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.     

Thermal and mechanical properties of liquid silicone rubber composites filled with functionalized graphene oxide

To improve the thermal and mechanical properties of liquid silicone rubber (LSR) for application, the graphene oxide (GO) was proposed to reinforce the LSR. The GO was functionalized with triethoxyvinylsilane (TEVS) by dehydration reaction to improve the dispersion and compatibility in the matrix. The structure of the functionalized graphene oxide (TEVS‐GO) was evaluated by Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD), and energy dispersive X‐ray spectroscopy (EDX). It was found that the TEVS was successfully grafted on the surface of GO. The TEVS‐GO/LSR composites were prepared via in situ polymerization. The structure of the composites was verified by FTIR, XRD, and scanning electron microscopy (SEM). The thermal properties of the composites were characterized by TGA and thermal conductivity. The results showed that the 10% weight loss temperature (T₁₀) increased 16.0°C with only 0.3 wt % addition of TEVS‐GO and the thermal conductivity possessed a two‐fold increase, compared to the pure LSR. Furthermore, the mechanical properties were studied and results revealed that the TEVS‐GO/LSR composites with 0.3 wt % TEVS‐GO displayed a 2.3‐fold increase in tensile strength, a 2.79‐fold enhancement in tear strength, and a 1.97‐fold reinforcement in shear strength compared with the neat LSR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42582.     

Improved flame retardancy and ceramifiable properties of PE composites by the combination of aluminum hypophosphite and zinc borate

Ceramifiable polyolefin materials protect circuits by forming compact ceramic layers under fire conditions, and can have an excellent application prospect in the refractory cable field. In this paper, Aluminum hypophosphite (AHP) and zinc borate (ZB) were added to further improve flame retardancy and ceramifiable properties of polyethylene (PE)/silicon powder (SP)/wollastonite (WS)/glass frits (GF) composites. The LOI values of composites with AHP/ZB can reach 23.5%, significantly higher than that of PE/SP/WS/GF composites (19.6%). The thermal stability behavior and char yield behaviors of composites could also be characterized by the TG test. The incorporation of AHP/ZB enhances the flexural strength of residue formed at 1000°C from 0.1 to 20.5 MPa. In addition, a new crystal is formed at high temperatures and is identified as the calcium aluminum phosphate phase [CAP, Ca₉Al (PO₄)₇] by XRD analysis. The flow of molten ZB accelerates the reaction of AHP and WS, and this eutectic reaction promotes the formation and stability of ceramics. Furthermore, the SEM analysis reveals the fluxing effect of ZB at low temperatures and AHP at high temperatures. The incorporation of AHP/ZB with a ratio of 1:1 could effectively avoid the vitrification of ceramics and improve their dimensional stability.     

Thermal stability and ablation properties of silicone rubber composites

Effects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy‐acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS₄: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS₄ layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS₄ composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy‐acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF ≈ HTV/MMTS₄ < HTV/CF/MMTS₄ ≈ HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS₄ compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS₄ specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal stability and ablation properties study of aluminum silicate ceramic fiber and acicular wollastonite filled silicone rubber composite

The thermal stability and ablation properties of silicone rubber filled with silica (SiO₂), aluminum silicate ceramic fiber (ASF), and acicular wollastonite (AW) were studied in this article. The morphology, composition, and ablation properties of the composite were analyzed after oxyacetylene torch tests. There were three different ceramic layers found in the ablated composite. In the porous ceramic layer, the rubber was decomposed, producing trimers, tetramers, and SiO₂. ASF and part of AW still remained and formed a dense layer. The SiO₂/SiC filaments in the ceramic layer reduced the permeability of oxygen, improving the ablation properties of the composites. The resultant ceramic layer was the densest, which acted as effective oxygen and heat barriers, and the achieved line ablation rate of the silicone composite were optimum at the proportion of 20 phr/40 phr (ASF/AW). Thermogravimetric analysis (TGA) confirmed that thermal stability of the composites was enhanced by the incorporation of ASF and AW. The formation of the ceramic layer was considered to be responsible for the enhancement of thermal stability and ablation properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39700.     

Aluminum powder filled nitrile rubber composites

Effect of aluminum powder on the properties of nitrile rubber (NBR) composites and the role of bonding agent viz. hexamethylene tetramine‐resorcinol has been investigated. Shore A hardness of the aluminum powder filled composites is lower than that of high abrasion furnace (HAF) and acetylene black (ACB) filled nitrile rubber composites and can be increased by the addition of bonding agent. Equilibrium swelling decreased considerably by the use of hexamethylene tetramine‐resorcinol, suggesting an improved nitrile rubber–aluminum powder adhesion. A marked increase in thermal conductivity is obtained with the incorporation of aluminum powder. Increased thermal conductivity reduced the additional time needed for the vulcanization of thick rubber articles and imparted uniform curing throughout the material. In nitrile rubber, the modulus and tensile strength followed the order HAF > ACB > aluminum powder. Combination of HAF and aluminum powder in NBR gave composites with good thermal conductivity and mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3156–3161, 2004     

Improving properties of silicone rubber composites using macromolecular silane coupling agent (MMSCA)

Two types of vinyl silicone oil (VSO), allyl‐capped hyperbranched polycarbosilane (HBP), and triethoxysilane (TES) were employed to synthesize macromolecular silane coupling agent (MMSCA) by hydrosilylation. VSOs, HBP, and the hydrosilylated products were used as crosslinker, respectively, to improve weak mechanical properties of silicone rubber (SR). Structures of the crosslinkers were studied by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Crosslinking density test and scanning electron microscope (SEM) observation showed an increased interaction between silicone rubber and fumed silica by the use of MMSCA. Mechanical properties of the resulted composites using MMSCAs were increased to varying degrees compared with those possessing crosslinkers without ethoxy group. MMSCAs were effective for further property enhancements of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43415.     

Improving properties of ceramic silicone rubber composites using high vinyl silicone oil

Reactive high vinyl silicone oil (HVSO) was selected to prepare the ceramic silicone rubber composites. The effects of HVSO on the mechanical properties and thermal stabilities of ceramic silicone rubber composites were investigated. The structures of the cross‐linked network of silicone rubber with or without HVSO were studied. The intermolecular space of silicone rubber was enlarged, and the cross‐linked point was concentrated by addition of HVSO, which was demonstrated by cross‐linking densities, scanning electron microscope (SEM) images, and dynamic mechanical analysis (DMA). The cross‐linked network model was formed with the slipping of the cross‐linked points along with the silicone rubber chain. Mechanical properties of composites were enhanced by the formation of this cross‐linked network. The tear strength, tensile strength, and elongation at break of the composites were increased by 18.5%, 13.2%, and 37.4% by the adding of 2 phr HVSO, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41864.     

氮化硼填充甲基乙烯基硅橡胶导热复合材料的性能

用0.3,6.0,20.0μm 3种粒径的氮化硼(BN)(质量比为1:1:3)混合填充甲基乙烯基硅橡胶(MVQ),研究了BN用量对MVQ导热系数、热失重、热膨胀系数、硫化特性的影响.结果表明,随着BN用量的增加,MVQ的导热系数和热分解温度升高,热失重量和热膨胀系数明显降低,但对MVQ的硫化反应影响不大;当BN填充量为150份时,MVQ的综合性能较佳.     

Magnetically aligning multilayer graphene to enhance thermal conductivity of silicone rubber composites

The increasing demand for packaging materials calls for new technologies to achieve excellent thermal conductivity of polymer composites with low content of thermal conductive filler. This article prepared a kind of magnetically functionalized multilayer graphene (Fe₃O₄@MG) via electrostatic interactions, which efficiently enhanced the thermal conductivity of silicone rubber (SR) composites by the alignment of Fe₃O₄@MG in an external magnetic field. The morphology and structure of the Fe₃O₄@MG together with the thermal conductivity of corresponding Fe₃O₄@MG/SR composites were systematically investigated by SEM, TEM, XRD, elemental mapping, and thermal conductivity tester. The obtained results showed that Fe₃O₄@MG was induced to form chain-like bundles in silicone rubber matrix under the applied magnetic field, which enhanced the MG–MG interaction, and formed effective thermal pathways in the alignment direction. Furthermore, as coating mass ratio of Fe₃O₄@MG increased, the thermal conductivity of randomly oriented Fe₃O₄@MG/silicone rubber composites (R-Fe₃O₄@MG/SR) decreased gradually, whereas the through-plane thermal conductivity of vertically aligned Fe₃O₄@MG/silicone rubber composites (V-Fe₃O₄@MG/SR) increased even filled with same contents of thermal conductive filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47951.     

Electrically insulating ZnOs/ZnOw/silicone rubber nanocomposites with enhanced thermal conductivity and mechanical properties

In this work, hybrids of surface modified zinc oxide spherical (ZnOs) nanoparticles and tetrapod‐shaped whiskers (ZnOw) were incorporated into the silicon rubber (SR) to prepare the ZnOs/ZnOw/SR nanocomposites. The incorporation of the ZnOs/ZnOw facilitated the formation of three‐dimensional thermally conducting network. It was found that the thermal conductivity of the ZnOs/ZnOw/SR reached up to 1.309 W m^?1 K^?1 when the ZnOs/ZnOw content was 20 vol % (V_m‐ZnOs:V_ZnOw = 7:3), which was nearly 6.5 times that of the pristine SR. The dielectric and resistivity measurements showed that the incorporation of the ZnOs/ZnOw hybrids did not cause much change in the electrical properties. In addition, the results show that the tensile strength of ZnOs/ZnOw/SR nanocomposites is higher than that of pristine SR. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46454.     

Dielectric and microwave properties of carbon nanotubes/carbon black filled natural rubber composites

Abstract

Natural rubber (NR) based nanocomposites containing a constant amount (50 phr) of standard furnace carbon black and carbon nanotube (CNT) at a concentration from 1 to 5 phr have been prepared. Their dielectric (dielectric permittivity and dielectric loss) and microwave properties (coefficients of absorption and reflection of the electromagnetic waves and electromagnetic interference shielding effectiveness) have been investigated in the 1–12 GHz frequency range. The results achieved allow recommending CNTs as second filler for NR based composites to afford specific absorbing properties.     

A comparison of ablative resistance properties of liquid silicone rubber composites filled with different fibers

Flexible ablative materials play a key role in thermal protection systems to protect space vehicles during hypersonic flight missions. In this work, epoxy resin modified liquid silicone rubber was adopted as elastomeric matrix. Two inorganic fibers (carbon fibers (CF) and quartz fibers (QF)) and two organic fibers (aramid fibers (AF) and poly (p-phenylene benzobisoxazole) fibers (PBO)) were chosen as functional fillers. The ablation resistance and thermal insulation properties were evaluated using oxyacetylene torch test. Microstructure and phase composition of the char layer was fully characterized to investigate the ablation mechanism. SEM observations revealed that the fibers are well dispersed and integrated in the matrix. TGA analysis indicated that the inorganic fibers possess significantly higher thermal stability than organic fibers. In addition, a molten silica film can be formed on the material surface, which can exert a better thermal protection effect on the matrix. Furthermore, the ablation test shows that the linear ablation rate decreases first and then increases with an increase of fiber content. This work provides basic data to guide optimal selection of fibrous ablatives to enhance ablation performance.     

Effect of hybrid hollow microspheres on thermal insulation performance and mechanical properties of silicone rubber composites

Hollow microspheres (HM) of ceramic, silica, and glass‐filled silicone rubber (SR) composites were prepared, and the effects of hybrid HM on thermal and mechanical properties of composites were investigated. The results indicate that hybrid HM can effectively improve the thermal insulation property of HM/SR composites. Especially, for sample 15S, the thermal conductivity and thermal degradation temperature reached 0.1273 W/m K and 521 °C (45 °C higher than that of neat SR), respectively. Besides, thermal insulation performance was improved, showing as a temperature of 103.2 °C after 15 min heating, which is 37.8 °C lower than that of SR. The tensile strength of composites was enhanced from 1.92 MPa at 11.56 vol % hollow silica microspheres (HSM) loading to 3.08 MPa at 21.88 vol % HSM loading. Moreover, the compressive strength was improved from 3.33 to 5.68 MPa by introducing more hollow ceramic microspheres into the matrix, in this case, from 7.79 to 15.33 vol %. Furthermore, the failure mechanism was analyzed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46025.     

Effect of hollow glass beads on density and mechanical properties of silicone rubber composites

In this work, low density hollow glass beads (HGB)/silicon rubber (SR) composites were prepared by solution method and flocculation process. The prepared samples were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, tensile test, and friction test. The results show that the densities of SR composites decrease from 1.140 to 0.792 g/cm³ with the addition of HGB. By comparing theoretical density with true density, it can be estimated that the ratio of shattered HGB increase from 8.79% to 24.76%. Especially, the mechanical properties of SR composites were improved by surface modification of HGB. By adding surface-modified HGB at 5 and 10 wt%, the tensile strengths of SR composites were enhanced by 17.8% and 28.2%, respectively. In addition, tear strength, shore A hardness, compression set, and friction property were significantly ameliorated. Furthermore, the mechanism of surface-modified HGB in mechanical properties was analyzed.     

Processibility and mechanical properties of micronized polytetrafluoroethylene reinforced silicone rubber composites

Various micronized polytetrafluoroethylene (PTFE) powders were compounded with silicone rubber (MQ) and mechanical properties of the MQ/PTFE composites were evaluated. The fracture surface morphologies of prepared composites were also investigated using scanning electron microscopy (SEM). At a level of only 5 wt %, the fractured surface of MQ/PTFE composites show layered structure morphology. This structure effectively improves the tear strength of MQ but it also led to lower the tensile properties of the composites. The addition of fluorosilicone rubber (FMQ) as compatibilizer, tensile and tear strength of the composites improved considerably. However, tensile properties of the MQ/solution of sodium in liquid ammonia treated PTFE composite decreased compared with those of the untreated one. To investigate the production potential of extrusion process, an electric wire was extruded with MQ/PTFE/FMQ composites. During the curing process, volatile molecules lead to bubble and void formation of extruded layer depending on the filler shapes. The spherical PTFE powder was suitable for extrusion process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of palm ash loading and maleated natural rubber as a coupling agent on the properties of palm‐ash‐filled natural rubber composites

Natural rubber composites were prepared by the incorporation of palm ash at different loadings into a natural rubber matrix with a laboratory‐size two‐roll mill (160 × 320 mm²) maintained at 70 ± 5°C in accordance with the method described by ASTM D 3184–89. A coupling agent, maleated natural rubber (MANR), was used to improve the mechanical properties of the natural rubber composites. The results indicated that the scorch time and cure time decreased with increasing filler loading, whereas the maximum torque exhibited an increasing trend. Increasing the palm ash loading increased the tensile modulus, but the tensile strength, fatigue life, and elongation at break decreased. The rubber–filler interactions of the composites decreased with increasing filler loading. Scanning electron microscopy of the tensile fracture surfaces of the composites and rubber–filler interaction studies showed that the presence of MANR enhanced the interfacial interaction of the palm ash filler and natural rubber matrix. The presence of MANR also enhanced the tensile properties and fatigue life of palm‐ash‐filled natural rubber composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effective thermal conductivity behavior of filled vulcanized perfluoromethyl vinyl ether rubber

The effective thermal conductivity behavior of vulcanized perfluoromethyl vinyl ether (PMVE) rubber filled with various inorganic fillers was investigated and analyzed with thermal conductivity models. Experimental results showed that there was no significant improvement in the thermal conductivity of PMVE rubber if the intrinsic thermal conductivity of the fillers was greater than 100 times that of the rubber matrix, and this agreed with the prediction of Maxwell's equation. The thermal conductivity of PMVE rubber filled with larger size silicon carbide (SiC) particles was greater than that of PMVE filled with smaller size SiC because of the lower interfacial thermal resistance, and there existed a transition filler loading at about 60 vol %. It was also found that flocculent graphite was the most effective thermally conductive filler among the fillers studied. A modified form of Agari's equation with a parameter independent on the units used was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of the particle size of Al2O3 on the properties of filled heat‐conductive silicone rubber

An elastomeric thermal pad with a thermal conductivity of 1.45 W/m K, needed for the heat dissipation of microelectronics, was obtained with hybrid alumina of different particle sizes as a filler and silicone rubber (vinyl‐end‐blocked polymethylsiloxane) as the matrix. The effects of the amount, particle size, and mixing mass ratio of the filler particles on the thermal conductivity and mechanical properties of silicone rubber were investigated. The results indicated that the thermal conductivity of the rubber filled with larger particles was superior to that of the rubber filled with the smaller grain size, and the rubber incorporated with a mixture of hybrid particles at a preferable mass ratio exhibited higher thermal conductivity than the rubber for which a filler with only a single particle size was used. In addition, the surface treatment of the hybrid filler with 3‐methacryloyloxypropyltrimethoxysilane could increase the thermal conductivity of the composite rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1312–1318, 2007     

Modification of liquid silicone rubber by octavinyl‐polyhedral oligosilsesquioxanes

To develop an efficient, simple, and biocompatible method for improving the thermal and mechanical properties of an addition‐type liquid silicone rubber (LSR), octavinyl‐polyhedral oligosilsesquioxane (OPOSS) modified LSR samples were prepared through the addition of 0.5–4.0 wt % OPOSS as a modifier to a platinum‐based silicone curing system before vulcanization. The characterization and measurement of the OPOSS and LSR samples were carried out by Fourier transform infrared spectroscopy, X‐ray diffraction, NMR, gas chromatography/mass spectrometry (electron impact ionization), scanning electron microscopy, thermogravimetric analysis/differential scanning calorimetry, and universal testing. The experimental results show that the crosslinking of the OPOSS and LSR polymer had a significantly positive effect on the thermal and mechanical properties. Compared with the unmodified sample, its tensile strength was enhanced by 423–508%, its tear resistance was increased from 22 to 44%, the residue at 600 °C was increased by 36–75% in an N₂ atmosphere and 8–65% in an air atmosphere, respectively. These results were obviously superior to those from other similar reported methods that used larger molecular or nonreactive polyhedral oligosilsesquioxane (POSS) derivatives as modifiers at similar POSS loadings. Furthermore, a significant correlation was found between the loading rate of OPOSS and the thermal properties. However, the mechanical properties seemed negatively correlated with the OPOSS content within the experimental range; this may have been due to a material defect caused by the uneven distribution and agglomeration. The results of this study proved that the incorporation of OPOSS into an LSR polymer matrix by a hydrosilylation reaction could be an efficient way to improve the mechanical properties, thermal stability, and biocompatibility of LSR in the future. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43906.