有限元模拟在橡皮成型中的应用

橡皮成形过程中常会发生起皱、开裂等缺陷,应用有限元分析软件Abaqus对框缘凸弯边橡皮成型过程仿真,研究了模具圆角尺寸变化对成型过程中钣金件的厚度变化、应力分布、起皱等的影响,从而可进一步修正模具设计,消除加工缺陷、为进一步开展精密成型研究奠定基础。     

基于数值模型的金属橡胶干摩擦迟滞特性研究

以完全基于实际材料、工艺参数的数值模型为基础,对金属橡胶的干摩擦迟滞特性进行了研究。从成形压力曲线、材料组织结构、尺寸、加载-卸载曲线等四个方面对数值模型的可靠性进行了验证。建立了弹性微元模型及其局部坐标,对接触对数量、滑动接触对比例、接触对形态进行了研究。接触对数量随加载量的增加而增加,随卸载量的增加而减小,滑动接触对约占所有接触对数量的80%。将接触对分为典型接触对和非典型接触对,其中典型接触对占主要成分。根据接触对的细观特征,建立了接触对力学模型,进而建立了金属橡胶迟滞特性曲线的数学模型。数学模型准确性、可靠性较好、各参数物理意义充分,能够较好地对材料的干摩擦迟滞特性进行描述,对材料的设计具有一定指导意义。     

Real‐time property prediction for an industrial rubber‐mixing process with probabilistic ensemble Gaussian process regression models

In internal rubber‐mixing processes, data‐driven soft sensors have become increasingly important for providing online measurements for the Mooney viscosity information. Nevertheless, the prediction uncertainty of the model has rarely been explored. Additionally, traditional viscosity prediction models are based on single models and, thus, may not be appropriate for complex processes with multiple recipes and shifting operating conditions. To address both problems simultaneously, we propose a new ensemble Gaussian process regression (EGPR)‐based modeling method. First, several local Gaussian process regression (GPR) models were built with the training samples in each subclass. Then, the prediction uncertainty was adopted to evaluate the probabilistic relationship between the new test sample and several local GPR models. Moreover, the prediction value and the prediction variance was generated automatically with Bayesian inference. The prediction results in an industrial rubber‐mixing process show the superiority of EGPR in terms of prediction accuracy and reliability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41432.     

Polymer properties associated with chemical permeation performance of disposable nitrile rubber gloves

Unlike other chemical protective clothing and devices, disposable gloves are not reliably certified to exceed chemical permeation performance standards. In light of generalized chemical compatibility charts, significant variability in performance exists between similar products on the market. This study evaluates whether nitrile rubber composition and uniformity are better associated with the observed product variability in chemical resistance than the available mechanical testing (e.g., tensile strength) done on these products. The independent variables evaluated include two physical, three mechanical, and four compositional parameters. Based on correlation and multiple regression analyses, the factors associated with variation in permeation of ethanol are area density, acrylonitrile content, carboxylation of the base polymer, the amount of extractable oils and oily plasticizers, and polymer uniformity. Increases in area density, acrylonitrile content, and carboxylation improve chemical resistance. Decreases in extractable oils and polymer variability (uniformity) also improve chemical resistance. On average, these combined factors accounted for about 53–67% of the observed variability in permeation, which were moderate but not strong associations. In contrast, tensile strength accounted for about 1% of the observed variability, a negligible effect. These results support the notion that standardized tests and certification criteria need to address polymer composition and uniformity to reduce gaps in performance. However, in light of the lack of strong correlations, further evaluation with tighter control over chemical composition is warranted. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41449.     

Preparation and properties of acrylonitrile–butadiene rubber–graphene nanocomposites

The graphene oxide (GO) was prepared by sonication‐induced exfoliation from graphite oxide, which was produced by oxidation from graphite flakes with a modified Hummer's method. The GO was then treated by hydrazine to obtain reduced graphene oxide (rGO). On the basis of the characterization results, the GO was successfully reduced to rGO. Acrylonitrile–butadiene rubber (NBR)–GO and NBR–rGO composites were prepared via a solution‐mixing method, and their various physical properties were investigated. The NBR–rGO nanocomposite demonstrated a higher curing efficiency and a change in torque compared to the gum and NBR–GO compounds. This agreed well with the crosslinking density measured by swelling. The results manifested in the high hardness (Shore A) and high tensile modulus of the NBR–rGO compounds. For instance, the tensile modulus at a 0.1‐phr rGO loading greatly increased above 83, 114, and 116% at strain levels of 50, 100, and 200%, respectively, compared to the 0.1‐phr GO loaded sample. The observed enhancement was highly attributed to a homogeneous dispersion of rGO within the NBR matrix; this was confirmed by scanning electron microscopy and transmission electron microscopy analysis. However, in view of the high ultimate tensile strength, the NBR–GO compounds exhibited an advantage; this was presumably due to strong hydrogen bonding or polar–polar interactions between the NBR and GO sheets. This interfacial interaction between GO and NBR was supported by the marginal increase in the glass‐transition temperatures of the NBR compounds containing fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42457.     

Design and preparation of cross‐linked α‐methylstyrene acrylonitrile copolymer nanoparticles and their interfacial investigation with rubber

Cross‐linked α‐methylstyrene and acrylonitrile (MStAN) copolymer particles in a latex form were synthesized by free radical emulsion polymerization. The particles showed a narrow size distribution and an average diameter of 65 nm. The amount of the vinyl groups at the surface of the (MStAN) copolymer particles resulted from varied amount of the initiator (APS) and the cross‐linking agent (DVB) was detected by iodine titration method. When filled into ethylene propylene rubber (EPR), the MStAN nano‐particles exhibited excellent reinforcing capabilities, and with the increase of the vinyl groups at the surface of MStAN particles, the tensile stress of MStAN/EPR increased. Results demonstrated that the vinyl groups at the surface of the (MStAN) copolymer particles provided certain chemical interactions between the filler particles and the macromolecular chains of rubber matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41914.     

Friction and wear behavior of styrene butadiene rubber‐based composites reinforced with microwave‐devulcanized ground tire rubber

In this work, the tribological properties of a new material obtained by revulcanization with styrene butadiene rubber (SBR) and devulcanized ground tire rubber (GTR) were investigated. GTR was devulcanized using the microwave method at a constant power while varying the microwave exposure time. Devulcanized rubber (DV‐R) and untreated GTR were revulcanized by mixing with SBR at different rates (10, 30, 50 phr). To determine friction and wear characteristics of the samples, pin (ball) on disc and abrasion tests were conducted. Scanning electron microscopy (SEM) was employed to observe the worn surfaces of the composites to correlate the experimental test results to the wear mechanisms. All of these tests and experiments were performed on original vulcanized rubber samples for comparison. The composites exhibited different friction and wear behavior due to morphology, dispersion behavior and devulcanization functionalization of ground tire rubber. In general, DV‐R/SBR composites exhibited improvement in both mechanical and tribological properties. However, the enhanced compatibility of DV‐R resulting from the specific chemical coupling of DV‐R with SBR was crucial for the mechanical, friction and wear properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42419.     

高岭土与膨润土复配填充丁苯橡胶复合材料的性能

以高岭土与不同类型的膨润土JZ-PRT、Na-PRT和Ca-PRT复配,用硅烷偶联剂Si-69进行球磨改性,得到复配黏土K-JZPRT、K-Na PRT和K-Ca PRT,将其作为增强剂填充到丁苯橡胶(SBR)中,制备了复配黏土/SBR复合材料,用X射线衍射仪、傅里叶变换红外光谱仪以及冷场发射扫描电子显微镜对复配黏土及复合材料进行了表征,并考察了复合材料的加工性能、力学性能和气阻隔性能。结果表明,复配黏土中膨润土的特征衍射峰强度都有所降低,高岭土除d001衍射峰外,其他特征衍射峰强度都有不同程度的弱化。与填充K-JZPRT的SBR复合材料相比,填充K-Na PRT和K-Ca PRT的复合材料的硫化速率更快,门尼黏度更低,因而加工性能也更好。填充复配黏土的复合材料的力学性能和气阻隔性能较SBR均有明显改善,其中K-Na PRT的填充效果最好,拉伸强度增加了652%,透气率降低了43%。复配黏土在SBR基体中分散比较均匀,与橡胶分子的结合良好。     

Bilaterally Microstructured Thin Polydimethylsiloxane Film Production

Thin PDMS films with complex microstructures are used in the manufacturing of dielectric electro active polymer (DEAP) actuators, sensors and generators, to protect the metal electrode from large strains and to assure controlled actuation. The current manufacturing process at Danfoss Polypower A/S produces films with a one-sided microstructured surface only. It would be advantageous to produce a film with both surfaces microstructured, as this increases the film’s performance efficiency. The new technique introduced herein produces bilaterally microstructured film by combining an embossing method with the existing manufacturing process. In employing the new technique, films with microstructures on both surfaces are successfully made with two different liquid silicone rubber (LSR) formulations: 1) pure XLR630 and 2) XLR630 with titanium dioxide (TiO₂). The LSR films (～70 µm) are cast on a carrier web substrate using a coating blade. The carrier web, which has a sinusoidal corrugation with wave height of 7 µm and a wave period of 7 µm on its surface, imparts corrugations to the bottom surface of the film. The elastomer film on the carrier web is preheated to the gel point, where the elastomer film can retain an imprint made on it. The preheated film at gel point is embossed between the rolls of a gravure lab coater, which corrugates the top surface of the film. The films are then heated, in order to cure completely. For the LSR systems used in this process, the optimum conditions for preheating are 110°C for 4–7 s, while for embossing the temperature is 110°C with 25 psi pressure between the rolls at a speed of 1.4 rpm. Scanning electron microscope (SEM) images confirm the formation of microstructures on both the surfaces of the film.     

丁腈橡胶的烯烃复分解及其产物的非均相加氢

采用烯烃复分解方式制备低相对分子质量的丁腈橡胶并对其进行非均相加氢,考察了烯烃复分解催化剂加入量、反应温度及反应时间对丁腈橡胶相对分子质量及其分布的影响。结果表明,在10 m L三氯甲烷中溶解1 g丁腈橡胶、催化剂用量0.001 g、反应温度30℃及反应时间3 h的条件下,所制备丁腈橡胶的数均分子量为(1.5~5.5)×104,重均分子量为(3.0~12.0)×104。采用非均相催化剂对低相对分子质量丁腈橡胶进行加氢的氢化度可达99%以上。