Silicone Rubber Nanocomposites Research Articles

Influence of chromium oxide nanoparticles and fiber fillers on silicone rubber nanocomposite

The development of polymer composites, considering the environmental issues, is aimed for minimizing the industrial content. New environmental-friendly nanocomposites, based on silicone rubber matrix and different concentrations of natural fiber/chromium oxide fillers, are prepared for the first time. The microstructural analysis confirms the successful obtaining of microfibers after treatment and chromium oxide nanoparticles and the formation of the final composite. The nanocomposites achieved improved physical and mechanical properties due to the dual effect of both fillers and attachment to the matrix. The 1% optimized nanocomposite achieved the highest modulus, dielectric properties, hydrophobicity, and surface stability. The effect of exposure to weathering conditions was studied. The characterization sentence asserts the preparation of a novel silicone rubber nanocomposite with improved properties, along with the environmental impact, regarding the dual effect of natural fiber waste and chromium oxide nanoparticles.

A novel electrical depercolation model for stretchable nanocomposite strain sensors.

Flexible strain sensors have been subject to intense research efforts in recent years, in an attempt to overcome the limitations of their rigid counterparts and find use in demanding applications. In this work, the effective calibration of resistive-type, stretchable strain sensors is discussed. A new model for the piezoresistive response of stretchable polymer nanocomposite strain sensors is presented which facilitates calibration over the full conducting strain range of the material. This offers the potential to vastly improve the practical working range of sensors made using soft conductive nanocomposites, as well as to obtain key information towards improvement of sensing performance. The model has been successfully applied to multiple experimental measurements on silicone rubber (SR) nanocomposites reinforced with reduced graphene oxide (rGO) over a range of filler loadings. The effect of parameters such as filler dimensions, filler orientation and dispersion state is discussed, while predictions on sensitivity and working range are made on the basis of interparticle distance modelling.

Performance Evaluation of Thermally-Aged RTV Silicone Rubber/TiO2 Nanocomposites in Mineral Oil for Transformer Bushings

The room temperature vulcanized (RTV) silicone rubber is regarded as a coating material for power transformer bushings. However, the performance of silicone rubber may get severely degraded in the event of leakage of mineral oil from the transformer. Nevertheless, little attention has been paid to exploring the viability of silicone rubber nanocomposites in retarding transformer oil-induced damages. Therefore, this article investigates the effect of mineral oil on silicone rubber material doped with Titania (TiO2) nanofillers. Silicone rubber nanocomposites with 1, 3, 5, and 7 wt.% of nano-TiO2 were synthesized and thermally aged in transformer oil at 80oC for 18 hours. Performance evaluation was done based on the experimental outcomes of 3-D microscopy, fourier transform infrared spectroscopy (FTIR), contact angle, corona inception voltage (CIV), thermogravimetric analysis (TGA), infrared thermography, surface potential, and water diffusion tests. Finally, based on the experimental investigations, 5 wt.% nanocomposite was found to be superior in performance against transformer oil-induced degradation.

Effects of functionalization and silane modification of hexagonal boron nitride on thermal/mechanical/morphological properties of silicon rubber nanocomposite

Hexagonal boron nitride (h-BN) nanoparticles could induce interesting properties to silicone rubber (SR) but, the weak filler-matrix interfacial interaction causes agglomeration of the nanoparticles and declines the performance of the nanocomposite. In this work, h-BN nanoparticles were surface modified using vinyltrimethoxysilane (VTMS) at different concentrations. Before silane modification, h-BN nanoparticles were hydroxylated using 5 molar sodium hydroxide. The nanoparticles were characterized to assess success of silane grafting. The pure and modified h-BN nanoparticles were applied at 1, 3 and 5 wt% to HTV silicon rubber (SR). The curing, thermal, mechanical and morphological properties and hydrophobicity of the nanocomposites were evaluated. The morphology of the SR nanocomposites was characterized using AFM and FE-SEM analysis. It was found that silane grafting on the h-BN nanoparticles improves crosslink density but declines curing rate index (CRI) of the SR nanocomposite (at 5 wt% loading content) by 0.7 (dN m) and 3.5%, respectively. It also increased water contact angle of the nanocomposites from 97.5° to 107°. The improved nanoparticle-rubber interfacial interactions caused better dispersion of h-BN nanoparticles in SR matrix (at 5 wt%) that enhanced the elongation at break, modulus at 300% and Tg of the SR nanocomposites.

Appraising the dielectric properties and the effectiveness of electromagnetic shielding of graphene reinforced silicone rubber nanocomposite

Abstract The aim of this research is to measure the dielectric properties and electromagnetic interference (EMI) shielding effectiveness (SE) of silicone rubber reinforced with graphene nanoplates. In a two-roll mill, different amounts of graphene are mixed together. This is followed by compression moulding at 170°C and post-curing for 4 h at 200°C. Between 1 MHz and 1 GHz, the waveguide transmission line method and a vector network analyser are used to measure the dielectric and EMI SE parameters. As the amount of graphene is increased from 0 to 7 wt%, AC conductivity goes up, reaching 1.19 × 10−3 S/cm at 7 wt%. The same composition gives the highest EMI SE of 43.22 dB at 1 GHz. The high-frequency structural simulation of different compositions shows how shielding works, and the results agree with what has been seen in experiments.

A Portable One-Hand Braille Input System Enabled by Dual-Interlocked Tactile Sensors for Communication

This article presents a novel portable one-hand Braille input system (BIS) to assist visually impaired users in entering text on electronic devices. The proposed BIS is designed based on a flexible Braille keyboard (FBK), it mainly consists of five dual-interlocked tactile sensors, a processing circuit, and a software modulus. The fully elastomeric graphene/carbon nanotube/ silicone rubber nanocomposites are synthesized and used as tactile sensing material and polydimethylsiloxane (PDMS) as the structural and encapsulation for the fabrication of sensors. Characterization tests showed the tactile sensor has relatively high force sensing sensitivity of 0.649 N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-\text{1}}$</tex-math> </inline-formula> at sensing range of 0–5 N and a frequency sensing ability of 0.5–2.0 Hz, which can meet human finger pressing requirements. A specific Braille input method is proposed, and personalized parameters are set for users to fit different pressing habits. The average input speed of 3.37 words per minute (WPM) with an average accuracy of 92.2% for Braille characters input is demonstrated by evaluating text entry performance. The results indicated that our developed tactile sensor enabled portable one-hand BIS can assist visual impaired users with enhanced text entry on electronic devices effectively and privately.

Improving thermal/electrical properties of silicone rubber nanocomposite using exfoliated boron nitride nano sheets made by an effective/novel exfoliating agent

In this work, boron nitride nano sheets (BNNSs) were prepared by exfoliation of h-BNs using mono ethylene glycol (MEG) as a novel exfoliating agent. For comparison, isopropyl alcohol (IPA)/water mixture was also used for exfoliation of h-BNs. It was found that using MEG caused preparing nano layers with higher yield and lower thickness compared to the IPA/water mixture. Thereafter, silicon rubber nanocomposites contained 3 and 5 wt% of pure and exfoliated BNNSs were prepared and evaluated for thermal and electrical performances. It was found that h-BNs and exfoliated-BNs drastically enhanced thermal conduction of SR. The silicon rubber contained 5 wt% of the h-BN and exfoliated-BNs illustrated around 20 times higher thermal conductivities compared to pure SR. Exfoliation of h-BNs had negligible effect on improvement of thermal properties, however, it caused 5.7 and 2.3 times enhancement in the electrical volume resistivity compared to the pristine SR and pure h-BN containing nanocomposite, respectively. Both of the BNNSs caused improvement in the heat dissipation performances of SR matrix, however, the exfoliated one with MEG showed better performances. Based on the results, it was claimed that mono ethylene glycol could improve exfoliation of h-BNs and enhance the performances of silicon rubber.

Synergistically toughened silicone rubber nanocomposites using carbon nanotubes and molybdenum disulfide for stretchable strain sensors

Stretchable rubber nanocomposites have been investigated for detection in piezoresistive strain sensors. Tensile toughness must be improved while maintaining stretchability to realize high-performance, robust, stretchable nanocomposites. We investigate a stretchable and synergistically toughened silicone nanocomposite-based, piezoresistive strain sensor using multiwalled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS2). One-dimensional MWCNTs mechanically reinforce the silicone rubber matrix, improving tensile strength by 95% but decreasing fracture strain by 27% at 5 phr, providing an electrical percolation network. Adding two-dimensional nanolayers of MoS2 as a single filler increases fracture strain from 205% (unfilled) to 320% (5 phr MoS2), possibly due to cure retardation in the silicone rubber, preventing over-curing. Silicone nanocomposites exhibit improved tensile toughness at 8.46 kJ/m3 for 5-phr MWCNT-MoS2 hybrids due to the synergistic effects of the hybrid filler, a 125% improvement over unfilled rubber. Nanocomposites maintain a low elastic modulus (<0.45 MPa) suitable for stretchable sensors. The nanocomposite utility is demonstrated as body-attachable, piezoresistive strain sensing with a gauge factor of ∼25.95 (100%<Δε<155%), stretchability of up to 155%, and durability of over 5000 cycles. Toughened nanocomposites with MWCNT and MoS2 hybrid fillers could be useful for applications requiring robust stretchability and sensitivity.

Effects of Vinyl Functionalized Silica Particles on Thermal and Mechanical Properties of Liquid Silicone Rubber Nanocomposites

It is very important to develop a new method of preparing high-performance liquid silicone rubber-reinforcing filler. Herein, the hydrophilic surface of silica (SiO2) particles was modified by a vinyl silazane coupling agent to prepare a new type of hydrophobic reinforcing filler. The structures and properties of modified SiO2 particles were confirmed using Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectrometer (XPS), specific surface area and particle size distribution and thermogravimetric analysis (TGA), the results of which demonstrated that the aggregation of hydrophobic particles is greatly reduced. Additionally, the effects of the vinyl-modified SiO2 particle (f-SiO2) content on the dispersibility, rheology, and thermal and mechanical properties of liquid silicone rubber (SR) composites were studied for application toward high-performance SR matrix. The results showed that the f-SiO2/SR composites possessed low viscosity and higher thermal stability, conductivity, and mechanical strength than of SiO2/SR composites. We believe that this study will provide ideas for the preparation of high-performance liquid silicone rubber with low viscosity.

Understanding the Surface Condition of Silicone Rubber Nanocomposite Due to Corona Aging Using AFM Imaging and LIBS Spectroscopy

Silicone rubber insulators undergo degradation when they are exposed to corona discharges. The present study explores the surface degradation behavior of silicone rubber alumina nanocomposites due to corona aging using high-frequency ac voltage. The electric field distribution on the sample surface during corona aging is simulated using COMSOL. The change in silicone rubber functional group is studied using Fourier transform infrared (FTIR) spectroscopy analysis. The influence of corona aging time on the surface roughness recovery of silicone rubber nano alumina composites is studied using an atomic force microscopy (AFM). The elemental distribution behavior and change in the emission spectra persistence time are analyzed during recovery period of corona-aged silicone rubber nanocomposites using laser-induced breakdown spectroscopy (LIBS) technique. The addition of alumina nanofiller to the silicone rubber improves the resistance to aging due to corona discharge. Loss and recovery of hydrophobic property of silicone rubber due to corona aging were determined using static contact angle measurement. The results show a direct correlation between the contact angle and the surface roughness recovery characteristics. They indicate that the nanocomposite having a 5 wt% alumina content exhibits the highest resistance to corona discharge with least surface damage. Furthermore, fast recovery was observed in the first few hours after corona aging, and most samples eventually regained their properties after about 8 h of recovery time.

The Effects of Nano-ZrO₂ on the Mechanical and Electrical Properties of Silicone Rubber and a Corresponding Mechanism Analysis

Improving the performance of silicone rubber (SiR) for cable accessories is the key to the safety and reliability of high-voltage direct-current (HVDC) transmission. In this article, the effects of zirconia nanoparticles (nano-ZrO2) on the electrical and mechanical properties of SiR were investigated. Nano-ZrO2 at different mass fractions was doped into SiR matrices. Then, a series of experiments was carried out to evaluate the performance of the modified SiR in terms of tensile strength, breakdown strength, and space charge characteristics. The results showed that both the mechanical and electrical properties of the modified SiR improved. The tensile strength and the breakdown strength increased significantly with the mass fraction of nano-ZrO2, maximally increasing by 21.3% and 15.4%, respectively. In addition, the incorporation of nano-ZrO2 into SiR inhibited space charge accumulation and accelerated the dissipation of the charges. Nano-ZrO2 also improved the degree of cross-linking of the modified SiR, resulting in a more compact interior structure. The synthetic effect of the improved structure and interfaces facilitated by the nanoparticles may be the origin of the improved properties of the SiR nanocomposites.

Performance evaluation of gamma‐ray irradiated silicone rubber nano‐micro composites using electrical, thermal, physiochemical and deep learning techniques

AbstractSilicone rubber insulation used in nuclear power stations is inevitably exposed to highly energetic gamma‐ray irradiations which may lead to premature failure. Therefore, it is mandatory to develop silicone rubber composites capable of withstanding the stress posed by gamma‐ray irradiation. The present research involves the development of micro aluminum tri hydrate (ATH) and nano silica (SiO2) doped/co‐doped silicone rubber nanocomposites best suited for use in nuclear power stations. The samples were exposed to gamma‐ray irradiation of 500 kGy. Surface changes incurred were assessed using atomic force microscopy (AFM), fourier transform infrared (FTIR) spectroscopy, contact angle, surface potential/impedance, water droplet‐initiated corona inception voltage (CIV) measurements thermogravimetric analysis (TGA) was adopted to characterize the thermal stability of the specimens. Further moisture absorption behavior of the test specimens under strong electrolytic NaCl solution has been investigated. The erosion resistance of the virgin and gamma‐ray irradiated specimens has been classified using GoogLeNet convolution neural network.

The impacts of graphene dosage on the friction and wear performance of a graphene-reinforced silicone rubber nano composite

Lightweight elastomer nanocomposites have several uses in the automotive and aerospace industries. There ought to be no compromises in terms of efficiency, durability, or performance when it comes to new technological products. This results in the ongoing quest for innovative materials. This study contributes to the development of graphene-reinforced silicone rubber by evaluating its mechanical and tribological properties. The two-roll mill mixing process, followed by the moulding step, is utilised in commercial nanocomposites preparation. As a result, the man-made composite can be justified financially. The moulding process was carried out at 170 °C, and the final curing took place at 200 °C for 4 h. Testing is done using filler weight percentages of 0, 1, 3, 5, and 7% graphene to determine the optimal filler weight %. The mechanical performance of silicon rubber was enhanced by over 213% when the graphene weight percentage was increased. With increasing load, the coefficient of friction decreases, with the lowest value found at 3% graphene by weight. The coefficient of friction and the specific wear rate were discovered to vary with sliding speed.

Study the synergistic effect of fumed silica and reduced graphene oxide insertion on the thermal, mechanical, tribological, and solvent transport properties of silicone rubber nanocomposites

AbstractThis study explored the effects of hybrid nanofillers such as fumed silica (FSiO2) and reduced graphene oxide (rGO) on the mechanical, thermal, solvent transport, and tribological properties of silicone rubber nanocomposite (QMSirGO). A pin‐on‐disc test system was used to investigate the friction and wear properties of QMSirGO nanocomposites, which were significantly influenced by the applied load, temperature, and rGO concentration. Study shows that better graphene oxide dispersion in the matrix paved the way for improved tensile and dynamic mechanical properties and lowered the coefficient of friction and specific wear rate (Ws) values. Compared to silicone rubber (QM), the friction coefficient of the QMSirGO1.5 composite was reduced by around 40%. The mechanism involves the formation of a lubricant layer, which smooths the material surface that comes into contact with the metal surface. In the solvent transport study, we investigated the effect of solvents' structure, molecular size, filler concentration, and the transport mechanism of composites, and the extent of reinforcement was evaluated using Kraus equations.

The Role of the Accumulated Surface Charge on Nanoparticles in Improving the Breakdown Strength of Liquid and Solid Insulation

In this paper, the role of the accumulated surface charge on the surfaces of nanoparticles on breakdown strength for liquid and solid dielectrics is presented. The breakdown strengths of a nanofilled liquid dielectric and a solid dielectric are evaluated. The evaluation was conducted considering different nanoparticle material types with different nanofiller loadings. Accordingly, the preparation of transformer oil nanofluid and silicone rubber nanocomposites was performed with different nanofillers of the same average particle size. Breakdown voltage was measured for all the prepared samples, both liquid and solid. The interpretation of the obtained results is presented.

Molecular-dynamics study on the thermodynamic properties of nano-SiO2 particle-doped silicone rubber composites

Polymer dielectric materials doped with nanoparticles show promising applications in the insulation of electrical equipment. In experiment, however, the doping amounts of nanoparticles significantly affect the mechanical and dielectric properties of polymer nanodielectrics. In this paper, the doping amounts and agglomeration of nanoparticles are considered in molecular dynamics (MD) simulations to reveal the probable microscopic mechanism. The effects of doping amounts and agglomeration of nano-SiO2 particles on the thermodynamic properties of silicone rubber (SR) nanocomposites are studied from the aspects of the mean square displacement, free volume fraction, pore size distributions, interaction energy, cohesive energy density and hydrogen bond analysis. The results show that with increasing doping amounts of nano-SiO2, the interfacial interactions and intermolecular force of the SR composites are enhanced. Therefore, the mean square displacement, the free volume fraction and the maximum pore size for SR composites all decrease, which is beneficial to the improvement of mechanical and dielectric performances for nano-SiO2/SR composites. However, the agglomeration of nano-SiO2 particles (the increase of the size of nanoparticles), will lead to a decline in the intermolecular forces among SR chains and the destruction of hydrogen bond networks. Therefore, the mean square displacement, the free volume fraction and the maximum pore size in SR composites will increase, which will degrade the mechanical and dielectric performances of SR composites. This work reveals a generalized relationship between the doping amounts and agglomeration of nanoparticles and the thermodynamic properties of polymer dielectric composites.

Effect of graphite nanoplatelets surface area on mechanical properties of room‐temperature vulcanized silicone rubber nanocomposites

AbstractGraphite nanoplatelet (GNP) flakes have attracted attention for the production of polymeric nanocomposites owing to their excellent mechanical, thermal, and electrical properties. In this work, the impact of three grades of GNP flakes with different surface area on the properties of room‐temperature vulcanized silicone rubber (RTV‐SR) nanocomposites was analyzed. The surface area was determined by the Brunauer–Emmett–Teller (BET) method using N2 adsorption isotherms. The BET analysis showed that the GNP grades had BET surface areas of 422, 295, and 123 m2/g. Nanocomposites based on the three grades of GNP flakes with different surface area and RTV‐SR were prepared using the solution‐casting process. Mechanical analysis of the samples showed that the compressive modulus increased from 3.8 MPa (0 phr) to 4.4, 4.34, and 5.26 MPa at the filler loading of 15 phr of GNPs with 422, 295, and 123 m2/g, respectively. In addition, the fracture strain of the nanocomposites increased from 116% (0 phr) to 228%, 198%, and 151% in the samples with 422, 295, and 123 m2/g, respectively, at the filler loading of 15 phr GNP.

Epoxy-POSS/silicone rubber nanocomposites with excellent thermal stability and radiation resistance

Due to the rigid Si-O-Si backbone, silicone rubber (SR) have a widespread application in extreme environment such as high temperature and high-level radiation. However, the radiation stability of SR still does not meet the practical needs in special radiation environments. Herein we prepared epoxy POSS(ePOSS)/SR nanocomposites with excellent thermal stability and radiation resistance. As a physical crosslinking point in the SR, addition of small amount of ePOSS not only enhanced the mechanical properties of the matrix, but also improved its thermal stability greatly due to their good compatibility. ePOSS/SR had higher radiation stability in air than SR owing to the inhibition of radiation oxidation by ePOSS, and the yield of main gaseous radiolysis products (CH4, H2, CO and CO2) of SR and ePOSS/SR nanocomposites was determined. By analyzing the changes of chemical structure, thermal properties and mechanical properties of the ePOSS/SR nanocomposite, combined with the characteristics of gas products after γ-irradiation, the radiation induced crosslinking and degradation mechanism of the nanocomposites was proposed comprehensively.

Performance evaluation of room temperature vulcanized silicone rubber nanocomposites aged in strong aqueous solutions

AbstractIn the present study moisture absorption behavior of titania (TiO2) and silica (SiO2) doped room temperature vulcanized (RTV) silicone rubber (SR) nanocomposites immersed in deionized water, aqueous sodium chloride (NaCl) and nitric acid (HNO3) solution was investigated. It is realized that the diffusion coefficient of the material is high with nanocomposites compared to virgin RTV SR material. To understand the surface condition of the material and characteristic variation in material properties water droplet‐initiated corona inception voltage measurements, atomic force microscopy study, surface potential variation studies, Fourier transform infrared spectroscopy and thermogravimetric analysis was carried out with the virgin and aqueous solution aged specimens. The discharge resistance of the material was analyzed using corona discharge studies. The level of hydrophobicity variations was analyzed through contact angle measurements. The experimental results confirmed that the performance of TiO2 doped RTV SR nanocomposites is superior to the SiO2 doped and virgin RTV SR material.

Fabrication, characterization and properties of silane functionalized graphene oxide/silicone rubber nanocomposites

AbstractIn this work, octadecyl trichlorosilane (ODTS) was used to modify the surface of graphene oxide. Further, varied concentrations of silane‐modified graphene oxide were used to make silicone rubber nanocomposite. The mechanical, thermal, and tribological properties of the composite were studied. The results showed that a small amount of silane‐modified graphene oxide significantly increased the mechanical and tribological performances. Under dry sliding, silane‐modified graphene oxide to the silicone matrix significantly reduced wear and friction properties. Nanocomposites have a lower wear rate than neat silicone rubber; their friction coefficient is almost 36% less than pure silicone rubber: the higher the load and temperature conditions, the more significant the difference in friction and properties. Wear mechanisms were revealed by scanning electron micrographs of the worn surface. The transfer film formation on the counter surface and acceptable wear debris improved the nanocomposites friction and wear resistance characteristics.