Mechanical Properties Of Silicone Rubber Research Articles

Properties and Mechanism of Friction‐Reducing Silicone Rubber Modified with Hyperbranched Polysiloxane

AbstractDuring the utilization of silicone rubber, excessive friction can cause damage to the contact surface and the material itself. Therefore, friction‐reducing modification of silicone rubber has attracted much attention. In this paper, hyperbranched polysiloxanes with different structures is synthesized for friction‐reducing modification of silicone rubber. Infrared spectroscopy, nuclear magnetic resonance spectroscopy, and amine titration tests reveal that hyperbranched polysiloxanes are successfully synthesized by the hydrolytic condensation of 3‐aminopropyltriethoxysilane and their Michael addition with four acrylates with different alkyl chains. The friction coefficients and mechanical properties of silicone rubber are evaluated. Hyperbranched polysiloxanes significantly reduces friction and maintained excellent mechanical properties of silicone rubber. Silicone rubber with butyl‐ester‐secondary‐amino hyperbranched polysiloxane displays the best overall performance, with static and dynamic friction coefficients decreasing by 33.99% and 43.16% compared with that of pure silicone rubber, respectively, and a tensile strength of 10.80 MPa. The friction‐reducing mechanism of hyperbranched polysiloxanes on silicone rubber is investigated by contact angle test and dynamic mechanical analysis. Hyperbranched polysiloxanes migrates to the surface due to the incompatibility of alkyl chains with silicone rubber matrix. Consequently, the shielding effect produced by hyperbranched polysiloxanes on the surface depresses the adsorption activity of silicone rubber surface thereby reducing friction.

Research on damage behavior of silicone rubber under dynamic impact

Viscoelastic rubber materials are widely used in various vibration reduction structures of military and construction machinery. The complex driving and working conditions make the mechanical structure suffer severe impact, which leading to the damage or lose efficacy of the important viscoelastic elements. In order to reveal the dynamic mechanical properties of silicone rubber after impact, the Uniaxial compression tests of silicone rubber under different high strain rates were carried out with the separated Hopkinson pressure bar (SHPB) dynamic impact experiment, and the original Zhu-Wang-Tang (ZWT) constitutive model was modified by combining logarithmic law and power function law. The dynamic impact simulation model of silicone rubber was established using the modified ZWT-rate-dependent constitutive model, and the dynamic impact damage behavior of silicone rubber was studied under the condition of high strain rate, and the microscopic damage analysis was carried out on the experimental silicone rubber samples by scanning electron microscopy (SEM). The results show that the silicone rubber has obvious strain rate effect and strong deformation resistance at high strain rate. The modified ZWT-rate-dependent constitutive model can be used to obtain the constitutive expression of unified parameters, which can better describe the dynamic mechanical properties of silicone rubber at high strain rates. After dynamic impact compression, a damage line zone appears in the silicone rubber sample. There is a certain rule between the position of the line zone and the loading strain rate and the friction coefficient of the end face, and the silicone rubber is significantly affected by the friction effect of the end face.

Stress-thermal aging properties of silicone rubber used for cable accessories and electric-thermal-stress multiple fields coupling simulation

During the long-term operation of a cable, the electrical field, high temperature, and interface stress may age or deteriorate the silicon rubber (SIR) insulation of the cable accessories, affecting the combined electrical-thermal-force performance of the accessories, and easily causing discharge faults. In this work, the electrical-thermal-force properties of silicone rubber for cable accessories under thermal aging and combined force-thermal aging are studied experimentally and numerically. The changes and mechanisms of physical and chemical properties, electrical properties, thermal properties and mechanical properties of silicone rubber are tested and compared before and after aging. The changes of electric, thermal and force field of cable accessories, caused by the change of SIR material parameters under different aging time and aging form, are further simulated. The experimental results show that the crosslinking degree and molecular motion system of SIR will change with the deepening of the aging degree, which will change the electrical-thermal-force properties of the material to different degree. After aging, large agglomeration protrudes and small cavities appear in SIR section, and the damage is more serious under force-thermal aging. The relative dielectric constant first decreases and then increases with the aging time increasing. The volume resistivity, breakdown strength and flashover voltage all first increase and then decrease. The thermal conductivity first increases and then decreases with aging time increasing. In addition, with the increase of aging time, the tensile strength and elongation at break decrease gradually. Considering the change of properties after aging, the destruction of SIR material by force-thermal aging is more serious. The simulation results show that under the two aging modes, the maximum electric field strength at the stress cone root of the cable accessories first increases and then decreases with the increase of time. The electric field strength at the stress cone root of the cable accessories, caused by the force-thermal aging, changes little, maintaining about 2.2 kV/mm. The difference in temperature between the inside and the outside of the insulation layer is obvious under different aging degree, and the temperature difference shows a first decreasing and then increasing trend under both aging modes, and the maximum temperature gradient is 9.15 ℃. The interface stress at the stress cone root decreases from 0.263 to 0.230 MPa, which is about 12.5% lower. This work has guiding significance in evaluating the insulation performance and analyzing the fault of distribution cable accessories.

Effect of zinc oxide/layered double hydroxide on the mechanics of silicone rubber at low temperature

Low-temperature conditions can degrade various properties of rubber, impacting the application of rubber products in such conditions. In this study, we incorporated zinc oxide (ZnO) and magnesium aluminum layered double hydroxide (LDH) into silicone rubber (SR) to produce x-ZnO/LDH/SR composites, where X represents the addition ratio of ZnO to LDH. The results indicated that, at −40 °C, the tensile strength and elongation at break for 1/2-ZnO/LDH/SR were 10.6 % and 5.0 % greater than the original silicone rubber, respectively. In addition, after aging at −40 °C for 3 days, the compression set of the composites decreased by 48.6 %. This improvement was attribute to ZnO and LDH forming a physical cross-linking network within the rubber. This not only enhanced the mechanical properties of silicone rubber at low temperatures but also offers a straightforward and viable approached to producing high-performance, low-temperature-resistant sealing products.

Analysis of the Influence of Single-Walled Carbon Nanotubes on the Fluid–Structure Interaction Vibration Control in Bionic Hydraulic Pipelines

In previous research, a bionic hydraulic pipeline (BHP) with a three-layer structure for absorbing pulsation was invented. This paper proposes to disperse single-walled carbon nanotubes (SWCNTs) in the elastic layer material, namely silicone rubber (RTV), to enhance its ability to absorb pulsation. Firstly, the RTV-SWCNTs composite specimens with different SWCNT proportions are prepared and tested. It was found that the mechanical property is optimal when the volume content of the SWCNTs is 0.5 vol%. On this basis, BHPs with RTV-SWCNTs composite material as the elastic layer are fabricated to study the influence of the thickness and length of the elastic layer on the absorption flow pulsation. The results show that the addition of SWCNTs significantly improves the mechanical properties of silicone rubber and reduces the friction between the elastic material and oil, so that the BHP can absorb the pressure pulsation better. With the appropriate thickness and length of the elastic layer, the addition of SWCNTs can increase the pulsation suppression effect by 20%. Moreover, to analyze the influence of nanomaterials on pipeline friction, a comprehensive fourteen-equation model for describing the fluid–structure interaction (FSI) of the pipe conveying fluid considering friction coupling is established. And through numerical analysis and modal tests, the evaluation error for the modified dynamic model of the BHP is less than 5%, verifying the correctness of the proposed model and solution method.

An eco-friendly, bio-inspired and synergistic flame retardant system with outstanding water tolerance and ultra-low addition for silicone rubber

To address the bottleneck problem for flame-retarding silicone rubber (SR) in poor water resistance and low efficiency, a halogen-free and synergistic system was fabricated by the introduction of hydrophobic melamine polyphosphate (MPP) modified by layered double hydroxide (P-MPP@LDH) and expandable graphite (EG) in this paper. Dramatically, the limited oxygen index (LOI) of composites (SR/P-MPP@LDH2.5/EG2.5) can reach as high as 36.4 % with UL-94V-0 rating when the total flame retardant loadings is only 5 phr, revealing the superior efficiency of novel system. Compared with neat SR, the fire risk of SR composites is observably decreased by conducting cone calorimeter tests. Significantly, bio-inspired hydrophobic modification is feasible for the excellent balance in simultaneously improving the flame retardancy, water resistance, and mechanical properties of SR in one system. Based on the analysis for residue and thermal degradation process, the effective flame retardant mechanism for SR composites can be attributed to the joint effect of LDH-catalyzed char-formation and physicochemical synergistic intumescence barrier. Therefore, this paper has provided a new and effective strategy to achieve the goal of flame retardancy with high performance in SR, which offers a new choice for designing and applying rubber composite materials in buildings.

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.

Characterization Method for the Swelling Effect of an Insulating Washing Agent on Silicone Rubber in Power Systems.

Insulating washing is a valid method to recover the electrical performance of silicone rubber composite insulators under accumulation contamination; however, its swelling effect may deteriorate the electrical and mechanical properties after live washing. The swelling effect of the insulating washing agent on the electrical and mechanical properties of silicone rubber and its mechanism were investigated by macroscopic and microscopic characterization methods. The results showed that the swelling degree of silicone rubber increased as the immersing time increased and the increasing trend gradually slowed down. The degradation in mechanical properties is much greater than that in electrical properties, and the tensile strength at break dropped greatly by 16.3% at 20 min of immersing. Physical defects such as holes and cracks were observed by scanning electron microscopy. The main and side chains were partially broken, and the inorganic flame retardant Al(OH)3 was decreased by Fourier transform infrared spectroscopy. The damage to the microstructure caused by the swelling effect under the action of the washing agent is the main reason for the decrease in the mechanical properties of silicone rubber.

Effect of Ultraviolet-A Radiation on Alicyclic Epoxy Resin and Silicone Rubber Used for Insulators.

Compared with the high-temperature vulcanized silicone rubber (HTVSR) insulator, the alicyclic epoxy resin insulator has higher hardness and better bonding between the core and the sheath. This makes the latter very promising in the coastal area of Southern China. Outdoor insulators are often subjected to high intensity of ultraviolet (UV)-A radiation. The influence of UV-A radiation is significant for alicyclic epoxy resin insulators. To help address the concern, the surface of two kinds of samples, namely the alicyclic epoxy resin insulator and HTVSR insulator, with UV-A aging time was characterized by tests of scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The operation properties (mechanical properties, hydrophobicity) for outdoor insulators were also analyzed. It was found that the appearance color of the alicyclic epoxy resin has changed greatly, and there is a certain degree of fading. The mechanical properties of the alicyclic epoxy resin are maintained well and, the hydrophobicity decreases gradually. For silicone rubber, the appearance color change of silicone rubber is smaller, and the mechanical properties of silicone rubber decreased greatly. In addition, although the hydrophobicity of silicone rubber decreased gradually, it is still better than that of alicyclic epoxy resin. Both materials have broken chemical bonds, but the degree is relatively light, which meets the requirements of insulators for outdoor operation.

Dynamic mechanical characteristics of aged silicone rubber blend

The effect of aging on the mechanical properties of silicone rubber (SR) was investigated by means of ultrasonic, dynamic mechanical analysis, and FTIR techniques. Both longitudinal and shear (Ultrasonic wave velocities) were measured at room temperature and at frequencies of 2 MHz. Density, molar volume, ultrasonic wave velocities, tensile strength, mechanical properties, and FT–IR showed the improvement of the silicone rubber network with aging time from 0 to 70 days, while loosening of the network structure was observed at 14 days and 50 days aging. These behaviours were explained in terms of the change in cross-link density and average stretching force constant of bonds with aging. Thermogravimetric analysis and differential scanning calorimetric techniques showed quite low thermal stability and temperature performance for aged SR at 14 and 50 days than virgin SR which was confirmed by the cracks and voids appeared under scanning electron microscope.

Split-Hopkinson Pressure Bar Test of Silicone Rubber: Considering Effects of Strain Rate and Temperature.

Using a split-Hopkinson pressure bar test instrument with a temperature control device, in this work, silicone rubber was tested at different temperatures (−40 °C–200 °C) and different strain rates (1.2 × 103 s−1–7.2 × 103 s−1). The results showed that the dynamic mechanical properties of silicone rubber were strain-rate sensitive at different temperatures and the yield strength of the silicone rubber increased with an increase in the strain rate. At a higher strain rate, silicone rubber showed temperature sensitivity. With a decrease in the strain rate, the influence of temperature on silicone rubber gradually decreased. Differential scanning calorimetry analysis showed that silicone rubber had good thermal stability at high temperatures. When the temperature was as low as −40 °C, the silicone rubber underwent a glass transition, showing the characteristics of brittle materials.

Mechanical properties of thermo-oxidative aged silicone rubber thermally stabilized by titanium oxide based fillers

In this work, the mechanical properties of thermo-oxidative aged and thermally stabilized high consistency silicone rubber were investigated. The thermal oxidative stabilization is achieved by titanium oxide based fillers that were incorporated at different concentrations into the silicone compounds. Besides a pure titanium oxide filler, AEROXIDE® TiO2 P25, also an iron oxide doped heat stabilizer, AEROXIDE® TiO2 PF 2, was studied. The addition of the AEROXIDE® TiO2 fillers significantly improves the thermal stability of the compounds and maintains the mechanical properties on a good level after thermal aging. The thermal stabilization depends on the type and concentration of the AEROXIDE® TiO2 fillers. Due to iron oxide doping, the efficiency of AEROXIDE® TiO2 PF 2 is higher in comparison to AEROXIDE® TiO2 P25. However, a too high concentration, especially of AEROXIDE® TiO2 PF 2, induces a catalytic effect and favors the thermal degradation of the silicone. Therefore, the optimum concentration depends on the behavior of the heat stabilizer, its catalytic effect, and the thermal-oxidative conditions applied to the silicone. This study has revealed that titanium oxide based fillers are efficient heat stabilizers to preserve the mechanical properties of silicone rubber on a good level during applications at elevated temperatures.

Deformation Modeling and Simulation of a Novel Bionic Software Robotics Gripping Terminal Driven by Negative Pressure Based on Classical Differential Algorithm.

A general pneumatic soft gripper is proposed in this paper. Combined with the torque balance theory, the mathematical theoretical model of bending deformation of soft gripper is established based on Yeoh constitutive model and classical differential geometry. Assuming that the pressure in each inner cavity is evenly distributed, the input gas is in an ideal state, which is approximately treated as an isothermal condition, and all orifices experience blocked flow. In addition, compared with the mechanical work of gas, the energy related to gas flow and heat transfer is negligible. The nonlinear mechanical properties of silicone rubber are studied. It is regarded as isotropic and incompressible material, which is characterized by strain energy per unit volume. The material constant coefficients C10 and C20 are determined through the uniaxial tensile test, and the software gripper is simulated on the ABAQUS platform. The bending deformation models of grippers with three different force-bearing cavity structures are analyzed and compared, and the software clamping structure with the bending deformation most in line with the application conditions is selected. The limit input air pressure of the gripper and the situation of enveloping the clamping target object are analyzed. Through the bending deformation experiment, the maximum deformation angle is 72.4°. The relative error between the simulation analysis data and the prediction results of the mathematical model is no more than 3.5%, which verifies the effectiveness of the simulation and the correctness of the mathematical theoretical model of bending deformation. The soft manipulator proposed in this paper has good adaptability to grasping objects of different shapes and sizes. The minimum diameter of the target object that can be clamped is 0.1 mm. It can clamp the object weighing up to 1 kg. It has compact size, light weight, high ductility, and flexibility.

Effect of poly(catechol/polyamine) modified boron nitride on microstructure and properties of thermally vulcanized silicone rubber

AbstractWith the increasing integration of electronic devices, better heat dissipation of components is urgently required. In this work, a poly(catechol/polyamine) (PCPA) layer is formed on the surface of boron nitride (BN) through chemical modification and then grafted modification by a silane coupling agent. The effect of modified BN (mBN) on microstructure, thermal conductivity and mechanical properties of silicone rubber (SR) is investigated by FTIR, XPS, SEM, thermal and mechanical property testing. Results show that the thermal property of SR composites is improved. When the filling content of mBN is 100 phr, the thermal conductivity of the SR/100mBN composites reaches 1.26 W m−1 K−1, which is 26% higher than that of the SR/100BN composites. For the purpose of further building a thermal network to improve the thermal conductivity of composites, blocky SiC and flaky BN are introduced into the SR composites. When the ratio of mSiC to mBN is 1:9 in SR composites, the thermal conductivity of the SR/mSiC/mBN composites is 1.35 W m−1 K−1, which is higher than that of SR composites filled with a single type of filler.

Enhancing the magnetization, electric resistivity and mechanical properties of silicone rubber loaded by Co-Zn ferrite nanoparticles as filler

High temperature vulcanized silicone rubber samples filled with Co0.5Zn0.5Fe2O4 ferrite nanoparticles were prepared using an ordinary standard rubber mixer. The compounds were prepared by dry mixing in two roll-mixing mills (outside diameter 470 mm, working distance 300 mm, speed of slow roll 24 rpm and fraction ratio of 1:1.4). Structure and Morphology of Co-Zn ferrite were characterized by X-ray diffraction and transmission electron microscope (TEM). The homogeneity of Co-Zn nanoferrite-filled silicone rubber was evaluated by scanning electron microscope (SEM). The influences of ferrite concentration on the rheological and the physico mechanical properties: tensile strength, elongation at break, Young’s modulus were measured. An enhancement of those properties were noticed by increasing ferrite load till 8 phr. The hardness showed an enhancement for all composite samples. Magnetization of the samples showed an increase with high rate at high ferrite concentration while the electric resistivity decreases up to 8 phr ferrite loaded sample then increases for higher ferrite loads. These results were discussed and interpreted in the light of the morphology and different interactions between the phase of ferrite and rubber matrix. Comparisons which were held between the obtained results with those in the literature showed superiority for the values of measured properties in this study.

Effect of the cure time on the Mechanical Properties of Silicone Rubber used as Socket Liners

This work is focused on the upper part of the prosthesis which is called a socket, it is in contact connect with the amputated part. The shear force between skin and socket, local pressure, sweating, and bacteria generation, all lead to skin inflammation and a bad smell. Consequently, the prosthesis became uncomfortable for a patient. To address this issue silicone rubber liners is proposed to use because it can absorb moisture, stress distribution, and anti-bacterial. The curing time and temperature are important factors for determining crosslink density, from the results obtained, can be noticed that, the cross-link density can greatly affect the silicone rubber properties, it can have a direct effect on the tensile strength, modulus of elasticity, percentage of elongation as well as the water absorption, and the cure time (15 min.) shoes the best resalt. As a result, using it making the prosthesis more comfortable and acceptable to the patient. In this paper, the effect of cure time on physical properties was studied.

Mechanical Properties of Silicone Rubber Enhanced Microcellular EPDM Foams Based on Supercritical CO2Foaming Technology

AbstractMicrocellular ethylene‐propylene‐diene monomer (EPDM) foams derived from miniaturizing the cellular structure can improve mechanical properties of traditional EPDM foams. It is a current challenge that microcellular EPDM foams prepared by supercritical CO2foaming technology cannot undergo the post‐crosslinking process due to the disappearance of cellular structure, which strongly restricts the development of the mechanical properties of EPDM foams. Hence, a scalable and blending route by selecting the silicone rubber (SR) with different crosslinking temperature compared to EPDM is developed to improve mechanical properties of EPDM foams. During the pre‐crosslinking process of EPDM, SR forms a complete crosslinking network, which can make up for the strength of EPDM without the post‐crosslinking. Meanwhile, the silica can reduce the domain size of SR and enhance the compatibility between EPDM and SR. As expected, the addition of SR improves the storage modulus, viscosity and matrix strength of EPDM, which shows enhanced mechanical properties of EPDM foams. When the foam density is basically the same, the tensile strength and compressive strength of SR/EPDM foam are increased by 461% and 283% respectively compared with that of EPDM foam. Finally, the maximum tensile strength and compressive strength (40% strain) of SR/EPDM foam achieves 3.58 MPa and 0.59 MPa, respectively.

Effects of titanate on the bonding properties of silicone rubber and polyester fabric

AbstractThe effects of titanate on the mechanical properties of silicone rubber and peel strength of polyester fabric with silicone rubber are studied. The tests show that the hardness and mechanical properties of silicone rubber containing 0.2 phr titanate are similar to those of pure silicone rubber, and the peel strength (1.11 N/mm) between fabric and rubber matrix without inner fabric is the highest in the test groups. Fourier transform infrared spectra (FT‐IR) and contact angle test indicate that the surface wettability of silicone rubber is effectively enhanced with the addition of titanate, which is a key factor to improve the bonding properties between silicone rubber and polyester fabric because of the more adequate contact between the adhesive and silicone rubber surface. Due to the difference in the modulus of the fabric along different yarn directions, the peel direction has a significant effect on the peel force between the outer fabric and silicone rubber.

Preparation of boron-containg hybridized silicon rubber by in-situ polymerization of vinylphenyl-functionalized polyborosiloxane and liquid silicone rubber

In this study, a kind of boron-containg hybridized silicon rubber (VP–PBSi/SR), which possess great thermal and mechanical properties, was successfully prepared. First, the vinylphenyl-functionalized polyborosiloxane (VP–PBSi) possessing good storage stability were synthesized by reacting triethoxyvinylsilane (VTEOS), phenyltriethoxysilane (PTEOS) and boric acid (BA) by sol-gel method. From the results of GPC, FT-IR, 13C-, 29Si, 11B-NMR characterization, the structures of VP-PBSi were confirmed to be the cage structure. Then, the VP-PBSi/SR were prepared by in situ polymerization of vinylphenyl-functionalized polyborosiloxane (VP–PBSi) and addition liquid silicone rubber (SR). The effect of VP-PBSi on thermal stability and mechanical properties of SR were mainly discussed by scanning electron microscope (SEM), thermal gravimetric analysis (TG), universal testing machine, and dynamic mechanical analysis (DMA), respectively, and the results showed that the thermal stability and mechanical properties of the SR were significantly enhanced. The maximum thermal decomposition temperature (Tmax), char yield and tensile strength can reach 675 °C, 72.3% and 4.65 MPa, respectively, and 21.8%, 26.1% and 20.2% higher than that of neat SR. We believe this work can provide reference for the preparation of high-performance heat resistance rubber materials.

Property Failure of Silicone Rubber Caused by Silicone Grease Absorption

This study focuses on the absorption characteristics and evolution of key properties of silicone rubber (SiR) in the presence of silicone grease; a typical material used in power cable accessories. Diffusion mechanism of silicone grease within the SiR is investigated and the results indicate that it follows Langmuir diffusion model in the absence of significant swelling. Silicone grease absorption behavior is also explored under tensile strain and at various temperatures. The tensile strain accelerates and increases the absorption of silicone grease. In addition, the influence of the absorbed silicone grease on the key electrical and mechanical properties of SiR is surveyed. The investigation shows that the properties deteriorate. In addition, the mechanism of the mechanical property deterioration of SiR is discussed.