Efficient Benzodioxole‐based unimolecular photoinitiators: From synthesis to photopolymerization under UV‐A and visible LED light irradiation

The narrow emission spectra of light emitting diodides (LED) as irradiation source has brought great challenge for the development of efficient photoinitiators sensitive to LED light. This paper described a series of novel unimolecular type II photoinitiators, containing thioxanthones as chromophores and benzodioxoles as coinitiators. The structures of the photoinitiators were characterized by ¹H NMR, ¹³C NMR and high‐resolution mass spectrometer. Study on the photophysical properties of the photoinitiators indicated that electron donors/acceptors as spacers between thioxanthone and benzodioxole affected both the UV–Vis absorption and the fluorescence emission. The long wavelength absorptions from 385 nm to 402 nm as well as low fluorescence quantum yields make the investigated benzodioxole derivatives quite attractive as efficient photoinitiators under UV‐A and visible LED light irradiation. With a proper molecular design, the unimolecular photoinitiator exhibited higher initiation efficiency than the thioxanthone derivatives from the literature. Possible initiation mechanism was also proposed based on the photolysis study. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43239.     

The role of conductive pathways in the conductivity and rheological behavior of poly(methyl methacrylate)–graphite composites

Up to now, research on the dynamic process of conductive network formation has tended to focus on composite particles with one‐dimensional geometry, such as carbon black and carbon nanotubes. However, studies on this subject based on fillers with two‐dimensional structure, such as graphite, are rare in the literature. In this work, the dynamic percolation and rheological properties of poly(methyl methacrylate) (PMMA)–graphite composites under an electric field were investigated. The activation energies of conductive network formation and polymer matrix mobility were calculated from the temperature dependence of the percolation time and the zero‐shear viscosity. It was found that the activation energy calculated from the zero‐shear viscosity was not influenced by the electric field in the concentration range investigated, but the electric field had an effect on the activation energy calculated from the percolation time. This finding emphasizes that the electrical and rheological properties have different physical origins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43810.     

Gas‐liquid mass transfer behavior in a surface‐aerated vessel stirred by a novel long‐short blades agitator

For a recently developed long‐short blades (LSB) agitator, its critical rotational speed for the onset of gas entrainment, power number, and gas‐liquid mass transfer behavior in the case of surface aeration is investigated. The effect of the LSB configurations and the liquid level on the agitator performance has been studied in details. The obtained results clearly show several advantages of the LSB agitator in gas‐liquid mass transfer with respect to the agitators in the literature. It is found that its gas‐liquid volumetric mass‐transfer coefficient at a given specific power can be several times larger than those shown in the literature. It can also avoid decrease in the gas‐liquid mass transfer rate as the liquid level increases. In addition, the bubble distribution in the system is more uniform with respect to conventional agitators, resulting from better distribution of the dissipated energy for the LSB agitator. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1322–1330, 2016     

Effects of Heat‐Treatment Temperature on the Properties of (1–x)(Na0.5Bi0.5)TiO3–xBiAlO3 Lead‐Free Piezoelectric Thin Films

Lead‐free sodium bismuth titanate–aluminate bismuth [0.97(Na_0.5Bi_0.5)TiO₃–0.03BiAlO₃] solid‐solution films deposited on (100) Pt/TiO₂/SiO₂/Si substrates by a sol–gel process were pyrolyzed and annealed at different temperatures. The film annealed at 725°C with a pyrolysis temperature of 410°C exhibited the optimal electrical properties and excellent piezoelectric properties, with a remanent polarization 2P_r of 38 μC/cm² and a leakage current density of 10^?7–10^?6 A/cm² (E < 200 kV/cm). The values of the dielectric constant and dissipation factor at 100 kHz were 422 and 0.039, respectively. The piezoelectric coefficient of the film after poling at 168 kV/cm was found to be 57 pm/V, making the BNT‐BA films a viable lead‐free alternative to the lead‐based materials in such as biosensors and ultrasonic transducers.     

乘用车橡胶密封条气味研究

为找到密封条气味的来源,采用气相色谱-质谱联用仪对气味成分进行检测和分析,将气味的来源锁定在与成分相关的三元乙丙橡胶(EPDM)配方中的发泡剂、石蜡油、促进剂三种物质。通过进一步的对比实验,确认改进这三种物质的措施对降低气味是有效的:发泡剂的含量减少0.92份,气味等级平均值提升0.9级;若不使用发泡剂偶氮二甲酰胺ADCA,则气味等级提高0.3级;用闪点高、芳香烃含量低的石蜡油,气味等级平均值提升1.6级;使用无亚硝胺硫化体系,气味等级提高0.8级。这三种措施都能使气味等级达到标准要求的6级及以上。     

溶聚丁苯橡胶2564S在冬季轿车子午线轮胎胎面胶中的应用研究

试验研究溶聚丁苯橡胶(SSBR)2564S在冬季轿车子午线轮胎胎面胶中的应用。结果表明:在冬季轿车子午线轮胎胎面胶中采用SSBR2564S替代乳聚丁苯橡胶(ESBR)1723,并调整炭黑/白炭黑并用比例,胶料的邵尔A型硬度较低,300%定伸应力和拉伸强度略有降低,低温下(0℃)邵尔A型硬度变化较小,湿地抓着性能较好,滚动阻力较低;工艺性能良好;试制的185/60R14轿车子午线轮胎的强度性能、耐久性能和高速性能良好,且实际应用中轮胎在冰雪路面上操控性能优良。     

放样技术在承重瓦刮削中的应用

鲁碧公司的PEJ900×1200颚式破碎机传动主轴轴承内衬由巴氏合金制成,维修时刮研要求比较高。利用放样拉线法测量承载区域,阐述了该方法的主要实施步骤。效果表明,该方法简单有效,使检修作业效率提升显著,职工劳动强度大幅降低,提高了检修的精准度与可控性。     

Preparation and characterization of hydrophilicity fibers based on 2-(dimethyamino)ethyl mathacrylate grafted polypropylene by UV- irradiation for removal of Cr(VI) and as(V)

The hydrophilic fibers based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) which could remove Cr(VI) ions rapidly were prepared by UV-irradiation induced grafting of DMAEMA through pre-coating photoinitiator on the fibers and modifying with bromoethane(BE). The FTIR, FESEM, XPS, TG-DTG and contact angle spectra manifested that DMAEMA was grafted onto the surface of PP fibers and subsequently was quaternized. The maximum grafting degree (22.9 %) and exchange capacity of DMAEMA (1.2 mmol g^?1) was obtained when PP fibers was immersed in BP concentration of 0.3 % for 4 h, irradiated with the DMAEMA concentration of 100 % and irradiation time of 20 min, and then was modified with BE. The modified fibers of PP-g-DMAEMA with bromoethane were proved to remove Cr(VI) and As(V) with removal rate of 97.3 % and 96.2 % within 10 min, respectively. The prepared fibers have potential application for the removal of Cr(VI) and As(V) from wastewater highly and rapidly.     

Human-tracking strategies for a six-legged rescue robot based on distance and view

Human tracking is an important issue for intelligent robotic control and can be used in many scenarios, such as robotic services and human-robot cooperation. Most of current human-tracking methods are targeted for mobile/tracked robots, but few of them can be used for legged robots. Two novel human-tracking strategies, view priority strategy and distance priority strategy, are proposed specially for legged robots, which enable them to track humans in various complex terrains. View priority strategy focuses on keeping humans in its view angle arrange with priority, while its counterpart, distance priority strategy, focuses on keeping human at a reasonable distance with priority. To evaluate these strategies, two indexes(average and minimum tracking capability) are defined. With the help of these indexes, the view priority strategy shows advantages compared with distance priority strategy. The optimization is done in terms of these indexes, which let the robot has maximum tracking capability. The simulation results show that the robot can track humans with different curves like square, circular, sine and screw paths. Two novel control strategies are proposed which specially concerning legged robot characteristics to solve human tracking problems more efficiently in rescue circumstances.     

Nondestructive testing and characterization of residual stress field using an ultrasonic method

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designedto conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.