Effects of thinner on RTV silicone rubber nanocomposites reinforced with GR and CNTs

The effects of thinner on rubber specimens with carbon nanotubes (CNTs) and graphitic nanofillers (GR) was studied for robotics applications. Rubber specimens were prepared by dispersing GR, CNTs and thinner in room temperature vulcanized (RTV) silicone rubber through solution mixing. Microscopic studies have confirmed occurrence of swelling in polymer chains due to migration of thinner. It results an increase in topological depth from 40 nm (no thinner) to 120 nm (40 phr of thinner). An elastic modulus of ~4.4 MPa (without thinner) was higher than 2.8 MPa (10 phr of thinner). At 100% strain, the lower dissipation losses of 110% (without thinner) and 70% (40 phr of thinner) were obtained. The resistance increases from 4.6 kΩ (without thinner) to 5.7 kΩ (10 phr of thinner). At 0.4‐mm‐thick elastomer slab, an actuation displacement of 0.81 mm (without thinner) was obtained which increased to 1.1 mm (60 phr of thinner). Thus, the thinner can be useful for easier processing, controlled stiffness, minimizing dissipation losses, increasing the actuation displacement and decreasing the cost of the device. Copyright © 2017 John Wiley & Sons, Ltd.     

乙醇对柴油机燃油系统橡胶和塑料的腐蚀特性分析

采用浸泡的方法,研究了丁腈橡胶燃油管和聚四氟乙烯塑料在乙醇和0#柴油中常温浸泡672 h后的腐蚀溶胀性的变化.利用扫描电子显微镜分析丁腈橡胶管道内表面和聚四氟乙烯表面的微观变化.结果表明:常温672 h浸泡后,橡胶和塑料中的一部分物质进入到乙醇溶液中;乙醇对橡胶和塑料有极性力的作用,乙醇浸泡后的丁腈橡胶燃油管出现了喷霜现象,随时间的增加喷霜效果明显,乙醇浸泡后的聚四氟乙烯塑料表面颜色变浅;结合微观结构说明乙醇对柴油机燃油系统的橡胶和塑料都产生了腐蚀,现阶段柴油机燃油系统还不能长期使用乙醇.     

Peroxide‐initiated chemical modification of poly(isobutylene‐co‐isoprene): H‐atom transfer yields and regioselectivity

The yield and regioselectivity of H‐atom abstraction by cumyloxy radicals from poly(isobutylene‐co‐isoprene) (IIR) are quantified and discussed in the context of cross‐linking/degradation outcomes and vinyltriethoxysilane (VTEOS) graft yields. Studies of IIR materials with different isoprene contents show that H‐atom abstraction from the allylic functionality provided by isoprene mers is responsible for the heightened H‐atom transfer reactivity of IIR relative to poly(isobutylene). Differences in the reactivity of allylic and alkyl macroradical intermediates makes high isoprene IIR materials less prone to peroxide‐initiated chain scission, but less responsive to VTEOS grafting formulations. Improved knowledge of H‐atom transfer reactivity is extended to a new approach for IIR cross‐linking involving acrylate‐functionalized nitroxyl chemistry. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3102–3109     

Influences of different dimensional carbon-based nanofillers on fracture and fatigue resistance of natural rubber composites

The dimensions of reinforcing filler is a key factor in influencing the fracture and fatigue of rubbers. Here, the fracture and fatigue resistance of natural rubber (NR) filled with different dimensional carbon-based fillers including zero-dimensional spherical carbon black (CB), one-dimensional fibrous carbon nanotubes (CNTs) and two-dimensional planar graphene oxide (GO) were explored. To obtain equal hardness, a control indicator in the rubber industry, the amounts of CB, CNTs, and GO were 10.7 vol%, 1.2 vol%, and 1.6 vol%, respectively. J-integral and dynamic fatigue tests revealed that NR filled with CB exhibited the best quasi-static fracture resistance and dynamic crack growth resistance. The much higher hysteresis loss of NR filled with CNTs weakened its fatigue resistance. The planar GO played a limited role in preventing crack growth. Furthermore, digital image correlation revealed that NR filled with CB had the highest strain amplification level and area at the crack tip, which dissipated the most local input energy and then improved the fracture and fatigue performance.     

吹扫捕集-气相色谱-质谱法测定水中痕量甲基叔丁基醚

研究建立吹扫捕集-气相色谱质谱法测定水中痕量甲基叔丁基醚(MTBE)的方法.以氘代甲苯为内标物,此方法的检出限(MDL)为0.005μg/L,线性相关系数R为0.999 8,精密度RSD范围0.87%~1.63%,加标回收率范围92.6%~98.9%.该方法快速、简单,干扰较少,样品需求量少,结果准确、可靠,重现性好,检出限低,实用价值高,适用于水中痕量甲基叔丁基醚的测定.     

A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for 1H,6Li spin pairs

Heteronuclear TOCSY (HEHAHA) experiments for ¹H,⁶Li spin pairs in organolithium compounds with adjacent strongly coupled ¹H,¹H spin systems showed unexpected cross peak behaviour: for n‐butyllithium ¹H,⁶Li cross peaks were completely missing, whereas for the dimer of (Z)‐2‐lithio‐1‐(o‐lithiophenyl)ethane, a cross peak for remote protons was observed even at very short mixing times. It was assumed that strong magnetization transfer within the proton spin systems was responsible for these results, which prevented unambiguous chemical shift assignments. Selective experiments with the ⁶Li,¹H‐HET‐PLUSH‐TACSY sequence then showed the expected ⁶Li,¹H cross peaks for the transfer via the directly coupled ¹H and ⁶Li nuclei. For n‐butyllithium transfer to H(C_α) via an unresolved heteronuclear coupling constant below 0.1 Hz is unambiguously observed. Cross peaks in the 2D ⁶Li,¹H‐HET‐PLUSH‐TACSY spectra for the dimer of (Z)‐2‐lithio‐1‐(o‐lithiophenyl)ethane are readily explained by the measured coupling network and the corresponding active mixing conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

多孔硅橡胶有限变形的弹性行为

针对孔隙度较大 (孔隙度大于 5 0 % )的硅橡胶材料在压缩情况下的大变形 ,提出了可描述此类可压橡胶材料力学行为的应变能密度函数 ,推导了硅橡胶材料的本构方程。利用硅橡胶材料的单轴压缩实验进行了材料参数拟合 ,讨论了多孔硅橡胶的孔隙度和体积变形对压缩性能的影响     

Chemorheological response of elastomers at elevated temperatures: Experiments and simulations

An experimental study and a method for simulating the constitutive response of elastomers at temperatures in the chemorheological range (90-150 °C for natural rubber) are presented. A comprehensive set of uniaxial experiments for a variety of prescribed temperature histories is performed on natural rubber specimens that exhibit finite elasticity, entropic stiffening with temperature, viscoelasticity, scission, and oxygen diffusion/reaction effects. The simulation approach is based on a multi-network framework for finite elasticity, isothermal incompressibility, thermal expansion, and temperature-induced degradation. The model extends previous work to account for kinetics of scission for arbitrary time-varying temperature histories and incorporates the effects of viscoelastic relaxation and diffusion-limited oxidative scission. The model is calibrated to experiments performed on a commercially-available filled natural rubber material, and numerical simulations are compared favorably to experiments for a variety of temperature histories.     

TEST AND CHARACTERIZATION FOR THE INCOMPRESSIBLE HYPERELASTIC PROPERTIES OF CONDITIONED RUBBERS UNDER MODERATE FINITE DEFORMATION

In this paper, the automated grid method is applied to test for the mechanical properties of conditioned rubbers under the moderate ?nite deformation (not exceeding 100%). More accurate stress-strain curves of conditioned rubber specimens unde…     

橡皮薄膜缺口顶端场的大变形分析

分析了橡皮类薄膜缺口顶端的弹性场，借助于文［１］引入的本构关系得到了缺口顶端场的渐近方程．通过将缺日顶端场划分为收缩角区和扩张角区，得到了顶端场的解．该解表明，奇异特性与本构参数和缺口角度有关，这一结论得到了数值解的证实．