of this work is to emphasize the particular mechanical behavior of some systems filled with nanospherical particles such as in situ silica-filled poly(dimethylsiloxane) networks that display a strong polymer-filler interface and whose mechanical response is typical of double network elastomers. Additionally, the potential of carbon dots as a reinforcing filler for elastomeric materials is highlighted. Different results are reported on the reinforcement imparted by carbon nanotubes and graphenic materials that is far below their expected capability despite the development of various techniques intended to reduce particle aggregation and improve interfacial bonding with the host matrix.

Preparation of Carbon Nanotubes/Alumina Hybrid-Filled Phenolic Composite with Enhanced Wear Resistance

Hybrid fillers can be produced via various methods, such as physical mixing and chemical modification. However, there is a limited number of studies on the effect of hybridisation on the mechanical performance of hybrid filler-reinforced polymer composites, especially in the context of wear performance. This study investigated the wear resistance of carbon nanotubes (CNTs)/alumina hybrid-filled phenolic composite, where two hybrid methods were used to produce the CNTs/alumina hybrid filler. The CNTs/alumina (CVD hybrid) was synthesised using the chemical vapour deposition (CVD) method, whereas the CNTs-/alumina (physically hybrid) was prepared using the ball milling method. The CNTs/alumina hybrid filler was then used as a filler in the phenolic composites. The composites were prepared using a hot mounting press and then subjected to a dry sliding wear test using a pin-on-disc (POD) tester. The results show that the composite filled with the CVD hybrid filler (HYB composite) had better wear resistance than the composite filled with physically hybrid filler (PHY composite) and pure phenolic. At 5 wt%, the HYB composite showed a 74.68% reduction in wear, while the PHY composite showed a 56.44% reduction in wear compared to pure phenolic. The HYB composite exhibited the lowest average coefficient of friction (COF) compared to the PHY composite and pure phenolic. The average COF decreased with increasing sliding speeds and applied loads. The phenolic composites' wear and average COF are in the order HYB composite < PHY composite < pure phenolic under all sliding speeds and applied loads.