Processing–Morphology–Property Relationships and Composite Theory Analysis of Reduced Graphene Oxide/Natural Rubber Nanocomposites

Filled Elastomers: Mechanistic and Physics-Driven Modeling and Applications as Smart Materials

Elastomers are made of chain-like molecules to form networks that can sustain large deformation. Rubbers are thermosetting elastomers that are obtained from irreversible curing reactions. Curing reactions create permanent bonds between the molecular chains. On the other hand, thermoplastic elastomers do not need curing reactions. Incorporation of appropriated filler particles, as has been practiced for decades, can significantly enhance mechanical properties of elastomers. However, there are fundamental questions about polymer matrix composites (PMCs) that still elude complete understanding. This is because the macroscopic properties of PMCs depend not only on the overall volume fraction (ϕ) of the filler particles, but also on their spatial distribution (i.e., primary, secondary, and tertiary structure). This work aims at reviewing how the mechanical properties of PMCs are related to the microstructure of filler particles and to the interaction between filler particles and polymer matrices. Overall, soft rubbery matrices dictate the elasticity/hyperelasticity of the PMCs while the reinforcement involves polymer-particle interactions that can significantly influence the mechanical properties of the polymer matrix interface. For ϕ values higher than a threshold, percolation of the filler particles can lead to significant reinforcement. While viscoelastic behavior may be attributed to the soft rubbery component, inelastic behaviors like the Mullins and Payne effects are highly correlated to the microstructures of the polymer matrix and the filler particles, as well as that of the polymer-particle interface. Additionally, the incorporation of specific filler particles within intelligently designed polymer systems has been shown to yield a variety of functional and responsive materials, commonly termed smart materials. We review three types of smart PMCs, i.e., magnetoelastic (M-), shape-memory (SM-), and self-healing (SH-) PMCs, and discuss the constitutive models for these smart materials.

Effect of dispersibility of graphene nanoplatelets on the properties of natural rubber latex composites using sodium dodecyl sulfate

Natural rubber latex/graphene nanoplatelet (NRL/GNP) composites containing GNP-pristine and GNP–SDS were prepared by a simple mechanical mixing method. The main objective was to study the effect of dispersibility of GNP on the properties in NRL. X-ray diffraction confirmed the adsorption of sodium sulfate dodecyl (SDS) on the GNP surface. The results showed that high filler loading diminished the physical and mechanical properties of the composites but successfully endured to satisfy electrical conductivity to the NRL/GNP composites. Besides, the SDS surfactant-filled system demonstrated better physical, tensile, electrical, and thermal stability properties than the GNP-pristine. The intercalated and dispersed GNP–SDS increased the number of routes for stress and heat transfer to occur and facilitated the formation of conductive pathways as well, leading to the improvement of the properties as compared to NRL/GNP-pristine composites. However, as the GNP–SDS loading exceeded 5 phr, the GNP–SDS localized in the interstitial layer of NRL, restricted the formation of crosslinking, and interfered with the strain-induced crystallization ability of the composites.

Comparative Structure–Property Relationship between Nanoclay and Cellulose Nanofiber Reinforced Natural Rubber Nanocomposites

Natural rubber (NR) nanocomposites reinforced with five parts per hundred rubber (phr) of two different nano-fillers, i.e., nanoclay (abbrev. NC) and cellulose nanofiber (abbrev. CNF), were prepared by using latex mixing approach, followed by mill-compounding and molding. The morphology, stress–strain behavior, strain-induced crystallization, and bound rubber of the NR nanocomposites were systematically compared through TEM, tensile test, WAXS, DMA, and bound rubber measurement. The aggregated CNFs were observed in the NR matrix, while the dispersed nanosized clay tactoids were detected across the NR phase. The reinforcement effects of NC and CNF were clearly distinct in the NR nanocomposites. At the same nano-filler content, the addition of NC and CNF effectively accelerated strain-induced crystallization of NR. The high tensile strength obtained in the NC-filled NR nanocomposite was attributed to strain-induced crystallization of NR accelerated by well-dispersed NC. However, the larger tensile modulus and low strain for the CNF-filled NR were related to the formation of immobilized NR at the interface between CNF aggregate and NR. The immobilization effect of NR at the CNF surface offered by a mutual entanglement of CNF aggregate and NR chain led to local stress concentration and accelerated strain-induced crystallization of CNF/NR nanocomposite. From the present study, the NR nanocomposites combined with 5 phr CNF shows high-tensile modulus and acceptable breaking tensile stress and strain, suggesting the application of CNF/NR based nanocomposite in automotive and stretchable sensors for next-generation electronic devices.

A comprehensive review on the recent advancements in natural rubber nanocomposites

Natural rubber (NR) is an eminent sustainable material and is the only agricultural product among various rubbers. Use of nanofillers in NR matrix as a reinforcing agent has gained huge attention because they offer excellent matrix-filler interaction upon forming a good dispersion in the NR matrix. Nanoscale dispersion of fillers lead to greater interfacial interactions between NR and fillers compared to microfillers, which in turn lead to a conspicuous reinforcing effect. Addition of various nanofillers into NR matrix improves not only the mechanical properties but also the electrical, thermal and antimicrobial properties to an extreme level. The current review describes the reinforcing ability of various nanofillers such as clay, graphene, carbon nanotube (CNT), titanium dioxide (TiO₂), chitin, cellulose, barium titanate (BaTiO₃) and lignin in NR matrix. Moreover, reinforcement of various hybrid nanofillers in NR is also discussed in a comprehensive manner. The review also includes the historical trajectory of rubber nanocomposites and a comprehensive account on the factors affecting the properties of the NR nanocomposites.

Beyond homogeneous dispersion: oriented conductive fillers for high κ nanocomposites

Rational design of structures for regulating the thermal conductivities (κ) of materials is critical to many components and products employed in electrical, electronic, energy, construction, aerospace, and medical applications. As such, considerable efforts have been devoted to developing polymer composites with tailored conducting filler architectures and thermal conduits for highly improved κ. This paper is dedicated to overviewing recent advances in this area to offer perspectives for the next level of future development. The limitations of conventional particulate-filled composites and the issue of percolation are discussed. In view of different directions of heat dissipation in polymer composites for different end applications, various approaches for designing the micro- and macroscopic structures of thermally conductive networks in the polymer matrix are highlighted. Methodological approaches devised to significantly ameliorate thermal conduction are categorized with respect to the pathways of heat dissipation. Future prospects for the development of thermally conductive polymer composites with modulated thermal conduction pathways are highlighted.

Graphene and water-based elastomer nanocomposites - a review

Water-based elastomers (WBEs) are polymeric elastomers in aqueous systems. WBEs have recently continued to gain wide acceptability by both academia and industry due to their remarkable environmental and occupational safety friendly nature, as a non-toxic elastomeric dispersion with low-to-zero volatile organic compound (VOC) emission. However, their inherent poor mechanical and thermal properties remain a drawback to these sets of elastomers. Hence, nano-fillers such as graphene oxide (GO), reduced graphene oxide (rGO) and graphene nanoplatelets (GNPs) are being employed for the reinforcement and enhancement of this set of elastomers. This work is geared towards a critical review and summation of the state-of-the-art developments of graphene enhanced water-based elastomer composites (G-WBEC), including graphene and composite production processes, properties, characterisation techniques and potential commercial applications. The dominant production techniques, such as emulsion mixing and in situ polymerisation processes, which include Pickering emulsion, mini-emulsion and micro-emulsion, as well as ball-milling approach, are systematically evaluated. Details of the account of mechanical properties, electrical conductivity, thermal stability and thermal conductivity enhancements, as well as multifunctional properties of G-WBEC are discussed, with further elaboration on the structure-property relationship effects (such as dispersion and filler-matrix interface) through effective and non-destructive characterisation tools like Raman and XRD, among others. The paper also evaluates details of the current application attempts and potential commercial opportunities for G-WBEC utilisation in aerospace, automotive, oil and gas, biomedicals, textiles, sensors, electronics, solar energy, and thermal management.

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Engineering Segregated Structures in a Cross-Linked Elastomeric Network Enabled by Dynamic Cross-Link Reshuffling

Construction of segregated structures in polymer composites is an efficient way to improve the electrical conductivity and reduce the percolation threshold by confining conductive fillers into the interstitial areas between polymer domains. Yet, it remains a great challenge to engineer segregated structures into thermosets as the cross-linked structure prohibits the "sintering" of polymer domains into a coherent material. Thus far, the state of art approaches to create segregated network in cross-linked polymers involve tedious procedures and are limited to latex mixing technology. Here, inspired by solid state plasticity of vitrimers, we present a simple method to create segregated structures in covalently cross-linked networks by compression molding of conductive filler-coated vitrimer granules. Specifically, dynamic boronic ester-cross-linked styrene-butadiene rubber vitrimers was ground into granules and then mechanically mixed with carbon nanotubes (CNTs) to coat CNTs onto vitrimer granules, followed by hot-press molding. During the molding process, the transesterifications of boronic esters enable cross-linked granules to adhere together through molecular bonding, and the high viscosity of granules forces CNTs to selectively localize at their boundary region. As a result, coherently segregated composites with an ultralow percolation threshold, good flexibility, and healing capability are obtained. With this example, we envisage that this work provides a conceptual method to create segregated structures in cross-linked polymers.

Styrene-Based Elastomer Composites with Functionalized Graphene Oxide and Silica Nanofiber Fillers: Mechanical and Thermal Conductivity Properties

The mechanical and thermal conductivity properties of two composite elastomers were studied. Styrene-butadiene rubber (SBR) filled with functionalized graphene oxide (GO) and silica nanofibers, and styrene-butadiene-styrene (SBS) block copolymers filled with graphene oxide. For the SBR composites, GO fillers with two different surface functionalities were synthesized (cysteamine and dodecylamine) and dispersed in the SBR using mechanical and liquid mixing techniques. The hydrophilic cysteamine-based GO fillers were dispersed in the SBR by mechanical mixing, whereas the hydrophobic dodecylamine-based GO fillers were dispersed in the SBR by liquid mixing. Silica nanofibers (SnFs) were fabricated by electrospinning a sol-gel precursor solution. The surface chemistry of the functionalized fillers was studied in detail. The properties of the composites and the synergistic improvements between the GO and SnFs are presented. For the SBS composites, GO fillers were dispersed in the SBS elastomer at several weight percent loadings using liquid mixing. Characterization of the filler material and the composite elastomers was performed using x-ray photoelectron spectroscopy, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, tensile testing, nanoindentation, thermal conductivity and abrasion testing.

Full-color natural rubber latex with a photonic nanostructure composite

As environmental problems increase, there is an urgent demand for new eco-friendly materials. Natural rubber latex (NRL) is a natural material extracted from rubber trees. But its dyeing process with chemical dyes might result in contamination and environmental degradation. Here, NRL is composited with a photonic crystal (PhC) structure by spin coating for the first time. The polymethyl methacrylate (PMMA) photonic nanostructure has been embedded into NRL to give it colors and provide it with optical functionalities. Colors of the composite could be designed and controlled by the sizes of the nanocolloids from 180 nm to 295 nm. The colors have strong stability under external stretching. The 3D natural rubber latex photonic crystal (NRLPC) is used as a responsive material to detect volatile organic compounds (VOCs) including formaldehyde, acetone, toluene, xylene and styrene. With its visual color appearance, biocompatibility and flexibility, NRLPC has promising potential in various sensing applications.

High-Performance Natural Rubber/Graphene Composites from a Uniquely Designed Physical and Chemical Hybrid-Network

It is well-known that strength and stiffness are commonly inversely related with toughness and ductility for organic filler filled elastomer nanocomposites. These performances are governed by the dispersion of organic fillers and interface of elastomer nanocomposites. Herein, the designed physical and chemical hybrid-network based on tannic acid (TA) as interface regulator and cross-link agent can endow graphene/elastomer nanocomposites with reinforcement as well as toughness simultaneously. The results indicate the formation of a strong and stable network structure composed of elastomer chains and graphene, contrary to traditional graphene/elastomer nanocomposites. The present composites with a physical and chemical hybrid-network effectively improve the load transfer and show excellent mechanical properties.

Graphene Layers Functionalized with A Janus Pyrrole-Based Compound in Natural Rubber Nanocomposites with Improved Ultimate and Fracture Properties

The ultimate properties and resistance to fracture of nanocomposites based on poly(1,4-cis-isoprene) from Hevea Brasiliensis (natural rubber, NR) and a high surface area nanosized graphite (HSAG) were improved by using HSAG functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol (serinol pyrrole) (HSAG-SP). The functionalization reaction occurred through a domino process, by simply mixing HSAG and serinol pyrrole and heating at 180 °C. The polarity of HSAG-SP allowed its dispersion in NR latex and the isolation of NR/HSAG-SP masterbatches via coagulation. Nanocomposites, based either on pristine HSAG or on HSAG-SP, were prepared through traditional melt blending and cured with a sulphur-based system. The samples containing HSAG-SP revealed ultimate dispersion of the graphitic filler with smaller aggregates and higher amounts of few layers stacks and isolated layers, as revealed by transmission electron microscopy. With HSAG-SP, better stress and elongation at break and higher fracture resistance were obtained. Indeed, in the case of HSAG-SP-based composites, fracture occurred at larger deformation and with higher values of load and, at the highest filler content (24 phr), deviation of fracture propagation was observed. These results have been obtained with a moderate functionalization of the graphene layers (about 5%) and normal lab facilities. This work reveals a simple and scalable way to prepare tougher NR-based nanocomposites and indicates that the dispersion of a graphitic material in a rubber matrix can be improved without using an extra-amount of mechanical energy, just by modifying the chemical nature of the graphitic material through a sustainable process, avoiding the traditional complex approach, which implies oxidation to graphite oxide and subsequent partial reduction.

Constructing 3D Graphene Network in Rubber Nanocomposite via Liquid-Phase Redispersion and Self-Assembly

A three-dimensional graphene (GE) segregated network structure is of significance for improving the conductivity of composites. However, constructing such a GE network structure in composites still remains a challenge. Here, we demonstrate a facile process, that is, liquid-phase redispersion and self-assembly (LRS) to prepare polymer nanocomposites with graphene segregated networks. High shear liquid-phase mixing accompanied by the diffusion of dissolved polymer chains into the interstices and voids of the loose graphene powders can lead to redispersion of GE in polymer solution. Once the stirring is stopped, the self-assembly and segregation of redispersed GE occurs in a poor solvent driven by π-π interaction. After solvent evaporation, the GE assembly structures are retained as networks in the GE/polymer composite prepared by hot pressing. The graphene/(isobutylene-isoprene rubber) nanocomposite (GE/IIR) was investigated as a demonstration for the advantages of the LSR method. The morphologies of GE assemblies in the liquid phase and GE networks in the solid composite were observed. Due to the existence of the homogeneously distributed graphene segregated networks, the tensile strength and elongation at break for GE/IIR nanocomposites increase by ∼410 and ∼126%, respectively, and the electrical conductivity reaches ∼10⁰ S m^-1 at a GE content of 3.76 vol %. The LRS method was also successfully tried for systems with different polymer matrixes and different solvents, suggesting the robustness of the proposed method. The prepared flexible GE/IIR nanocomposites with GE networks are sensitive to tiny strain and can be applied in wearable sensors for the detection of human physiological signals.

Facile Strategy for the Biomimetic Heterogeneous Design of Elastomers with Mechanical Robustness, Malleability, and Functionality

It remains challenging to simultaneously realize mechanical robustness, malleability, and functionality in elastomers via facile yet efficient methods. Herein, a simple strategy for the biomimetic heterogeneous design is proposed to achieve mechanically strong, malleable, and functionalized elastomers. We demonstrate the strategy by straightforward mechanical mixing of a highly cross-linked vitrimeric elastomer with a homogeneous gum and subsequent curing, resulting in heterogeneous vitrimeric elastomers (hetero-VEs). The hetero-VEs comprise two phases: a hard phase with dense cross-links and a soft matrix with few cross-links, with excellent interface between the two phases. The hard phases can be deformed upon loading, dissipating energy, which significantly improves the overall mechanical performance of the hetero-VEs. When conductive fillers are incorporated into the soft matrix, due to the volume exclusion effect of the hard phases, the resultant hetero-VEs exhibit high conductivity with a small fraction of fillers. In view of the facile and generic preparation process, this strategy should be a promising way to reinforce and functionalize many vitrimeric elastomer systems.

Bio-elastomer nanocomposites reinforced with surface-modified graphene oxide prepared via in situ coordination polymerization

This article proposes a method to produce bio-elastomer nanocomposites, based on polyfarnesene or polymyrcene, reinforced with surface-modified graphene oxide (GO). The surface modification is performed by grafting alkylamines (octyl-, dodecyl-, and hexadecylamine) onto the surface of GO. The successful grafting was confirmed via spectroscopic (FTIR and Raman) and X-ray diffraction techniques. The estimated grafted amines appear to be around 30 wt%, as calculated via thermogravimetric analysis, increasing the inter-planar spacing among the nanosheets as a function of alkyl length in the amine. The resulting modified GOs were then used to prepare bio-elastomer nanocomposites via in situ coordination polymerization (using a ternary neodymium-based catalytic system), acting as reinforcing additives of polymyrcene and polyfarnesene. We demonstrated that the presence of the modified GO does not affect significantly the catalytic activity, nor the microstructure-control of the catalyst, which led to high cis-1,4 content bio-elastomers (>95%). Moreover, we show via rheometry that the presence of the modified-GO expands the capacity of the elastomer to store deformation or applied stress, as well as exhibit an activation energy an order of magnitude higher.

This article proposes a method to produce bio-elastomer nanocomposites, based on polyfarnesene or polymyrcene, reinforced with surface-modified graphene oxide (GO).

Hybrid Green Bionanocomposites of Bio-based Poly(butylene succinate) Reinforced with Pyrolyzed Perennial Grass Microparticles and Graphene Nanoplatelets

Bio-based poly(butylene succinate) (BioPBS) was combined with pyrolyzed Miscanthus microparticles (biocarbon) and graphene nanoplatelets to create a hybrid bionanocomposite. Pyrolyzed biomass, known as biocarbon, was incorporated into a BioPBS matrix to improve the thermo-mechanical properties of the bioplastic while simultaneously increasing the value of this co-product. Biocomposites loaded with 25 wt % biocarbon showed 57, 13, and 32% improvements in tensile modulus, heat deflection temperature, and thermal expansion, respectively. Further improvements were found when graphene nanoplatelets (GnPs) were added to the biocomposite, forming a hierarchical hybrid bionanocomposite. Two processing methods were used to incorporate graphene into the composites: (I) graphene, BioPBS, and biocarbon were added together and directly compounded, and (II) a masterbatch of graphene and BioPBS was processed first and then diluted to the same ratios as those used in the direct compounding method I. The two methods resulted in different internal morphologies that subsequently impacted the mechanical properties of the composites; little change was observed in the thermal properties studied. Bionanocomposites processed using the direct compounding technique showed the greatest increase in tensile strength and modulus: 17 and 120%, respectively. Bionanocomposites processed using a masterbatch technique had slightly lower strength and modulus but showed almost twice the impact strength compared with the direct compounding method. This masterbatch technique was found to have a superior balance of stiffness and toughness, likely due to the presence of superclustered graphene platelets, confirmed through a scanning electron microscope and a transmission electron microscope.

Monolithic 3D printing of embeddable and highly stretchable strain sensors using conductive ionogels

Medical training simulations that utilize 3D-printed, patient-specific tissue models improve practitioner and patient understanding of individualized procedures and capacitate pre-operative, patient-specific rehearsals. The impact of these novel constructs in medical training and pre-procedure rehearsals has been limited, however, by the lack of effectively embedded sensors that detect the location, direction, and amplitude of strains applied by the practitioner on the simulated structures. The monolithic fabrication of strain sensors embedded into lifelike tissue models with customizable orientation and placement could address this limitation. The demonstration of 3D printing of an ionogel as a stretchable, piezoresistive strain sensor embedded in an elastomer is presented as a proof-of-concept of this integrated fabrication for the first time. The significant hysteresis and drift inherent to solid-phase piezoresistive composites and the dimensional instability of low-hysteresis piezoresistive liquids inspired the adoption of a 3D-printable piezoresistive ionogel composed of reduced graphene oxide and an ionic liquid. The shear-thinning rheology of the ionogel obviates the need to fabricate additional structures that define or contain the geometry of the sensing channel. Sensors are printed on and subsequently encapsulated in polydimethylsiloxane (PDMS), a thermoset elastomer commonly used for analog tissue models, to demonstrate seamless fabrication. Strain sensors demonstrate geometry- and strain-dependent gauge factors of 0.54-2.41, a high dynamic strain range of 350% that surpasses the failure strain of most dermal and viscus tissue, low hysteresis (<3.5% degree of hysteresis up to 300% strain) and baseline drift, a single-value response, and excellent fatigue stability (5000 stretching cycles). In addition, we fabricate sensors with stencil-printed silver/PDMS electrodes in place of wires to highlight the potential of seamless integration with printed electrodes. The compositional tunability of ionic liquid/graphene-based composites and the shear-thinning rheology of this class of conductive gels endows an expansive combination of customized sensor geometry and performance that can be tailored to patient-specific, high-fidelity, monolithically fabricated tissue models.

Synergistic Effect of Aligned Graphene Nanosheets in Graphene Foam for High-Performance Thermally Conductive Composites

Graphene shows a great potential for high-performance thermally conductive composite applications because of its extremely high thermal conductivity. However, the graphene-based polymer composites reported so far only have a limited thermal conductivity, with the highest thermal conductivity enhancement (TCE) per 1 vol% graphene less than 900%. Here, a continuous network of graphene foam (GF), filled with aligned graphene nanosheets (GNs), is shown to be an ideal filler structure for thermally conductive composite materials. Compared to previous reports, a clear thermal percolation is observed at a low graphene loading fraction. The GNs/GF/natural rubber composite shows the highest TCE of 8100% (6.2 vol% graphene loading) ever reported at room temperature, which gives a record-high TCE per 1 vol% graphene of 1300%. Further analyses reveal a significant synergistic effect between the aligned GNs and 3D interconnected GF, which plays a key role in the formation of a thermal percolation network to remarkably improve the thermal conductivity of the composites. Additionally, the use of this composite for efficient heat dissipation of light-emitting diode (LED) lamps is demonstrated. These findings provide valuable guidance to design high-performance graphene-based thermally conductive materials, and open up the possibility for the use of graphene in high-power electronic devices.

Preparation and Comparison of Reduced Graphene Oxide and Carbon Nanotubes as Fillers in Conductive Natural Rubber for Flexible Electronics

Conductive natural rubber (NR) nanocomposites were prepared by solvent-casting suspensions of reduced graphene oxide (rGO) or carbon nanotubes (CNTs), followed by vulcanization of the rubber composites. Both rGO and CNT were compatible as fillers in the NR as well as having sufficient intrinsic electrical conductivity for functional applications. Physical (thermal) and chemical reduction of GO were investigated, and the results of the reductions were monitored by X-ray photoelectron spectroscopy for establishing a reduction protocol that was useful for the rGO nanocomposite preparation. Field-emission scanning electron microscopy showed that both nanofillers were adequately dispersed in the main NR phase. The CNT composite displays a marked mechanical hysteresis and higher elongation at break, in comparison to the rGO composites for an equal fraction of the carbon phase. Moreover, the composite conductivity was always ca. 3-4 orders of magnitude higher for the CNT composite than for the rGO composites, the former reaching a maximum conductivity of ca. 10.5 S/m, which was explained by the more favorable geometry of the CNT versus the rGO sheets. For low current density applications though, both composites achieved the necessary percolation and showed the electrical conductivity needed for being applied as flexible conductors for a light-emitting diode.

Strain-sensitive electrical conductivity of carbon nanotube-graphene-filled rubber composites under cyclic loading

Conductive rubber nanocomposites have been attracting interest for strain sensing applications owing to their large deformation and high sensitivity. In this paper, the strain sensing behavior of room temperature vulcanized (RTV) hybrid silicone rubber composites containing carbon nanotubes and graphene was systematically investigated. We studied the effects of the nanofiller content and strain amplitude on the strain sensing behavior of the nanocomposites, and found good stability and durability during cyclic loading. The shoulder peaks appeared in the cyclic loading curves owing to the competition between the reconstruction process of the conductive network during deformation and time-dependent features of the polymer material. Furthermore, our test results of different loading histories indicated that a sufficient recovery time could reduce or even eliminate the shoulder peak. Finally, the mechanical structure with a negative Poisson's ratio is designed to regulate the resistance response of the RTV nanocomposites, exhibiting a monotonic and more sensitive resistance response. Our research results explain the main factors contributing to the shoulder peak phenomenon of conductive nanocomposites and provide a regulation strategy for achieving a monotonic and highly sensitive resistance response.

REINFORCEMENT OF RUBBER USING REACTIVE OLIGO(β-ALANINE) SUPRAMOLECULAR FILLERS

Oligo(β-alanine)–based supramolecular fillers that possess an 11-mercaptoundecanoyl oleophilic moiety and an oligo(β-alanine) oleophobic moiety of varied lengths (SA1, SA2, and SA3, having a β-alanine unimer, dimer, and trimer moiety, respectively) have been systematically investigated for reinforcement of SBR. An analog of SA2 with 11-mercapto-undecanoyl being replaced by 3-mercaptopropanoyl, SA2′, was also studied for comparison. Fourier transform infrared evidence has confirmed that all supramolecular fillers exist exclusively as hydrogen-bonded β-sheets in the rubber composites. Differential scanning calorimetry studies have revealed that SA2, SA2′, and SA3 form crystalline domains in the SBR phase at all filler loadings, while SA1 only forms crystalline domains at &gt;15 phr, indicating that microphase separation from the SBR phase is weaker for SA1 than for its higher congeners. Transmission electron microscopy investigations have shown that the filler crystalline domains are dispersed uniformly as short fibers in a continuous SBR phase. The widths of the fibers are below 10 nm, and the lengths range from a few tens to a couple of hundreds of nanometers. The oligo(β-alanine)–based supramolecular fillers exhibit diverse reinforcing characteristics among themselves and in comparison with carbon black. SA1 gives comparatively high extensibility and low tensile strength, while SA2 and SA3 give relatively low extensibility, high stiffness, and high strength. SA2′ behaves similarly to SA1 at low filler loadings but significantly compromises the extensibility at relatively high loadings. Cyclic tensile testing shows that SA1 gives high hysteresis and high set, while SA2 and SA3 give low hysteresis at low elongation and high hysteresis at high elongation in comparison with carbon black. Dynamic mechanical study at 2% strain shows that SA1, SA2, and SA3 result in markedly lower tan δ at 60 °C than carbon black. In addition, abrasion study shows that SA1 and SA2 result in lower weight loss than carbon black at 30 phr of filler loading.

A New Approach of Fabricating Graphene Nanoplates@Natural Rubber Latex Composite and Its Characteristics and Mechanical Properties

Graphene has been demonstrated to be one of the most promising candidates to use as filler to improve the electrical, thermal, chemical and mechanical properties of natural rubber due to exceptional high surface area, superior electrical and thermal conductivity, and remarkable gas impermeability resistance. In this study, graphene nanoplates (GNPs) were mass-produced by a one-step chemical exfoliation of natural graphite and used as a filler for the fabrication of GNPs@natural rubber composite by a simple mixing method. The resultant GNPs/rubber composite was characterized by using scanning electron microscopy (SEM), and a rheometer. The prepared graphene nanoplates had a thickness of less than 10 nm and a lateral size of tens of microns. The GNPs@rubber composite revealed an exceptional improvement of abrasion loss up to seven to ten fold, along with an approximately 400%, 200% and 30% increment of elongation at break, tear strength and tensile strength, respectively. Other mechanical properties, such as hardness, compression set and rebound, as well as the effect of the GNPs loadings on the mechanical properties of the composite, were also investigated in detail.

Facile, environmentally benign and scalable approach to produce pristine few layers graphene suitable for preparing biocompatible polymer nanocomposites

The success of developing graphene based biomaterials depends on its ease of synthesis, use of environmentally benign methods and low toxicity of the chemicals involved as well as biocompatibility of the final products/devices. We report, herein, a simple, scalable and safe method to produce defect free few layers graphene using naturally available phenolics i.e. curcumin/tetrahydrocurcumin/quercetin, as solid-phase exfoliating agents with a productivity of ∼45 g/batch (D/G ≤ 0.54 and D/D' ≤ 1.23). The production method can also be employed in liquid-phase using a ball mill (20 g/batch, D/G ≤ 0.23 and D/D' ≤ 1.12) and a sand grinder (10 g/batch, D/G ≤ 0.11 and D/D∼ ≤ 0.78). The combined effect of π-π interaction and charge transfer (from curcumin to graphene) is postulated to be the driving force for efficient exfoliation of graphite. The yielded graphene was mixed with the natural rubber (NR) latex to produce thin film nanocomposites, which show superior tensile strength with low modulus and no loss of % elongation at break. In-vitro and in-vivo investigations demonstrate that the prepared nanocomposite is biocompatible. This approach could be useful for the production of materials suitable in products (gloves/condoms/catheters), which come in contact with body parts/body fluids.