Room Temperature Vulcanizing Silicone Research Articles

Preparation and Properties of One Component RTV Silicone Resin Composed of Polysiloxane Block Copolymer

One component room temperature vulcanized (RTV) silicone resin was prepared by combination of a kind of D-T polysiloxane block copolymer with crosslinker and catalyst. Transparent coating with good elastoplasticity without any inorganic filler could be obtained by exposing the RTV silicone to air at room temperature. The structure of D-T block copolymer played an important role in the properties of the cured products. It was synthesized by polycondensation of partially hydrolyzed phenyltrimethoxysilane (phenylsilsesquioxane, T units) with silanol end-capped polydimethylsiloxane (PDMS, D units). The effects of the viscosity of phenylsilsesquioxane and the D/T ratio on the properties of cured product were investigated. When phenylsilsesquioxane (10000cP at 80°C) was used and the D/T ratio was 2.0~2.3, cured products with tensile strength above 2.5MPa and elongation above 70% were prepared. RTV silicone resin composed of such kind of D-T block copolymer had good heat resistance because the existence of phenyl group and the highly cross-linked 3D structure. The Tonset was 387.6°C and the Tmax was 518°C.

Investigation on leakage current, erosion, and hydrophobic performance ofhigh-voltage insulator coatings of different thicknesses

Room-temperature vulcanizing (RTV) silicone rubber is used as a high-voltage insulator coating to enhance the pollution performance of conventional insulators, and the electrical performance of RTV coating depends on the several parameters. The present study shows the effects of the thickness on the leakage current, erosion, and hydrophobic performance of high-voltage insulator coating. Several different thicknesses of RTV silicone rubber were taken into consideration on porcelain substrates. Erosion and leakage current performances of the samples were evaluated by using inclined-plane tests (IPTs) based on the IEC 60587 standard. Eroded masses and fundamental and harmonic components of the leakage currents were investigated with respect to coating thicknesses. On the other hand, hydrophobic features of the samples were evaluated by using dynamic drop tests (DDTs) with regard to CIGRE TB442 documentation. Time to loss of hydrophobicity and the level of the leakage currents were investigated in DDTs considering the thicknesses.

Studies on composites based on HTV and RTV silicone rubber and carbon nanotubes for sensors and actuators

Nanofillers such as carbon nanotubes (CNT) are well known to significantly improve the properties of composites. In this work, CNTs were used as a reinforcing nanofiller in high-temperature vulcanized (HTV) silicone rubber, and room-temperature vulcanized (RTV) silicone rubber. At a low CNT content of 3 phr in HTV silicone rubber, the compressive and tensile moduli improved by 65% and 96%, respectively, and the resistance fell to 13 kΩ. Similarly, at 3 phr of CNT in RTV silicone rubber, the compressive and tensile moduli improved by 110% and 105%, respectively, and the resistance fell to 0.4 kΩ. The improved properties were used for applications in piezo-electric actuation and piezo-resistive strain sensors. With increase in voltage supply from 2 kV to 12 kV at 2 phr CNT, the piezoelectric actuation displacement increases to 920% (RTV silicone elastomer slab) and 1025% (HTV silicone elastomer slab). In addition, the rubber-based piezoresistive strain sensors showed a higher gauge factor with RTV silicone rubber than HTV silicone rubber. The piezoresistive strain sensors showed >100% stretchability. A series of experiments demonstrate that the use of CNTs improves the reinforcing, electrical properties, actuation, and strain sensors based on RTV and HTV silicone composites.

Structure-property relationship in silicone rubber nanocomposites reinforced with carbon nanomaterials for sensors and actuators

A small amount of nanofillers can significantly improve the mechanical and electrical properties of nanocomposites, which have a wide range of applications such as sensing and actuation. In this work, rubber nanocomposites were prepared with 0-dimensional (0-D) carbon black (CB), 1-D carbon nanotube (CNT), 3-D graphitic nanofiller (GR), and room temperature vulcanizing (RTV) silicone rubber. The different structures of the CB, CNT, and GR nanofillers were characterized. In addition, the effects of the structures on the mechanical properties and electromechanical applications of the nanocomposites were experimentally demonstrated. At a filler loading of 6 phr, the elastic modulus was improved by 150, 350, and 130 % with the nanofillers of GR, CNT, and CB, respectively. We found that the CNT-based silicone rubber nanocomposite exhibited the highest tensile strength and the reinforcing effect compared to that of others. Based on the improved mechanical, electrical properties of RTV rubber by the nanofillers, the nanocomposites were successfully adopted for strain sensing and actuation applications. The CNT- and CB-based nanocomposites have been used as piezoresistive strain sensors with a gauge factor of 1.3 and 7.8, respectively. The stretchability of strain sensor is up to 80 and 100 % for CNT and CB nanocomposites, respectively, while both of them show high durability. In addition, the nanocomposites are used as an electrode for piezoelectric actuation, and the mechanical displacement was 2.5, 0.34 and 0.5 mm for CNT-, GR-, and CB-based nanocomposite, respectively, under identical actuation voltage of 12 kV. A series of experiments demonstrate the dependency of properties of nanocomposites on the structural characteristic of carbon nanofillers.

Fabrication and characterization of silicone rubber/multiwalled carbon nanotubes nanocomposite sensors under impact force

Fabrication of miniature and macro elastic sensors from dispersed multiwalled carbon nanotubes (MWCNTs) in room temperature vulcanization (RTV) silicone rubber (SR) is described. The nanocomposite sensor displays a very low percolation threshold of 3 wt.% (i.e. 2.16 vol%) of MWCNT in SR. The nanocomposite samples are characterized by scanning electron microscope (SEM) to show the formation of three-dimensional conductive networks of the MWCNTs within the SR matrix. Characterization and fabrication procedures of four SR/MWCNT sensors with different electrode configurations are shown. An impact-resistance model is developed to describe the SR/MWCNT sensor response subjected to impact force range (0.030 to 45 N). The analysis of the impact model shows a good agreement with the experimental data. The effect of sensor initial resistance on its sensitivity and force range is also shown.

Effects of RTV Coating on the Discharge Characteristics of A Suspension Glass Insulator

DOI : 10.26650/electrica.2019.19024 The present study shows the effects of room temperature vulcanizing (RTV) silicone rubber high voltage insulator coatings on the discharge characteristics of a cap-and-pin type suspension glass insulator. The study covers both laboratory investigations and 3D electric field analysis, considering the coated and uncoated glass insulators. An ultraviolet corona camera is used to detect the location of the discharges, and a partial discharge test system is used to obtain the discharge patterns and pulse magnitudes. The experimental work is only conducted for 50 Hz power frequency voltage. In addition to the laboratory investigations, 3D electrostatic field analysis is performed to determine how the RTV coatings on the glass insulators affect the field distributions. Cite this article as : Ilhan S. Effects of RTV Coating on the Discharge Characteristics of A Suspension Glass Insulator. Electrica, 2019; 19(2): 173-181.

Synthesis and Characterization of Room Temperature Vulcanized Silicone Rubber Using Methoxyl-Capped MQ Silicone Resin as Self-Reinforced Cross-Linker.

Methoxyl-capped MQ silicone resin (MMQ) was first synthesized by the hydrosilylation of vinyl-containing MQ silicone resin and trimethoxysilane and then used in condensed room-temperature vulcanized (RTV) silicone rubber as a self-reinforced cross-linker. Results show that modified silicone rubber exhibits good light transmission. Compared with unmodified silicone rubber, the hardness, tensile strength and elongation of MMQ at the break are increased by 26.4 A, 2.68 MPa and 65.1%, respectively. In addition, the characteristic temperature of 10% mass loss is delayed from 353.5 °C to 477.1 °C, the temperature at maximum degradation rate is also delayed from 408.9 °C to 528.4 °C and the residual mass left at 800 °C is increased from 1.2% to 27.7%. These improved properties are assigned to the synergistic effect of the rigid structure of MMQ, the formation of a dense cross-linking structure in polymers and the uniform distribution of MMQ cross-linking agent in RTV silicone rubber.

Multi-walled carbon nanotubes as secondary fibre fillers for property improvement of short carbon fibre-reinforced silicone rubber

To improve the properties of room temperature vulcanized (RTV) silicone rubber, functional multi-walled carbon nanotubes (MWCNTs) and short carbon fibres were added into the RTV silicone rubber as hybrid fibre fillers. The functionalized MWCNTs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The mechanical, thermal and ablative properties of the fabricated RTV silicone rubber composites were investigated. Their properties were enhanced by adding the functionalized MWCNTs with appropriate contents. The tensile strength and tear strength of the composites are improved from 4.0 MPa and $$20.3\hbox { kN m}^{-1}$$ to 4.3 MPa and $$21.3\hbox { kN m}^{-1}$$, respectively, when the MWCNT content increased from 0 to 0.5 phr. In addition, the decomposition temperatures at the onset point and 50% mass loss increased from 493.4 and $$564.4{^{\circ }}\hbox {C}$$ to 498.8 and $$612.4{^{\circ }}\hbox {C}$$, respectively. The mass and line ablation rates also decreased from $$0.062\hbox { g s}^{-1}$$ and $$0.148\hbox { mm s}^{-1}$$ to $$0.059\hbox { g s}^{-1}$$ and $$0.145\hbox { mm s}^{-1}$$, respectively.

Treated knitted fabric for hip protective pads for elderly women. Part II. Performance relevant to thermal comfort

This paper describes Part II of a study of hip protective pads made from spacer fabric treated with shear thickening fluid (STF). Hip fractures are a substantial contributor to morbidity and mortality in the elderly, and incidence is rising worldwide. Hip protective pads reduce fractures, but wearing adherence is poor. Pads made from breathable and comfortable fabrics can increase adherence and prevent more hip fractures. In this research, warp-knitted spacer fabrics were treated with STF using one of two methods. Treatment I involved STF and room temperature vulcanizing (RTV) silicone, while treatment II consisted of STF and a mixture of isopropyl alcohol and tetraisopropyl titanate. In Part I, STF-treated knitted spacer fabric was shown to have significantly greater force attenuation capacity than untreated fabric and comparable to force attenuation capacity of closed cell foam. In Part II, the effects on performance relevant to the thermal comfort of the wearer of each treatment method, the amount of STF used, and layering were assessed using a sweating guarded hot plate, and comparisons made between treated fabrics and with closed cell foam. Treatments I and II produced pads with significantly different permeability index and mass compared to closed cell foam. Treatment II produced pads with high force attenuation capacity, suitable permeability indexes, and low mass – preferred characteristics in hip protective pads. The study concluded that knitted spacer fabrics treated with STF, isopropyl alcohol, and tetraisopropyl titanate are potentially useful materials for hip protective pads.

Development of One‐Step Water‐Repellent and Flame‐Retardant Finishes for Cotton

AbstractPyrovatex is a well‐known commercial flame‐retardant which is commonly applied for cotton fibers. Unfortunately, Pyrovatex has the concern of discharging toxic formaldehyde, and additionally it necessitates formaldehyde‐based cross‐linking agents to enhance the flame retardant character and durability. Thus, formaldehyde level is considerably increased in the treated cotton fabrics. Herein, we develop a simple approach toward superhydrophobic and flame‐retardant coating for cotton fabrics. We apply one‐bath pad‐dry‐cure technique in absence of formaldehyde which is usually applied as a cross‐linker for the application and fixation of the Pyrovatex flame‐retardant. Room temperature vulcanized (RTV) silicone was employed as a formaldehyde free cross‐linking agent which allowed using Pyrovatex at lower concentration compared to commercial cross‐linkers. The flame retardancy of the fabric was improved as a result of the higher bonding of Pyrovatex with both cotton fibers and RTV which in turn was bonded to cotton fibers too. Only 150 g/L of Pyrovatex with RTV silicone introduced much better flame retardant efficiency than applying 450–500 g/L of Pyrovatex ACS alone. Furthermore, RTV silicone further improved the water‐repellent effect on the fabric surface. Washing properties of the treated cotton fabrics proved durability. The surface morphology and comfort properties of the treated cotton was explored.

Effects of Hollow CeO2 Nanospheres on Flame Retardance and Smoke Suppression of Room-Temperature-Vulcanized Silicone Rubber

The effects of hollow CeO₂ nanospheres on the flame-retardance and smoke-suppression properties of room-temperature-vulcanized (RTV) silicone rubber were studied. It was observed that the flame retardance of RTV silicone rubber composites was improved by hollow CeO₂ nanospheres. Surprisingly, the nanospheres also enhanced the smoke-suppression characteristics of the composites. The limited oxygen index of RTV/Mg(OH)₂ was raised from 23.7 to 25.9 by the addition of hollow CeO₂ nanospheres, while the smoke density was reduced markedly, from 35.1 to 17.6. The thermal stability and char yield of the RTV silicone rubber composites were characterized by thermogravimetric techniques. Furthermore, the degradation product of the composites was analyzed by pyrolysis-gas chromatography-mass spectroscopy. A mechanism to explain the observed results is proposed.

Prosthetic rehabilitation of a microtia patient by adhesive retained auricular prosthesis: A dental technique.

Introduction: Auricular deformity can be emotionally traumatising and affects social behavior of an individual. In such cases, aesthetically acceptable prosthesis serves as a viable alternative technique to surgical reconstruction.
 Case description: Impression of the auricular defect was taken by light and regular body of poly vinyl siloxane impression material. Wax sculpting was challenging due to the bulgy remnant of the defected ear. The wax pattern was made very thin to accommodate and mask the remnant without compromising the aesthetic. Trial on the patientwas done for correction of the contours, angulation, height and width according to the normal contralateral ear. The intrinsic coloration of a Room Temperature Vulcanizing silicone was done and poured in a custom-made three-piece mold. Before the final issue of the auricular prosthesis, extrinsic coloration was done based on the surrounding area of the defect.
 Discussion: Fabrication of adhesive retained prosthesis is challenging in patients with large deformed soft tissue who refuse to undergo surgical repair. A modified wax sculpting was done to overcome this challenge. Medical grade silicone was the choice of material because of its flexibility, biocompatibility and life like appearance.
 Conclusion: Replacement of missing ear is a difficult and multi-step task in which extensive array of materials and techniques need to be employed. This fabrication technique is alternative to surgical repair with the utilization of available and economical materials.
 Bangladesh Journal of Medical Science Vol.18(2) 2019 p.437-439

Facile fabrication of superhydrophobic alloy surface based on room temperature vulcanized silicone modification

Superhydrophobicity of alloy surfaces is generally determined by the low-energy chemical composition and geometric structure of the surface. The appropriate geometry on alloy surfaces can be easily constructed via chemical etching methods. However, the subsequent low-energy modifications for pre-etched alloys are time-consuming or expensive, thus preventing their further application. Here, we prepared superhydrophobic alloy surfaces based on combining wet chemical etching and room temperature vulcanized (RTV) silicone treatment. Compared to traditional immersion methods, RTV silicone treatment for superhydrophobic 6061 Al alloy surfaces needs only 30 s, which is several thousand times faster than stearic acid or polymethyl triethoxy silane solution treatment. Mechanisms of RTV silicone treatment were investigated. The results show that dip-coating modification is different from these traditional methods. We found that the optimized proportion for RTV silicone rubber is HPDMS, PMTSi, and DBTDL with hexane solvent (HPDMS:PMTSi:DBTDL:hexane = 4:3:1:46, weight ratio), and the water contact angles of treated surfaces of pre-etched 6061 Al alloy, pure Al, and steels are 159° ± 2.7°, 168° ± 1.2°, and 169° ± 1.5°, respectively. Herein, our results demonstrate a facile, low-cost strategy to fabricate superhydrophobic alloy surface that is notable and easy to scale up for industrial applications.

Prosthetic Rehabilitation of a patient with partially amputated index finger

Hands are capable of a wide variety of functions like touching, grasping, feeling, holding, manipulating, caressing, and more. It is a vital and important part of a person's identity and well being. Loss of part of the hands can affect esthetics; functions are undermined depending upon the severity of loss and it causes a great psychological disturbance. The prosthetic rehabilitation of a partially amputated finger presents a challenge to the Prosthodontist. This case report illustrates the procedure of fabrication of finger prosthesis using room temperature vulcanizing (RTV) silicone and intrinsic staining with modern prosthetic design to improve the esthetics of a patient with partially amputated left index finger.

Detecting Defects in Porcelain Postinsulator Coated With Room Temperature Vulcanized Silicone Rubber by Pulsed Thermography

Nondestructive testing is of great significance for preventing fracture accidents of porcelain postinsulators, especially coated with room temperature vulcanized (RTV) silicone rubber. In this paper, the feasibility of pulsed thermography for defects detection of porcelain postinsulators was investigated. 110-kV porcelain postinsulators with crack defects were tested by utilizing the investigated approach. The results show that crack defect as small as 0.4 mm under the RTV silicone rubber coating with the thickness of 1 mm can be accurately identified. Homomorphic filtering method with Fourier transform was applied to correct the nonuniform heating and improve the defect contrast in the thermal images. With the advantages of simple operation, contactless measurement, full-field imaging, and quantitative defect estimation capability, the pulsed thermography would have promising applications in live detection of porcelain postinsulators.

Effects of thermal properties on tracking and erosion resistance of micro-ATH/AlN/BN filled silicone rubber composites

Silicone rubber is a hydrophobic polymer which is widely employed for high voltage outdoor insulation. The material offers excellent electrical performance under contaminated environments. However, pristine silicone rubber has low thermal properties and this may cause tracking and erosion failure due to severe dry band arcing and ohmic heating on the insulating surface. This work investigates the effect of material thermal characteristics on the tracking and erosion resistance of silicone rubber filled with micron sized alumina tri-hydrate (ATH), aluminum nitride (AlN) and boron nitride (BN) particles. Composites with different loading were synthesized by dispersing particles in pristine room temperature vulcanizing (RTV) silicone rubber and IEC 60587 inclined plane test (IPT) was conducted to evaluate tracking and erosion resistance. Apart from physical parameters and leakage current, an infrared thermal imager was used to measure the surface temperature distribution during the course of IPT. Experimental results showed tracking and erosion resistance is significantly enhanced with addition of BN particles followed by ATH. AlN composites exhibit poor tracking and erosion resistance, similar to pristine silicone rubber. It is concluded that addition of BN-composites improves ability to impede the tracking and erosion process, the reasons being better thermal stability and enhanced thermal conduction in the discharge region. On the other hand, infrared analysis revealed thermal accumulation is remarkably higher in AlN-composites which promotes dry band arcing and results in tracking and erosion failure.

Research of biological contamination and its effect on the properties of RTV-coated insulators

Recently, to improve the anti-fouling flashover performance of porcelain and glass insulators, room temperature vulcanized (RTV) silicone rubber coatings have been widely applied to their surface. However, it was found that, in warm and humid areas in China, the presence of RTV silicone coating could facilitate the growth of biological contamination such as algae. This study firstly analyzed the biofouling regularity of algae growth on the surface of outdoor RTV-coated insulators, considering growth direction, distribution on sheds, substation equipment, insulating material and effect of corona discharge. The effects of algae on the surface micro morphology, functional groups and flashover voltage of field insulator were then studied. The effects of environmental factors on algae growth were studied in detail. Finally, the influence of algae on the hydrophobicity and flashover characteristics of the RTV coating was examined. Through research, the growth regularity of algae on insulator surface is presented and put forward some measures to prevent and control algae growth. The results also showed that the presence of algae could decrease flashover performance of the RTV-coated insulators. However, the effect of algae on the aging of materials was insignificant.

Effect of incompletely condensed tri-silanol-phenyl-POSS on the thermal stability of silicone rubber

In most cases, incompletely condensed tri-silanol-phenyl-polyhedral oligomeric silsesquioxane (SSOH) was used as an intermediate to synthesize the polyhedral oligomeric silsesquioxane (POSS) with special structure. In this paper, SSOH was well synthesized and then immediately incorporated into hydroxyl-terminated polydimethylsiloxane (PDMS) as a co-cross-linking agent to prepare room-temperature-vulcanized (RTV) silicone rubber (SSOH-PDMS). Thermogravimetric analysis (TGA) results showed that the chemical incorporation of POSS into PDMS networks exerted significant enhancement of thermal stability for the rubber nanocomposites. For SSOH-PDMS with 5 wt% SSOH, the degradation temperature of 5% weight loss were delayed from 364.78 to 379.50 °C, while the temperature for 30% weight loss were increased by 47.4 °C. By monitoring the degradation behavior by TGA coupled with Fourier transform infrared spectroscopy (FTIR), the degradation mechanism of the modified RTV silicone rubber containing different concentration of the cross-linker SSOH has been investigated. The results showed that the SSOH greatly influenced the degradation mechanism of PDMS rubber in two ways: ① The reaction with the silanols in PDMS can diminish the degradation initiated by hydroxyl-terminal during the first degradation stage; ② the nanoreinforcement effect of POSS on the PDMS can delay the temperatures of the second thermal degradation stage.

Theoretical Investigation of the Hydrolytic Mechanism of α-Functionalized Alkoxysilanes as Effective Crosslinkers and the Difficulty of Deep Vulcanization in RTV Silicone Rubber.

The reactions between α-, γ-ethylenediaminemethyl trimethyl-ketoxime silane (α-, γ-EAMOS) and H2O were investigated on the geometries of stationary points, the reaction pathway (IRC), thermodynamic and kinetic analysis by density functional theory (DFT) at the B3LYP/6-311G (d, p) level. Interestingly, the results showed that the hydrolysis activity of α-EAMOS is higher than that of γ-EAMOS, due to the influence of an amino substituent in position α-C on silicon. α-EAMOS can be used as a superior crosslinker for room temperature vulcanized (RTV) silicone rubber to achieve rapid crosslinking without a toxic catalyst. Besides, compared with the reaction between α-EAMOS and H2O, the reactivity between α-EAMOS and hydroxy siloxane (HO–Si(CH3)2–OSiH3) was discussed. Particularly, it revealed that the deep vulcanization of RTV silicone rubber is difficult.

Increasing the field-of-view of row–column-addressed ultrasound transducers: implementation of a diverging compound lens

The purpose of this work is to investigate compound lenses for row-column-addressed (RCA) ultrasound transducers for increasing the field-of-view (FOV) to a curvilinear volume region, while retaining a flat sole to avoid trapping air between the transducer sole and the patient, which would otherwise lead to unwanted reflections. The primary motivation behind this research is to develop a RCA ultrasound transducer for abdominal or cardiac imaging, where a curvilinear volume region is a necessity. RCA transducers provide 3-D ultrasound imaging with fewer channels than fully-addressed 2-D arrays (2N instead of N2), but they have inherently limited FOV. By increasing the RCA FOV, these transducers can be used for the same applications as fully-addressed transducers while retaining the same price range as conventional 2-D imaging due to the lower channel count. Analytical and finite element method (FEM) models were employed to evaluate design options. Composite materials were developed by loading polymers with inorganic powders to satisfy the corresponding speed of sound and specific acoustical impedance requirements. A Bi2O3 powder with a density of 8.9g/cm3 was used to decrease the speed of sound of a room temperature vulcanizing (RTV) silicone, RTV615, from 1.03mm/μs to 0.792mm/μs. Using micro-balloons in RTV615 and a urethane, Hapflex 541, their speeds of sound were increased from 1.03mm/μs to 1.50mm/μs and from 1.52mm/μs to 1.93mm/μs, respectively. A diverging add-on lens was fabricated of a Bi2O3 loaded RTV615 and an unloaded Hapflex 541. The lens was tested using a RCA probe, and a FOV of 32.2° was measured from water tank tests, while the FEM model yielded 33.4°. A wire phantom with 0.15mm diameter wires was imaged at 3MHz down to a depth of 14cm using a synthetic aperture imaging sequence with single element transmissions. The beamformed image showed that wires outside the array footprint were visible, demonstrating the increased FOV.