Preparation of an organomontmorillonite master batch and its application to high‐temperature‐vulcanized silicone‐rubber systems

N,N‐Di(2‐hydroxyethyl)‐N‐dodecyl‐N‐methyl ammonium chloride was used as an intercalation agent to treat Na⁺‐montmorillonite and form a novel type of organic montmorillonite (OMMT). An OMMT master batch (OMMT‐MB) was prepared by solution intercalation and was used in the preparation of high‐temperature‐vulcanized silicone rubber (HTV‐SR)/OMMT‐MB nanocomposites. The properties, such as the tensile and thermal stability, were researched and compared with those of composites directly incorporated with OMMT or aerosilica. A combination of Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and transmission electron microscopy studies showed that HTV‐SR/OMMT‐MB composites were on the nanometer scale, and their structure was somewhat hindered by the presence of OMMT. The results showed that the tensile properties of HTV‐SR/OMMT‐MB and HTV‐SR/OMMT systems were better than those of pure HTV‐SR. Compared with those of HTV‐SR/OMMT‐20%, the tensile strength and elongation at break of HTV‐SR/OMMT‐MB‐20% were improved about 1.5 and 0.9 times, respectively. This was probably due to the nanoeffect of the exfoliated silicate layers. Moreover, the tensile strength of HTV‐SR/OMMT‐MB‐20% was nearly equal to that of HTV‐SR/aerosilica‐20%, and the elongation at break even showed much improvement. Additionally, the thermal degradation center temperature of the HTV‐SR/OMMT‐MB‐20% nanocomposite was increased by 30°C compared with that of the HTV‐SR/OMMT‐20% composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of hyperbranched organo‐montmorillonite and its application into high‐temperature vulcanizated silicone rubber systems

N,N‐Di(2‐hydroxyethyl)‐N‐dodecyl‐N‐methyl ammonium chloride was used as intercalation agent to treat Na⁺‐montmorillonite and form a type of organic montmorillonite (OMMT). Hyperbranched OMMT (HOMMT) was prepared by condensation reaction between OMMT and the monomer we synthesized. It was then used in the preparation of high‐temperature vulcanizated silicone rubber (HTV‐SR)/HOMMT nanocomposite. Different types of HTV‐SR/HOMMT nanocomposites were prepared with different amounts of HOMMT and compared with the composites directly incorporated with OMMT. Tensile properties such as tensile strength, elongation at break, permanent distortion, and shore A hardness were researched and compared. A combination of Fourier transform infrared spectroscopy, wide angle X‐ray diffraction, and transmission electron microscopy studies showed that HTV‐SR/HOMMT composites were on the nanometer scale, and the structure of HTV‐SR was not interfered by the presence of HOMMT. Results showed that the tensile properties of HTV‐SR/HOMMT systems were better than that of the HTV‐SR/HOMMT and HTV‐SR. This was probably due to the surface effect of the exfoliated silicate layers and anchor effect of HOMMT in the SR matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

硅橡胶隔热复合材料的制备及性能

采用空心玻璃微珠（HGB）和膨胀蛭石（EVMT）作为隔热填料,分别与高温硫化硅橡胶（HTV）共混制备HGB/HTV和EVMT/HTV隔热复合材料,并考察了隔热填料的种类和用量对隔热复合材料的隔热性能和力学性能的影响。结果表明,随着HGB和EVMT用量的增加,隔热复合材料的导热性能明显下降。相比于HTV试样,当HGB与HTV的质量比为20/100,EVMT与HTV的质量比为10/100时,隔热复合材料的导热系数分别下降了20.44%和12.34%。HGB和EVMT均能提高HTV隔热复合材料的100%定伸应力和邵尔A硬度,降低其拉伸强度与扯断伸长率。当HGB与HTV的质量比为20/100,EVMT与HTV的质量比为10/100时,隔热复合材料的拉伸强度分别为10.51 MPa和11.59 MPa,邵尔A硬度分别为71.6和59.1。     

Effects of crosslinking reaction and extension strain on the electrical properties of silicone rubber/carbon nanofiller composites

Stretchable conductive silicone rubber (SR) composites are important in wearable electronic devices and the crosslinking of SR composites is necessary for their applications. But the effect of the crosslinking reaction on the electrical conductivity of SR composites is rarely reported. In this article, the effect of crosslinking reaction on the electrical conductivity of SR composites filled with conductive carbon black, carbon nanotubes, and graphene are studied. The crosslink density of SR composites increases with increasing curing time, but the electrical conductivity decreases sharply at the early stage of crosslinking, especially for SR/conductive carbon black composite, which is ascribed to the reaggregation of conductive nanofillers in SR during the crosslinking process. The elastic modulus of the three SR composites gradually increases while the elongation at break decreases with increasing curing time, and the SR/carbon black composite shows ultra-high elongation at break (1578%). In addition, SR/graphene composite is more sensitive to the extension strain than SR/carbon black and SR/carbon nanotubes composites, and its gauge factor is 414 at the strain ranges of 3–25%. This research work brings a new method to optimize the crosslinking structure of conductive SR composites.     

Effect of incorporation of carbon fiber and silicon carbide powder into silicone rubber on the ablation and mechanical properties of the silicone rubber‐based ablation material

This study examined the effects of the incorporation of carbon fiber (CF) and silicon carbide powder (SCP) into a high temperature vulcanized (HTV) silicone rubber, poly(dimethylsiloxane) (PDMS) containing vinyl groups on the ablation properties using an oxy‐acetylene torch test. The ablation test results showed that CF enhanced the hardness of the char formed on the composite surface during the oxy‐acetylene torch test and was an important factor determining the ablation properties. SCP was also beneficial in enhancing the surface char hardness of the HTV/CF composite. A new method was devised to evaluate the ablation properties more objectively by measuring the time elapsed for a rectangular‐shaped silicone rubber composite with specimens loaded with a constant weight to burn and fail off during the oxy‐acetylene torch test. The mechanical properties of the silicone rubber composites were also examined as a function of the additive content using a universal test machine (UTM). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Investigation of polysiloxanes containing phenylethynyl groups as cross‐linkers of heat‐curable silicone rubber

Hydrosilation‐curing vulcanizates (HCV) and peroxide‐curing vulcanizates (PCV) were prepared respectively by using polysiloxanes containing phenylethynyl groups (PE‐PDMS) as cross‐linkers. The mechanical properties and average molecular weights of effective units (M̄_c) of HCV and PCV were measured. The experimental results show that PE‐PDMS can be used as cross‐linkers of heat‐curable silicone rubber instead of C gum, and when adding suitable amounts of PE‐PDMS, the vulcanizates exhibited good mechanical properties. The tear strength of some vulcanizates reached 30.0 kN/m, the tensile strength 11.7 MPa, the modulus at 100% extension 3.3 MPa, and the permanent deformation is low. PE‐PDMS also has cure retardation to hydrosilation‐cure silicone rubber and thus can prolong the shelf time of stocks. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1554–1557, 2000     

Preparation and properties of peroxide dynamically vulcanized poly(vinylidene fluoride)/silicone rubber/zinc dimethacrylate composites

Composites of poly(vinylidene fluoride) (PVDF), silicone rubber (SR), and zinc dimethacrylate (ZDMA) were prepared via peroxide dynamic vulcanization. The effect of ZDMA loading on the morphology, mechanical properties, and rheology of the PVDF/SR/ZDMA composite was investigated. It was found that, some rubber particles with different diameters were aggregated and distributed in the PVDF matrix. The average diameters of rubber particles increased when ZDMA was incorporated into the PVDF/SR blend. A higher content of ZDMA seemed to show a favorable effect on the mechanical properties of PVDF/SR/ZDMA composites. The tensile strength, flexural strength, and flexural modulus of PVDF/SR/ZDMA composites decreased with increasing the ZDMA loading, which was due to the decreased tensile strength and total crosslink density of SR/ZDMA composite and the increased diameter of rubber particles, but the compatibility and interfacial interaction between PVDF phase and SR phase were obviously improved, which contributed to improved the Izod impact strength. In addition, the rheology analysis also suggested that interfacial adhesion between PVDF phase and SR phase was improved due to the incorporation of ZDMA. POLYM. COMPOS. 37:1093–1100, 2016. © 2014 Society of Plastics Engineers     

Influence of fluorine interface to the crystallization of poly (vinylidene fluoride)/silicone rubber/fluororubber elastomeric tertiary blends via dynamical curing

ABSTRACT

We demonstrate the influence of fluorine interface to the crystallization of poly(vinylidene fluoride) (PVDF)/silicone rubber (SR)/fluororubber (FKM) tertiary dynamic curing blends. In contrast to PVDF/SR binary blend, the average size of PVDF spherulites turns smaller and the crystallization rate is lower in PVDF/SR/FKM tertiary blend when more fluororubber component was added into the blends at the same crystallization temperature. Incorporation of FKM does not change the crystalline form of PVDF in the blends. The resulting mechanical properties of tensile strength, flexural strength, Izod impact strength and elongation at break for PVDF/SR/FKM tertiary blends are enhanced compared with PVDF/SR binary blend.     

Functionalized multi‐wall carbon nanotubes/silicone rubber composite as capacitive humidity sensor

Functionalized multi‐wall carbon nanotubes (MWCNTs) treated by mixed acids have been used to develop a capacitive humidity sensor based on MWCNTs/silicone rubber (SR) composite film. The MWCNTs/SR composites were prepared through conventional solution processed method. The micrographs of MWCNTs/SR composites were observed by transmission electron microscopy (TEM) and scanning electron microscope. The FT‐IR spectra demonstrated the successfully grafting of ? OH groups on the treated MWCNTs. The sensing properties of the composite at different relative humidity (RH) and frequency were characterized and linear sensing responses of the MWCNTs/SR composites to RH were observed. The treated MWCNTs/SR composite film (Tr‐film) had higher sensitivity than that of the untreated MWCNTs/SR composite film (Un‐film). Experimental data indicate that the Tr‐film exhibits an excellent long‐term stability, small hysteresis, and fine reproducibility. The response and recovery time of the Tr‐film were 30 and 27 s, respectively. Thereby, such Tr‐film had potential applications as humidity sensors. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40342.     

Effect of surface chemistry and morphology of silica on the thermal and mechanical properties of silicone elastomers

In this study, high‐temperature vulcanized silicone rubbers (HTV‐SRs) using fumed silica (FSi), precipitated silica (PSi), and modified precipitated silica (MPSi) as reinforcing fillers were prepared. The effect of morphology and surface chemistry of the silica on the thermal and mechanical properties of the resultant silicone rubbers was investigated using curing rheometer, scanning electron microscopy, mechanical test, and dynamic mechanical analysis. The thermo‐oxidative stability and solvent resistance of the vulcanized silicone rubbers were further evaluated via heat ageing test, extraction, and swelling experiments. It is shown that the mechanical properties (tensile modulus and tensile strength) of the as‐prepared HTV‐SRs are in the order of FSi > PSi > MPSi, which could be attributed to the molecular interaction between the filler and the matrix. FSi has the highest surface area, which enhances the hydrogen bonding interaction between the filler and the silicone matrix; while MPSi, in which part of Si? OH groups have been consumed during modification, shows the weakest interaction among the three. The filler–matrix interaction could also explain the lowest swelling and sol fraction in FSi‐filled HTV‐SR, and the low viscosity and good processibility of PSi‐ and MPSi‐filled HTV‐SR. Furthermore, it is also shown that the MPSi‐filled HTV‐SR exhibits the highest retention of mechanical properties after thermal aging at 250 °C for 24 h, which could be attributed to the lowest acidity of the fillers. The possible mechanism for acid catalyzed hydrolytic chain scission and intramolecular chain backbiting has been proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46646.     

Synergistic effects between red phosphorus and alumina trihydrate in flame retardant silicone rubber composites

Abstract

The synergistic flame retardant effects between red phosphorus (RP) and alumina trihydrate (ATH) in silicone rubber (SR) composites were evaluated using limiting oxygen index, UL 94 rating, cone calorimeter, thermogravimetric analysis and digital photographs. It has been found that the SR composite containing only ATH does not show good flame retardancy at 39·0 wt-% loading. The cone calorimeter results showed that the heat release rate, mass loss rate, mass and total heat release of SR/ATH/RP composites decrease greatly in comparison with the SR/ATH composites. The digital photographs demonstrated that 1·0 wt-%RP could promote the formation of the homogenous and compact char layer. Thus, a suitable amount of RP has a synergistic effect with ATH in the flame retardant SR composite system.     

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     

Electrically Conductive Silicone/Organic Polymer Composites

Electrically conductive silicone elastomers carbon composites are the current state-of-art for electrically conductive elastomers. The combination of inorganic and organic polymers leads to a highly electrically conductive composite which has improved thermal stability. In this work, composites were formed, from two different classes of room temperature vulcanizing inorganic silicone polymers (vinyl & hydroxyl methyl silicone elastomers) (RTV-SI), which undergo curing by addition and condensation curing respectively, by a mixing and casting method. The organic polymer, which is the camphor sulfonic acid doped polyaniline (Pani.CSA) was synthesized by oxidative polymerization of aniline. By selecting RTV-SI system, the possibility of oxidative interaction of Pani.CSA that takes place at high temperature with curatives (peroxides) is ruled out. This helps to retain the conductivity of Pani.CSA and avoids the curing retardation of rubber. The concentration of Pani.CSA in the composites was varied from 20–40 phr. The electrical, thermal, morphological and short term stress - strain properties of the composites were studied after curing. A sharp decrease was observed in the resistance from ～10?15 Ω for blank silicone rubber to 27–31.5 KΩ for the filled composites with good thermal stability. The homogeneity of the composites was verified from SEM. The hardness of the composites was observed to increase by 3–5 on the Shore A scale. Tensile strength, tear strength and rebound resilience all decreased slightly.     

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

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

双金属稀土促进剂对丁苯橡胶/天然橡胶胎面胶的影响

通过配位反应制备得到双金属硫化促进剂二乙基二硫代氨基甲酸锌镧配合物(ZnLaDC),在不添加传统活化体系氧化锌(ZnO)/硬脂酸(SA)的情况下,考察了ZnLaDC用量对丁苯橡胶(SBR)/天然橡胶(NR)胎面胶复合材料硫化特性及物理机械性能的影响,并与传统硫化体系二乙基二硫代氨基甲酸锌(ZnDC)/ZnO/SA制备的硫化胶性能进行了对比。结果表明,随着ZnLaDC用量的增加,SBR/NR胎面胶复合材料的硫化特性、压缩疲劳生热性能及耐磨性得到有效提高,当ZnLaDC用量为5份时,复合材料的综合性能最佳。与传统硫化体系ZnDC/ZnO/SA制备的硫化胶相比,采用ZnLaDC制备的硫化胶具有更优异的静态力学性能及耐切割性。     

加成型高温硫化液体硅橡胶的气泡消除及性能研究

研究了交联剂、催化剂和消泡剂等对加成型高温硫化(HTV)液体硅橡胶气泡消除及性能的影响。结果表明：随着交联剂与催化剂用量增加,硅橡胶的固化时间变短,产生气泡增多;使用消泡剂可有效抑制硅橡胶中气泡的产生。当交联剂用量为0.95phr、催化剂用量为1.05phr、消泡剂4用量为4‰时,加成型HTV液体硅橡胶的综合性能最佳。     

Thermo-oxidative stability of rubber magnetic composites cured with sulfur,peroxide and mixed curing systems

Rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber. The sulphur, peroxide and mixed sulphur/peroxide curing systems were applied for cross-linking of rubber compounds. The main goal of the work was to investigate the influence of the curing system composition on the physical–mechanical and magnetic properties of prepared composites. The thermo-oxidative stability of the composite materials was assessed by evaluation of thermogravimetric analysis and ageing test. The results showed that the composition of curing system influences the physical–mechanical properties of composites, but in strong dependence on the type of rubber matrix. After exposure of test sample to the conditions of thermo-oxidative ageing, the changes in composite properties were also recorded. The influence of thermo-oxidative degradation was more pronounced in the case of composites based on NR, where the sample cured only with peroxide system was almost completely degraded in the given conditions of ageing. On the other hand, the magnetic characteristics of composites seem to be influenced neither by curing system composition nor by ageing.     

Mechanical properties and processibilty of glass‐fiber‐, wollastonite‐, and fluoro‐rubber‐reinforced silicone rubber composites

The reinforcement of silicone rubber (SR) imparted by different types of fillers was investigated. Glass fiber (GF), wollastonite and fluoro rubber (FR) as nontraditional filler for rubber were compounded SR and mechanical properties of the prepared composites were evaluated. The addition of silane pretreated GF and wollastonite into SR, tensile strength, abrasion resistance and tear strength of the composites improved considerably. The improvement in the properties was assigned to an increased interaction between the filler and the polymer matrix. For the SR/FR composites system, the elongation at break was increase with increasing concentrations of FR due to sponge like structure resulting from poor compatibility between the two components. To investigate the production potential of extrusion processing method, prepared composites were extruded in a rod type sample. During the curing stage, GF, wollastonite and FR lead to the formation of void in the matrix resin. When GF and wollastonite were treated with silane, the void formations were reduced significantly. The silane treatment process improves not only mechanical strength but also processibility of SR composites in dry conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of KH550 on the Preparation and Compatibility of Carbon Fibers Reinforced Silicone Rubber Composites

Silicone rubber has good heat resistance, but its mechanical properties are poor. To improve the mechanical properties of the silicone rubber, the carbon fiber / silicone rubber composites were prepared in this paper, in which the silicone rubber was used as the matrix, the high-performance carbon fiber (CF) treated with coupling agent is used as the reinforcement. The best composite formulation, the types and content of coupling agent are determined by testing mechanical properties of the composites. The morphology structures of the composites were observed by scanning electron microscope (SEM), the compatibility between carbon fiber and silicone rubber was studied by infrared spectrum analysis (IR), dynamic thermal mechanical analysis (DMA) and X-ray photoelectron spectroscopy (XPS). The results show that the best composite formulation is silicone rubber of 100 phr, carbon fiber of 12 phr, coupling agent KH550 of 2.5 phr. The best first curing conditions are at 175 ^°C under 10 MPa for 30 min, the postcuring conditions are at 200 ^°C for 2h. The compatibility between carbon fiber treated with KH550 and silicon rubber is the best by SEM, IR, DMA and XPS analysis, and confirm that the coupling agent KH550 plays a compatilizer role in the preparation process of the carbon fiber/silicone rubber composites.     

影响HTV硅橡胶撕裂强度的因素

考察了白炭黑种类、羟基硅油用量、含氢硅油用量以及不同乙烯基含量生胶并用对热硫化(HTV)硅橡胶撕裂强度的影响。结果显示,气相法白炭黑的补强效果强于沉淀法白炭黑,且比表面积越大,硅橡胶的撕裂强度越高;随着羟基硅油加入量的增加,硅橡胶的撕裂强度先增后趋于稳定;含氢硅油的用量对HTV硅橡胶的撕裂强度基本没有影响;高乙烯基含量生胶和低乙烯基含量生胶并用能显著提高HTV硅橡胶的撕裂强度。较佳配方是:166 g 110-0生胶,4 g 112生胶、80 g QS-102气相法白炭黑、8.5 g羟基硅油、1.0 g含氢硅油、0.5 g乙烯基硅油,此时,HTV硅橡胶的撕裂强度达到21 KN/m。