Silicone Rubber Foam Research Articles

Mechanical properties of microcellular and nanocellular silicone rubber foams obtained by supercritical carbon dioxide

In this work, nanocellular silicone rubber foams were first prepared by supercritical carbon dioxide. The cellular morphologies and mechanical properties of the microcellular and nanocellular silicone rubber foams are presented. The cell size and cell density of the microcellular silicone rubber foams can reach 1–4 μm and 1011 cells/cm3, respectively. The nanocellular silicone rubber foams have an upper limit diameter of 59 nm, and the density of the nanocellular silicone rubber foams is on the order of 1014 cells/cm3, which is several orders of magnitude greater than that of the typical microcellular silicone rubber foams. The stretching-induced cavitation can play an important role in the formation of the nanocellular structure on cell walls. The effect of the cellular structure on the mechanical properties is investigated. As a result, the nanocellular structure causes an early breakdown, resulting in a decrease in the tensile strength. Furthermore, when the open-cell content (OCC) increases, the compressive curves change from having three regions to two regions, indicating that the compression plateau disappears when the OCC is greater than 0.45. Microcellular and nanocellular silicone rubber foam are prepared by supercritical carbon dioxide in this work. The tpre and Ps are important factors which affect the open-cell content (OCC). When the tpre and Ps increases, the OCC sharply improves and could reach to more than 96%. The OCC has a significant effect on the mechanical properties of the nano/micro silicone rubber foam.

In situ reactive self-assembly of a graphene oxide nano-coating in polymer foam materials with synergistic fire shielding properties

We report a facile and green in situ reactive self-assembly strategy to achieve a compact and ultrathin GO nano-coating bonded onto silicone rubber foam surface, producing excellent high-temperature resilience and synergistic fire resistance.

Ceramifiable and mechanical properties of silicone rubber foam composite with frit and high silica glass fiber

In this paper, ceramifiable silicone rubber foam composite was prepared by silicone rubber, fumed SiO2, talc, frit, high silica glass fiber, foaming and vulcanizing agents. Thermal property, micromorphology, phase transformation and compressive strength of pyrolysis residues at different temperatures were discussed. Thermogravimetric analysis (TGA) results indicated that the amount of ceramic residues increased from 34.5% to 41.1% at 1000 °C with the increase of frit content, whereas T5 and Tmax decreased by 43°C and 103°C, respectively. SEM images showed that pore size became well-distributed by adding frits to the silicone rubber. And after pyrolysis at 1000°C, bridged structure was formed well, which made the structure of residues be coherent and integrated. XRD tests indicated that new crystalline phase, MgSiO3, was appeared at above 1000°C. The effect of frit on compressive strength of composite at room temperature was little, but there was a great improvement after being treated at high temperature, especially at 1000°C.

Automated, robotic dry-cleaning of solar panels in Thuwal, Saudi Arabia using a silicone rubber brush

The challenge of mitigating power loss in solar photovoltaic (PV) systems—due to dust—is critical to the economical deployment of solar in arid regions. These areas suffer from high aerosol concentration levels and frequent sand storms that lead to an accumulation of a layer of dust on the surface of solar arrays. The dust stays in place due to only slight and occasional rain fall. This paper presents the results from a study conducted on the effectiveness of dry cleaning solar panels, using an automated robotic cleaning system. The robotic cleaning system is part of a research program related to robotic dust mitigation technologies for solar panels, and includes a new type of brush, which uses silicone rubber foam flaps mounted onto an aluminum core. The study found that the robotic system, using this silicone rubber foam brush, was able to effectively minimize the impact of dust on the solar panels’ power output, providing an increase in power output versus the weekly-cleaned controls. This new brush shows promise for use in solar panel dust mitigation due to its effective cleaning performance and low cost, and does not induce any damage to the surface of the solar panels.

Establishment of Constitutive Model of Silicone Rubber Foams Based on Statistical Theory of Rubber Elasticity

In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was modified to build this model. When a strain amplification factor (X) was introduced, the theoretical model could fit the tensile stress-strain data of mono- and bi-modal foam matrix well (Adj. R-Square = 0.9989, 0.9983). Parameters related to the polymer network, namely, average molecular weight (Mc) and volume fraction (ϕ) of chain segments between adjacent cross-linking points (network strands), were calculated by probabilistic method from the number-average molecular weight (Mn), vinyl content (wVi) of the primary polysiloxanes and percent conversion (q) of vinyl groups. The primary and infinite strain amplification factors (X0, X∞) and decay exponent (z), introduced by X and related to the nanoparticles, were obtained by fitting. Inspired by the fact that the actual strain of matrix was lower than that of the foams’, we introduced another item, strain hysteresis item (H, related with the foam porosity and cell structure), into the statistical model as well. With the same above values of Mc, ϕ, X0 and X∞, the model could also fit the compressive stress-strain data of mono- and bi-modal foams well (Adj. R-Square = 0.9948, 0.9985). Interestingly, the strain hysteresis items of the mono- and bi-modal foams almost completely coincided under all experimental strains, which may be attributed to the almost equal porosity and similar cell structure of the two foams. This constitutive model may connect the macroscopic stress-strain behaviour to the parameters of microscopic molecular structures, promisingly providing a basis for the performance improvement and optimization of silicone rubber foams.

Microcellular silicone rubber foams: The influence of reinforcing agent on cellular morphology and nucleation

A series of microcellular silicone rubber foams were prepared by supercritical carbon dioxide (scCO2). The effect of reinforcing agent (silica) on the rheological behavior, cellular morphology and nucleation of silicone rubber composites was investigated. The results show that the silica not only acts as reinforcing agent but also plays an important role in the cellular nucleation. When the content of silica increases from 40 phr to 70 phr, the range of the calculated surface tension of silicon rubber composites/scCO2 (γmix) and radius of the critical nucleus (r*) are 158.95∼1,092.74 nN/m and 14.45–99.34 nm, respectively. Meanwhile, aggregated silica has good heterogeneous nucleation as the diameter of aggregated silica particles is approximate to twice r*. The smallest cell diameter and the highest cell density of the silicone rubber foam can reach to 708 nm and 1.02 × 1011 cells/cm3, which indicate that the silicone rubber nanofoams can be obtained by means of the supercritical foaming technology. POLYM. ENG. SCI., 59:5–14, 2019. © 2018 Society of Plastics Engineers

Solid‐state microcellular high temperature vulcanized (HTV) silicone rubber foam with carbon dioxide

ABSTRACTA series of microcellular high temperature vulcanized (HTV) silicone rubber foams were prepared using CO2 as a physical blowing agent. Rheological properties, gas diffusive behavior, and foaming parameters of silicone rubber were investigated. The results show that saturation pressure has a significant effect on the diffusivity of CO2 in HTV silicone rubber matrix. The gas concentration and diffusivity increase from 2.45 wt % to 3.24 wt %, and from 1.62 × 10−5 cm2/s to 7.83 × 10−5 cm2/s as the saturation pressure increases from 2 MPa to 5 MPa, respectively. The value of the gas diffusivity in HTV silicone rubber is almost 1000 times higher than that of the gas diffusivity in polyetherimide (PEI) matrix. Additionally, microcellular HTV silicone rubber foams with the smallest cell diameter of 9.8 μm and cell density exceeding 108 cells/cm3 are achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44807.

Fabrication of Silicone Rubber Foam with Tailored Porous Structures by Supercritical CO2

In spite of great concern on the wide application of silicone rubber foams, few works have been reported about easy-operating foaming method. In this study, the effects of silica content and foaming process on the porous structure of high-temperature-vulcanized silicon rubber foams are evaluated, which are prepared by supercritical CO2 at different conditions, with fumed silica used for reinforcement. Silicone rubber foams with cell size in 8–120 μm, cell density in 105–108 cm−3, and density between 0.45 and 0.9 g cm−3 are prepared under different saturation conditions. The results show that increasing silica content can decrease cell size. It is also found that cell density improves exponentially with increasing saturation pressure and decreasing saturation temperature. Besides, it demands less than 1 h for specimens to reach equilibrium on thickness around 3 mm. All the results indicate that the porous structures of silicone foams can be tailored by foaming process parameters facilely and are predictable with fitted equation.

A Green and Structure-Controlled Approach to the Generation of Silicone Rubber Foams by Means of Carbon Dioxide

Silicone rubber foams were successfully generated by environmentally friendly blowing agent, supercritical carbon dioxide (scCO2), in this research. Firstly, the effect of the saturation time on the cellular structure was investigated. The diffusion of scCO2 into the rubber matrix would be enhanced thus decreasing the viscosity as increasing the saturation time. It would further promote the cell growth, which has a close connection with the cellular structure. After that, the effect of pre-curing time on cellular morphology of silicone rubber foams was further researched in detail. When increasing pre-curing time in the short time range, cell nucleation would be affected more than cell growth in the foaming process. If continuously increasing pre-curing time, both cell nucleation and growth would be restricted thus resulting in the formation of silicone rubber foams with small cell density and small cell size. This investigation not only provided a green way to produce silicone rubber foams, but also guided us to control cellular morphology via the saturation time and pre-curing time.

Thin Fresnel zone plate lenses for focusing underwater sound

A Fresnel zone plate (FZP) lens of the Soret type creates a focus by constructive interference of waves diffracted through open annular zones in an opaque screen. For underwater sound below MHz frequencies, a large FZP that blocks sound using high-impedance, dense materials would have practical disadvantages. We experimentally and numerically investigate an alternative approach of creating a FZP with thin (0.4λ) acoustically opaque zones made of soft silicone rubber foam attached to a thin (0.1λ) transparent rubber substrate. An ultra-thin (0.0068λ) FZP that achieves higher gain is also proposed and simulated which uses low-volume fraction, bubble-like resonant air ring cavities to construct opaque zones. Laboratory measurements at 200 kHz indicate that the rubber foam can be accurately modeled as a lossy fluid with an acoustic impedance approximately 1/10 that of water. Measured focal gains up to 20 dB agree with theoretical predictions for normal and oblique incidence. The measured focal radius of 0.68λ (peak-to-null) agrees with the Rayleigh diffraction limit prediction of 0.61 λ/NA (NA = 0.88) for a low-aberration lens.

The effects of viscoelastic properties on the cellular morphology of silicone rubber foams generated by supercritical carbon dioxide

Silica content, saturation temperature and pressure all have an effect on silicone rubbers' viscoelastic properties, which further has a close connection with the cellular structure.

Study on the Cell Structure and Mechanical Properties of Methyl Vinyl Silicone Rubber Foam Materials

The mechanical properties of methyl vinyl silicone rubber foam materials with different cell diameters of the spherical cell structure were investigated. The results showed that the cell diameter had significant effects on the mechanical properties,the foam materials with cell diameter range 300~450μm had the best compression stress property and stress-relaxation property. The changing of cell shape of the spherical cell foam materials in the process of dynamic compression were analyzed by using micro focus uCT technology, with obtaining the parameters of cell volume, porosity and so on.

Preparation of silicone rubber foam using supercritical carbon dioxide

Silicone rubbers were successfully foamed by supercritical carbon dioxide (SC CO2). Samples were precured and fully cured before and after the basic foaming process with SC CO2. The effects of precuring time and soaking pressure on the density and pore morphology of prepared silicone rubber foams were investigated. It was found that a crosslinked network structure affected by precuring time played an important role in the foaming process. In current study, 5min was the optimum precuring time for foaming and the corresponding minimum sample density was 0.239g/cm3. The best prepared foam had polygonal pores and the pores were interconnected. Our results indicate that SC CO2 foaming technology can be used to prepare crosslinked elastomer foams by appropriately controlling the crosslinked network structure.

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO2 as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.

The Dispersion Estimation Method for Assembly Stress of Silicone Rubber Foam Pad Based on Extreme Value Distribution

The silicone rubber foam is a suitable material used for heat insulation and vibration reduction. Because of dispersion of its mechanical character, it is difficult to quantify the assemble stress in reliability analysis. Based on reduced hyper-foam Ogden Model, the interval of model parameter is obtained through fitting the test data, and the predicted assemble stress distribution is also achieved by Monte-Carlo random simulation method. Then, the regression analysis of predicted data estimated is introduced by the extreme value distribution. The predicted assembly stress distribution described in this paper achieves high confidence by the extreme value distribution. Thus, combined with strain uncertain quantification, the reliability analysis of assemble stress can be performed.

Preparation and properties of hollow glass bead filled silicone rubber foams with low thermal conductivity

Silicone rubber foams filled with various content and different particle size of hollow glass bead (HGB) were prepared by compression molding. It was revealed that compared with silica filled silicone rubber foams, HGB filled materials achieved higher foaming extent, lower thermal conductivity, and lower hardness, which can be significant for thermal insulation materials. For HGB filled materials, the morphology indicated the average cell size decreased with higher HGB content and larger particle size of HGB. The density, thermal conductivity, hardness and tensile strength increased with higher HGB content and larger particle size of HGB.

A Flexible Fin with Bio-Inspired Stiffness Profile and Geometry

Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the caudal part of the body is passive and, acting as a carrier of energy, transfers the momentum to the surrounding water. Inspired by those findings we hypothesize that certain swimming patterns can be achieved without copying the distributed actuation mechanism of fish but rather using a single actuator at the anterior part to create the travelling wave. To test the hypothesis a pitching flexible fin made of silicone rubber and silicone foam was designed by copying the stiffness distribution profile and geometry of a rainbow trout. The kinematics of the fin was compared to that of a steadily swimming trout. Fin's propulsive wave length and tail-beat amplitude were determined while it was actuated by a single servo motor. Results showed that the propulsive wave length and tail-beat amplitude of a steadily swimming 50 cm rainbow trout was achieved with our biomimetic fin while stimulated using certain actuation parameters (frequency 2.31 Hz and amplitude 6.6 degrees). The study concluded that fish-like swimming can be achieved by mimicking the stiffness and geometry of a rainbow trout and disregarding the details of the actuation mechanism.

Numerical Study on the Large Deformation of Silicone Rubber Foams Based on Random Cell Models

Two-dimensional (2D) random cell models composed of circular cells with different sizes are developed to simulate the microstructure of silicone rubber foams. The two-parameter Mooney-Rivlin strain energy potential model is employed to characterize the hyperelasticity of the solid of which the foams are made. Finite element method is used to simulate the large deformation of the foams. Predicted uniaxial compressive stress-strain curves exhibit universally three deformation regions: an initial linear-elastic response, an extended plateau region, and a final densification stage as cell collapsing. It is also found that with the foam relative density increasing, the initial linear-elastic region is found to extended, the buckling plateau section becomes indistinctive, and final densification stage is hastened.

Structure and properties of closed‐cell foam prepared from irradiation crosslinked silicone rubber

AbstractSilicone rubber foam was prepared through crosslinking with electron beam irradiation and foaming by the decomposing of blowing agent azobisformamide (AC) in hot air. The crosslinking and foaming of silicone rubber was carried out separately, which was different from the conventional method of chemical crosslinking and foaming. After foaming, the silicone rubber foam was irradiated again to stabilize the foam structure and further improve its mechanical properties. The effects of irradiation dose before and after foaming, and the amount of blowing agents on the structure and properties of silicone rubber foam were studied. The experimental results show that with the increase of AC content, the average cell diameter of silicone rubber foam increases a little, the foam density decreases to a minimum value when AC content is 10 phr. With the increase of irradiation dose before foaming from 10 to 17.5 kGy, the cell nucleation density of silicone rubber foam increases, the average cell diameter decreases, and the foam density increases. With the increase of irradiation before foaming, the tensile strength, tensile modulus, and the elongation at break of the silicone rubber foam increase. Through irradiation crosslinking again after foaming, the foam density is decreased and the mechanical properties of silicone foam are further improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mechanical properties and antibacterial activity of peroxide‐cured silicone rubber foams

AbstractSilicone rubber (SR) foams were prepared by the peroxide curing of a silicone compound with 2,4‐dichlorobenzoyl peroxide (DCBP), di‐t‐butyl peroxide (DTBP), or 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (DBPH) in the presence of 2,2′‐azobisisobutyronitrile (AIBN) as a blowing agent. The cells were formed in the foam as a result of nitrogen produced by the decomposition of AIBN during the foaming process. The cell size, hardness, and tensile properties of the SR foams were examined as a function of the peroxide concentration. When the peroxide concentration increased, the hardness and tensile strength of the SR foams increased, whereas the cell size and elongation at break decreased. The antibacterial activity of the prepared foams was also evaluated via their effects on Staphylococcus aureus and Escherichia coli. The peroxide‐cured SR foams had antibacterial activity because a toxic residue was generated by the peroxide decomposition. The foam prepared by the AIBN/DCBP system showed more antibacterial activity than the AIBN/DBPH and AIBN/DTBP ones. However, after postcuring at 250°C for 2 h, the antibacterial activity of the SR foams significantly decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008