Hardness measurements of silicone rubber and polyurethane rubber cured by ionizing radiation

This work investigates the hardness of both silicone rubber and polyurethane rubber cured by ionizing radiation. Shore A hardness is used to characterize the subject elastomers in relation to the crosslinking process. Various formulations of both materials have been investigated in order to achieve the optimum cure conditions. A small amount of a chemical curing agent has been incorporated in some formulations in order to reduce the required dose to achieve full cure conditions. Silicone rubber improved in hardness with increasing absorbed dose, whereas hardness remained constant over a broad range of absorbed doses for polyurethane rubber.     

Parameters influencing fatigue life prediction of dielectric elastomer generators

For energy scavenging applications, estimating fatigue life of dielectric elastomer is as crucial as computing the amount of scavenged energy. Crack growth approach, well known in rubber industry, is a fast methodology to estimate fatigue life. We adapt this methodology to dielectric silicone elastomers (Elastosil 2030) and we focus in particular on the factors influencing this estimation such as sample geometry, tearing energy, power law. We underline that the variation in tearing energy estimation induces a small dispersion on the fatigue life estimation whereas power law identification is the crucial and critical parameter. Finally, we define an index of performance based on fatigue life and scavenged energy density, and we compare two materials (acrylic 3MVHB4910 and silicone Elastosil 2030).     

Comparative study on degradation of ethylene-propylene rubber for nuclear cables from gamma and beta irradiation

Considering safety is the priority concern of nuclear power plants, equipment qualification testing of the nuclear components manufactured should be paid special attention to. Thereinto, equivalent conversion (1:1) from the absorbed beta doses to gamma doses is a rule of thumb for irradiation qualification testing of the polymers used as nuclear cables, however whether it is reasonable and applicable to Chinese domestic polymers still requires investigation. In this paper, both gamma and beta irradiation testing with the actual dose rates and total absorbed doses in China Advanced Passive (CAP) series nuclear power plant was performed upon one domestically manufactured ethylene-propylene rubber intended for nuclear cable insulation in China. The mechanical and the electrical properties before and after irradiation were measured to compare the extent and the trend of degradation between the two irradiation types, and related oxidation degradation mechanism especially its attenuation along the thickness was quantitatively addressed.     

New membrane materials for potassium-selective ion-sensitive field-effect transistors

Several polymeric materials were studied as membrane materials for potassium-selective ion-sensitive field-effect transistors (ISFETs) to overcome the problems related with the use of conventional plasticized poly(vinyl chloride) membranes casted on ISFET gate surfaces. Several acrylate materials, such as ACE, Epocryl and derivatives, showed no reproducible results. Three room-temperature vulcanizing (RTV)-type silicone rubbers were tested. The addition-type RTV-2 silicone rubber was not suitable as a membrane material, but the condensation-type RTV-1 and especially the RTV-2 silicone rubber showed good results. ISFETs with a Silopren membrane showed a durability of at least 2 months.     

Comparison of tear test methods

Tear strength is an important property of a rubber vulcanisate, particularly when considering it for applications such as cables, hoses and tyres. In the present study four test methods, as specified for vulcanised rubbers in British Standards (BS 903 Part A3 and BS 6899), have been investigated on five different compositions based on a nitrile natural rubber, an ethylene acrylic rubber, a polyurehane and undisclosed chloroprene elastomer. The objective of the study was to examine the influence of thickness, grain effects and strain rate on the tear strength. It was also intended to establish if the different tear test methods would rank materials in the same order and whether a constant ratio exists between the tear strength values obtained using the different methods for different materials.

Sample thicknesses in the range 0·5–3 mm and strain rates in the range 100–500 mm/min all produced small but significant variations in the tear strength, confirming that standardisation of these variables is very desirable. Grain effects were found to produce even larger variations in the test results, particularly for the trouser test pieces. It was found that the tests could be divided into two groups:

• (a) trouser and cable tests;

• (b) angle and crescent tests. The tests in each group ranked materials in the same order and the ratios between tests on different materials within each group was approximately the same.

     

聚氯乙烯表皮成分对加成型硅橡胶固化的影响

采用流变学方法研究了双组分加成型硅橡胶在不同聚氯乙烯(PVC)表皮上的固化动力学,并利用红外光谱、核磁共振波谱、电感耦合等离子体质谱仪等手段分析了PVC表皮成分,以确定导致双组分加成型硅橡胶不固化的具体原因。 结果表明,PVC表皮中导致硅橡胶不固化的主要元素为P元素。 在固定硅橡胶厚度为1 mm的情况下,当PVC表皮中的P元素质量分数低于3×10^-3%时,浇注在其上的双组分加成型硅橡胶依然能固化;而当PVC表皮中的P元素质量分数超过约2.4×10^-2%时,虽然浇注在其上的双组分加成型硅橡胶的中间层依然能固化,但与PVC表皮接触部分的硅橡胶不固化,且不固化层厚度随P元素质量分数增加而增加。 本文还研究了在P元素质量分数低于3×10^-3%的PVC表皮上,降低硅橡胶厚度至微米级时的固化行为,在P元素质量分数低于3×10^-3%的PVC表皮上,当硅橡胶厚度低于2 μm时,硅橡胶出现不完全固化现象。 双组分加成型硅橡胶在含有P元素的PVC表皮表面的固化行为主要是由硅橡胶样品中铂催化剂总含量及PVC表皮中的P元素含量确定的,同时也会受到双组分加成型硅橡胶反应速率以及铂催化剂、P元素在硅橡胶中的扩散速率的影响。     

In vitro drug release from silicone rubber–polyacrylamide composite

Composite materials containing drugs were prepared from silicone rubber and hydrogel. Cross linked polyacrylamide (PAAm) hydrogel particles were incorporated into a silicone rubber to enhance the hydrophilicity and drug release capacity of silicone rubber as a matrix. Progesterone and Thymol Blue were used as a hydrophobic and hydrophilic drug model, respectively. Different amounts of polyacrylamide (PAAm) were mixed with the drugs and uncured silicone rubber at room temperature. The composite matrices were formed using a compression molding press and cured by thermal and γ-irradiation curing methods. In vitro drug release behavior of composites and their physical and mechanical properties were investigated. The results indicated that the hydrophilic character of silicone rubber was more pronounced with increasing the amount of PAAm. Also, a significant effect on the drug release profiles was observed. The γ-irradiation curing method improved mechanical properties of composites and affected the drug release profiles. It was found that the amounts of released progesterone from γ-irradiated samples increased in comparison with the thermally cross linked composite since released Thymol Blue was reduced.     

Investigation of the hydrothermal stability of cross-linked liquid silicone rubber (LSR)

We investigate the hydrothermal stability of cross-linked liquid silicone rubber (LSR) in water at 100 °C up to period of two years. Optical microscopy of cross-sections of the exposed samples reveal that only the outer 100 μm of the surface layer is affected after two years. However, the surface chemistry of the material after prolonged exposure becomes significantly modified, as monitored by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR), which probes depths of 10 nm and 1 μm, respectively. In addition, changes to the bulk physical properties of the rubber samples, prior to and after the exposure, were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Micro-hardness analysis showed that surface roughness of the two year exposed sample increased from 60 (IRHD) to 75 (IRHD). Furthermore, the volume change (%) measurement showed a significant decrease in the course of exposure at prolonged time. The results provide the experimental basis for development of LSR materials suitable for numerous technical applications.     

An investigation of dynamic mechanical, thermal, and electrical properties of housing materials for outdoor polymeric insulators

The present paper reports the results about a study of mechanical, thermal, dynamic mechanical and electrical properties of housing (weather shed) materials for outdoor polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as housing in high voltage insulators. The result of dynamical mechanical measurement shows that the storage modulus of blends enhances with increase EPDM in formulation. It can be seen from the result of TGA measurement that initial thermal degradation of silicone rubber improves by the effect of EPDM in blends. The blends of silicone-EPDM show good breakdown voltage strength compared to silicone rubber. Surface and volume resistance of silicone rubber improve by EPDM content. The mechanical properties of EPDM such as strength, modulus and elongation at break improve by silicone.     

Radiochemical methods in nuclear waste management

Radiochemical techniques play an important role in nuclear waste management studies at the Centre for Analytical Research in the Environment. Current research includes the measurement of atmospheric emissions from a reprocessing plant, modelling of environmental pathways, and evaluation of reactor materials for the prediction of releases from ultimate disposal sites. A radiochemical separation procedure has been developed for¹²⁹I, which has been applied to a study of emissions from the Sellafield nuclear reprocessing plant. Atmospheric emissions, rainfall, grass, milk and wild food are analysed to model the ultimate fate of¹²⁹I. A new procedure has been developed for measuring sub-ppm concentrations of chlorine in archive steel samples as part of programme to produce an inventory of arisings of³⁶Cl from nuclear power stations. The method has been extended to other reactor materials and this paper describes the application of the radiochemical method for Magnox alloys, mild steel and cast iron.     

The Chemistry and Properties of the Medical-Grade Silicones

The medical grade silicones are probably the most widely used of all the synthetic polymers for permanently implanted subdermal devices. This paper reviews the chemistry of these materials from the original polymer manufacturing through the various stages necessary to obtain the types of heat vulcanizing silicone rubber, room temperature vulcanizing silicone rubber, and silicone rubber adhesive most commonly used in medical applications.     

硅橡胶复合材料阻燃研究进展

将功能填料引进到硅橡胶及其复合材料中可以获得特定功能的硅橡胶复合材料,已经成为近些年研究热点。目前阻燃剂种类繁多,但是性能比较单一,这已经不能满足人们的需要。人们在关注硅橡胶复合材料阻燃性能的同时,也考虑与其它性能兼备以及成本等问题。因此,本文综述了铂化合物、磷系阻燃剂、阻燃涂层、阻燃填料和微胶囊化阻燃剂等阻燃体系下硅橡胶复合材料的阻燃研究现状,总结了不同阻燃剂的阻燃机理,并且给出了其今后的改进方法,最后对硅橡胶复合材料阻燃研究的发展做了展望。     

聚合物的分子结构与吸声性能研究

以甲苯二异氰酸酯和聚乙二醇为原料合成了聚氨酯,同时以乙烯基聚二甲基硅氧烷和含氢硅油为原料合成了硅橡胶.然后,以上述合成的硅橡胶和聚氨酯橡胶分别作为消声涂层的基体材料,研究了聚合物分子结构对涂层吸声性能的影响.采用傅利叶变换红外光谱(FTIR)表征了聚合物的分子结构,用驻波管法测量了涂层的吸声系数,用拉伸法和剪切法测定涂层的拉伸模量和剪切模量,并利用有限元程序ANSYS8.0模拟分析了涂层在水压下的形变.测试结果表明,不同结构的聚合物,在常压和高压下呈现出不同的吸声性能.具有柔性链状结构的硅橡胶基涂层,在水压作用下形变较大,吸声系数随水压增大而迅速减小;而含氢键结构的聚氨酯基涂层,在水压作用下形变较小,吸声系数随水压增大而升高.分析认为聚合物自由体积的大小和运动可能是影响涂层吸声性能的重要因素.橡胶体积压缩后,在一定程度上减少了自由体积的大小,限止了自由体积的运动,因此,选择刚性结构的聚合物作为涂层基体,调节自由体积,是制备在高压下具有高吸声性能涂层的重要途径.     

Calcium and aluminium-based fillers as flame-retardant additives in silicone matrices. I. Blend preparation and thermal properties

This series investigates silicone composites with enhanced thermal behaviour for cable applications. Calcium and aluminium-based fillers introduced into silicone formulations were classified according to three categories: non-hydrated fillers such as CaCO₃ (precipitated calcium carbonate and natural calcite) and wollastonite, water-releasing fillers such as calcium hydroxide, ATH, boehmite, and hydroxyl-functionalized fillers including alumina and mica. The fillers were first characterized in detail, and the thermal stability of their blends with silicone was recorded by thermogravimetric analyses. A discussion on various aspects of the filler morphology (size, microstructure, release profile with temperature) on the silicone stability is finally given.     

Hydrophobic modification of poly(phthalazinone ether sulfone ketone) hollow fiber membrane for vacuum membrane distillation

New hydrophobic poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber composite membranes coated with silicone rubber and with sol–gel polytrifluoropropylsiloxane were obtained by surface-coated modification method. The effects of coating time, coating temperature and the concentration of silicone rubber solution on the vacuum membrane distillation (VMD) properties of silicone rubber coated membranes were investigated. It was found that high water permeate flux could be gotten in low temperature and low concentration of silicone rubber solution. When the coating temperature is 60 °C, the coating time is 9 h and the concentration of silicone rubber solution is 5 g L⁻¹ the water permeate flux of the silicone rubber coated membrane is 3.5 L m⁻² h⁻¹. The prepolymerization time influence the performance of polytrifluoropropylsiloxane coated membranes, and higher prepolymerization time decrease the water permeate flux of the membrane. The water permeate flux and the salt rejection was 3.7 L m⁻² h⁻¹ and 94.6%, respectively in 30 min prepolymerization period. The VMD performances of two composite membranes during long-term operation were studied, and the results indicated that the VMD performances of two composite membranes are quite stable. The salt rejection of silicone rubber coated membrane decreased from 99 to 95% and the water permeate flux fluctuated between 2.0 and 2.5 L m⁻² h⁻¹. The salt rejection of polytrifluoropropylsiloxane coated membrane decreased from 98 to 94% and the water permeate flux fluctuated in 1 L m⁻² h⁻¹ range.     

白炭黑增强型硅橡胶的组成及抗原子氧性能分析

为明确空间级硅橡胶的化学组成及填料添加对材料物理性能的影响, 采用填料复合方式制备硅橡胶高聚物材料, 并通过化学成分测试、 原子氧暴露试验及力学性能测试等研究其结构组成与物理性能. 经微观粒径测试得出硅橡胶中白炭黑填料粒径主要分布在8~16 μm; 经傅里叶变换红外光谱(FTIR)、 核磁共振波谱( ¹H NMR和 ²⁹Si NMR)和溶胶凝胶渗透色谱(GPC)测试得出硅橡胶中含有Si—Me, Si—Ph, Si—O—Si等基团和甲基、 苯基等官能团, 其分子量分散系数为1.56, 并进一步推断出硅橡胶的分子结构及基胶与交联剂的反应类型为脱羟胺型; 经原子氧暴露试验及力学试验证实, 与未改性白炭黑填充的硅橡胶高聚物材料相比, 经硅烷改性白炭黑填充的硅橡胶高聚物材料表现出更好的抗原子氧性能, 动态力学测试后储能模量高54%, 并具有更好的应力应变响应性能. 研究结果表明, 采用表面改性处理方式可增强填料与硅橡胶基质的相互作用, 从而提高填料复合型硅橡胶高聚物材料的抗原子氧性能及综合力学性能.     

The quantitative determination of fission and nuclear reaction products

Definitions are given to the terms “per cent atom burn-up” and “per cent atoms consumed” as applied to nuclear fuel analysis at the Argonne National Laboratory. The radiochemical and analytical methods which have been adapted and developed especially for this type of analysis are discussed. The analysis of nuclear reaction products by paper chromatographic methods and scintillation spectrometry is emphasised and demonstrated.     

Effect of the surrounding aeration on microcapillary electrochemical cell experiments

In the microelectrochemical capillary cell technique a silicone rubber gasket is used to avoid any electrolyte leakage between the pulled glass capillary and the working electrode (the metallic tested material). In this study, it is demonstrated that the oxygen reduction reaction (ORR) is strongly affected by the use of the silicone rubber. Experiments under a surrounding argon gas shielding of the pulled capillary in contact with the metallic surface have been performed showing a large effect on the ORR. Considering the high permeation rate of oxygen through silicone, the decrease of the reaction rate observed experimentally was validated by FEM modelling assuming that the air/silicone/water interface at the tip can be described as an air/water interface.     

加成型液体硅橡胶的研究进展

结合加成型液体硅橡胶的硫化原理,综述了加成型液体硅橡胶导热性能、耐高温性能及粘结性能的最新研究进展,发现加入金属氮化物导热填料是提高加成型液体硅橡胶导热性能的有效途径;改善分子结构是提高加成型液体硅橡胶耐高温性能的主要途径;共混粘结促进剂是提高加成型液体硅橡胶粘结性能的重要途径。介绍了加成型液体硅橡胶的最新应用领域,提出功能化加成型液体硅橡胶,如3D个性化打印硅橡胶、人体器官硅橡胶、高折光封装硅橡胶等功能材料是未来加成型液体硅橡胶的发展方向。     

Evaluation of the surface tension measurement of axisymmetric drop shape analysis (ADSA) using a shape parameter

A quantitative criterion called “shape parameter” to evaluate the quality of surface tension measurement of Axisymmetric Drop Shape Analysis (ADSA) is presented. ADSA is a powerful technique for the measurement of interfacial tensions and contact angles of pendant drops, sessile drops, and bubbles. Despite the general success of ADSA, deficient results may be obtained for drops close to spherical shape. Therefore, the “shape parameter” was used to determine the range of drop shapes in which ADSA succeeds or fails. The “shape parameter” is a dimensionless parameter that expresses quantitatively the difference in shape between a given experimental profile and an inscribed circle. The surface tension measurements of ADSA were evaluated for both pendant drop and constrained sessile drop configurations using the shape parameter. Different shapes of the pendant drop were studied using different sizes and materials of holders. For each drop configuration, a “critical shape parameter” was defined based on the minimum value of the shape parameter that guarantees an error of less than ±0.1 mJ/m². Furthermore, the effects of the type of liquid and constellation on the “critical shape parameter” were studied.