剪切速率对聚苯乙烯／超临界CO2发泡体系的影响

在挤出发泡过程中聚合物／超临界CO2发泡体系的形成是气体在剪切混合作用下，通过对流扩散，完全溶解进聚合物形成物理性质均一的均相体系的过程。剪切作用对均相体系的形成具有重要的影响，为了研究剪切对均相体系形成的影响，成功设计了微孔发泡模拟实验机，研究了不同剪切速率作用下均相体系的形成。研究结果表明，随着剪切速率的增加，聚合物和气体的混合程度明显增强，泡孔分布变得均匀，泡孔密度增大。     

微孔发泡中气溶阶段的研究进展

综述了气体在聚合物中的溶解度和扩散系数，聚合物气体均相体系形成的机理和模型及影响聚合物均相体系形成的各种因素。     

微孔发泡过程中脉动剪切对聚合物/超临界 CO2均相体系形成的影响

提出一种聚合物／超临界CO2均相体系快速形成的新方法——将振动力场引人到发泡过程，在简单剪切的基础上垂直叠加一个脉动剪切场，考察了该方法对均相体系形成的影响。实验材料用聚苯乙烯(PS)，用自行设计的电磁动态发泡模拟机，了不同剪切速率、振动力场及混合时间对聚合物／超临界CO2均相体系形成的影响。结果表明，随着剪切速率的增加，聚合物和气体的混合程度明显增强；而振动力场的引入进一步增强了剪切混合的效果，使聚合物／超临界CO2均相体系能够在较短的时间内形成。     

剪切对聚合物微孔发泡成型过程的影响

分别运用有螺纹转子系统和无螺纹转子系统进行试验,并分析研究剪切作用对聚合物微孔发泡成型过程3个阶段的影响.结果表明,增加剪切作用有利于气体的分散和溶解,减少均相体系彤成的时间,提高均相体系形成的质量;在较强的剪切作用下,较小的分子基团也能形成稳定的气泡核,在聚合物熔体中形成大量均匀细密分布的气泡核;但长时间、过强的剪切作用会导致气泡塌陷.     

微孔发泡过程中聚合物/超临界CO2均相体系形成的研究

阐述以超临界CO2为发泡剂的微孔发泡中均相体系的形成过程，研究聚合物熔体和气体的混合机理，并分析影响均相体系形成过程的因素。结果表明，聚合物和气体本身的结构和性质、工艺条件、加工设备、外力场等均影响均相体系的形成，振动力场的引入可以提高多相体系的混合程度，在聚合物／气体均相体系的形成过程中引入振动力场是一个全新的研究方向。     

微孔发泡塑料挤出成型中聚合物—气体均相体系形成研究

微孔发泡塑料是一种内部含有很多小泡孔的新型材料，具有很多优异性能。在微孔塑料挤出成型加工过程中，聚合物－气体均相体系能否形成是保证产品质量的关键因素之一。对其进行分析和计算，推导出挤出过程中聚合物－气体均相体系形成所需时间计算公式。结果表明，通过增加挤出压力，从而获得泡孔细密的泡沫塑料。     

微孔发泡聚合物/CO_2体系基础研究进展及概况

本文综述了微孔发泡技术的最新研究进展及当前的研究方向,聚合物/气体均相体系的热动力学和流变行为是影响整个发泡过程的关键问题,重点介绍了聚合物/气体体系的PVT特性和剪切黏度的研究概况。     

HF62208/NPAC二元复配体系中各组分浓度快速测定方法

针对梳形聚合物(HF62208)与壬基酚聚氧乙烯醚羧酸盐(NPAC)复配的二元体系中单一组分浓度测定问题,提出了一种采用紫外光度法快速检测该类聚/表二元体系中单一组分浓度的方法,同时考察了NPAC浓度、HF62208浓度、矿化度、温度、老化时间及剪切作用等因素对测定结果的影响。结果表明,NPAC可直接在277nm波长下测定,HF62208可采用双波长系数倍率法消除NPAC的干扰,检测波长对为240nm和277nm;双波长系数倍率法在检测聚合物浓度时受到矿化度、温度、老化时间以及剪切等的影响。该方法简便、快速、准确。     

时间扫描研究低剪切条件下PP／PS合金材料的静态流变特征

选用典型的不相容体系聚丙烯／聚苯乙烯（PP／PS）合金材料为研究对象，采用时间扫描的方式讨论了合金在恒定温度和剪切速率条件下的静态流变特征，结果表明：PP和PS作为均相纯聚合物，在时间扫描过程中，其黏度均随时间呈线性下降趋势，该现象可归结为材料的热氧降解作用。对非相容PP／PS合金材料进行时间扫描发现，扫描过程中黏度先升高后下降，可分为前期和后期两个阶段，前期相结构在剪切力传递过程中导致合金材料的黏度相对较低，甚至低于连续相纯聚丙烯的黏度，具有明显的瞬态作用特征，时间扫描后期因相结构在稳定剪切条件下引起能量损耗而呈现较高的黏度，但因热氧作用整体趋于下降。     

CO_2-1,3-PDO-PTT三元体系相平衡的研究

溶质-超临界流体-聚合物三元体系相平衡的研究为超临界流体辅助聚合物脱挥技术提供了热力学基础数据,利用自行研制的一套超临界CO_2高压装置,采用静态法,研究了温度为313.15—353.15 K、压力为7—19 MPa条件下,二氧化碳(CO_2)/1,3-丙二醇(1,3-PDO)/聚对苯二甲酸丙二醇酯(PTT)三元体系相平衡时超临界流体相中的组成。实验测得PTT模拟样品中1,3-PDO在SCCO_2中的溶解度,并计算得到了1,3-PDO在SCCO_2相与PTT相间的分配系数,同时分析了温度和压力对溶解度、分配系数的影响。在上述条件下,1,3-PDO的溶解度为0.262—3.597g/L,分配系数为0.020 5—0.076 2。研究结果显示:当温度一定时,溶解度随压力的增大呈现增大的趋势;溶解度随温度的变化会存在一转变压力(约18 MPa),在转变压两侧,溶解度会呈现相反的变化趋势;分配系数等温线随压力的增大呈现倒U型,即先增大后减小。     

The kinetics of crosslinking in process of intumescence of fireproof polymer compositions

A mathematical model is proposed to calculate the expansion coefficient of the elementary volume of intumescent polymer material at an arbitrary change of temperature. It implies that parallel reactions of cure and gas formation take place simultaneously in the volume of the polymer composition. It was assumed that after attainment of some threshold values of the composition viscosity the gas released may be retained in the foam. Influence of the rate of heating, composition of the blend, and functionalities of the initial monomers on the effectiveness of foaming was investigated for the system phenol—formaldehyde resin with boron oxide. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 329–338, 1997     

Kinetic analysis of the radiation polymerization of methyl methacrylate–kaolin clay composites

In the first of a two-part series, a kinetic study has been made on the effects of gamma rays (⁶⁰Co) in air and inert gas on the polymerization of a 50:50 weight-mixture methyl methacrylate (MMA)–kaolin clay system. The effect of dose rate (7.35–24.9 rads/sec), temperature (25° to 75°C), and total dose on the percentage conversion of monomer to polymer was studied. The rate of formation of polymer at 25°C in the composite system was found to be faster when compared to a bulk MMA system at the same dose rate. This acceleration showed that the clay had a catalytic effect on the formation of polymer. The effect decreased as temperature increased. Two types of poly(methyl methacrylate) (PMMA) were formed in the composite. One type was called homopolymer and could be removed from the composite by extraction with organic solvents. The other type was called inserted polymer and could only be removed by dissolving the clay matrix with hydrofluoric acid. The total polymer conversion was the summation of these two types of polymer formed. The kinetic analysis examined the orders of reaction and activation energies of the homopolymer, inserted polymer, and total polymer. The initial reaction orders of the homopolymer and total polymer based on dose were ?0.46 and ?0.49, respectively. These indicate a definite free-radical reaction. The reaction order of the inserted polymer was temperature dependent. The activation energies for the homopolymer and total polymer in both atmospheres were approximately 1 kcal/mole less than the bulk activation energy at the same conditions. The inserted polymer had an activation energy which was dose rate dependent.     

减少乙二醇装置循环气冷凝液系统聚合物生成

针对环氧乙烷/乙二醇装置循环气洗涤泵入口过滤器频繁堵塞的问题,分析了循环气冷凝液系统固体聚合物的生成机理,聚合物生成对装置生产造成的影响,以及可能减少聚合物生成的因素,并在操作优化上进行实践,操作优化后固体聚合物生成明显减少,对装置平稳生产带来了积极影响。     

Thermal analysis of the droplet solidification in the PGSS-process

In this work, a manufacturing process for powders from polybutylenterephthalate (PBT) is analysed in terms of the formation of differently shaped particles. For the micronization of the polymer the particles from gas saturated solutions (PGSS) process is used. Several applications require specific particle shapes and particle size distributions. In particular, spherical particles are required to obtain a free flowing powder. To optimise the quality, powders were produced at different spray temperatures and pressures and with varying mass flows of polymer and gas. With different spray conditions, powders with various shapes, morphologies and apparent densities were obtained. The temperatures before and after the expansion appear to have the main influence on the sphericity. To obtain further knowledge about the solidification process, the temperature distribution in the spray was analysed. For this purpose, heat images of the spray were taken. Based on the results, a simple model is introduced, which is able to estimate the temperature field in a polymer droplet during the spray process. An explanation for the formation of differently shaped particles is proposed.     

Open-celled microcellular foaming and the formation of cellular structure by a theoretical pattern in polystyrene

An open-celled structure was produced using polystyrene and supercritical carbon dioxide in a novel batch process. The required processing conditions to achieve open-celled structures were predicted by a theoretical model and confirmed by the experimental data. The theoretical model predicts that at least a saturation pressure of 130 bar and a foaming time between 9 and 58 s are required for this system to produce an open-celled structure. The foaming temperature range has been selected to be higher than the polymer glass transition temperature yet not higher than a temperature limit where the gas starts leaving the system. The experimental results in the batch foaming process verified the model substantially. The SEM pictures showed the presence of pores between the cells, and the mercury porosimetry test results verified the overall open-celled structure. Experimental results also showed that by increasing the saturation pressure and the foaming temperature, there was a drop in the time required for open-celled structure formation. At saturation pressure of 130 bar, foaming temperature of 150 °C and a foaming time of 60 s, open-celled microcellular polystyrene foams were obtained using supercritical CO₂ in the batch process. Based on the results, a schematic diagram, depicting the process of foam structure formation from nucleation to bubble coalescence and gas escape from polymer, was proposed. Theoretical calculations showed that by increasing foaming time, cell size was increased and cell density was reduced and the experimental results verified this prediction.     

Hydrogenation of nitrile butadiene rubber in a multistage agitated contactor: Experiments and numerical simulation

The performance of a multistage agitated contactor (MAC) with cocurrent reactive gas liquid upflow was studied for the hydrogenation of nitrile butadiene rubber using a homogenous osmium complex catalyst. The hydrogenation performance was investigated under various catalyst concentrations, liquid flow rates, pressures, and polymer concentrations. The desirable hydrogenation conversion of over 95% was achieved under the industrially relevant operation conditions. A comprehensive reactor model consisting of stirred tanks in series with back flow (CTB) was applied to describe the liquid flow behaviour in the presence of the hydrogenation process. The established model satisfactorily predicted dynamic hydrogenation performance considering the gas liquid mass transfer effect and temperature profile in each stage. A modified CSTRs-in-series model accounting for mass transfer effect was proposed to predict the hydrogenation degree at steady state and a good agreement was demonstrated between the model prediction and the experimental data.     

Microcellular PVC

Novel microcellular PVC foams with a very homogenous cell distribution and cell densities ranging from 10⁷ to 10⁹ cells/cm³ have been created using carbon dioxide as the nucleating gas. Microcellular foams with relative densities (density of foam divided by the density of unfoamed polymer) ranging from 0.15 to 0.94 have been produced. It was found that the bubble nucleation density has and Arrhenius-type dependence on temperature, while the average bubble diameter is relatively independent of the foaming temperature. A majority of the cell growth was found to occur in the early stages of foaming.     

Effect of solvent balance on the surface properties of poly(vinyl chloride)

Films of poly(vinyl chloride) have been cast from solutions of varying thermodynamic quality and the film properties studied by inverse phase gas chromatography. The solvents included tetrahydrofuran, cyclohexanone, and mixtures of toluene with both tetrahydrofuran and cyclohexanone. The solvent composition was followed during evaporation and film formation for the mixed solvents, and it was shown that the slower evaporating solvent component has the greatest effect on the surface properties of the films. The porosity of the polymer film surfaces is interpreted in terms of the mobility of the polymer chains during film formation. At high concentrations, polymer chain–polymer chain interactions become stronger when thermodynamically less powerful solvents are used or are last to leave during film formation; therefore, the solvent balance has a critical influence on the film surface properties. Annealing the poly(vinyl chloride) above the glass transition temperature reduces the surface porosity of the cast polymer.