Effect of peroxide crosslinking on the dynamic modulus of silicone rubber

The effect of peroxide crosslinking on the dynamic modulus of a silica‐reinforced silicone [poly(dimethylsiloxane)] elastomer was investigated. Three different peroxides (t‐butyl peroxide, t‐butyl perbenzoate, and benzoyl peroxide) were employed at various practical loadings and differences in the nonlinear behavior of the dynamic modulus were found. Results are discussed with respect to changes in crosslinking density and the identity of the peroxide. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1504–1512, 2005     

导电硅橡胶导电性和电热性的研究

对乙炔炭黑作导电填料的导电硅橡胶的导电性和电热性进行了研究。结果表明，由乙炔炭黑用量和渗滤阈可以预测和控制导电硅橡胶的体积电阻率；导电硅橡胶的电阻－温度变化规律符合隧道效应理论模型，导电硅橡胶的电压－电流特性呈非线性欧姆性，且乙炔炭黑用量越大，电压－电流特性的非线性欧姆性越显著；发热量与热损耗量达到平衡时，导电硅橡胶的表面温度可维持140℃，导电硅橡胶可作面状发热体使用；在满足导电性能的前提下，为保证导电硅橡胶良好的物理性能，应控制乙炔炭黑用量。     

Influence of crosslinking degree of silicone rubber particles on properties of epoxy resin

Silicone rubber particles with different degrees of crosslinking were prepared. Silicone oils containing Si—H groups and vinyl groups were reacted at various mol ratios in their composite emulsions. Epoxy resin was modified using these particles and the results indicated that the content of the silicone rubber particles, the crosslinking degree of the rubber particles, and the addition of a coupling agent affected the properties of the modified epoxy resins. The influence of the coupling agent depends on the crosslinking degree of the silicone rubber particles. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 619–625, 1998     

DC current voltage characteristics of silicone rubber filled with conductive carbon black

Direct current (DC) current‐voltage (I‐V) characteristics of silicone rubber filled with conductive carbon black (CB) were studied at room temperature in the voltage range of 1–46 V. The current‐voltage relationship can be expressed as I = AV^B, where A and B are constants that show capability and property of electrical conduction, respectively. The I‐V curve can be divided into ohmic and nonohmic regions. In nonohmic region, B < 1, and the resistance increases with the rise of voltage. Higher CB loading leads to lower transforming voltage from ohmic to nonohmic region and much deviation from Ohm's law. The reason for this deviation is the unbalance between the heat generated and the heat loss of conductive silicone rubber during the measurement. When the heat effect is eliminated completely, the electrical conduction is ohmic. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 587–592, 2004     

Vinyl‐containing silicone resin as the crosslinking agent of heat‐curable silicone rubber

Heat‐curable silicone rubber (HCSR) was prepared by using vinyl‐containing silicone resin (VSR) as the crosslinking agent instead of polyvinylsilicone oil (C gum). Mechanical properties and crosslink density of the vulcanizates were measured. The results indicate that VSR is a good crosslinking agent for HCSR. The tensile strength, tearing strength, elongation at break, and hardness of the vulcanizate can reach 10.2 MPa, 29.1 kN/m, 720%, and 58 SHA, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3123–3127, 2002; DOI 10.1002/app.10054     

硫化对镀银铝粉/甲基乙烯基硅橡胶导电复合材料性能的影响

研究了硫化时间、硫化温度、交联剂及助交联剂用量对镀银铝粉/甲基乙烯基硅橡胶(MVQ)复合材料导电性能及力学性能的影响。结果表明,镀银铝粉/MVQ复合材料最佳硫化条件:一段硫化时间为硫化仪所测得的正硫化时间(14min),二段硫化时间为4h,硫化温度为170℃,交联剂2,5-双(叔丁基过氧化)-2,5-二甲基己烷的用量为3份,助交联剂三烯丙基异氰脲酸酯的用量为2份。     

Studies on conductive silicone rubber compounds

The electrical conductivity of silicone rubber vulcanizates containing carbon blacks [e.g., acetylene black, lamp black, and ISAF (N-234) black] were investigated. The change in electrical conductivity with varying amounts of carbon blacks and the temperature dependence was measured. The mechanical properties like tensile strength, tear strength, elongation at break, hardness, etc., of the vulcanizates were determined. A comparative study of the electrical conductivity of the composites revealed that the electrical conductivity of the composites made with acetylene black was higher than that of the composites made of other blacks. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1043–1050, 1998     

Effect of the particle size of Al2O3 on the properties of filled heat‐conductive silicone rubber

An elastomeric thermal pad with a thermal conductivity of 1.45 W/m K, needed for the heat dissipation of microelectronics, was obtained with hybrid alumina of different particle sizes as a filler and silicone rubber (vinyl‐end‐blocked polymethylsiloxane) as the matrix. The effects of the amount, particle size, and mixing mass ratio of the filler particles on the thermal conductivity and mechanical properties of silicone rubber were investigated. The results indicated that the thermal conductivity of the rubber filled with larger particles was superior to that of the rubber filled with the smaller grain size, and the rubber incorporated with a mixture of hybrid particles at a preferable mass ratio exhibited higher thermal conductivity than the rubber for which a filler with only a single particle size was used. In addition, the surface treatment of the hybrid filler with 3‐methacryloyloxypropyltrimethoxysilane could increase the thermal conductivity of the composite rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1312–1318, 2007     

Al2O3对导热硅橡胶性能的影响

考察了微米Al2O3的填充量及其粒径对甲基乙烯基硅橡胶导热性能及力学性能的影响,与纳米Al2O3填充硅橡胶进行了对比。结果表明:硅橡胶的导热系数随微米Al2O3填充量的增加而升高,但微米Al2O3填充量过大时,硅橡胶的力学性能和加工性能变差,最大填充量不宜超过220份。当微米Al2O3填充量小于100份时,大粒径Al2O3填充硅橡胶的导热性能优于小粒径Al2O3填充硅橡胶;当微米Al2O3填充量超过100份后,5μmAl2O3填充硅橡胶的导热性能优于50μmAl2O3填充硅橡胶;0·5μmAl2O3填充硅橡胶的导热性能始终低于5μm和50μmAl2O3填充硅橡胶;纳米Al2O3填充硅橡胶的导热性能明显优于微米Al2O3填充硅橡胶。小粒径Al2O3填充硅橡胶的力学性能优于大粒径Al2O3填充硅橡胶。与单一微米粒径的Al2O3填充硅橡胶相比,在高填充量(180份)下,50,5,0·5μm与50nm的AlO(质量比2∶5∶1∶1)混合填充硅橡胶呈现较高的导热性能和拉伸强度。     

镀银玻璃微珠/硅橡胶导电复合材料导电性能的影响因素

研究镀银玻璃微珠的用量、粒径、表面改性工艺以及导电硅橡胶硫化程度等对镀银玻璃微珠/硅橡胶复合材料导电性能的影响.结果表明,镀银玻璃微珠的粒径越大,复合材料的导电性能越好;湿法预处理和原位改性-分散工艺制得复合材料的导电性能和导电稳定性优于直接干混工艺;导电硅橡胶硫化程度的提高有利于提高材料的导电性能;Payne效应的大小与导电硅橡胶的体积电阻率有很强的相关性.     

The effect of pre-curing UV-irradiation on the crosslinking of silicone rubber

A recent work made use of selective pre-curing UV-irradiation and its effect on the kinetics of reaction of heat-cure silicone elastomers to spatially tune its viscoelastic properties and design architected solid membranes. The present study adds to the possibility of controlling the local properties of spatially graded materials by exploring the effect of key processing parameters such as the UV dose and the silicone mix thickness on the vulcanization kinetics. Dynamic Differential Scanning Calorimetry measurements have been performed showing that, over the conditions explored, the higher the UV dose, the slower the kinetics reaction. Additionally, complete crosslinking was always reached. Companion modeling effort using the Kissinger reaction model is attempted and the effects of processing parameters on the apparent activation energy are discussed. This work is a crucial first step towards the control of the processing settings needed to design architected silicone rubber membranes with spatially controlled mechanical property gradients obtained from a unique macromolecular network.     

Mechanical properties and antibacterial activity of peroxide‐cured silicone rubber foams

Silicone rubber (SR) foams were prepared by the peroxide curing of a silicone compound with 2,4‐dichlorobenzoyl peroxide (DCBP), di‐t‐butyl peroxide (DTBP), or 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (DBPH) in the presence of 2,2′‐azobisisobutyronitrile (AIBN) as a blowing agent. The cells were formed in the foam as a result of nitrogen produced by the decomposition of AIBN during the foaming process. The cell size, hardness, and tensile properties of the SR foams were examined as a function of the peroxide concentration. When the peroxide concentration increased, the hardness and tensile strength of the SR foams increased, whereas the cell size and elongation at break decreased. The antibacterial activity of the prepared foams was also evaluated via their effects on Staphylococcus aureus and Escherichia coli. The peroxide‐cured SR foams had antibacterial activity because a toxic residue was generated by the peroxide decomposition. The foam prepared by the AIBN/DCBP system showed more antibacterial activity than the AIBN/DBPH and AIBN/DTBP ones. However, after postcuring at 250°C for 2 h, the antibacterial activity of the SR foams significantly decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

乙烯基含量对热硫化硅橡胶抗撕裂性能的影响

研究不同乙烯基含量对热硫化硅橡胶的力学性能尤其是抗撕裂性能的影响,采用平衡溶胀法测定硅橡胶的交联密度,研究不同乙烯基含量的硅橡胶并用胶的撕裂强度和交联密度的关系。结果表明,随着硅橡胶乙烯基含量的增大,硅橡胶硫化胶的断裂伸长率减小,300%定伸应力和硬度升高,当乙烯基摩尔分数为0.15%时,撕裂强度和拉伸强度较高。乙烯基摩尔分数为0.15%的硅橡胶和乙烯基摩尔分数为0.06%的硅橡胶并用,当并用比为50/50时,撕裂强度高达45.8 kN/m,乙烯基摩尔分数为0.30%的硅橡胶和乙烯基摩尔分数为0.06%的硅橡胶并用,当并用比为4/96时,撕裂强度可达42.9kN/m。乙烯基摩尔分数为0.30%的硅橡胶和乙烯基摩尔分数为0.15%的硅橡胶并用,并用比对硫化胶的撕裂强度影响不大。高乙烯基含量和低乙烯基含量的硅橡胶并用,有利于使硅橡胶的交联结构由"分散交联"转变为"集中交联",当并用胶的乙烯基摩尔分数在0.15%以内,硅橡胶并用胶的撕裂强度随乙烯基摩尔分数的增加而先增大后降低,而此时并用胶的交联密度与撕裂强度成反比。     

多官能团单体对甲基乙烯基硅橡胶的辐射交联敏化效应

研究了在γ射线的作用下多官能团单体对甲基乙烯基硅橡胶(MVQ)的辐射交联敏化效应.结果表明,加入多官能团单体的MVQ经过辐射发生交联反应;四甘醇二甲基丙烯酸酯、三烯丙基异氰尿酸酯、三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)3种多官能团单体对MVQ的辐射交联具有明显的敏化作用,其中TMPTMA的敏化效果最好,其最佳用量为2份;加入TMPTMA或者加大辐射剂量,MVQ的损耗因子提高,玻璃化转变温度升高;当辐射剂量为40 kGy时,添加2份TMPTMA的MVQ的物理机械性能达到最佳.     

Transient effects in dynamic modulus measurement of silicone rubber,part 2: Effect of mean strains and strain history

The strain‐dependent dynamic storage modulus of a poly(dimethyl‐siloxane‐co‐methylvinyl‐siloxane‐co‐methylphenyl‐siloxane)‐based silicone elastomer (PVMQ), which is reinforced with fumed silica and crosslinked with peroxide, is investigated. The time dependence of the dynamic storage modulus on the magnitude of the mean strain at a particular test condition is investigated. The dynamic modulus results are shown to depend on the time of cycling as well as the relative magnitudes of the dynamic and mean strains. The relaxation of the force required to maintain the mean strain is observed to depend on the magnitude of the dynamic strains and the data are shown to be consistent with static stress relaxation experiments in the limit of zero dynamic strain. Recovery of the dynamic modulus from the exposure to higher strain cycling is seen to be facilitated by dynamic cycling with higher cycling strains yielding faster recovery rates. The observed phenomena are interpreted in terms of the role of entanglements in the polymer phase on the dynamic behavior of the elastomer material. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2197–2204, 2007     

导热电子灌封硅橡胶的研究进展

概述了导热电子灌封硅橡胶的研究背景。综述了导热电子灌封硅橡胶的组成,提高导热电子灌封硅橡胶导热性的途径及灌封工艺,灌封中常见的问题及改进措施,灌封材料的性能要求等,对导热电子灌封硅橡胶未来的研究方向进行了展望。     

导热硅橡胶的研究进展

综述了填充型导热橡胶的导热机理和各类导热填料的导热特性,介绍了提高导热硅橡胶导热性的途径。     

Oil bleed from elastomeric thermal silicone conductive pads

Oil bleed is a serious problem in elastomeric thermal silicone conductive pads. The components of the oil bleed and the effect of the silicone chemical parameters on the amount of oil bleed have been determined. The main components of oil bleeds are the uncrosslinked silicones in the cured resins, which include the unreacted silicone materials and the macromolecular substances produced by the hydrosilylation reaction. Cured resins with a high crosslinking density and a high molecular weight of vinyl silicone residues had a lower amount of oil bleed. In addition, a low Si-H content also reduced the amount of oil bleed.

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Highly thermally conductive room‐temperature‐vulcanized silicone rubber and silicone grease

In this study, the effects of thermally conductive filler type (α‐Al₂O₃, SiC), volume fraction of the filler, and filler particle size distribution on the thermal conductivity and viscosity of room‐temperature‐vulcanized (RTV) silicone rubber and silicone grease were investigated. We were interested to find that silicone grease (or the RTV silicone rubber) had a maximum thermal conductivity (～1.48 W/mK) and a minimum viscosity (～3.4 × 10⁴ mPa s), with a definite total volume fraction of the filler (0.55) when the distribution of filler sizes (the number ratio of two different particles sizes, i.e., 0.8 and 6 μm) was 600–700. We were able to increase the thermal conductivity of the RTV silicone rubber and silicone grease beyond 2 W/mK by increasing the total volume fraction of the filler with adequate filler size distributions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2397–2399, 2003