Photopatternable thin films from silyl hydride containing silicone resins and photobase generators

The photopatternability of various silyl hydride containing organosilicone resins containing the photobase generators N‐methylnifedipine or O‐(2‐nitrobenzyl)‐N‐octyl carbamate have been examined, with the goal of identifying potential photopatternable compositions with high thermal stability after cure. Two different categories of silicone resins have been prepared from combinations of diphenylsiloxane and methyl and hydrogen silsesquioxane units and a combination of phenyl and hydrogen silsesquioxane monomer units. The photobase generators were incorporated into these resins at concentrations up to 10 weight percent. UV‐irradiation of micrometer thick silicone resin‐photobase films through a photomask, under an air atmosphere, yielded micrometer scale features after development. Photopatternable compositions have been identified with photosensitivities of less than 50 mJ/cm2. The photopatterning process is believed to proceed by base‐catalyzed reaction of resin‐based silanol groups with neighboring silyl hydride groups to yield thermally stable siloxane crosslinks. Copyright © 1999 John Wiley & Sons, Ltd.     

Structure and dynamics of MG rubber studied by dynamic mechanical analysis and solid‐state NMR

Methyl‐methacrylate‐grafted natural rubber was prepared by free radical polymerization of methyl methacrylate in natural rubber latex, and their structure and dynamics were investigated by dynamic mechanical analysis and solid‐state nuclear magnetic resonance (NMR). Samples were prepared by chemical initiation and high‐energy radiation. The changes of glass transition temperature and tan δ max with different total poly(methyl methacrylate (PMMA) content are reported. The effect of the change in composition in copolymers on tan δ peak width, tan δ max, and area under the tan δ curve are used to understand the miscibility and damping properties. Solid‐state ¹³C‐NMR measurements were carried out to determine several relaxation time parameters, such as rotating frame and laboratory frame proton and carbon relaxation times. Cross polarization times and carbon relaxation times were interpreted based on the changes in the molecular motion. Proton relaxation times were interpreted based on the heterogeneity of the matrix. Results confirmed phase separation and a presence of an interfacial region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1141–1153, 1999     

Modeling of Anionic Polymerization of Isoprene in an Industrial Reactor

One of the most important reasons for modeling polymerization processes is to provide a tool for estimating the risks of runaway reactions in polymer industry. This is especially important for batch processes, such as anionic polymerization of isoprene or butadiene. This work presents a theoretical and experimental research of the anionic polymerization of isoprene using cyclohexane as solvent and n‐butyllithium as initiator. In the first part, a phenomenological kinetic expression is obtained that describes the anionic polymerization of isoprene initiated by n‐butyllithium in cyclohexane. In the second, the mass and energy balance equations are solved to model the anionic polymerization of isoprene in a quasi‐adiabatic batch reactor. Adjustment of reactor parameters is made using the data obtained from a laboratory reactor. The proposed model predicts adequately the obtained temperature, pressure, and conversion profiles from this set of experiments. Finally, a mathematical model is developed to predict the behavior for the anionic polymerization of isoprene in an industrial reactor.     

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.     

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.     

表面粗糙度对激光诱导击穿光谱信号的影响

硅橡胶复合绝缘子是高压输电线路的关键设备,长期在复杂外界环境条件下带电运行后会发生表面老化,表现为粉化、褪色、粗糙度和硬度上升等现象。粗糙度作为复合绝缘子的老化特征量之一,其测量是复合绝缘子在线带电检测的难题。激光诱导击穿光谱技术(laser-induced breakdown spectroscopy, LIBS)适用于开展输电线路复合材料的远程在线检测,但粗糙度对LIBS信号的影响还没有得到系统的研究,利用这种基体效应进行绝缘子表面粗糙度的测量尚无报道。制备了不同粗糙度的硅橡胶新样品,与500 kV线路退运的复合绝缘子样品进行对比分析,研究了硅橡胶材料的粗糙度对LIBS信号的影响,结果表明,对于新制备硅橡胶材料随着粗糙度的增加,各主体元素特征谱线强度会随之增强,不同主体元素之间的原子谱线强度比（Si 288.2 nm/C 247.9 nm和Al 394.4 nm/Si 288.2 nm）随之下降,说明样品粗糙度对LIBS测量结果影响显著。但特征谱线强度及不同主体元素原子谱线强度比与粗糙度之间的函数关系不明显,难以用于粗糙度测量。硅橡胶的主体元素为Si,Al,C和O等,考虑元素含量及特征谱线的选取方便选择Si为主要分析元素。对于Si原子谱线强度比,选取了两条上能级相近（E_ki＝40 991.88, 39 955.05 cm-1）的原子谱线（SiⅠ288.2 nm,SiⅠ250.7 nm）作为分析线,在满足局部热力学平衡与光学薄的条件下两条谱线的强度比应为定值,但样品粗糙度的改变会影响脉冲激光烧蚀材料表面的过程,从而改变等离子体的状态,使得谱线强度比值也随之变化。上述两条硅原子谱线强度比和粗糙度建立的定标关系,线性相关系数为0.88。对于500 kV输电线路退运的老化硅橡胶材料,其表面由于老化有部分氢氧化铝填料析出,使得基体成分不均匀性更为显著,其表面也变得更为粗糙,这导致一对谱线强度比值作为定标函数,实用性降低。因此针对老化硅橡胶材料,除了选择Si元素谱线(SiⅠ250.7 nm,SiⅠ251.4 nm,SiⅠ251.9 nm)以外,还引入了Al元素谱线(AlⅠ305.7 nm, AlⅠ305.9 nm),利用三组谱线强度比进行多元回归分析,对于两个实测粗糙度为2.659和2.523 μm老化硅橡胶样品,LIBS测量的相对误差分别为0.218和0.189。结果表明对同样成分的复合材料,表面粗糙度对LIBS信号的影响是必须考虑的,而利用这种基体效应,开展远程在线测试复合绝缘子表面粗糙度,对于高压输电线路检测运维具有重要的应用价值。     

Redesign of a soft conductive rubber strip electrode for measurement of surface resistance according to IEC 60079-32-2 within the context of the PTB Ex Proficiency Testing Scheme

To ensure worldwide quality and homogeneity in the field of explosion protection, not only uniform rules in the form of IEC standards but also the active participation in interlaboratory comparisons are necessary. The “PTB Ex Proficiency Testing Scheme” is the first global proficiency testing program of its kind in the field of explosion protection. It serves as proof of competence and provides laboratories with a complete system for their own performance evaluation.In 2015, the program “Electrostatic Charge - Test Round 2015” was launched within the PTB Testing Scheme. The participants of the program performed surface resistance and transferred charge tests according to IEC 60079-0 and IEC 60079-32-2 on various types of test samples. The new standard IEC 60079-32-2 proposes different kinds of electrodes for the user, such as conductive silver paint electrodes, soft conductive rubber strip electrodes on spring-mounted metal tongues or conductive foam strips mounted on an insulating support, depending on the geometry of the sample. These different types of electrodes as well as the construction latitude for each electrode could lead to deviations between the results of different test laboratories due to better or worse electrode contact with the test sample.Therefore, the proficiency team and electrostatic experts at PTB decided to design an accurate and user-friendly electrode which meets the requirements of IEC 60079-32-2. This paper provides information about the electrodes' design as well as the results of comparable measurements.     

橡胶硫化促进剂的研究进展

作为橡胶加工成形过程中最重要的步骤之一,橡胶硫化直接影响橡胶制品的性能。与单用硫黄相比,少量的促进剂与硫磺配合可以极大地提高硫化速率,改善硫化胶的性能。但目前橡胶硫化促进剂普遍具有潜在的人类健康和环境风险问题,同时硫化促进效能较低、功能单一。因此,开发无毒、无或少氧化锌、高效、多功能的新型硫化促进剂对橡胶工业具有非常重要的意义。本文首先简要介绍了橡胶硫化促进剂的发展历程,然后综述了近年来新型橡胶硫化促进剂的研究进展(包括离子液体促进剂、新型二硫代氨基甲酸盐类促进剂、稀土促进剂、以及含新型副促进剂的硫化并用体系等),并对橡胶硫化促进机理、新型橡胶硫化促进剂的设计进行了展望。     

The Coagulation Impact of 50% Epoxidised Natural Rubber Chain in Ethylene Carbonate-Plasticized Solid Electrolytes

In this research, thin, soft and flexible free standing films can be obtained from poly (methyl methacrylate) (PMMA)/50% epoxidised natural rubber (ENR 50)/lithium triflate (LiCF₃SO₃) blends. However, phase separation is observed on the surface of the films which indicates that the blending is not homogeneous. The blend became more homogeneous when ethylene carbonate (EC) plasticizer is introduced into the blend system. However, the anti-plasticization effect of EC on ENR 50 occurs at lower concentration of EC at which the rubber became coagulated due to immiscibility of the rubber with EC plasticizer during solution casting. These ENR 50 coagulates can be observed as large solid structures in the Field Emission Scanning Electron Microscope (FESEM) micrographs of the EC-plasticized rubber-based electrolytes. The presence of these coagulates, hinder the migration of lithium ions in the system and also trap the lithium ions within the coil. This in turn reduced the number of free lithium ions that contribute to the ionic conduction. As a result, the conductivity of the un-plasticized PMMA/ENR 50/LiCF₃SO₃ film dropped drastically by two orders of magnitude.     

Diffusion and permeability of aldehydes into blends of natural rubber and chemically modified low molecular weight natural rubber

Low molecular weight natural rubber (LMWNR) obtained from natural rubber (NR) by depolymerization of natural rubber latex (NRL) was modified by epoxidation to 35% epoxide level to yield epoxidized low molecular weight natural rubber (ELMWNR). The ELMWNR was in turn modified in a solution of thioglycollic acid (TGA) (0.5 mol phr) to yield a product of 20% conversion of its initial LMWNR epoxide. Blends of NR with LMWNR, ELMWNR and epoxidized low molecular weight natural rubber thioglycollic acid (ELWMNR‐TGA) adduct were made. The mixes were vulcanized at 150°C for 20 min before determining the system parameters (n and k), the sorption (S), diffusion (D) and permeability (P) of the vulcanizates in acetaldehyde and formaldehyde solutions at three different temperatures (25, 40 and 60°C) for a period of 90 days. The sorption, diffusion and permeability of the vulcanizates were found to be temperature dependent. The vulcanizates containing ELMWNR were found not to be easily penetrated by both acetaldehyde and formaldehyde when compared with base mix A that is vulcanizates with only NR. The reaction system was found not to be spontaneous but dependent on the activation energies. Copyright © 2005 John Wiley & Sons, Ltd.