聚醚-聚硅氧烷嵌段共混聚氨酯弹性体的研究

用共聚混合法制成聚硅氧烷-聚醚型嵌段聚氨酯,结果表明:在聚合物主链引入硅氧烷后,弹性体力学性能略有升高,对三元乙丙橡胶,异戊二烯橡胶的粘合剥离强度得到提高。NCO/OH当量比、硅氧烷和MOCA用量对材料的物理性能有很大的影响。DSC的分析表明,引入的聚硅氧烷链段主要分布于弹性体分子中的软段,使弹性体的相分离更加明显。     

Influence of the grafting topology of hydrophobic silica surfaces on the mechanical properties of silicone high consistency rubbers

Silica‐filled rubber materials exhibit stress softening and hysteresis under cyclic loadings. These phenomena are usually associated with both the Payne and Mullins effects. To better characterize these properties, five model silicas were produced and used in industrial‐like high consistency rubber (HCR) formulations: the native (hydrophilic) silica and four chemically modified silicas for which both the content of surface silanols and the nature of the grafted silicone chains differ. Silica ? polydimethylsiloxane HCR elastomer with constant silica content and optimal dispersion was tested via static (uniaxial tensile tests, cyclic and monotonic) and dynamic tests. The Payne and Mullins effects as well as the ultimate properties were evaluated as a function of particle surface treatment. It was found that the Payne amplitude decreases with the content of grafted chains, whereas the Mullins effect and ultimate strain decrease with an increase in molar mass between crosslinks. Finally, the ultimate strength is optimal as long as silica is surface treated, albeit independent of surface grafting topology. © 2015 Society of Chemical Industry     

PDA型PUR弹性体的制备与性能

以聚己二酸二乙二醇酯二醇(PDA)为软段,4,4′–二苯基甲烷二异氰酸酯(MDI)和1,4–丁二醇(BDO)为硬段,采用预聚体法制备一系列PDA型PUR弹性体。采用力学性能测试、广角X射线衍射(WAXD)、傅立叶变换红外光谱(FTIR)、差示扫描量热(DSC)、热重(TG)分析和维卡软化点温度测定等研究手段,研究硬段含量对其力学性能、微观形态和热性能的影响。结果表明,随着硬段含量的增加,PDA型PUR弹性体的硬度、拉伸强度、300%定伸应力、拉伸永久变形和撕裂强度都增大,当硬段含量为40.1%时,弹性体的综合力学性能最佳,硬度(邵A)为88,拉伸强度为33.9 MPa,300%定伸应力为12.5 MPa,拉伸永久变形为31%,撕裂强度为90.3 k N/m;WAXD分析表明,弹性体为无定型结构;FTIR分析表明,硬段含量的增加使弹性体总的氢键化程度增加,微相分离程度改善;DSC测试表明,硬段含量的增加使弹性体的微相分离程度提高;TG和维卡软化点温度测试表明,弹性体的热性能随着硬段含量的增加而提高,当硬段含量为40.1%时,弹性体的初始分解温度(失重5%的温度)和维卡软化点温度分别达到324.5℃和144.1℃,具有较好的热性能。     

耐刮擦、高流动PP/SEBS热塑性弹性体的研制

采用熔融共混法制备了聚丙烯(PP)/氢化苯乙烯–丁二烯–苯乙烯嵌段共聚物(SEBS)热塑性弹性体,研究了乙烯丙烯酸酯共聚物润滑偶联改性剂(YY–503和YY–5031)、芥酸酰胺和高分子量硅酮(E525)4种改性剂对PP/SEBS弹性体的加工性能、力学性能和耐刮擦性能的影响。结果表明,4种改性剂的加入能显著提高弹性体的熔体流动速率(MFR),添加YY–503和E525的弹性体MFR提升更为显著,分别为12.6 g/10 min和13.5 g/10 min,比未添加时提高了2 471.4%和2 655.1%;添加芥酸酰胺的弹性体拉伸强度和断裂伸长率最低,比未添加改性剂时分别下降了58.5%和63.2%,添加YY–503和YY–5031的弹性体拉伸强度分别为10.6 MPa和9.8 MPa,比未添加改性剂时分别提高23.2%和19.5%;未添加改性剂弹性体的色差值(ΔL)为18.5,而添加YY–503和YY–5031的弹性体ΔL仅为1.3和1.5;扫描电子显微镜测试发现,添加YY–503和YY–5031的弹性体中没有出现明显孔洞,碳酸钙良好分散,与基体结合力良好。添加质量分数为2%的YY–503可获得力学性能、加工性能和耐刮擦性能优异的PP/SEBS弹性体。     

Mechanical,dielectric, and magnetic properties of the silicone elastomer with multi‐walled carbon nanotubes as a nanofiller

Silicone elastomer and multi‐walled carbon nanotubes (MWCNTs) composites, applicable as actuators and controllable dampers, were studied. Dynamic mechanical analysis (DMA) and vibrating sample magnetometry (VSM) were used to investigate the mechanical and magnetic properties of silicone elastomers and MWCNTs composites. Also, measurement of their dielectric property was conducted. The addition of MWCNT was able to tailor the damping and dielectric properties of the silicone elastomer. In this study, a 0.7 wt% of MWCNT composite demonstrated an attractive condition for the damping and the dielectric property. Exceedingly, the modulus increased with the application of a magnetic field. The good filler effect with the small addition of the MWCNTs content is caused by their unique structure, catalytic effect, and magnetic property. POLYM. ENG. SCI., 47:1396–1405, 2007. © 2007 Society of Plastics Engineers     

Octakis(phenyl)-T8-silsesquioxane-filled silicone elastomers with enhanced electromechanical capability

The first dielectric elastomer actuators based on electroactive nanocomposites with octakis(phenyl)-T8-silsesquioxane (phenyl-T8), obtained ex-situ, used as voltage stabilizer filler for silicone elastomers are reported. The incorporation and homogeneous dispersion of crystalline phenyl-T8 in percentages of 2.5, 3.5, 5, and 10 into the amorphous matrix consisting in a polydimethylsiloxane-α,ω-diol with Mn = 240,000 g/mol was successfully achieved by solution mixing and crosslinking. For the sample with the best actuation performance (that containing 3.5 wt.% filler), an optimized filled elastomer was obtained by dispersing 3.6 wt. % phenyl-T8 in the matrix using a suitable surfactant (Pluronic L81), thus gaining an increased electrical breakdown of 30% compared with the pristine sample. Beside dielectric strength, the matured films were characterized in terms of morphology, mechanical, dielectric and actuation tests. In spite of structural incompatibility between the filler and the matrix, the obtained materials are soft elastomers showing high strain (~800%) and low Young's modulus of 50–100 kPa. The use of phenyl-T8 in a silicone matrix lead to electroactive films with slightly increased lateral actuation strain and electric breakdown strength.     

Self-Healable and Transparent Elastomers Based on Dual Reversible Networks

The fabrication of silicon elastomer with good mechanical properties and self-healing ability is still a challenge. Herein, a facile method to fabricate a transparent healable double-network (DN) elastomer by introducing polyborosiloxane (PBS) into self-healing polydimethylsiloxane (HPDMS) networks is demonstrated. Tensile testing shows that the mechanical properties of PBS and HPDMS are both improved. The DN elastomer shows high transparency across the visible spectrum with an average transmittance of 75%. Because of the breakage and reconstruction of reversible imine bonds and B O dative bonds, the elastomer exhibits excellent self-healing properties with a maximum healing efficiency of 98% at room temperature. Meanwhile, the elastomer can be repeatedly reprocessed with a recovery of 85% of virgin mechanical strengths. This work provides a new insight to design transparent, self-healing silicone elastomers with a simple and eco-friendly method.     

Post Curing as an Effective Means of Ensuring the Long-term Reliability of PDMS Thin Films for Dielectric Elastomer Applications

Post curing can be used to facilitate volatile removal and thus produce polydimethylsiloxane (PDMS) films with stable elastic and electrical properties over time. In this study, the effect of post curing was investigated for commercial silicone elastomer thin films as a means of improving long-term elastomer film reliability. The Young’s moduli and electrical breakdown strengths of commercial (silica-reinforced) PDMS elastomer films, with and without additional 35 parts per hundred rubber titanium dioxide (TiO₂), were investigated after high-temperature (200°C) post curing for various time spans. The elastomers were found to contain less than 2% of volatiles (significantly higher for TiO₂-filled samples), but nevertheless a strong effect from post curing was observed. The young’s moduli as well as the strain-dependent behavior were found to change significantly upon post curing treatment, where Young’s moduli at 5% strain increase with post curing. Furthermore, the determined dielectric breakdown parameters from Weibull analyses showed that greater electrical stability and reliability could be achieved by post curing the PDMS films before usage, and this method therefore paves a way toward more reliable dielectric elastomers.     

Polyurethane-elastomer-actuator

Polyurethane elastomers were investigated as electrically active materials for actuators. Components in hard segment and soft segment in the elastomers were varied. The elastomers with excellent electrostrictive properties were limited to those which had soft segments of polyesters and polylactones. It turned out, that the elastomers, whose soft segments are polyethers are electrically inert under the experimental conditions. The chemical structure of the hard segment seems not to influence to the electrostrictive property. The charging and discharging process was investigated. The charging process was found to proceed simultaneously with the contracting process caused by the electric field, suggesting that the orientation of the soft segment in the elastomer plays critical rolls in the electrostrictive action. In the elastomer, which has a soft polyether segment and was inactive to the electric field, could be actuated very efficiently when the elastomer was swollen with dimethyl sulfoxide. We conclude that the polyurethane elastomer, whose soft segment has chemical bonds with a relatively large dipole moment, can be actuated by the electric field application, and that even the elastomer, whose soft segment is inactive, could be actuated in the presence of a solvent with a large dipole moment. Thus, the concept found with the gel, could be applied to an elastomer, the soft segment of which plays partly the roll of the solvent in the gel.     

A novel electric elastomer based on starch/transformer oil drop/silicone rubber hybrid

The electrorheological fluid composed of starch particles and silicone oil/transformer oil was dispersed into 107 silicone rubber, and then two types of electric elastomers were prepared in the absence and presence of a curing electric field, respectively. The storage modules were measured using dynamic mechanical analysis with the round disk compression clamp. The results indicate that the storage modulus sensitivity of electric elastomers composed of pure transformer oil is the highest, that of electric elastomers composed of pure silicone oil takes second place, and that of electric elastomers composed of mixture oil is the smallest. For the given starch concentration, the storage modulus sensitivity attains a maximum value of 3.88 when the mass ratio between the transformer oil and 107 silicone rubber is 1. For the given mass ratio of 1, the effects of starch concentration and the presence or absence of the curing electric field on the storage modulus of electric elastomers were studied. When the starch concentration is 5 wt %, the storage modulus of the elastomer without the electric field (denoted as A‐elastomer) is 20.1 kPa, whereas that of the elastomer with the electric field (denoted as B‐elastomer) is 101.8 kPa. The storage modulus sensitivity attains a maximum value of 4.07. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hard coatings on elastomers for reduced permeability and increased wear resistance

Abstract

In this study, three different elastomers, namely hydrogenated nitrile butadiene rubber, fluoroelastomer and silicone, have been subjected to two different hard metallised coatings by ion implantation process. The three different elastomers are commonly used in various seal applications, where reduced wear and gas permeability are essential in maintaining seal performance and functionality. Samples of these rubbers have been coated with chromium coating in one set of tests. In the second set of tests, samples of elastomers have been coated with tungsten carbide coating being deposited on all the three different elastomers. Wear, gas permeability and mechanical behaviour of the coated samples were compared with each other and with the control uncoated elastomers. All the coated samples showed good reduction in gas permeability. With the use of metallised coatings, there has been improved resistance to wear in all the coated samples. Adhesion strength and effect of coating on the elastomer have been investigated by mechanical testing. Mechanical tests revealed good adhesion of metal coatings on all the rubber samples, and there was no detrimental effect on the mechanical properties after coating.     

Mechanism analysis on the increased stress softening of Mullins effect for rubber matrix composites

ABSTRACT

The stress softening phenomenon of Mullins effect is studied by investigating mechanical properties of Fe (abbreviation of Iron) powder-modified rubber composites via experiments and numerical simulation methods. The distinct reinforcements of composites are found experimentally on the elastic modulus and the softened stress of Mullins effect. Then, a representative volume method: unit cell model method is selected to simulate the particle-reinforced composites, and investigate the intrinsic mechanism in the viewpoint of mechanics. It is found that due to the existence of rigid inclusion, the surrounding strain distribution field is changed and the continuous increasing stress characteristic of the matrix acts an important role in the mechanical reinforcement. The proposed mechanism based on it, can account for the increasing softened stress of Mullins effect for the composites. This finding can be also extended to other rigid particle-reinforced rubber composite, which is confirmed by numerically simulating.     

The effect of freeze‐drying parameters on the cure characteristics of freeze‐dried BSA‐loaded silicone elastomer

To formulate therapeutic proteins into polymeric devices the protein is typically in the solid state, which can be achieved by the process of freeze‐drying. However, freeze‐drying not only risks denaturing the protein but it can adversely affect the cure characteristics of protein‐loaded silicone elastomers. This study demonstrates that a variation in the parameters of the freeze‐dryer can significantly affect the residual moisture content of freeze‐dried BSA, which in turn has an effect on the bulk density and flow properties of the BSA. The bulk density and flow properties of the BSA subsequently affect the cure characteristics of BSA‐loaded silicone elastomers. An increase in the residual moisture content results in the freeze‐dried BSA having a decreased bulk density and poor flow properties which can have a detrimental effect on the cure characteristics of a freeze‐dried BSA‐loaded silicone elastomer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical,dielectric, and electromechanical properties of silicone dielectric elastomer actuators

Silicone elastomer actuators were investigated to develop a simple and industrially scalable product with improved mechanical properties, such as a low modulus, high tearing strength, and good resilience, and enhanced electromechanical actuation properties. Silicone elastomers were fabricated via a hydrosilylation addition reaction with a vinyl‐end‐functionalized poly(dimethyl siloxane) (V), a multivinyl‐functionalized silicone resin, and a crosslinker in the presence of a platinum catalyst. For the larger electromechanical actuation response, the silicone dielectric elastomer actuator had to have a larger molecular weight of poly(dimethyl siloxane), a smaller hardener content, and a resin‐free composition. However, the silicone elastomer actuators needed to include a small amount of resin to improve the tearing strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40030.     

Silicone elastomers for electronic applications. II. Effects of noncrosslinked materials

We performed applied functional tests to examine how the noncrosslinked fraction of a cured silicone elastomer affected the performance of electrical devices and the solderability and adhesion on gold‐plated printed circuit boards. To obtain information about the spreading tendencies of commercial silicone elastomers, and to complement the function tests, we conducted so‐called creep tests to examine the migration and spreading of the noncrosslinked fraction. The electrical tests, performed with both reference oligomers and cured commercial poly(dimethyl siloxane)s, showed that failure occurred even at very low silicone contamination levels. The solderability and adhesion, however, were not affected by the presence of poly(dimethyl siloxane)s, especially not the reference solutions, which consisted mainly of volatile siloxanes. The creep tests, performed on commercial silicone elastomers, indicated that the noncrosslinked, nonvolatile part had to be taken into account in a discussion of silicone contamination. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3780–3789, 2003     

Reversible Dynamic Behavior of Condensation-Cured Silicone Elastomers Caused by a Catalyst

This study demonstrates that dibutyltin-dilaurate (DBTL), commonly used to catalyze condensation-cured silicone elastomers, causes dynamic behavior in the silicone network, which is attributed to the catalyst finding a way to become part of the elastomer network. Furthermore, it establishes that by choosing an appropriate silanol-terminated polydimethylsiloxane (HO-PDMS-OH) chain length, the catalyst causes the gelation of the system without a cross-linker. To the best of authors' knowledge, this is the first time that the DBTL catalyst is shown, apart from the catalytic effect, to have the ability to act as a cross-linker.     

Particulate reinforcement of polyacrylate elastomers. II. Mechanical properties

This paper presents and discusses results which have been obtained for the mechanical properties of crosslinked polyethylacrylates containing various amounts of microscopic glass beads. The adhesion between the glass beads and the elastomer matrix was varied by subjecting the beads to different surface treatments. That the adhesion is affected by surface treatment has been demonstrated in two ways: (i) Unfilled elastomer sheets have been cast in contact with glasses surfaces which had been treated with the same reagents as were used to treat the beads. The force required to peel the elastomer from the glass was then measured and found to depend strongly upon the surface treatment, (ii) Scanning electron micrographs of the ruptured surfaces of used tensile test-pieces cut from filled elastomer sheets confirm that surface treatment has a profound effect upon the adhesion between bead and matrix. Results are presented for the hardness and tensile stress-strain properties of elastomers containing various amounts of beads. In all cases, the stiffening effect of the beads increases as the adhesion between beads and matrix is improved. Beads which had been treated in such a way as to minimise the, adhesion to the matrix were found to cause an apparent softening of the material as revealed by the tensile stress-strain curve. It has been shown that this effect can be satisfactorily explained if it is assumed that in this case the beads merely serve to increase the void content of the material.     

Silicone rubbers for dielectric elastomers with improved dielectric and mechanical properties as a result of substituting silica with titanium dioxide

One prominent method of modifying the properties of dielectric elastomers (DEs) is by adding suitable metal oxide fillers. However, almost all commercially available silicone elastomers are already heavily filled with silica to reinforce the otherwise rather weak silicone network and the resulting metal oxide filled elastomer may contain too much filler. We therefore explore the replacement of silica with titanium dioxide to ensure a relatively low concentration of filler. Liquid silicone rubber (LSR) has relatively low viscosity, which is favorable for loading inorganic fillers. In the present study, four commercial LSRs with varying loadings of silica and one benchmark room-temperature vulcanizable rubber (RTV) were investigated. The resulting elastomers were evaluated with respect to their dielectric permittivity, tear and tensile strengths, electrical breakdown, thermal stability and dynamic viscosity. Filled silicone elastomers with high loadings of nano-sized titanium dioxide (TiO₂) particles were also studied. The best overall performing formulation had 35 wt.% TiO₂ nanoparticles in the POWERSIL® XLR LSR, where the excellent ensemble of relative dielectric permittivity of 4.9 at 0.1 Hz, breakdown strength of 160 V µm^?1, tear strength of 5.3 MPa, elongation at break of 190%, a Young’s modulus of 0.85 MPa and a 10% strain response (simple tension) in a 50 V μm^?1 electric field was obtained.     

Effect of elastomer type and functionality on the behavior of toughened polyamide nanocomposites

The only shortcoming of PA6‐based nanocomposites is low toughness, which is the same as that of the matrix. This work is focused on optimization of toughening these nanocomposites by introduction of small amounts of finely dispersed elastomers. A comparison of reactively compatibilized and analogous nonreactive elastomer‐containing nanocomposites indicates the best‐balanced mechanical behavior for polar nonreactive elastomers such as NBR and E‐MA. This is explained by a significant compatibilizing effect of clay. Besides the elastomer particle size and its properties, the clay localization and its degree of ordering in the interfacial region also significantly influenced mechanical properties of the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1571–1576, 2006     

Simultaneous interpenetrating networks based on castor oil elastomers and polystyrene. V. Behavioral trends and analysis

The morphology and/or mechanical properties of simultaneous interpenetrating networks, SINs, based on castor oil elastomers and crosslinked polystyrene, were studied by electron microscopy, stress–strain analysis, and/or Izod impact tests. Several synthetic details were changed systematically and the concomitant changes in morphology or particular properties observed. The toughness of elastomer SINs increased with decreasing domain size of the polystyrene dispersed phase. The use of a prepolymer for the elastomer network synthesis promotes the formation of larger polystyrene domains. The impact resistance of the SINs increased with the total elastomer content. Properly crosslinked and postcured compositions developed impact energies of about 60–70 J/m. SINs based on castor oil-derived elastomers and crosslinked polystyrenes form prototype engineering materials which already compared satisfactorily to commercial polymers in terms of mechanical behavior.