混合溶剂在高分子膜中的传递模型

以单溶剂在高分子膜中的蠕变传递模型为基础,通过考虑溶剂间的耦合作用对溶剂在高分子膜中传递过程的影响,建立了混合溶剂在高分子膜中传递的蠕变模型.对模型参数进行了数值模拟研究,并使用该模型关联了吸收实验曲线.计算结果显示模型具有一定的预测功能.     

溶剂在高分子膜中传递现象研究的进展

溶剂在高分子膜中吸收和解吸的传递机理非常复杂,对其传递过程的研究有助于膜分离过程的开发、膜材料的选择。本文对溶剂在高分子膜中传递现象研究的进展作简要介绍。     

高分子聚合物中溶剂扩散系数的预测

溶剂分子在高分子聚合物中的扩散现象广泛存在于日常生活和工业生产中,对其研究具有普遍意义.Vrentas-Duda模型以自由体积理论为基础,所有参数不需扩散实验测量,由溶剂和高分子的分子性质独立确定,可用于预测高分子聚合物中低相对分子质量溶剂扩散系数.研究Vrentas-Duda模型对典型高分子/溶剂体系中溶剂扩散系数的预测准确性,通过将预测值与实验值比较,评价该模型在不同高分子体系中的适用情况.对处于橡胶态的各向同性高分子聚合物体系,Vrentas-Duda模型能够准确计算除存在氢键以外多数体系的溶剂扩散系数;相对于溶剂互扩散系数而言,溶剂自扩散系数的预测精度更高.     

混合溶剂法回收顺酐

研究了有机溶剂回收顺酐的行为和性质,筛选了物理性能好,饱和溶解度大,吸收性能好的混合溶剂为吸收剂,进行了模拟工业连续吸收试验,确定了吸收和解吸的操作条件。顺酐的吸收率达99.7％以上,产品符合国家一级品标准。     

基于Simha-Somcynsky状态方程的高分子-溶剂体系扩散系数模型

将Simha-Somcynsky状态方程引入到Vrentas-Duda扩散系数模型，建立基于状态方程的溶剂在高分子中扩散系数模型。与原模型相比，改进的模型避免进行高分子的黏弹性实验测定，模型中高分子的相关参数仅由状态方程的特征温度和特征体积确定，提高了模型的预测能力。对苯、甲苯、乙苯、氯仿在聚苯乙烯、聚异丁烯和聚醋酸乙烯酯中的扩散系数计算结果表明，改进模型的预测值与实验值吻合较好。     

丙碳脱碳溶剂的改进研究

介绍一种由丙碳、叔胺和少量活化剂构成的复合溶剂的开发，并详细地测定了不同压力和操作工况下，这种复合溶剂对ＣＯ２的吸收和解吸性能，以及溶剂的缓蚀性能和抗氧化性能．实验证明这种复合溶剂与纯丙碳相比，具有吸收容量大、速率快、脱碳净化度高、对设备无腐蚀等特点，对改进现行的丙碳脱碳工艺具有应用价值．     

烯胺溶液吸收和解吸模拟烟气中二氧化碳实验研究

采用搅拌实验装置对二乙烯三胺(DETA)、三乙烯四胺(TETA)、三乙烯二胺(TEDA)溶液吸收和解吸模拟烟道气中二氧化碳特性进行研究,揭示了吸收速率、吸收容量和解吸速率与酸碱度、时间之间的内在联系,并与一乙醇胺(MEA)、二乙醇胺(DEA)溶液进行了对比分析。实验表明,同浓度DETA、TETA吸收速率及吸收容量均高于MEA和DEA,再生简单,是优良的烟道气CO2吸收剂,具有较高的研究价值。     

聚酰胺吸水率及其对弹性模量的影响研究

针对两种厚度(0.5 mm和4.1 mm)的聚酰胺样品对水的吸附和解吸过程,以及吸水率对弹性模量的影响进行研究;在此基础上,采用Fick模型和Langmuir模型分析了吸附和解吸曲线,讨论了聚酰胺样品的吸水行为。结果表明,不同温度条件下样品吸水达到饱和点之前,吸水率(wt)与t1/2基本呈线性关系;当样品吸水饱和后,在较长的浸泡时间内,样品的wt略有降低。吸附和解吸过程中,样品的弹性模量E随t1/2的变化不同;wt曲线取决于样品的厚度,研究中使用的聚酰胺样品wt曲线变化规律符合Langmuir曲线变化规律。     

胆甾醇和链甾醇在混合溶剂中溶解度的NRTL-SAC和COSMO-RS预测

使用两个热力学模型NRTL-SAC和COSMO-RS预测胆甾醇和链甾醇在混合溶剂中的溶解度,并以实验数据为计算基准,通过平均相对偏差(ARD)评价模型的预测效果。为填补溶解度数据空白,采用静态法结合高效液相色谱法(HPLC)测定了298.2 K下两种甾醇分别随混合溶剂组成变化的溶解度。NRTL-SAC对两种甾醇的溶解度预测在满意范围,最大ARD为50.58%。COSMO-RS预测结果非常不理想。通过改进,输入一个298.2 K时的实验值预测同一混合溶剂组成下随温度变化的溶解度,结果预测值与实验值吻合得较好,胆甾醇和链甾醇在(正己烷+乙醇)混合溶剂中,总的ARD分别从80.57%和82.30%降为12.77%和21.32%。上述结果表明,只需少量实验数据的NRTL-SAC和只需一个实验数据的COSMO-RS(ref)可用于两种甾醇溶解度的预测,为工业分离纯化过程中的溶剂快速筛选提供重要的理论依据。     

溶剂小分子在嵌段高分子膜中传递性质的研究

通过压电晶体微平衡法 (QCM法 )获得了乙醇、甲苯在由聚乙酸乙烯酯和聚甲基丙烯酸酯组成的嵌段共聚物中扩散的实验曲线 ,在由 Voigt蠕变模型和 Flory- Huggins混合模型建立的传递模型基础上 ,通过吸入吸附对扩散的影响 ,得到改进的传递模型 ,用以关联实验曲线 ,结果吻合良好。     

纯气体在非晶态高分子膜内的吸收机理模型(Ⅰ)理论

提出了一个描述非晶态高分子膜结构特征的模糊数学模型.基于这一模型,作者认为,橡胶态膜内也存在“特征微孔”,并且比玻璃态膜更多.该两种膜的主要吸收机理都是“充孔”机理.运用分子热力学原理,导出了一个普遍化吸收机理模型.本模型假设,非晶态高分子膜内存在两种“格位”,它们对渗透分子的作用各不相同.适用于玻璃态膜的双方式吸收模型和适用于橡胶态膜的Henry定律在这一模型中得到了统一,模型参数也从分子数量级上获得了明确的解释.     

Diffusivity of a drug preservative in bromobutyl rubber

Sorption of phenylethyl alcohol (a model drug preservative) by bromobutyl rubber (a polymer used in drug packaging) is characterized by relatively low apparent diffusivities at room temperature (D ≈︁ 10⁻¹⁰ cm²/s) and a high solubility that leads to considerable swelling of the polymer. The sorption curves for thin samples exhibit non-Fickian anomalies, which are normally observed only in glassy polymers, including two-stage sorption and sorption overshoot. The desorption curves were much more Fickian. The swelling kinetics were very slow, and true equilibrium was not reached in the time frame of most of the experiments, which ranged up to 78 days. This produced lower apparent diffusivities and higher activation energies for sorption compared to desorption.     

Sorption/desorption properties of ethanol,toluene, and xylene in poly(dimethylsiloxane) membranes

Sorption/desorption kinetics and sorption equilibria have been determined for ethanol, toluene, and xylene vapors in a poly(dimethylsiloxane) membrane containing about 32 wt % silica resin at 25°C. Dependence of diffusion coefficient on vapor activity and sorption isotherms have been compared to identify the transport mechanisms of those penetrants in the PDMS membrane. The analysis of Zimm–Lundberg clustering functions showed that all three penetrants had a tendency to form clusters and ethanol molecules might be immobilized by the residual silanol groups within the silica resin in the membrane. The diffusion coefficient of toluene was roughly constant and that of xylene slightly decreased as increasing the vapor activity due to the competing effects of penetrant clustering and solvent swelling of polymer. The diffusion coefficient of ethanol versus activity exhibited a maximum due to the effects of ethanol immobilization and cluster formation. The freevolume effect by solvent swelling to diffusion was obscured by either penetrant clustering or immobilization for the three penetrant–polymer systems. © 1994 John Wiley & Sons, Inc.     

Diffusion and relaxation in glassy polymer powders: 2. Separation of diffusion and relaxation parameters

Gravimetric sorption measurements for organic vapours in monodisperse glassy polymer powders have shown widely varied non-Fickian kinetic behaviour. These varied kinetics are interpreted by a single mathematical model involving a linear superposition of one or two phenomenologically independent first order relaxation terms upon the ideal Fickian diffusion equation. Analysis of experimental data for submicron powders through this model yields kinetic and equilibrium parameters describing the individual contributions of the diffusion and relaxation processes. This analysis has been applied to both integral and incremental sorption data for vinyl chloride, acetone, and methanol in poly(vinyl chloride) and for n-hexane in polystyrene. Sorption by initially penetrant-free polymer samples is dominated by a rapid Fickian diffusion process, while incremental sorptions show larger relative contributions from slow relaxation processes. The relaxation processes appear to be related to slow redistribution of available free volume through relatively large scale segmental motions in the relaxing polymer. The diffusion—relaxation model seems to provide a meaningful analysis of several non-Fickian ‘anomalies’, including a very slow approach to apparent equilibrium, two-stage and sigmoidal sorption curves, and sorption curves involving an initial maximum followed by temporary desorption and subsequent resorption.     

A novel transport model for sorption and desorption of penetrants in dense polymeric membranes

The transport of penetrants in polymeric membranes is assumed to be a process of mixing of penetrant and polymer molecules, in which a creep strain is induced concurrently. Based on the assumption and combined with the mass conservation equation and phenomenological diffusive flux expression, a new transport model of penetrant in polymeric membrane is established, in which the total change of excess Gibbs free energy is considered as a sum of three parts calculated by the modified Scatchard-Hildebrand model, Flory-Huggins theory and linear viscoelastic theory, respectively. The partial difference equations in the model are solved by implicit finite difference method of Crank-Nicolson form, and the model parameters are optimized by simplex algorithm. The model is used to calculate various diffusions (Fickian diffusion, and non-Fickian diffusion) of ethanol in polyphthalazine ether sulfone (PPES), and polyphthalazine ether sulfone ketone (PPESK) membranes at 293.15, 298.15, and 303.15 K. The calculated results are in agreement with the experimental data and the maximal relative deviation is no more than 10.54% and the average relative deviation is 4.35%.     

In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy

The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α₁ = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α₁ = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films.     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

Sorption and transport of linear and branched ketones in biaxially oriented polyethylene terephthalate

Equilibrium sorption and kinetics of acetone, methyl ethyl ketone (MEK), methyl n-propyl ketone (MnPK), and methyl i-propyl ketone (MiPK) uptake in uniform, biaxially oriented, semicrystalline polyethylene terephthalate films were determined at 35 °C and low penetrant activity. Sorption isotherms for all penetrants were well described by the dual-mode sorption model. Sorption and desorption kinetics were described either by Fickian diffusion or a two-stage model incorporating Fickian diffusion at short times and protracted polymer structural relaxation at long times. Diffusion coefficients and equilibrium solubility at fixed relative pressure decreased in the following order: acetone>MEK>MnPK>MiPK. Diffusion coefficients for each penetrant increased with increasing penetrant concentration.     

Effect of CO2 sorption and desorption on the creep response of polycarbonate

In this article, experimental results on the effect of CO₂ sorption and desorption on the creep response of polycarbonate (PC) are presented. Tensile specimens machined from PC sheets were exposed to CO₂ and the absorbed gas mass fraction ranged from 0.045 to 0.12. The creep/creep recovery response of as‐received PC, saturated PC, and saturation‐cycled PC was characterized. It was found that the saturated PC showed a creep behavior similar to heating the PC to its glass transition temperature. The creep compliance of saturation‐cycled PC was found to change with the desorption or aging time. The tests on PC saturated and then desorbed for up to 60 days showed that the effects of exposure to CO₂ on PC creep properties persist long after the gas has left the polymer, and could be permanent. POLYM. ENG. SCI., 45:1639–1644, 2005. © 2005 Society of Plastics Engineers     

Sorption,desorption, resorption,redesorption, and diffusion of haloalkanes into polymeric blend of ethylene–propylene random copolymer and isotactic polypropylene

Molecular transport of haloalkanes into sheets of a polymeric blend of an ethylene–propylene random copolymer and isotactic polypropylene has been studied by a sorption gravimetric technique in the temperature interval of 25–70°C. For all liquids, equilibrium sorption, desorption, resorption, redesorption, and degree of penetrant overshoot have been influenced by the nature of the liquid and the temperature. Diffusion coefficients were calculated from the sorption–desorption kinetic curves using Fick's mathematical relations. The values of diffusion coefficients followed the Arrhenius-type behavior. The temperature-dependent sorption data were analyzed using the van't Hoff relation. The activation parameters for diffusion and heat of sorption data were discussed in terms of the molecular interactions between liquids and the polymer chain segments. The experimental and calculated results are discussed on the basis of the chemical nature of liquids. © 1995 John Wiley & Sons, Inc.