Distributions of Crystal Size from DSC Melting Traces for Polyethylenes

Melting curves, obtained by differential scanning calorimetry, are used to estimate crystal size distributions. The proposed theoretical analysis is applied to different types of polyethylene, including high‐density polyethylene (HDPE), metallocene catalyzed linear low‐density polyethylenes (m‐LLDPE), blends of m‐LLDPEs, and Ziegler‐Natta catalyzed LLDPEs (ZN‐LLDPE). Theoretical predictions are in agreement with experimental results. A generalized melting temperature equation successfully predicts the melting temperatures of all the LLDPEs, although it was initially proposed for homogeneous copolymers with excluded comonomers. A new definition of the heat of fusion for pure crystals is proposed. This heat of fusion can be calculated from the average crystal size or the crystal size number distribution.     

Preparation of narrowly distributed nanoparticles of poly(n‐butyl methacrylate‐co‐vinyl pyrrolidone) through microemulsion polymerization

Narrowly distributed nanoparticles of poly (n‐butyl methacrylate‐co‐vinyl pyrrolidone) were prepared through microemulsion polymerization with a nonionic surfactant of Tween‐80 as emulsifier (6 wt % of the latex) and n‐butanol as coemulsifier. The polymerizations were initiated with benzoylperoxide (BPO), potassium persulfate (KPS), KPS/ferric sulfate (FeSO₄), and BPO/FeSO₄, respectively, where the initiation in the case of BPO/FeSO₄ took place mainly at the interphase between the oil phase and the reaction media. Namely, this interfacial‐initiated microemulsion polymerization resulted in larger particles with relatively narrower particle size distribution as well as higher limiting monomer conversion but lower polymerization rate compared with the polymerization initiated with KPS/FeSO₄. In this article, the influences of initiation method, monomer ratio, and addition of water‐soluble components on microemulsion polymerization and latex particle size were studied to discuss the mechanism of interfacial‐initiated microemulsion polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2334–2340, 2004     

Synthesis of Kenyaite, Magadiite and Octosilicate Using Poly(ethylene glycol) as a Template

Three types of layered silicates, namely octosilicate, magadiite and kenyaite, were synthesized using poly(ethylene glycol) (PEG). The influence of reaction parameters, including alkali source, silica source, PEG molecular weight, reaction time and temperature, on the formation of these three phases was investigated. The results indicate that magadiite is preferred when (i) using NaOH as the alkali source and at a lower temperature (150°C), with fumed silica, tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), Ludox-AS 40 or colloidal sol acting as the silica source in the presence of PEG 200; (ii) using fumed silica as the silica source and PEG 300 as the template at 150°C; (iii) at a higher temperature (180°C), using PEG 200 as template and TEOS as the silica source; and (iv) at 180°C with a combination of PEG 300 and fumed silica. Compared to magadiite, kenyaite was favored at a higher temperature (180°C) with PEG 200 and NaOH, KOH or RbOH, while using fumed silica, silica gel, or colloidal sol as silica source; or at the lower temperature (150°C) using NaOH as alkali source, PEG 200 as template, and silica gel or silicic acid as the silica source. Octosilicate was obtained at 90°C with the combination of NaOH, PEG 200 and fumed silica.     

Synthesis and properties of polystyrene‐b‐poly(ethylene oxide)‐b‐polystyrene triblock copolymers

A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by ¹H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (T_g) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006     

双核酞菁钴磺酸铵用于催化裂化汽油的脱臭

采用尿素法合成了双核酞菁钴磺酸铵;通过正交实验及单因素实验,考察了双核酞菁钴磺酸铵在液-液催化氧化法中对催化裂化汽油脱臭的最佳工艺条件:碱液质量分数为10%,催化剂加入量为1 0g·L-1,反应温度为40℃,反应时间为3min;与磺化酞菁钴和美国进口脱臭催化剂ARI100-EXL的脱硫醇效果进行了比较,结果表明双核酞菁钴磺酸铵对汽油的脱臭效果明显优越于磺化酞菁钴催化剂,与进口催化剂的脱臭效果基本相当。     

有机硫加氢(HDS)催化剂的预硫化

预硫化是HDS、HDN过程中决定催化剂活性的最重要环节。在分析催化剂硫化反应原理、硫化条件、硫化与还原的关系等基础上进一步指出了在工业过程中预硫化的一些原则。     

21世纪国外固体推进剂的研究与发展趋势

从5个主要发展方向分别评述了21世纪固体推进剂研究发展趋势,认为固体推进剂的发展趋势是朝着高能量、低特征信号、钝感、“洁净”和低毒或无毒的方向发展。     

Numerical Study of Solid-Liquid Two-Phase Flow in Stirred Tanks with Rushton Impeller (Ⅰ) Formulation and Simulation of Flow Field

Three-dimensional solid-liquid flow is mathematically formulated by means of the "two-fluid" approach and the two-phase k-ε-Ap turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved "inner-outer" iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of     

协同处置危废对烧成系统的影响

列举了水泥窑协同处置危废的特点和现状，阐述了水泥窑协同处置危废的过程中，危废对水泥窑烧成系统运行状况、熟料质量和烟气排放等的影响，并做了直接、深入的分析，根据实际运行情况提出了一些有效措施。     

The kinetics of B‐a and P‐a type copolybenzoxazine via the ring opening process

The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005