锰系固体超强酸催化合成苯甲醛乙二醇缩醛

在微波辐射下,自制的固体超强酸SO2-4/MnO2为催化剂,以乙二醇和苯甲醛为原料催化合成苯甲醛乙二醇缩醛。考察了微波辐射的时间、微波输出的功率、催化剂的焙烧温度、催化剂的焙烧时间因素的影响。实验结果显示:当醇醛物质的量之比为2∶1、微波输出的功率为550 W、微波辐射的时间5 min、催化剂用量为0.5 g时,苯甲醛乙二醇缩醛的产率为76.3%。     

多丝束碳纤维湿法缠绕系统研究

研究了多丝束碳纤维湿法缠绕机工艺,对影响张力的摩擦张力调节环节、碳纤维放卷辊及缠绕辊环节、同步运动环节分别进行了分析。在此基础上,研究了系统控制策略、设计PID张力控制系统和目标跟随式的同步运动控制系统,保证了缠绕的高质量。对碳纤维预浸缠绕机的控制系统软硬件进行设计和实现。结果表明:采用以上算法后,碳纤维张力达到±1N;缠绕精度达到±0.1mm。研究了触摸屏与远端监控相结合的双上位控制结构,设计了触摸屏本地人-机接口,利用RS-485总线传输,实现了碳纤维湿法缠绕机远端监控。     

Conceptually new entries into cells

This article summarizes the background and a few preliminary results concerning project 7 of the NCCR Chemical Biology. The general objective is to explore new concepts for cellular uptake, membrane tunneling, sensing and labeling. Emphasis is on the use of dynamic covalent chemistry for counterion activation, slow release of polyions and fluorescent probes, and the generation of activator libraries and polyions that grow and shrink.     

Preparation of C/C composites by the chemical vapor infiltration (CVI) of propane pyrolysis

The preparation of C/C composites by the chemical vapor infiltration (CVI) of the pyrolysis carbon from propane was studied. Pyrolysis carbon was deposited at 30 torr and at temperatures between 1,173 and 1,233 K. The rate of carbon deposition increased slightly with time. The main gas products in the exit gas were methane, ethylene, and acetylene. The fraction of ethylene decreased and that of acetylene increased with the reaction temperature and the propane concentration. The produced propyl radicals reacted further at a high temperature and at a high propane concentration. These trends were similar to those of the reported data. Changes of the shapes of deposited carbon in the pores of preform were confirmed with SEM photos. The mathematical modeling of the system with the deposition rate constant from the reference estimated experimental data well.     

Combustion and emission characteristics of converging group-hole nozzle under lean engine operating conditions

This paper describes the combustion and emission characteristics of converging group-hole nozzles and compares the results to those of a single hole nozzle with the same overall nozzle exit hole area. Engine experiments were performed using a single-cylinder diesel engine operating under overall lean conditions (i.e., equivalence ratio 0.45). The considered nozzle configurations in the experiments included a converging group-hole nozzle (cGHN) with 3° converging angle, 0.090 mm hole diameter, and a single hole nozzle (SHN) of 0.128 mm hole diameter. The CFD calculations used the KIVA engine simulation code integrated with a Gasjet superposition model. Using the validated calculation models, the test conditions were also expanded to consider wider converging angle cGHNs (up to 12°). The results show that the evaporation of sprays from the cGHN-3° nozzle is more delayed than that of the SHN case and the cGHNs entrain more ambient gas due to smaller droplet sizes in the outer spray periphery. In addition, an increase in the converging angle of the cGHNs promotes fuel evaporation and produces a more homogeneous fuel–air mixture.     

Hollow graphitic carbon spheres for Pt electrocatalyst support in direct methanol fuel cell

Hollow graphitic carbon spheres (HGCSs) with a high surface area are produced by the carbonization of hollow polymer spheres obtained by the polymerization of core/shell-structured pyrrole micelles. HGCSs are employed as a carbon support material in a direct methanol fuel cell catalyst, and their effect on the electrocatalytic activity toward methanol oxidation is investigated. Pt catalyst supported on HGCSs shows a better electrocatalytic activity compared to that on Vulcan XC-72, which has been commonly used in fuel cell catalysts. The observed enhancement in the electrocatalytic activity is attributed to the improved electronic conductivity and high surface area of HGCSs.     

Effect of repetitive processing on the mechanical properties and fracture toughness of dynamically vulcanized iPP/EPDM blends

The effect of repetitive processing on the mechanical properties and fracture toughness of dynamically vulcanized isotactic polypropylene/ethylene‐propylene‐diene rubber blends (TPVs) with and without addition of β‐nucleating agent (β‐NA) was studied. The results showed that the repetitive processing did not cause much loss in the mechanical properties of TPVs, especially for TPVs with β‐NA, and TPVs with β‐NA showed better performance stability than TPVs without β‐NA. Essential work of fracture (EWF) approach was used to study the fracture behavior, and the results showed that the value of w_e (the specific essential work of fracture) of TPVs without β‐NA showed a significant decrease while that of TPVs with β‐NA almost kept constant after repetitive processing. Differential scanning calorimetry and wide‐angle X‐ray diffraction were used to study the variation of crystalline structures, and the results indicated that the repetitive processing showed no significant influence on the crystalline structures of TPVs, and the β‐NA maintained high‐nucleating efficiency after repetitive processing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and thermal characteristics and morphology of polyamide 6/isotactic polypropylene blends in the presence of a β‐nucleating agent

The mechanical and thermal characteristics and morphology of polyamide 6 (PA6)/isotactic polypropylene (iPP) blends (10/90 w/w) prepared with different processing procedures and incorporated with an aryl amide nucleating agent, a kind of β‐nucleating agent (β‐NA) for iPP, were investigated. The yield strength and flexural modulus of the blends decreased as β‐NA was introduced into the blends, whereas the impact strength and elongation at break improved. The crystalline structures of the blends closely depended on (1) the processing conditions and (2) competition between the β‐nucleating effect of β‐NA and the α‐nucleating effect of PA6 for iPP. Scanning electron microscopy, differential scanning calorimetry, and X‐ray diffraction were adopted to reveal the microstructures of the blends. At a low β‐NA content (<0.1 wt %), the α‐phase iPP dominated the blends, whereas the relative content of the β‐phase iPP increased remarkably when the β‐NA content was not less than 0.1 wt %. The processing conditions also showed profound influences on the supermolecular structures of iPP; this resulted in different mechanical properties of the blends. As for PA6, the crystallization behavior and crystalline structure did not exhibit obvious changes, but PA6 did play an important role in the epitaxial crystallization of iPP on PA6. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Extraction of halide quaternary salts in an organic solvent/water system: Hydrodynamics and mass transfer

The hydrodynamic characteristics and mass transfers of halide quaternary salts between two immiscible phases in a stirred membrane permeation cell were investigated. The concentration of quaternary salt, temperature, solvent and the four kinds of halide quaternary salts were evaluated to achieve the extractive optimum condition. The diffusivity, overall mass‐transfer coefficients and individual mass‐transfer coefficients were determined and correlated in terms of the conventional Sh‐Re‐Sc relationship. The transfer time of quaternary salts across the membrane and the thickness of the hydrodynamic diffusion boundary layer were determined as well, so as to characterize the extractive phenomenon of quaternary salts between the two phases that is useful in phase‐transfer catalysis.     

Morphologies and dynamic mechanical properties of core‐shell emulsifier‐free latexes and their copolymers for P(BA/MMA)/P(MMA/BA) and P(BA/MMA)/PSt systems in the presence of AHPS

Different poly(methyl methacrylate/n‐butyl acrylate)/poly(n‐butyl acrylate/methyl methacrylate) [P(BA/MMA)/P(MMA/BA)] and poly(n‐butyl acrylate/methyl methacrylate)/polystyrene [P(BA/MMA)/PSt] core‐shell structured latexes were prepared by emulsifier‐free emulsion polymerization in the presence of hydrophilic monomer 3‐allyloxy‐2‐hydroxyl‐propanesulfonic salt (AHPS). The particle morphologies of the final latexes and dynamic mechanical properties of the copolymers from final latexes were investigated in detail. With the addition of AHPS, a latex of stable and high‐solid content (60 wt %) was prepared. The diameters of the latex particles are ～0.26 μm for the P(BA/MMA)/P(MMA/BA) system and 0.22–0.24 μm for the P(BA/MMA)/PSt system. All copolymers from the final latexes are two‐phase structure polymers, shown as two glass transition temperatures (T_gs) on dynamic mechanical analysis spectra. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3078–3084, 2002