顺丁橡胶挤出过程中熔体不稳定流动的研究

<正> 在高聚物挤出过程中,当挤出速率在一定条件下增大到某一数值时,挤出物表面将出现竹节状或鲨鱼皮状、扭曲等现象,此即为熔体破裂或不稳定流动。它严重影响着高聚物制品的外观质量,并限制了生产速率的进一步提高。所以,深入探讨不稳定流动产生的机理,进而建立判定不稳定流动的临界条件,对指导高聚物压出成型加工过程参数的选择及过程控制,具有实际意义。     

线型聚乙烯及其共聚物的挤出畸变与熔体粘弹性的关系

采用恒速型双筒毛细管流变仪研究了一类线型聚乙烯熔体的挤出畸变与熔体非线性粘弹性的关系。实验研究了发生畸变时挤出压力的振荡规律,发现线型大分子或带小侧基的大分子熔体,容易发生壁滑和挤出压力振荡;而有较大侧基、或分子量分布宽、或带大量短支链的熔体,挤出畸变现象较轻。挤出畸变与熔体的弹性及熔体．壁面吸附状态紧密相关。容易发生壁滑和挤出压力振荡的熔体,弹性较大(入口压力降大);在壁面的吸附作用强(壁面临界剪切应力大)。稳态剪切粘度大小与挤出畸变和压力振荡的关系不大;而拉伸应力和拉伸粘度大的熔体较易发生壁滑和挤出压力振荡。     

热塑性塑料熔体质量流动速率测量不确定度的评定

以聚乙烯为例讨论了热塑性塑料熔体质量流动速率测量不确定度的来源,依据JJF 1059-1999对熔体流动速率测试过程中的测量不确定度分量进行了分析和评定。7149型聚乙烯熔体质量流动速率测量结果的扩展不确定度为0.096 g/(10 m in)。     

基于不稳定反应的流动注射催化光度法测定铁

近年来,由于含铁水处理剂的广泛应用,水体中铁含量逐渐增高.含铁量高的水在管道内易生长铁细菌,增加水的浑浊度,使水产生特殊的色、嗅、味,易污染衣物、器皿,影响某些工业产品的质量.因此,研究准确快速测定水中铁的分析方法具有重要意义.     

Selkov模型不同扩散和流速下非Turing不稳定化学反应机制

建立了Selkov模型中间反应物具有不同扩散和不同流速条件下的反应-扩散-流动方程,理论分析了非Turing不稳定形成的条件,求得其参数区间,对Andresen的结论作了拓展.研究还发现,在振荡Hopf区域之外,静止波动(空间周期结构FDS)仍然可以存在.因而,此结构存在的参数空间大于Andresen的结果.同时,还将此种不稳定参数区间与Turing不稳定和差速流动引起不稳定(DIFI)的结果进行了比较,结果发现静态FDS值总是处于DIFI临界曲线相应的最小值之上,这表明动力学机制是由DIFI不稳定造成的,DIFI不稳定区是产生静止波FDS不稳定结构的必要条件.     

界面不稳定现象与相间迁移

包含有流动界面的多相体系中的溶质相间迁移在一定条件下可导致表现为界面变形、界面流和多种形式界面运动的不稳定现象．该现象的直接驱动力是界面局部区域出现的张力梯度，表面活性物质在该现象中起重要作用[1，2]．溶质相间迁移通常可考虑为三步：（1）溶质在原所在相内部向     

界面不稳定现象与相间迁移

The interfacial instability due to the transfer of the 1-butanol from water to oil in two systems of 1-butanol oil/water has been studied. The dynamic characteristics of the phenomenon are investigated by analysing the motion of an oil lens deposited at the surface of the aqueous solution of 1-butanol. The interfacial adsorption kinetics based on diffusion-controlled transfer is analysed. It is found that the linear relation between the frequence of the oscillatory motion of the lens and t1/2 is a characteristic relation. The type of the solute transfer in the interfacial instability is discussed by comparing experimental results with the linear characteristics.     

轴不稳定手性配体的开发及其在不对称催化反应中的应用

轴不稳定配体应用于不对称催化有其独到的特点, 不同于传统的轴稳定手性配体. 综述了轴不稳定的噁唑啉、双膦、单膦、双羟基及N—O等配体的开发及其在不对称催化中的应用.     

反应挤出条件对PP-g-GMA接枝率、接枝效率和熔体流动速率的影响

聚丙烯;反应挤出条件对PP-g-GMA接枝率、接枝效率和熔体流动速率的影响;甲基丙烯酸环氧丙烷;接枝共聚;共聚     

ENSO的海气耦合不稳定发生、发展理论

在高背景表面海温作用下,波——CISK的凝结潜热和海水蒸发感热加热可以引起海气耦合系统正反馈,从而激发甚低频强不稳定的海气耦合似Kelvin波。这一海气耦合不稳定理论可以相当好地解释1982—1983年ENSO事件发生、发展的演变过程。     

The Rheology of Linear and Long-chain Branched Polymer Melts

By generalising the Doi-Edwards tube model to the Molecular Stress Function theory, the non-linear rheology of polymer melts can be described quantitatively. The strain-hardening of linear polymer melts in extensional flows can be accounted for by a strain energy function, which reflects the increase of strain energy due to tube squeeze. In comparison to linear polymer melts, long-chain branched polymer melts show enhanced strain-hardening. This is due to the fact that while the backbone of the branched macromolecule is stretched by deformation, side chains are compressed. It is demonstrated that the experimentally observed slope of the elongational viscosity after inception of strain-hardening depends on the ratio β of total molar mass to backbone molar mass as predicted by the model. The steady-state (plateau) value of the elongational viscosity depends on the maximum relative stretch, , which can be supported by chain segments and which represents the maximum elastic energy storable in the polymeric system.     

毛细管电泳分离I^—和IO3^—中的电渗流的控制与调节

毛细管电泳分离是基于带电粒子在电场下的电动现象，当电场加到带电粒子所处的介质上时，存在电泳和电渗两种电动现象，其中电泳与带电粒子的大小、电荷和形状有关，而电渗与毛细管的表面及电泳介质的组成有关．由于电渗流能显著地影响分析时间和分离效率，因此，控制电渗流在毛细管电泳分离中是一个重要的环节［‘·‘j．此外，调节PH值、离子强度和缓冲液的粘度也是常用的控制电渗流的方法［’j．Ewing［‘与1入一个附加电场来控制电渗流．在缓冲液中加入足够浓度的阳离子表面活性剂将改变电渗流的方向．与通常的电渗流相比，人们对反向…     

The Application of Silane as a Processing Aid (PA) in High Speed Extrusion

Summary: Silane grafting is one of the most recently used technologies in manufacturing crosslinked products due to its enormous advantages. In highspeed extrusion Polymer Processing Aid materials (PPA) additives are usually a copolymer of vinylidene fluoride and hexafluoropropylene. They are added during extrusion process to improve the process-ability and to eliminate surface meltfracture that's occurred during processing of various polyolefin's resins. In this paper an attempt was made to investigate the application of VTEOS (Vinyltriethoxysilanes) and VTMOS (Vinyl trimethoxysilane) as a replacement of PPA and to determine its improvement in high speed extrusion of Polyethylene cable. It has been found that silane did contribute to eliminate meltfracture and improvement has been made. Nevertheless interaction phenomenon with carbon black and other additives did influencing significantly the performance of the silane and minimized its efficiency. Rheological measurements confirm this behaviour. Factors such as chemical reaction, physical adsorption and abrasiveness are involved in many of these situations. The presence of other storage stabilizer in the polyethylene contributes in negative way as well for formulation deficiency. Special attention in selecting the ingredient to minimize adverse effect is also very important in assuring optimum effectiveness.     

Coupled Orientation and Stretching of Chains in Mesoscale Models of Polydisperse Linear Polymers in Startup of Steady Shear Flow Simulations

Polydisperse linear polymers are studied in startup of steady shear flow simulations using dissipative particle dynamics. The results show that with an increase in polydispersity the stress overshoot declines while the steady‐state stress increases. Various physical characteristics of the systems are studied including frequency of nonbonded interactions, gyration radius data, flow alignment angles, and average bond lengths. The patterns in the data suggest higher forces are necessary to orient and stretch long chain fractions in the flow direction. Relaxation modulus data prove the broad range of relaxation mechanisms in polydisperse systems. Linear viscoelasticity theory is used to quantify the relaxation spectrum. The results indicate an increase in the longest relaxation time in systems with higher polydispersity. The steady‐state shear viscosity results show higher viscosities with an increase in polydispersity at all shear‐rates. The good agreement of the characteristic behaviors of modeled polydisperse polymers with experiments is encouraging for future work.

     

The magnitude and reproducibility of the electroosmotic flow in silica capillary tubes

The influence of a number of factors, such as the nature of the buffer, the presence of additives therein, the manufacturing conditions, and the pretreatment of the capillary, on the magnitude and repeatability of the electroosmotic flow (EOF) in silica capillary tubes has been investigated. It was established that the nature of the buffer plays the most significant role in respect of the stability and magnitude of EOF, whereas the conditions used for manufacture and pretreatment of the tubing are less important. The EOF obtained using buffers consisting of tris(hydroxymethyl)aminomethane and ethylenediamine was more repeatable than that obtained using pure phosphate buffers. Buffer additives such as sodium dodecylsulfate, 1-butanol, sodium salts of 1-pentanesulfonic acid and 1-heptanesulfonic acid, altered the magnitude of the EOF only, not its repeatability.     

Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds

The synthetic utilities of the diazo and diazonium groups are matched only by their reputation for explosive decomposition. Continuous processing technology offers new opportunities to make and use these versatile intermediates at a range of scales with improved safety over traditional batch processes. In this minireview, the state of the art in the continuous flow processing of reactive diazo and diazonium species is discussed.     

Treatment and Determination of Organophosphorous Pesticides in Waste Water by Using Continuous Flow Methodologies Coupled On Line With High Performance Liquid Chromatography

Abstract

The treatment of waste water containing three organophosphorous pesticides: diazinon, azinphos-methyl and fenthion by using continuous flow methodologies coupled on line with HPLC-UV detection is presented.

Two continuous flow techniques: completely continuous flow and flow injection, both combined with two separation methods: liquid-liquid extraction and adsorption resins are discussed, as well as the influence of physical and chemical parameters on the analysis.

Adsorption resins seem to be more suitalbe for the treatment of waste water at low pesticide concentraions while liquid-liquid extraction is more selective.