Preparation and heat resistance of hollow glass microbead/silicone rubber composite coating

Hollow glass microbead/silicone rubber composite coatings were prepared to improve the heat-resistance and mechanical properties of silicone rubber-based composites, using CE modified SR as the matrix and HGM as the filler. The microscopic morphology and thermal stability of the composites were characterized by scanning electron microscopy (SEM) and thermogravimetric analyzer (TGA), respectively. The results showed that the thermal stability of the composites increases with the increase of filler content. For the composite sample with a HGM mass content of 16.7%, the initial decomposition temperature (T₅) is 408°C, which is 84°C higher than that of silicone rubber. The low density and high sphericity of HGM make it easier to uniformly disperse in the polymer matrix. In addition, compared to silica, which is commonly used as an inorganic filler, the lower thermal conductivity of HGM is also beneficial for achieving better thermal shielding effect. It is confirmed that the insufficient thermal stability of the polymer matrix above 400°C can be compensated for by the properly dispersed inorganic fillers. Therefore, the thermal stability of the composite is improved by the synergistic effect of modified heat-resistant matrix and inorganic filler.     

Effect of phenolic resin structure on the bonding properties of nitrile rubber-based adhesives

Three phenolic resins were used to study the effect of resin structure and its percentage content on the bonding properties of nitrile rubber-based adhesives. The phenolic resins studied are derived from phenol, resorcinol and para-t-butyl phenol, and are of novalac type. These resins were characterized by infra-red and thermal studies. Several formulations were prepared by varying the phenolic resin/nitrile rubber ratio and these formulations were tested for viscosity and bonding properties. At a given resin-to-rubber ratio, the viscosity for resorcinol-formaldehyde resin was higher than phenol-formaldehyde resin followed by para-t-butyl phenol-formaldehyde resin. The peel strength of nitrile rubber-based adhesive prepared from resorcinol-formaldehyde resin was higher than adhesives that from para-t-butyl phenol-formaldehyde resin followed by phenol-formaldehyde resin. The lap shear strength of nitrile rubber-based adhesive containing para-t-butyl phenol-formaldehyde resin was higher than of adhesives containing the other two resins. The trend observed in peel strength could be explained on the basis of hydrogen bonding between hydroxyl groups of phenolic resin (adhesive) and hydroxyl groups of the starch-coated canvas cloth (adherend), whereas the trend observed in lap shear strength could be explained on the basis of extent of linearity in the resin structure.     

Ablation properties of aluminum silicate ceramic fibers and calcium carbonate filled silicone rubber composites

The ablative performance of aluminum silicate ceramic fiber (ASF) and calcium carbonate (CaCO₃) filled silicone rubber composites prepared through a two‐roll mill was examined. The properties of the composites were investigated by thermogravimetry, thermal conductivity measurements, and oxyacetylene torch testing. After the material was burnt, the structure and composition of the char were analyzed by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy (SEM). The results of the ablation test showed that the ablation resistance improved greatly in an appropriate filler scope. Combined with SEM, it was proven that a firm, dense, and thermal insulation layer, which formed on the composites surface during the oxyacetylene torch test, was a critical factor in determining the ablation properties. Thermogravimetric analysis revealed that the thermal stability of the composites was enhanced by the incorporation of ASF and CaCO₃. The thermal conductivity measurements showed that the silicone rubber composites had a very low thermal conductivity ranging from 0.206 to 0.442 W m^?1 K^?1; this significantly prevented heat from transferring into the inner matrix at the beginning of the burning process. The proportion of 20/40 phr (ASF/CaCO₃) was optimum for improving the ablation resistance of the silicone rubber composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41619.     

The synthesis,characterization and properties of silicone adhesion promoters for addition-cure silicone rubber

Two types of polysiloxanes, GVPMS and GVHMS, were synthesized through nonhydrolytic sol-gel reaction from vinyltrimethoxysilane(VTMS), 3-glycidoxypropyltrimethoxysilane(KH560) and diphenylsilandiol(DPSD) or hydroxyl silicone oil, respectively. The chemical structures were characterized by Fourier transform infrared (FTIR) spectroscopy, ¹H nuclear magnetic resonance (¹H-NMR) spectroscopy and gel permeation chromatography (GPC). GVPMS and GVHMS were used as adhesion promoter for addition-cure silicone rubber. It was found that the adhesion promoters not only greatly improved adhesion strength but also had excellent compatibility with silicone rubber. Among them, GVPMS gave better adhesion strength in silicone rubber. The shear strength of silicone rubber reached 1.70 MPa with addition of 1.5 phr GVPMS, which was about 317% higher than that of silicone rubber without the adhesion promoter. Meanwhile, the shear strength of silicone rubber reached 1.14 MPa with addition of 2.0 phr GVHMS, which was 183% higher than that of silicone rubber without the adhesion promoter. Optical property test results revealed that the refractive indexes of GVPMS and GVHMS were 1.5185 and 1.4133 respectively and both of them had good compatibility with silicone rubber, which satisfied the application demand of high-refractive and low-refractive electron encapsulation. Thermal resistance test and SEM results further proved that adhesion promoter could significantly increase the adhesion between the copper substrate and silicone rubber, in which GVPMS had a better performance. Oxidation treatment experiment further explained the mechanism that adhesion promoter functioned as a bridge, linked silicone rubber and copper substrate through chemical bonds.     

PGS/HAp Microporous Composite Scaffold Obtained in the TIPS-TCL-SL Method: An Innovation for Bone Tissue Engineering

In this research, we synthesize and characterize poly(glycerol sebacate) pre-polymer (pPGS) (¹H NMR, FTiR, GPC, and TGA). Nano-hydroxyapatite (HAp) is synthesized using the wet precipitation method. Next, the materials are used to prepare a PGS-based composite with a 25 wt.% addition of HAp. Microporous composites are formed by means of thermally induced phase separation (TIPS) followed by thermal cross-linking (TCL) and salt leaching (SL). The manufactured microporous materials (PGS and PGS/HAp) are then subjected to imaging by means of SEM and µCT for the porous structure characterization. DSC, TGA, and water contact angle measurements are used for further evaluation of the materials. To assess the cytocompatibility and biological potential of PGS-based composites, preosteoblasts and differentiated hFOB 1.19 osteoblasts are employed as in vitro models. Apart from the cytocompatibility, the scaffolds supported cell adhesion and were readily populated by the hFOB1.19 preosteoblasts. HAp-facilitated scaffolds displayed osteoconductive properties, supporting the terminal differentiation of osteoblasts as indicated by the production of alkaline phosphatase, osteocalcin and osteopontin. Notably, the PGS/HAp scaffolds induced the production of significant amounts of osteoclastogenic cytokines: IL-1β, IL-6 and TNF-α, which induced scaffold remodeling and promoted the reconstruction of bone tissue. Initial biocompatibility tests showed no signs of adverse effects of PGS-based scaffolds toward adult BALB/c mice.     

Preparation of high-performance epoxy-containing silicone rubber via hydrosilylation reaction

A novel epoxy-containing silicone rubber network was constructed by hydrosilylation reaction among the synthesized vinyl-containing epoxy resin prepolymers, vinyl terminated silicone oil and hydrogen-containing silicone oil. The structure of the vinyl-containing epoxy resin prepolymers was characterized by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy. Morphology observations revealed that uniform “sea-island” phase separation structure was present in modified silicone rubbers. The compatibility between silicone rubber and epoxy resin was enhanced, thanks to the good dispersion of vinyl-containing epoxy prepolymers in silicone rubber matrix. The adhesion and tensile properties of modified silicone rubbers were greatly enhanced when compared with those of unmodified counterparts. The thermal degradation behavior of cured silicone rubbers was studied using thermogravimetric analysis and thermogravimetric/infrared spectrometry analysis. Results showed that the formation of epoxy-containing silicone rubber network altered the degradation process of silicone rubber, thereby yielding a higher residue at 800 °C under nitrogen atmosphere. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48397.     

Silicone resin synthesized by tetraethoxysilane and chlorotrimethylsilane through hydrolysis–condensation reaction

Silicone pressure‐sensitive adhesives compositions contain a polydimethylsiloxane and a silicone resin, which can enhance the instant bonding ability and bonding strength of the adhesive. In this study, silicone resin was designed to have a low molecular weight and a highly nonpolar chemical structure. The silicone resin was applied to silicone pressure‐sensitive adhesives. The molecular structure of silicone resin was characterized by FT‐IR, GPC, ¹H‐NMR, and ²⁹Si‐NMR spectroscopic techniques. Properties such as thermal stability, solubility, hydrophobic, and transparent properties were researched and compared. When the chlorotrimethylsilane increased, it appeared that the amount of silanol groups, molecular weight and thermal stability decreased, while the hydrophobic and transparent properties increased. The silicone resin was completely soluble in toluene and xylene. It was also applied to silicone pressure‐sensitive adhesives, resulting in good peel adhesion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40317.     

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

With 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.     

Thermal conductivity of filled sol‐gel‐derived hybrid materials

A novel sol‐gel‐based hybrid material has been synthesized from organofunctional silanes and aluminates via hydrolysis and condensation reactions. The hybrid material was—in comparison to a silicone rubber—filled with equal amounts of metal filler particles in order to investigate the effective thermal conductivity. The data obtained were compared with theoretical models available in literature to gain understanding of mechanisms responsible for the measured conductivities. Samples were prepared via casting and spin‐coating techniques on Teflon® and silicon substrates and characterized using laser flash analysis (LFA) and scanning electron microscopy (SEM). It was demonstrated, that the hybrid material with an aluminum content of 40 vol % offers the possibility to achieve an up to five times higher thermal conductivity than filled silicone references. The influence of thermal transition between matrix material and filler was evaluated by a sandwich‐layer setup. The results suggest that increased thermal conductivity is also caused by the lower thermal resistance and improved interphase connections within the hybrid material. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41037.     

有机杂化纳米CaCO3/SiO2复合粒子对硅橡胶性能的影响

以纳米碳酸钙（CaCO3）为原料,采用溶胶沉积法制备出具有核/壳结构的纳米CaCO3/SiO2复合粒子,并将其原位有机杂化。用纳米CaCO3/SiO2复合粒子替代部分气相法白炭黑作为硅橡胶的补强填料,采用扫描电子显微镜、拉力试验机、热失重仪等对改性硅橡胶的力学性能和热稳定性能进行表征。结果表明：有机杂化剂的种类不同,纳为CaCO3/SiO2复合粒子对硅橡胶的补强效果不同;与用未杂化的纳米CaCO3/SiO2复合粒子取代部分气相法白炭黑的硅橡胶相比,用经A-151杂化的复合粒子取代部分气相法白炭黑的硅橡胶,其拉伸强度、断裂伸长率得到明显改善,耐热性也得到提高;但撕裂强度大大降低。同时还发现,硅橡胶的力学性能及耐热性能在很大程度上也与复合粒子的取代量有关;即使是经KH-570杂化的复合粒子,当取代量小于10%时,其硅橡胶的性能也优于全部用气相法白炭黑补强的硅橡胶。     

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

A 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.     

Synthesis and properties of silicone rubber/organomontmorillonite hybrid nanocomposites

In this article, silicone rubber/organomontmorillonite hybrid nanocomposites were prepared via a melt-intercalation process. The resulting hybrid nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results proved that the organomontmorillonite could be exfoliated into ca. 50-nm thickness and uniformly dispersed in the silicone rubber matrix during the melt-intercalation process. Furthermore, the mechanical properties and thermal stability of the hybrids were very close to those of aerosilica-filled silicone rubber. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1557–1561, 1998     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black

The kinetics of the thermal degradation and thermal stability of conductive silicone rubber filled with conductive carbon black was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 5°C/min. The rate parameters were evaluated by the method of Freeman–Carroll. The results show that the thermal degradation of conductive silicone rubber begins at about 350°C and ends at about 600°C. The thermal degradation is multistage, in which zero‐order reactions are principal. The kinetics of the thermal degradation of conductive silicone rubber has relevance to its loading of conductive carbon black. The activation energies are temperature‐sensitive and their sensitivity to temperature becomes weak as temperature increases. In addition, the conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber without any fillers. Also, conductive silicone rubber filled with conductive carbon black has better thermal stability than that of silicone rubber filled with the same amount of silica. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1548–1554, 2003     

Thermally conductive silicone rubber reinforced with boron nitride particle

Thermally conductive silicone rubber used as elastomeric thermal pad is successfully developed with boron nitride powder as conductive filler. The effects of content and particle size of filler on the thermal conductivity and mechanical property of silicone rubber are investigated. The results indicate that the use of hybrid boron nitride with three different particle sizes at a preferable weight ratio gives silicone rubber better thermal conductivity compared with each boron nitride with single particle size at the same total filler content. Furthermore, scanning electron microscopy, differential scanning calorimeter, thermogravimetric, etc., are used to characterize the morphology, curing behavior, thermal stability, and coefficient of thermal expansion (CTE) of the silicone rubber composites. POLYM. COMPOS., 28:23–28, 2007. © 2007 Society of Plastics Engineers     

Low-stress encapsulants by vinylsiloxane modification

Dispersed silicone rubbers were used to reduce the stress of cresol–formaldehyde novolac epoxy resin cured with phenolic novolac resin for electronic encapsulation application. The effects of structure, molecular weight, and contents of the vinylsiloxane oligomer on reducing the stress of the encapsulant were investigated. Morphology and dynamic mechanical behavior of rubber-modified epoxy resins were also studied. The dispersed silicone rubbers effectively reduce the stress of cured epoxy resins by reducing flexural modulus and the coefficient of thermal expansion (CTE), whereas the glass transition temperature (T_g) was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended device use life. © 1994 John Wiley & Sons, Inc.     

Study of Resistance of Silicone Resin to Heat and Irradiation

Resistance of silicone resin to heat and irradiation was studied. The chemical structure of silicone resin before and after being heated and irradiated was analyzed by Fourier Transform Infrared Spectroscopy (FT-IR). The thermal stability of silicone resin was investigated by thermogravimetric analysis (TG) and differential thermogravimetry analysis (DTG), and its improvement was indicated by TG and DTG analyses of silicone resin after being irradiated by ⁶⁰Co γ-ray under different fluence. The surface morphology, mechanical properties, corrosion resistance and chemical resistance of silicone resin clear paints before and after being heated and irradiated were studied by SEM, EIS et al.     

Morphology and properties of the PA66/PC/silicone rubber composites

The research focused on the PA66/PC/silicone rubber composites. By adding silicone rubber as a toughener, the composites were prepared via dynamic vulcanization. The morphology and properties of the composites were characterized by FTIR, TEM, SEM, XRD, etc. The FTIR spectrum of the composites presented an increase of the 1730, 1240, and 1450 cm^?1 that can be due to the C?O interaction and the presence of the O? CO? O group, and this fact can mean the formation of the PA66–PC copolymer. The crosslinking of silicone rubber in the PA66/PC matrix formed the net‐like structure like semi‐IPN, which is propitious to enhance the interaction between PA66 matrix and PC and in further makes the PC particles embed in PA66 matrix closely. Novel composites are gained with outstanding mechanical properties and high temperature resistance, so the combine toughening by silicone rubber and PC is an ideal toughening system owing to the synergistic effect. In addition, the PA66/PC/silicone rubber/OMMT composite exhibits better flexile strength and flexile modulus without weakening other mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of high loading of titanium dioxide particles on the morphology,mechanical and thermo-mechanical properties of the natural rubber-based composites

The aim of this work was to prepare and characterize the natural rubber vulcanizates containing different amounts of titanium dioxide particles. At first, a rubber mixture was prepared using a laboratory two-roll mill and then samples were vulcanized by a hydraulic press. The formulation of the rubber mixture and rubber-processing technique were based on our earlier investigations. Samples were obtained with different titanium dioxide loadings of 15, 25, 45, and 85 parts by weight per hundred parts of natural rubber. This research is focused on the determination of the influence of different loadings of titanium oxide particles on the chemical structure, morphology, mechanical and thermo-mechanical properties of the natural rubber-based composites. It was found that vulcanizates with different amounts of TiO₂ particles possess good characteristic in terms of all measured properties. The results of Fourier transform infrared spectroscopy analysis showed that the chemical structure of the obtained natural-based composites was not influenced by titanium dioxide particles. The SEM micrographs showed the uniform dispersion of TiO₂ particles in the natural rubber matrix. The agglomeration of filler was seen at the higher contents of TiO₂ in the matrix. The thermogravimetric analysis showed slightly different thermal stability for the obtained natural rubber composites. The dynamic mechanical thermal analysis showed that the prepared materials have similar glass transition temperatures. However, increase in the content of titanium dioxide in the obtained materials is connected with higher energy loss (higher dissipation of energy) during the mechanical work of material and higher cross-link density of the prepared materials.     

Preparation of liquid crystal 4'‐allyloxy‐biphenyl‐4‐ol functionalized MWCNTs and their application on improving mechanical and thermal properties of silicon resin

A liquid crystalline molecule, 4'‐allyloxy‐biphenyl‐4‐ol (AOBPO), was used to functionalize carbon nanotubers (CNTs) via physical means and chemical means, respectively. The physically functionalized CNTs (AOBPO‐CNTs) and chemically functionalized CNTs (AOBPO‐O‐CNTs) were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), fluorescent spectroscopy, and Raman spectroscopy. The two functionalized CNTs were mixed with silicone resin as fillers to fabricate organosilicone nanocomposites. Scanning electron microscopy (SEM) images indicated that the dispersion of CNTs in silicone resin and compatibility of CNTs with silicone resin were improved effectively after functionalization with liquid crystal via physical or chemical means. The thermal and mechanical properties testing indicated that, the chemically functionalized CNTs got a better effect in improvement of mechanical properties of silicon resin than the physically functionalized CNTs, whereas the physically functionalized CNTs was more applicable to enhance the thermal conductivity of silicon resin. The tensile strength of AOBPO‐O‐CNTs/silicon resin increased by 37.8% over that of neat CNTs/silicon resin when the mass fraction of AOBPO‐O‐CNTs was 1.0%, and the elastic modulus of AOBPO‐O‐CNTs/silicon resin increased by 32.8% over that of CNTs/silicon resin if it came up to 2.0%. The thermal conductivity of the resin filled with AOBPO‐CNTs was improved to be 1.176 W (m^?1 K^?1) at the mass fraction of 5.0%, which was enhanced more than 73.2% over that of CNTs/silicon resin. POLYM. ENG. SCI., 56:1118–1124, 2016. © 2016 Society of Plastics Engineers