Addition-cure Liquid Silicone Rubber Research Articles

Development of Lead-Free Radiation Shielding Material Utilizing Barium Sulfate and Magnesium Oxide as Fillers in Addition Cure Liquid Silicone Rubber.

The radiological protection has the purpose of safeguarding the physical well-being of the user, preventing exposure to detrimental levels of ionizing radiation. This study introduces a novel, cost-effective category of lead-free elastomeric material designed for radiation shielding. The filler compounds utilized are notably lighter than conventional lead-based materials, enhancing user ergonomics during application. They comprise of a blend of barium sulfate combined or not with magnesium oxide with addition-cure liquid silicone rubber. To ensure the effectiveness of the radiation shielding, X-ray transmission measurements were performed for the different thicknesses of the materials and the results compared with Monte Carlo simulations. Additionally, the physical properties of the new materials, such as density, homogeneity, tensile strength, viscosity, and wettability, were also evaluated. The findings indicate that both materials fulfill the requirement for application in radiation protection garments.

Synthesis and application of adhesion promoter containing phenolic hydroxyl/acrylate groups for addition-cure liquid silicone rubber

Grafting polar polysiloxanes to addition-cure liquid silicone rubber (ALSR) is a promising method to improve its adhesion performance. Herein, we synthesized a novel silicone adhesion promoter containing phenolic hydroxyl and acrylate groups via hydrosilylation reaction, denoted as PMHS-g-(EE/TD). It was found that PMHS-g-(EE/TD) effectively enhanced the bond strength of ALSR with polycarbonate (PC) and polyamide (PA) substrates. When the PMHS-g-(EE/TD) content was 2 phr, the bond strength of ALSR with PC and PA substrates were 3.8 MPa and 3.1 MPa, respectively. More importantly, after being heat-treated at 150 °C for 72 h or soaked in 25 °C distilled water for 8 h, the bond strength of ALSR/PMHS-g-(EE/TD) with PC and PA substrates maintained a rather high value. The adhesion promotion mechanism of PMHS-g-(EE/TD) for ALSR was further discussed and revealed. On the one hand, PMHS-g-(EE/TD) participated in the curing process of ALSR through CC bonds and formed chemical bond connections with the ALSR chain; on the other hand, PMHS-g-(EE/TD) was enriched on the ALSR surface to establish a boundary layer containing –OH and –COO, forming hydrogen bonds with the substrate. PMHS-g-(EE/TD) acted as a bridge to tightly connect the substrate and ALSR, which greatly improved the adhesion performance. This work provides a simple approach to fabricating ALSR with prominent adhesive properties.

Effects of Curing Temperature and Adhesion Promoters on Adhesion of Addition-cure Liquid Silicone Rubber

Effects of Curing Temperature and Adhesion Promoters on Adhesion of Addition-cure Liquid Silicone Rubber

Preparation of one-component addition-cure liquid silicone rubber coating with enhanced storage stability and bond strength

It is of great interest and challenge to simultaneously improve the storage stability and bond strength of one-component addition-cure liquid silicone rubber (OLSR) coating for electronic circuit board. In this work, we proposed an efficient approach to address this issue by incorporating both cyano-modification platinum catalyst (CN–PT) and urethane-containing poly(hydromethylsiloxane) (N-PHMS) into OLSR coating using a mechanical mixer. The CN–PT and N-PHMS were synthesized through thermal polymerization reaction and hydrosilylation reaction, respectively. The OLSR coating containing 0.3 phr CN–PT and 3 phr N-PHMS showed the best properties, with a tensile bond strength of 1.63 MPa, a storage period > 180 d at 25 °C, and a curing rate < 2 h at 80 °C. The salt-spray resistance and continuous power-on performance of OLSR coating were also improved, compared with pure OLSR coating. The synergism of CN–Pt and N-PHMS on the enhancement of both the storage stability and bond strength of OLSR coating was also explored. Our findings exhibited great potentials for fabricating OLSR coating with excellent long-term stable service performance including high storage stability and protective ability.

Effects of eucommia gum filler on the dielectric properties and chemical resistances of addition-cure liquid silicone rubber

It is of great interest and remains a challenge to simultaneously improve the low dielectric properties and chemical resistances of addition-cure liquid silicone rubber (ALSR). In this work, we proposed an efficient approach to address this issue by filling silicone-modified Eucommia ulmoides gum nanofiller (SEUG) into ALSR. By adding 5 wt% SEUG, the dielectric constant of the SEUG/ALSR composite rubber was significantly lower than that of neat ALSR both at 102 Hz, 103 Hz, and 104 Hz. Simultaneously, the SEUG/ALSR composite rubber exhibited better mechanical and insulation properties than the neat ALSR after HCl, NaCl, and oil resistance tests. Our findings demonstrated the great potential for fabricating silicone rubber with low dielectric properties and erosion resistance by the utilization of natural biomass rubber material, endowing it with excellent mechanical performance and degradability.

Phase‐change composites silicone rubber/paraffin@ SiO 2 microcapsules with different core/shell ratio for thermal management

A series of paraffin (Pa)@silicon dioxide (SiO2) microcapsules with different core/shell ratios were constructed by interfacial-polycondensation of tetraethoxysilane (TEOS) and γ-Methacryloxypropyltrimethoxysilane (MPS), and then were embedded in addition-cure liquid silicone rubber (ALSR) to fabricate ALSR/Pa@SiO2 phase-change composites. The SiO2 shell can avoid the leakage of Pa. Meanwhile, the in-situ modification of the SiO2 shell by MPS can enhance the interface bonding between Pa@SiO2 and ALSR, because the C═C bond introduced by MPS on the SiO2 shell can participate in the curing reaction of ALSR. The study explored the effects of the core/shell ratio on the Pa@SiO2 microcapsules and ALSR/Pa@SiO2 composites. Differential scanning calorimetry analysis demonstrated that ALSR/Pa@SiO2 composites have dependable thermal energy storage capability which can reach to 90.7 J g−1 and phase-change enthalpy of the composites increase with the core/shell ratio. The ALSR/Pa@SiO2 composites were found as form-stable phase-change materials with low leakage rate, which is attributed to the protection of both SiO2 shell and ALSR matrix. Due to the chemical interfacial interaction, the composites displayed improved mechanical strength. The composites can be used for thermal management and temperature regulation as an electronic packaging material.

Study on aluminum nitride/addition-cure liquid silicone rubber composite for high-voltage power encapsulation.

In view of the development direction of high power and miniaturization of high-voltage power supply, higher requirements are put forward for the breakdown strength, thermal conductivity of packaging materials for its high voltage output module. An electric-insulated heat-conducted material with aluminium nitride as heat conducting filler and addition-cure liquid silicone rubber (ALSR) as matrix for high voltage power encapsulation has been studied. Initially, the thermal conductivity and breakdown strength of composites were explored at different filler fractions. With increase of filler fraction, the thermal conductivity increased and the breakdown strength decreased. Then, with the packaging module volume as the optimization objective and the working temperature as the optimization condition, the temperature distribution of high voltage power supply was studied by using the finite element method, and 40wt% filling fraction was selected as the optimal ratio. Finally, the actual packaging experiment of the high voltage module is carried out. and the variation of the output voltage and temperature with the working time is obtained. According to the experimental results, the output voltage of the high voltage module is basically stable, and the maximum surface temperature is 40.4°C. The practicability of the electric-insulated heat-conducted material has been proved.

Remarkable enhancement of tracking resistance of addition-cure liquid silicone rubber by alkyl-disubstituted ureido siloxane immobilized on the silica filler surface

It is urgent and significant to prepare silicone rubber with excellent tracking resistance in a harsh environment. In this work, alkyl-disubstituted ureido siloxane immobilized on silica (U-SiO2) was prepared by the dehydration condensation of hydrolysates of alkoxy groups in alkyl-disubstituted ureido siloxanes (US) and hydroxyl groups on the silica surface. The effect of U-SiO2 on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IP test). It was found that U-SiO2 could effectively enhance the tracking resistance of ALSR. Especially, diisopropylureidopropyltriethoxysilane and diisobutylureidopropyltriethoxysilane with isomeric substitution immobilized on silica (DIPUPES-SiO2 and DIBUPES-SiO2) performed the best. With less than 1.00 phr content, ALSR samples could reach 1A4.5 level. The erosion mass was only 0.40 % and 0.62%, respectively. Moreover, ALSR / DIPUPES-SiO2 had excellent water resistance. It could still reach 1A4.5 level and the erosion mass was almost unchanged after ALSR / DIPUPES-SiO2 was immersed in the water for five days. The results of plasma irradiation and thermal treatment showed that U-SiO2 could effectively inhibit the aggregation of platinum in Karstedt's catalyst, which could promote the crosslinking of ALSR chains under the elevated temperature to form a compact ceramic protected layer. It could not only isolate the oxygen and heat and suppress the thermal degradation of ALSR, but also resist the plasma bombardment. Therefore, the tracking resistance of ALSR was remarkably enhanced.

Facile preparation and flame retardancy mechanism of cyclophosphazene derivatives for highly flame‐retardant silicone rubber composites

AbstractA novel and efficient flame retardant cyclophosphazene derivative Hexa (p‐acetamidophenoxy) cyclotriphosphazene (HACP) was successfully prepared via a facile one‐step reaction. The chemical structure of HACP was characterized and confirmed by FT‐IR, 1H and 13C NMR. Then the as‐prepared HACP was incorporated into addition‐cure liquid silicone rubber (ALSR) matrix to prepare highly flame‐retardant rubber composites. It was found that the incorporation of HACP can significantly enhance the flame resistance of ALSR. Typically, the ALSR composites filled with 30 phr HACP achieved UL‐94 V‐0 rating and meanwhile the total heat release and total smoke release were decreased by 26.9% and 41.5%, respectively. Moreover, the flame‐retardant mechanism of ALSR/HACP composites was investigated by TGA, Py‐GCMS, FT‐IR, SEM and EDX, confirming that HACP plays a significant role in capturing free‐radicals and forming protective layers. This work designed a novel cyclophosphazene‐based flame retardant to significantly enhance the flame retardancy of ALSR, which may offer some valuable inspiration for the fabrication of highly flame‐retardant polymer composites.

Fabrication of iron oxide nanoparticle decorated boron nitride nanosheet for flame-retarding silicone rubber

To promote the application of silicone rubber in the electronics industry, it is urgent to improve its thermal stability and flame retardancy. In this work, iron oxide nanoparticle in-situ decorated boron nitride nanosheet (FeBN) was fabricated via sol–gel method and then incorporated into addition-cure liquid silicone rubber (ALSR). It was found that FeBN uniformly dispersed in polymer and effectively improved the thermal stability and flame retardancy of ALSR. With only 2.0 phr FeBN, the T10 and LOI of ALSR were increased to 438.2 °C and 28.5%, respectively, which was attributed to the synergism of free-radical quenching capability and layer barrier effect.

Improvement of fluorosilicone resin on the tracking resistance of addition-cure liquid silicone rubber

Enhancing the anti-fouling and tracking resistance of silicone rubber is important to expand its application in outdoor high voltage insulation field. In this work, fluorosilicone resin (FSR) was synthesized by the sol-gel reaction of perfluorooctyltriethoxysilane and ethyl silicate. The effect of FSR on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IPT), plasma irradiation test, static contact angle measurement, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and infrared thermal image. The results showed that FSR could effectively improve the tracking resistance of ALSR. When FSR content was 0.5 phr, ALSR/FSR passed the IPT without overcurrent in 6 h under the applied alternating voltage of 4.5 kV and the erosion mass was only 2.14 wt%. In addition, the anti-plasma irradiation of ALSR/FSR was enhanced. FSR could improve the hydrophobicity of ALSR and reduce the accumulation of contamination on the surface. During the IPT, FSR could delay the occurrence of intensive arc discharge and diminish the number of arc discharge. When the dry-band arcing happened, FSR could dissipate the injected charges and suppress the arc discharge. Thus, the tracking resistance of ALSR was enhanced.

Effective improvement of anti-tracking of addition-cure liquid silicone rubber via charge dissipation of fluorosilane-grafted silica

Improving the anti-fouling and anti-tracking of silicone rubber (SR) is significant to enlarge its application in the field of outdoor high voltage insulation. In this work, fluorosilane-grafted silica (F–SiO2) was prepared by the grafting reaction of silica with perfluorooctyltriethoxysilane. Inclined-plane test (IP test), surface potential decay test, plasma irradiation, XPS and SEM were applied to study the effect of F–SiO2 on the anti-tracking of addition-cure liquid silicone rubber (ALSR). The results demonstrated that F–SiO2 postponed the occurrence of intensive arc discharge and reduced arc discharge on ALSR surface. The anti-plasma irradiation and anti-tracking of ALSR were remarkably enhanced. When F–SiO2 content was 1 phr, ALSR/F–SiO2 passed the 1A4.5 kV IP test and the erosion mass was only 0.22 wt%. Moreover, the mechanical properties and hydrophobicity of ALSR were improved. Surface potential decay test showed that F–SiO2 could dissipate charges. Combining its excellent anti-plasma irradiation, it was revealed that F–SiO2 dissipated the injected charges and diminished the density of charges in ALSR during the arc discharge, which reduced the damage of charges to ALSR chains and suppressed the arc discharge. Therefore, the anti-tracking of ALSR was enhanced.

Research on the thermal conductivity and dielectric properties of AlN and BN co-filled addition-cure liquid silicone rubber composites.

The present work aims at studying the thermal and dielectric properties of addition-cure liquid silicone rubber (ALSR) matrix composites using boron nitride (BN) and aluminum nitride (AlN) as a hybrid thermal conductive filler. Composite samples with different filler contents were fabricated, and the density, thermal conductivity, thermal stability, dielectric properties, and volume resistivity of the samples were measured. According to the experimental results, the density, thermal conductivity, dielectric constant and dielectric loss tangent values all increased with the increasing addition of filler. When the weight fraction of hBN filler was 50 wt%, the thermal conductivity of composites was 0.554 W (m−1 K−1), which is 3.4 times higher than that of pure ALSR. The corresponding relative permittivity and dielectric loss were 3.98 and 0.0085 at 1 MHz, respectively. Furthermore, TGA results revealed that the AlN/BN hybrid filler could also improve the thermal stability of ALSR. The volume resistivity of ALSR composites was higher than that of pure ALSR. The addition of fillers improved the thermal properties of ALSR and had little effect on its insulation properties. This characteristic makes ALSR composites attractive in the field of insulating materials.

Investigation of ureido‐attached vinyl MQ silicone resin on tracking and erosion resistance of addition‐cure liquid silicone rubber

ABSTRACTWith the growing incidence of extreme climate and serious pollution, the capability to resist high‐voltage arc discharge has been considered as one of crucial performances for silicone rubber in the field of electrical power. Herein, to enhance the tracking and erosion resistance of addition‐cure liquid silicone rubber (ALSR), a kind of ureido‐attached vinyl MQ silicone resin [hydrolytic condensation products of monofunctional silane (M) and tetrafunctional silane (Q)] (U‐VMQ) was synthesized. The chemical structure of U‐VMQ was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the effects of U‐VMQ on the mechanical properties, thermal stability, and tracking and erosion resistance of ALSR were investigated. The results showed that U‐VMQ was beneficial for the improvement of mechanical properties and thermal stability of ALSR. With 2 phr of U‐VMQ containing 2.5 wt % of vinyl content, the ALSR successfully passed the inclined plane tracking at 4.5 kV, and the electrical erosion rate was only 0.13%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47360.

Effect and mechanism of hepta-phenyl vinyl polyhedral oligomeric silsesquioxane on the flame retardancy of silicone rubber

It is challenging to simultaneously improve the flame retardancy and mechanical properties of silicone rubber. We herein proposed an efficient method to address this issue by incorporating hepta-phenyl vinyl polyhedral oligomeric silsesquioxane (HPVPOSS) into addition-cure liquid silicone rubber (ALSR). HPVPOSS meanwhile enhanced the flame retardancy and thermal stability of ALSR. With the addition of 10 phr HPVPOSS, ALSR passed the V-0 rating in the vertical burning test (UL-94) and had a limiting oxygen index (LOI) value as high as 31.0%. Moreover, compared with ALSR, the peak heat release rate and total heat release were decreased by 31.8% and 28.7%, respectively. Besides, the ALSR/HPVPOSS nanocomposites were demonstrated to have excellent mechanical properties. The possible flame retardant mechanism of HPVPOSS, which was attributed to the free-radical quenching effect and the catalysis effect on the crosslinking charring of ALSR, was further revealed. By generating the rigid core free-radicals and phenyl free-radicals, HPVPOSS suppressed the thermal degradation of ALSR in the condensed phase and quenched the active free-radicals in the gas phase. Moreover, HPVPOSS promoted the crosslinking charring of ALSR and the formation of a compact ceramic protection layer on the ALSR surface, effectively hindering the heat transfer and oxygen diffusion. Our findings provided a new way to fabricate silicone rubber with prominent flame retardancy and outstanding mechanical properties.

Plasma resistance of addition-cure liquid silicone rubber with Ureido-attached MQ silicone resin

Ureido-attached MQ silicone resin (U-MQ) was synthesized and added into addition-cure liquid silicone rubber (ALSR) for the improvement of the plasma resistance. The morphology and chemical structure of the surface of ALSR/U-MQ after plasma treatment were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), and the water contact angles (WCAs) of the surface at different recovery time were also measured. The results indicated that the surface of ALSR/U-MQ was slightly destroyed after plasma treatment, exhibiting excellent plasma resistance. Furthermore, the increasing rate of WCAs of ALSR with U-MQ kept faster than that of ALSR without U-MQ at different recovery time after plasma treatment, also demonstrating the lower destruction degree of ALSR/U-MQ. It was possible that inorganic ceramic layer was gradually formed on the surface of ALSR/U-MQ under plasma treatment, which was beneficial to protect the inner matrix from serious destruction.

Efficiently enhancing the tracking and erosion resistance of silicone rubber by the synergism of fluorine-containing polyphenylsilsesquioxane and ureido-containing MQ silicone resin

It is of great interest and challenge to simultaneously improve the anti-pollution and tracking resistance of silicone rubber for its application in outdoor high voltage insulation. In this work, we proposed an efficient approach to address this issue by incorporating fluorine-containing polyphenylsilsesquioxane (F-PPSS) and ureido-containing MQ silicone resin (U-MQ) into addition-cure liquid silicone rubber (ALSR). F-PPSS/U-MQ significantly improved the tracking resistance and hydrophobicity of ALSR. By adding 2 phr F-PPSS and 1 phr U-MQ, ALSR passed the 1A 4.5 level inclined plane test with merely 0.2% eroded mass, and had a water contact angle as high as 121°. The synergism of F-PPSS and U-MQ on suppressing the ALSR degradation was further revealed and demonstrated. Our findings exhibited great potentials for fabricating silicone rubber with prominent tracking and erosion resistance by the combination of prevention and inhibition of tracking damage, endowing it with excellent long-term stable service performance.

Improving the tracking and erosion resistance performance of alumina trihydrate-free addition-cure liquid silicone rubber

Aiming to improve tracking and erosion resistance performance of addition-cure liquid silicone rubber (ALSR) without alumina trihydrate, A- and B-series ALSR samples with different fumed silica mass fraction and platinum catalyst concentration were prepared respectively. The tracking and erosion resistance performance of all the samples were evaluated. Also, the thermal decomposition products were detected. Basing on the comparative analysis of thermal decomposition characteristics, morphology, crystal structure, the improvement mechanism was discussed. Results showed that increasing the concentration of platinum catalyst and the mass fraction of fumed silica both can improve the tracking and erosion resistance performance, whereas the former was more effectively. Further analysis considered that platinum catalyst played a very important role in thermal decomposition process of ALSR, increasing the platinum catalyst content can not only promote the crosslinking reaction between the methyl groups, but also suppress backbone decomposition.

Suppression Effect and Mechanism of Amine-Containing MQ Silicone Resin on the Tracking and Erosion Resistance of Silicone Rubber.

How to effectively enhance the antitracking performance of silicone rubber is a huge challenge in the field of high-voltage insulation. In this contribution, amine-containing MQ silicone resin (A-MQ) was prepared to enhance the tracking and erosion resistance of addition-cure liquid silicone rubber (ALSR). The results showed that A-MQ imparted ALSR with excellent tracking and erosion resistance. When A-MQ content was 4 phr, all test samples passed the inclined plane test at 4.5 kV, and the erosion mass decreased by 67.8%. In addition, the tensile strength and tear strength increased by 13.2 and 13.6%, respectively, compared with that of ALSR without A-MQ. The suppression mechanism was further investigated in the aspects of heat attack and plasma bombardment by laser Raman spectroscopy, thermogravimetry, thermogravimetry-Fourier transform infrared spectrometry, scanning electron microscopy, attenuated total reflection-Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. This revealed that at the elevated temperature caused by arc discharge, A-MQ promoted crosslinking of the polysiloxane molecules and suppressed the generation of cyclic oligomers, which reduced the intensity of the electrical arc. Moreover, when suffering from plasma bombardment, which was also produced by arc discharge, A-MQ protected the silicone chains from degradation and eliminated the carbon deposited on the surface.

Effect of the platinum catalyst content on the tracking and erosion resistance of addition-cure liquid silicone rubber

An addition-cure liquid silicone rubber (ALSR) with ureido-containing MQ silicone resin (U-MTQ) was prepared by hydrosilylation with platinum catalyst (Pt). ALSR samples were characterized by thermogravimetric analysis (TGA) and thermogravimetry coupled with infrared spectroscopy (TG-FTIR), and the char layers of ALSR samples after inclined plate tracking and erosion test (IPT) were characterized by X-ray photoelectron spectroscopy (XPS). The effects of Pt content (5–100 ppm) on the curing characteristics, mechanical properties and tracking and erosion resistance of ALSR were investigated. It was found that the cure rate increased with increase of Pt content. When the Pt content was 10 ppm or 15 ppm, the ALSR had excellent tracking and erosion resistance, all specimens could pass the 4.5 kV level in IPT, and the erosion rate was only 0.13% and 0.15%, respectively. ALSR samples possessed optimum mechanical properties and thermal stability when the Pt content was 15 ppm. TG-FTIR results showed that ALSR generated less carbonyl compounds (CH2O) and cyclic oligomers but more methane (CH4) when the Pt content was 15 ppm. This demonstrated that there were lower levels of the oxidation of methyl groups and the main chain unzipping degradation of ALSR, and more homolysis of Si-CH3 during the degradation. The XPS results also showed that the macromolecular radicals would further cross-link to form a firm Si-C ceramic barrier to protect ALSR samples under Pt catalysis and high temperature, thus the tracking and erosion resistance of ALSR could be improved.