Recent studies of self-condensation and co-condensation of melamine-formaldehyde resins; cure at low temperatures

Self-condensation: recent research on the chemical pathways by which alcoholated melamine-formaldehyde (MF) resins react with themselves and on the product structures is summarized. Model compound studies suggest that bridges are less stable than widely thought unless they are in hexahydro-1,3,5-triazine ring structures. In acyclic structures they are probably less stable than bridges. Co-condensation: studies of how the composition of MF resins influences the rates of reaction with poly(ol) co-reactant show that MF resins that contain very low levels of and/or functionality are quite reactive. Reactivities of a variety of poly(ester) and acrylic coreactants were studied. By combining reactive MF resins with reactive co-reactants one can formulate high solids enamels that cure by co-condensation in 30 min at 50 to 65 °C with 0.5 parts per hundred (phr) of p-toluenesulfonic acid (p-TSA) catalyst. Cure at 25 °C appears feasible with higher catalyst levels.     

A molecular level mechanism ofn-butane oxidation to maleic anhydride over vanadyl pyrophosphate

A molecular level mechanism is proposed for the highly selective 14-e^– oxidative transformation ofn-butane to maleic anhydride on the surface of vanadyl pyrophosphate. The mechanism suggests that the dimeric active sites assume at any given time, one of four possible interconvertible states which differ from each other in the number of available oxygen atoms and the formal oxidation states of the individual vanadium atoms. The relative ratios of active sites in each of the four possible states are dictated by the reaction conditions, the redox properties of the reacting gases and the structure of the vanadyl pyrophosphate active surface. A crucial feature of the mechanism is a pseudo-ozonide surface species formed by the interaction of a chemisorbed dioxygen molecule and an adjacent metal-oxo group. This unusual species is responsible for the initial activation of then-butane, which occurs when the chemisorbed dioxygen abstracts an H-atom from the alkane and the adjacent metal-oxo group reacts with the incipient alkyl radical to form an alkoxy group. The proposed mechanism is entirely consistent with literature reports describing the behaviour of (VO)₂P₂O₇ in flow, pulse and TAP reactors.     

聚己二酸1,2-环己二醇酯的合成

采用正交实验方法,分别以钛酸四丁酯和对甲苯磺酸为催化剂,合成了聚己二酸1,2 环己二醇酯,对其合成工艺条件进行了研究,得出了最佳工艺条件。并以所得聚酯合成了具有透明度高、硬度大、耐磨、玻璃化温度高等优异性能的聚氨酯材料。     

高柔韧性聚氨酯丙烯酸酯的合成及应用

选用不同结构的多元醇作骨架，合成一系列高性能的聚氨酯丙烯酸树脂，并通过对聚氨酯丙烯酸树脂性能的对比研究，发现以聚丁二烯二元醇为骨架的聚氨酯丙烯酸酯树脂具有极佳的柔韧性和优异的低温耐曲折性。     

PVC-U型材弹性模量测试偏差分析

在对PVC-U型材弹性模量试验中发现，同一样品的规则样条与不规则样条的弯曲弹性模量相差较大。不规则样条的负荷-挠度曲线上会出现拐点，如果不对曲线进行处理直接计算得到的弯曲弹性模量偏小。在不规则样条的负荷-挠度取拐点后直线段切线与横坐标的交点作零点修正后所测得的弯曲弹性模量比较接近真实值。通过实验可以验证处理后的方法测得的弹性模量与均匀规则样条的弯曲弹性模量相近。     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.     

新增仪表空气干燥器的运行经济评价

介绍仪表空气干燥器功能、试车运行情况及在生产中所起的作用和使用后收到的效果。     

重钙装置改产磷铵后氨化造粒机内部构件的配置研究

重钙装置改产磷铵后,造粒机内的物料行为发生了变化,即“料浆涂布－水分蒸发－氨化反应”这一物理化学过程。喷氨孔与水平线的夹角是影响这一过程的重要因素,本文对夹角的确定进行了理论分析。在实验基础上,对造粒机预中和料浆喷头位置、氨分布管的长度和角度进行了重新配置。生产表明,重新配置的造粒机内部构件具有很好的造粒效果。     

2,2′-oxo-1,1′-azobenzene: microbial transformation of rye (Secale cereale L.) allelochemical in field soils byAcinetobacter calcoaceticus: III

Acinetobacter calcoaceticus, a gram-negative bacterium isolated from field soil, was found to be responsible for the biotransformation of 2(3H)-benzoxazolinone (BOA) to 2,2-oxo-1,1-azobenzene (AZOB). Experiments were conducted to evaluate the transformation of BOA to AZOB by this microbe in sterile and nonsterile soil. Transformation studies with soils inoculated withA. calcoaceticus indicated that the production of AZOB increased linearly with the concentration of BOA in sterile soil and showed a quadratic trend in nonsterile soils. This also indicated that all soil types studied for the transformation experiments might containA. calcoaceticus capable of the conversion of benzoxazolinones.     

Catalytic hydrogenation of nitrile rubber using palladium and ruthenium complexes

The catalytic hydrogenation of acrylonitrile‐butadiene copolymer (nitrile rubber, NBR) using Pd(OAc)₂ or RuCl₂(PPh₃)₃ catalysts has been investigated in order to produce a totally saturated nitrile rubber. The hydrogenation of NBR is effective with both catalysts and achieved total conversion under the appropriate reaction conditions. In the case of palladium the effects of reaction parameters such as reaction temperature, pressure, time, catalyst concentration, and NBR concentration have been investigated. Even though both ruthenium‐ and palladium‐based catalysts are effective in the production of HNBR, the former requires harsh reaction conditions and has the drawback of gel formation under high conversion, motivating the migration to RuCl₂ (PPh₃)₃ as an alternative catalyst. The degree of hydrogenation was determined by IR and NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007