硫化天然橡胶物理松弛时间的测量

硫化天然橡胶物理松弛时间的测量裘怿明刘从伟时锋傅政（青岛化工学院橡胶工程学院青岛２６６０４２）关键词硫化天然橡胶，应力松弛速率，数值计算方法，曲线拟合高分子热运动的特点之一是存在松弛现象，通常，人们描述高分子材料的松驰速度采用松驰时间τ［１］．实际...     

Preparation and properties of natural rubber/rectorite nanocomposites

Natural rubber (NR)/rectorite nanocomposite was prepared by co-coagulating NR latex and rectorite aqueous suspension. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to characterize the microstructure of the nanocomposite. The results showed that the nanocomposite exhibited a higher glass transition temperature, lower tan δ peak value and slightly broader glass transition region compared with pure NR. The gas barrier properties of the NR/rectorite nanocomposites were remarkably improved by the introduction of nanoscale rectorite because of the increased tortuosity of the diffusive path for a penetrant molecule. The nanocomposites have a unique stress-strain behavior due to the reinforcement and the hindrance of rectorite layers to the tensile crystallization of NR.     

自制固相微萃取探头用于分析大白菜中有机磷农药

采用溶胶-凝胶方法制备的聚甲基苯基乙烯基硅氧烷／羟基硅油（PMPVS／OH-TSO）固相微革取探头与气相色谱（GC）联用对大白菜样品中的有机磷农药（敌敌鼹、二嗪农、甲摹对硫磷、马拉硫磷和乙基对硫磷）进行了分析，同时优化了固相微革取的实验条件．该探头较商用探头萃取能力更强，方法的检出限低（1．01～2．56ng／g），重现性好（3．5％～9．9％），线性范围宽（2个数量级），对市售的大白菜样品进行了标准加入回收实验，5种有机磷农药的同收率分别为80．2％，90．3％，85．4％，81．9％和91.8％，     

Influence of accelerator type on properties of NR/EPDM blends

The effect of accelerator type on processability and mechanical properties of 60/40 natural rubber/ethylene propylene diene monomer (NR/EPDM) blend was investigated. Three groups of commercial accelerators were selected, i.e., sulfenamide group (Santocure-TBBS), thiuram group (Perkacit-TMTD) and mercapto group (Perkacit-MBT and Perkacit-MBTS). The results reveal that the accelerator type not only affects the cure characteristics, but also has great influence on compound viscosity. Among the accelerators studied, TBBS gives the best processing safety together with a relatively high state of cure. In addition, TBBS also provides good cure compatibility between the NR and EPDM phases, giving rise to superior mechanical properties. Although TMTD could give a high state of cure, it causes severe cure incompatibility, leading to poor tensile strength. Due to their lower reactivity, the two mercapto accelerators give a relatively low state of cure. Therefore, the vulcanizates obtained possess low modulus and hardness as well as degree of elasticity. Surprisingly, it is found that the tensile strength of the MBTS-cured blend is relatively high. Good cure compatibility given by MBTS could be used to explain the results.     

Rubber network in elastomer nanocomposites

The influence of inorganic nanoparticles on crosslinking mechanism of elastomers has been evaluated by applying the tube model on equilibrium statistical mechanics. The results have shown that a highly ordered structure with a huge amount of entanglements, wherein the polymer is nanoscopically confined, is formed by the addition of nanoparticles. These physical links exhibit freedom of movement under stretching, but in a lower volume because of confinement. That is, network molecular parameters such as lateral tube dimensions or average molecular mass of the chains decreased in presence of nanoparticles.     

Studies on erosion of silicone rubber exposed to partial arc discharges

The effect of electrolyte conductivity on the partial arc discharge development between two electrolyte electrodes on a silicone rubber sheet surface was investigated. Tests were executed by placing the salt-waterlogged glass-filter paper on a silicone rubber sheet to simulate a polluted electrolyte layer, and partial arc discharges with a constant current value of 10 mA were observed. It was found that the formation of an arc channel and a temperature distribution on the sample surface varied with the electrolyte conductivity. In addition, the relation between the electrolyte conductivity and the weight loss due to the heat erosion of specimens was also investigated by a 3D morphological observation and a simulated calculation. The partial arc discharge did significantly not influence on the sample surface erosion under serious polluted conditions. In contrast, the severest erosion appeared under the light pollution with comparatively lower conductivity of the electrolyte electrodes.     

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex was studied. The results indicate that Gc value of crosslinking (Gc) will be higher at the same radiation dose when a sensitizer exists, and Gc value decreases with the increase of radiation dose (D) conforming to the formula Gc=KD^-α, where K and α are constants depending on sensitizers. The more sensitizers added, the greater the Gc value. However, the viscosity of the natural rubber latex also increases rapidly along with the increase of sensitizers added.Some sensitizers, such as TMPTA, can decrease the optimum dose from about 200 kGy to approximately 20 kGy according to our experiment. The tensile strength of the film can reach round 20 MPa. Other physical properties are comparable to those of unsensitized.     

Syneresis and crystallinity in plasticized rubbery networks and composites

We prepared polycaprolactone networks plasticized (60 wt%) with triacetin, with and without filler particles to model high-energy solid rocket propellants. Under strain and at lower temperatures these materials partially crystallize but also undesirably exude plasticizer (syneresis). We measured both properties isothermally (30°C) on the basis of molecular mobility: crystallinity with rapid-passage cw proton nuclear magnetic resonance (NMR), and syneresis with pulsed-gradient spin-echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically with strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggesting that syneresis originates in expulsion of plasticizer from crystallizing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal, with plasticizer accumulating in strain-debonded void regions near filler particles. © 1994 John Wiley & Sons, Inc.     

PVDF压电计的动态响应特性及其在橡胶材料SHPB实验中的应用

通过夹心式PVDF(Polyvinylide Fluoride)压电计的动态分离式Hopkinson压杆(SHPB)标定实验,系统地讨论了传感器的动态响应特性,其中包括测量电路、PVDF表面应力集中、压电计的材料及结构特性和同一压电计受多次撞击对测试信号的影响,为PVDF压电计的制作工艺研究提供参考。利用标定好的压电计测试了橡胶材料在SHPB实验中的动态应力均匀过程。结果表明:调节并联电阻值可以提高压电计的传感精度;增大压电计的敏感面积可以减小因应力集中所造成的信号失真;材料的热粘塑性性质、摩擦效应等将使信号振荡幅度偏小;多次撞击对信号的加载与卸载段都将产生影响,但当传感器表面未发生明显损伤时,测试的应力平台平均值与真实信号近似相同。     

A simple and inexpensive "solvent in silicone tube extraction" approach and its evaluation in the gas chromatographic analysis of pesticides in fruits and vegetables

A novel, simple, and inexpensive approach to sorptive extraction, which we call solvent in silicone tube extraction (SiSTEx), was applied to pesticide residue analysis and its effectiveness and efficiency were evaluated. In SiSTEx, which is a form of open tubular sorptive extraction, a piece of silicone tubing (4 cm long, 1.47 mm ID, 1.96 mm OD in this study) is attached to the cap of a 20 mL glass vial that contains the aqueous sample. The tubing is plugged at the end dangling in the sample solution, and MeCN (e.g., 40 microL) added by syringe to the inner tube volume through a septum in the cap. A stir-bar is used to mix the sample for a certain time (e.g., 60 min), which allows chemicals to partition into the tubing where they diffuse across the silicone and partition into the MeCN. The final MeCN extract is then analyzed for the concentrated analytes. In this study, the SiSTEx approach was evaluated for the analysis of organophosphorus (OP) and organochlorine (OC) pesticides in fruits and vegetables using GC/pulsed flame photometric (PFPD) and halogen specific (XSD) detectors for analysis. The produced samples were initially extracted by a rapid MeCN procedure, and 5 mL of the initial extract was diluted four-fold with water to undergo sorptive extraction for 60 min. The final extract was analyzed by GC/PFPD + XSD for 14 OP and 22 OC pesticides. This simple approach was able to detect 26 of the 36 pesticides at 10 ng/g or less original equivalent sample concentration with average reproducibility of 11% RSD. For those 26 pesticides, a 44-fold lower detection limit on average was achieved in matrix extracts using SiSTEx despite the four-fold dilution with water.