Vulcanization and Thermal Properties of Silicone Rubber/Fluorine Rubber Blends

With the rapid development of automobile, aviation, aerospace, machinery and other fields, rubber products used in these fields required to meet higher requirements. Fluorine rubber (FKM) and silicone rubber (MVQ) have excellent performance in some areas. However, the FKM is poor in low-temperature resistance and processing performance, limiting its applicability. Although the MVQ has a wide range of temperature and excellent processing performance, but its mechanical properties and oil resistance are not good. In this work, the MVQ/FKM blends were prepared by two different mechanical blending methods. The effects of the mixing process, mass ratio, curing system and conditions of the blends were studied. The chemical compositions of the blends were analyzed by infrared spectroscopy (IR). The compatibility and the thermal properties of the blends were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The results showed that the mechanical properties, compatibility and thermal stability of the blends were the best when they were prepared by kneading the FKM and MVQ individually in a two-rool mill roll, then mixing them together homegeneously with an MVQ/FKM mass ratio of 10/90, curing system of (4 phr, 1/9) dicumyl peroxide (DCP)/N, N-Dicinnamylidene-1, 6-hexanediamine (3^# Vulcanizer), first curing conditions at 170?°C under 10?MPa for 30?min and post curing conditions at 200?°C for 6?hours at 1 atmospheric pressure.     

Styrene Butadiene Rubber/Silicone Rubber Blends Filled With Dough Moulding Compound

Blends of styrene butadiene rubber (SBR)/methyl-vinyl silicone rubber (MVQ) filled with dough molding compound (DMC) were prepared and the effects of various amounts of the SBR, as a compatibilizer of MVQ and DMC, on the mechanical properties and the oxygen index of the DMC filled SBR/MVQ blends were investigated. Dynamic mechanical analysis (DMA) and infrared spectrum analysis (IR) of the DMC/SBR/MVQ blends were also investigated. The results showed that the mechanical properties of the DMC filled MVQ blends were improved when SBR was used as a compatibilizer; the best mass ratio was 60 phr (parts per hundred total rubber) DMC, 25 phr SBR and 75 phr MVQ. The volume electric resistivities of the DMC filled SBR/MVQ blends with various DMC mass ratios were all above 5.8?×?10¹² Ω?m; i.e., the electrical insulating property of the blends was excellent. Compared with the blends without DMC and the blends without SBR, the energy storage modulus and the peak area of the loss factor tan δ of the DMC reinforced SBR/MVQ blends were largest; the addition of DMC and SBR improved the thermal properties of the blends.     

In Situ Dynamic Vulcanization of Poly(Vinyl Chloride)/Acrylonitrile-butadiene Rubber Blends

Poly(vinyl chloride) (PVC)/acrylonitrile-butadiene rubber (NBR) blends can be obtained through a dynamic vulcanization process as a melt-processible thermoplastic elastomer which produces parts that look, feel and perform like vulcanized rubber with the advantage of being processible as a thermoplastic material. In this study, a vulcanized thermoplastic was obtained by in situ dynamic vulcanization of PVC/NBR blends using a sulphur/ tetramethylthiuram disulphide (TMTD) and mercaptobenzothiazyl disulphide (MBTS) curative system during processing at the melt state. The blends were melt-mixed using a Haake Rheomix 600. The curing behavior of NBR was then investigated by a Monsanto rheometer. The thermal analyses were performed and the cross-linking at different mixing times was calculated using DSC. FT-IR was also performed for characterization of the blends. The cross-link densities of the samples were measured by a swelling method. The degree of cure increases with the mixing time. The cross-linking formation was verified through the formation of C─ S bonds in the blends.     

Effect of Silanes on Mechanical and Thermal Properties of Silicone Rubber/EPDM Blends

The effect of four types of silane coupling agents on the mechanical and thermal properties of silicone rubber and ethylene–propylene–diene monomer (M-class) rubber (EPDM) blends is studied, namely, isobutyltriethoxysilane (BUS), acryloxypropyltriethoxysilane (ACS), aminopropyltriethoxysilane (AMS), and vinyltriethoxysilane (VIS). ACS and VIS increase the crosslink density of the blends, which results in higher tensile strength, modulus, and thermal stability, but lower elongation at break compared with the other silanes. However, the blend containing BUS shows highest tanδ in the temperature range of 45°C to 200°C. Thermogravimetric analysis shows two steps of degradation for all the samples, but little difference with the varied silanes.     

Polyvinylidene Fluoride/Acrylonitrile Butadiene Rubber Blends Prepared Via Dynamic Vulcanization

Dynamically vulcanized blends based on polyvinylidene fluoride (PVDF)/acrylonitrile butadiene rubber (NBR) were prepared and characterized. The mixing torque and dynamic rheology analyses showed that the NBR phase increased the viscosity of the blends. Scanning electron microscopy (SEM) results showed that the NBR phase was in the form of spherical particles dispersed in the PVDF phase during dynamic vulcanization. Comparing PVDF-rich and NBR-rich blends, the size of the rubber particles in the NBR-rich blends were larger than those in PVDF-rich blends. Differential scanning calorimetry (DSC) results showed that the addition of the NBR phase reduced the PVDF crystallinity and T_m. Thermal gravimetric analysis (TGA) results showed that the dynamically vulcanized PVDF/NBR blends had a higher residual char mass than the neat PVDF and NBR. For PVDF-rich blends, the PVDF can be highly toughened by NBR; the Izod impact strength of the PVDF/NBR (70/30) blend was 77.5 kJ/m², which was about six times higher than that of pure PVDF. For rubber-rich blends, the PVDF component was beneficial to the mechanical properties of the blends, which can be used as thermoplastic elastomers.     

Thermal Properties of Fe-octacarboxyl Acid Phthalocyanine/Polyurethane Blends

The thermal stability of PU has been a critical factor to influence its applications as engineering materials. In this paper, the thermal properties of Fe-octacarboxyl acid phthalocyanine (Fe-OCAP)/polyurethane (PU) blends were investigated. The glass transition temperatures (T_g) of Fe-OCAP/PU blends were analyzed by differential scanning calorimetry (DSC). The results showed that with increasing Fe-OCAP content up to 10% T_g of the samples decreased. Thermal stability of the samples was studied by thermogravimetric analysis (TGA). The decrease of the degradation rate of the samples with increasing Fe-OCAP content indicated an improvement of thermal stability for the modified samples. The activation energy of thermal degradation was calculated by the Freeman and Carroll method. The results showed that the activation energy increased with increasing Fe-OCAP content, which also indicated the improved thermal stability obtained in the modified samples. The thermal properties of the samples were influenced by the incorporation of Fe-OCAP.     

Effect of Silica and Silicone Oil on the Mechanical and Thermal Properties of Silicone Rubber

The effect of three types of silicas with varied loading and the loading of hydroxyl terminated silicone oil on the mechanical and thermal properties of silicone rubbers (SRs) were investigated. Mechanical properties were affected by the silica loading because of the interaction between fillers and polymer and the filler dispersion. Fumed silica filled SRs showed higher tanδ, tensile strength, and elongation at break compared to those containing two types of precipitated silicas. With increasing silicone oil loading, the tensile strength, tear strength, hardness, and tanδ of SRs first increased and then decreased.     

高应变率下硅橡胶的本构行为研究

 硅橡胶是一种高分子聚合物,可以承受大变形,用途广泛。利用改进的分离式霍普金森压杆（SHPB）实验技术,对硅橡胶试样进行了不同应变率下的冲击压缩实验,基于实验数据,利用应变能函数构建了考虑应变率效应的材料本构形式。同时,实验过程中发现,在高应变率加载条件下,材料在压缩变形后出现了损伤线区,线区直径与加载应变率及试样尺寸之间存在一定的定量关系。     

Design and Dynamics Investigation for a Silicone Rubber Shock Absorber

A new kind of coupling-type silicone rubber shock absorber was prepared. Vibration and static stiffness tests were carried out to investigate the characteristics of vibration control. A mechanical model of the shock absorber was established, and the working principle of the shock absorber was studied by comparing the vibration test with simulation results. The dynamic results show the shock absorber has excellent vibration control performance. The coupling characteristics originate from the contact of inner and outer silicone rubber. It is shown that the stiffness and damping coefficients in the coupling process are critical for vibration control of the shock absorber.     

Mechanical and Flame Retardant Properties and Microstructure of Expandable Graphite/Silicone Rubber Composites

Flame-retardant expandable graphite (EG)/silicone rubber (SR) composites were prepared using nano-CaCO₃ particles as reinforcement filler. In addition to mechanical measurements, limited oxygen index (LOI), UL-94 and cone calorimeter tests (CCT), the thermal properties were tested by thermogravimetric analysis (TGA). The results showed that the content and particle size of the EG both had large effects on the flammability and mechanical properties of the EG/SR blends. The composites that contained 25 phr EG (50–80 mu) had excellent LOI values, 47–48, and achieved the UL-94 V-0 level while the pure SR sample had the LOI value of 25 and achieved the UL-94 V-2 level. The data obtained from the CCT indicated that the addition of EG decreased remarkably the heat release rate, smoke emission, and mass loss rate of the composites. SEM microphotographs of the EG/SR composites before and after combustion demonstrated that EG underwent a large volume expansion, and the multiporous char structure blocked heat transfer and protected the substrate from fire.     

Crystalline Morphology and Nonisothermal Crystallization Behaviors of iPP/PcBR Blends

Isotactic polypropylene/poly(cis‐butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. The influence of PcBR content on crystalline morphology and nonisothermal crystallization behaviors of iPP was investigated by polarized optical microscopy (POM), small angle light scattering (SALS), and differential scanning calorimetry (DSC). The POM showed that an increase of PcBR ranging from 10 vol% to 40 vol% led to less perfection of spherulites, vaguer boundaries between spherulites, and smaller spherulite size, which was quantitatively validated by SALS. The presence of PcBR also remarkably affected the nonisothermal crystallization behaviors of iPP. An addition of PcBR caused higher crystallization peak temperature and a faster crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak temperature moved to lower temperature and the crystallization rate increased as the cooling rate increased. The Ozawa and combined Avrami and Ozawa equations were used to describe the nonisothermal crystallization process of iPP and blends. The combined Avrami and Ozawa equation was more appropriate for the crystallization of the blends. Crystallization activation energy of iPP and blends was calculated by the Kissinger equation; the result showed that crystallization activation energy decreased as the content of PcBR increased from 30 vol% to 40 vol%.     

The Thermal Stability and Flammability of Expandable Graphite-Filled Polypropylene/Thermoplastic Polyurethane Blends

Polypropylene/thermoplastic polyurethane (PP/TPU) blends filled with two different particle sizes (45 and 150 μm) of expandable graphite (EG) were prepared by melt blending. Thermogravimetric analysis (TGA) was carried out to explain the effect of EG on the thermal stability of PP/TPU blends. In addition, the fire behavior of PP/TPU and PP/TPU/EG was investigated by a cone calorimeter. The char morphology and carbonation of the above systems were also characterized. The experimental results indicated that intumescent EG significantly enhanced the thermal stability and fire resistance of these blends. With the smaller particle size of EG, the thermal stability and flame retardancy were improved. The results from TGA and cone calorimeter demonstrated that the addition of EG could retard the degradation of the polymer materials above the temperature of 500°C by promoting the formation of a compact char layer. This char layer prevented further degradation of the polymer matrix and protected it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame-retarded performances.     

Thermoplastic Elastomers Based on Natural Rubber/Polypropylene Blends: Effect of Blend Ratios and Dynamic Vulcanization on Rheological,Thermal, Mechanical,and Morphological Properties

Thermoplastic elastomers (TPEs) based on natural rubber (NR)/polypropylene (PP) with different blend ratios were prepared and studied. The TPEs were obtained by dynamic vulcanization of NR/PP using a sulfur (S)/N-tert-butyl-2-benzothiazolesulphenamide (TBBS) and tetramethylthiuram disulphide (TMTD) curative system during processing in the melt state in an internal mixer equipped with cam rotors. Rheological, thermal, mechanical, dynamic, and morphological properties of the TPEs prepared were investigated. Based on this study a mechanism for the NR crosslinking was proposed where the sulfur vulcanization occurs through radical substitution in the forms of polysulfide bridges. The dynamic vulcanization process increases the stiffness of the NR phase in the TPEs and modifies the rheological and thermal behavior of the system compared to the behavior of the basic material PP. The crosslinked NR particles restrict the spherulitic growth and the regular arrangement of the spherulites of PP phase, decreasing the crystallinity degree. On the other hand, a reduction of mobility of the chain segments was also observed and, consequently, an increase of the T_g values. NR/PP TPEs with high content of NR showed superior mechanical performance compared to the uncrosslinked NR/PP blends in terms of tensile strength, Young's modulus and hardness. An increase of approximately 320% in Young's modulus values was obtained for the NR70/PP30 TPE compared to NR70/PP30. Morphological studies revealed the formation of large aggregates of NR domains in NR/PP TPEs which increased in size with an increase of the rubber content.     

Isothermal Crystallization and Miscibility of Isotactic Polypropylene/Poly(cis-butadiene) Rubber Blends

Isotactic polypropylene/poly(cis-butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. Isothermal crystallization and miscibility for neat iPP and blends of iPP/PcBR were investigated by differential scanning calorimetry. The presence of PcBR remarkably affected isothermal crystalline behaviors of iPP. An addition of PcBR caused shorter crystallization time and a faster overall crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak was broader and the supercooling decreased as the crystallization temperature increased. The Avrami equation was suitable to describe the primary isothermal crystallization process of iPP and blends. The addition of PcBR led to an increase of values of the Avrami exponent n, which we suggest was because the blends had a stronger trend of instantaneous three-dimensional growth than neat iPP. The equilibrium melting point depression of the blends was observed, indicating that the blends were partly miscible in the melt.     

紫外辐射加速老化高温硫化硅橡胶的X射线光电子能谱研究

高温硫化硅橡胶具有优良的电气性能、机械性能、憎水性而广泛应用于特高压输电线路,但亦会受外界环境的影响而老化,其抗紫外老化性能受到关注.课题组模拟户外紫外辐射环境,设计搭建了可调式紫外辐射加速老化试验箱,对A、B两个厂家的高温硫化硅橡胶样品进行了紫外辐射(0,500和1000 h)加速老化实验,重点对辐射前后的试样进行X...     

Organic Nano-Montmorillonite for Simultaneously Improving the Flame Retardancy,Thermal Stability,and Mechanical Properties of Intumescent Flame-Retardant Silicone Rubber Composites

The flammability of room temperature vulcanized silicone rubber (RTVSR) composites filled with melamine phosphate (MP) as intumescent flame-retardant additives was characterized by limiting oxygen index (LOI), UL-94 test, and cone calorimeter. In addition, the thermal degradation of the composites was studied using thermogravimetric analysis (TGA). Furthermore, in order to relate to actual application requirements, the comprehensive performance of the RTVSR/MP composites was optimized by adding organic nano-montmorillonite (OMMT) as a partial substitute for the MP. The as-prepared intumescent flame-retardant RTVSR/MP/OMMT nanocomposites were characterized by LOI, UL-94 test, TGA, cone calorimetry, scanning electron microscopy (SEM), and mechanical tests. The residue morphology formed after the burning of the nanocomposites was analyzed by its SEM and digital photographs. The results showed that the flame-retardant nanocomposites filled with 10 phr OMMT and 35 phr MP displayed the best comprehensive performance in terms of the flame retardancy, mechanical properties, and heat stability at low cost. It is expected that the intumescent flame-retardant silicone rubber composites with simultaneously improved flame retardancy, thermal stability, and mechanical properties will meet more requirements of the increasingly complex applications.     

Radiation Vulcanization of Magnetorheological Elastomers Based on Silicone Rubber

介绍了两种制备磁流变弹性体的硫化方法即高温硫化和辐射硫化. 研究中采用动态力学分析仪(DMA)测量了样品的动态力学特性.特别是对样品的磁流变效应和耐久性进行了详细的测试. 实验结果表明,经过辐射硫化的样品具有更大的零场模量和磁致模量,以及更好的磁流变效应和耐久性. 为了解释这些结果,文章对样品的体积形变和增塑剂渗出都作了详细的分析. 在硫化过程中样品的体积保持稳定是辐射硫化样品具有大磁致模量的重要原因,而增塑剂渗透性小也是辐射硫化样品具有高磁流变效应和耐久性的重要因素.     

High-Performance Silicone Rubber Composites via Non-Covalent Functionalization of Carbon Nanotubes

A high-performance silicone rubber (SR) composite (denoted as SCT) filled with 5 phr functionalized carbon nanotubes (CNTs) and 40 phr fumed silica (SiO₂) was prepared by mechanical blending. The CNTs were functionalized by tetrakis (phenylmethyl)-thioperoxydi (carbothioamide) (TBzTD); it contains four benzene rings that can interact with the CNTs via π–π interactions. Raman spectroscopy and X-ray photoelectron spectroscopy analysis demonstrated the existence of the π-π interactions between the CNTs and the TBzTD. Transmission electron microscopy and scanning electron microscopy confirmed the uniform dispersion of the CNTs in SR matrix and strong interfacial interactions between the SR and the CNTs. The effects of these non-covalently functionalized CNTs on the mechanical properties of the silica filled SR composites were fully investigated. The results showed that the tear strength of the SCT composite with TBzTD functionalized CNTs was significantly improved, by 249%, compared with that of the composite containing only SiO₂. An obvious crack deflection occurred in the SCT during the tearing process, resulting in the enhanced tear strength.     

Mechanical Properties and Corrosion Resistance of Vulcanized Silicone Rubber after Exposure to Artificial Urine

Medical devices, such as Foley catheters, which are commonly fabricated from silicone rubber, need to have excellent mechanical properties and physiological inertness. This study reports the development of a facile method to prepare silicone rubber with excellent long-term performance by controlling the vulcanization procedure parameters only. Mechanical, viscoelastic, and chemical properties of vulcanized silicone rubber were investigated. The corrosion resistance of vulcanized silicone rubber was assessed by exposure to artificial body urine for a period of up to 14 days. The mechanical properties of silicone rubber were changed via adjusting the vulcanization procedure parameters. The improved mechanical properties of silicone rubber are attributed to an increase in crosslink density resulting from the proposed vulcanization technology. After 14 days of immersion in urine, no significant changes in mechanical properties and internal structure were observed. This indicated that the as-prepared rubber samples had high tear resistance and physiological inertness. These long-term properties are important for their applications as semi-permanent implant materials, such as Foley catheter balloons in clinics. Our process of vulcanization of silicone rubber may have potential for fabrication of such medical devices.     

凹凸棒石/硅橡胶复合材料的热氧化降解和老化性能研究

本文采用高压均质结合对辊挤压工艺对天然凹凸棒石进行棒晶解离得到了纯度较高和比表面积较大(133.7 m²/g)的纳米解离凹凸棒石. 进一步通过机械共混法分别将天然凹凸棒石和纳米解离凹凸棒石与硅橡胶生胶复合制备了天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶材料,研究了天然凹凸棒石和纳米解离凹凸棒石对凹凸棒石/硅橡胶复合材料热氧化降解和老化性能的影响. 结果表明,天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶在300 oC热氧老化处理0.5 h后,相比于纯硅橡胶,初始5%失重温度从385 oC提高至396∽399 oC. 系列表征结果表明,天然凹凸棒石和纳米解离凹凸棒石增强了纳米粒子与硅橡胶之间的相互作用从而抑制了纳米颗粒聚集,并且可显著提高硅橡胶侧链Si-CH₃的保存率,从而提高了该复合材料的热氧化降解和老化性能. 此外,纳米解离凹凸棒石可大大抑制纳米粒子的长大;因此老化后,纳米解离凹凸棒石-硅橡胶表现出了比硅橡胶(10.6%、7.4%和5.0%)更高的拉伸强度、断裂伸长率和撕裂强度保留率(40.6%、34.9% 和30.1%).