Sorption and permeation of organic environmental contaminants through PVC geomembranes

The effect of penetrant diffusion on the barrier properties of PVC geomembranes have been determined for the following organic environmental contaminants: benzene, dichloromethane, and trichloroethylene. The membranes experienced swelling to a degree which depends on the type of penetrant used. Some dissolution may occur, and in general we are dealing with Case II transport. The experimental work was performed with an ASTM-cell, a Cahn balance, and an in-house built gravity (G-) cell. Those instruments generated comparable data on breakthrough times. The obtained diffusion coefficients as well as the breakthrough times obeyed an Arrhenius-type relation over the temperature range studied. Liquid sorption of the various penetrants modified the geomembrane structure. Membrane surface pretreatment with different contaminants influences the subsequent transport of organic penetrants through PVC geomembranes. That is to say: the induced swelling, as result of membrane contact with one penetrant, is likely to alter the system free volume, allowing for a different rate of mass transport for subsequent penetrants. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1189–1197, 1997     

Modeling diffusion through geomembranes

A phenomenological model that incorporates swelling is adopted and used to solve the one-dimensional sorption problem. The model predictions are in good agreement with experimental data, involving the transport of dichloromethane, trichloroethylene, and benzene through high-density polyethylene and poly(vinyl chloride) geo-membranes. The theoretical curves predict weight-gain and flux-time profiles, including the case where the flux goes through a maximum. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1885–1889, 1998     

Sorption/desorption,diffusion, and swelling characteristics of geomembranes in the presence of halo‐organic liquids

Sorption/desorption results of halogen‐containing liquids into high‐density polyethylene, linear low‐density polyethylene, very low‐density polyethylene, and polypropylene geomembranes are presented at 25, 50, and 70°C. Sorption results are obtained by a gravimetric method, and diffusion coefficients have been calculated by using Fick's equation from the initial linear portions of the sorption/desorption curves. Swelling of the geomembranes was studied from a measurement of the increase in volume, thickness, and diameter. From a temperature dependence of sorption and diffusion coefficients, the Arrhenius parameters have been calculated. Liquid concentration profiles have been computed using Fick's equation for the appropriate initial and boundary conditions. The results of this study may have relevance in selecting the suitable geomembrane for a specific application in hazardous waste chemical ponds and other similar situations.     

Theoretical and experimental investigations of molecular migration and diffusion kinetics of organic esters into tetrafluoroethylene/propylene copolymer membranes

A theoretical analysis of the experimental results on the migration and diffusion kinetics of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate and iso-amylacetate into tetrafluoroethylene/propylene copolymer membranes has been made. Diffusion and permeability coefficients have been calculated from Fick's equation. The concentration profiles of the liquids have been calculated from a solution of Fick's equation as well as using an empirical relation for the esters into the varying penetration depths of the membranes at different time intervals. The diffusion coefficients show a systematic decrease with increasing size of esters and the results are discussed in terms of the membrane-solvent interactions.     

纸塑复合包装材料中化学物迁移的改进预测模型及其通用性

以真实纸塑包装-化学物-食品体系为依据,基于一维Fick扩散理论,考虑化学物在纸和塑料涂层内具有不同的扩散系数及纸的厚度为有限厚,引入纸和塑料涂层界面处的分配系数,给出初始条件和边界条件,建立迁移预测模型,得到解析解。同时,对模型进行简化处理,分析其用于双层同种塑料-化学物-食品体系的使用通用性,并与Laoubi-Vergnaud模型进行对比分析,结果发现所建模型不仅可用于纸塑复合包装材料中化学物的迁移预测,同时还可用于双层同种塑料包装材料中化学物的迁移预测。     

有机分子在聚乙烯膜中扩散过程的分子动力学模拟

引言聚乙烯(PE)是由乙烯单体聚合而成的相对分子质量较高的线性烷烃,是合成树脂中应用最广泛的品种。扩散系数是描述传递现象的基本物性参数,在聚合物材料开发方面具有重要的理论特性和广阔的应用前景。用实验方法测定扩散系数时,操     

Molecular transport of organic esters and ketones into fluoropolymer membranes

The effect of different fluorine contents of DuPont VITON fluoropolymers and their transport characteristics in the presence of phenyl acetate, diethyl oxalate, diethyl malonate, diethyl succinate, acetone, methyl ethyl ketone and methyl iso-butyl ketone has been investigated over the temperature interval of 25?60°C. The average values of diffusion coefficients are obtained from the Fickian relation and the molecular transport is found to follow an anomalous behavior. Kinetic rate constants and pentration velocities are also calculated. The experimental results and the calculated quantities are studied in terms of polymer-solvent interactions.     

Kinetic migration of PBS and PBSA biopolymers prepared by cast film extrusion and biaxial stretching: A combined experimental and modeling approach

The kinetic migration of poly(butylene succinate) (PBS) and poly(butylene succinate-co-adipate) (PBSA) biopolymers, prepared by cast film extrusion (thin film) and biaxial stretching (biaxially oriented [BO] film) techniques, were investigated based on experimental and mathematical modeling. MATLAB coding was used to fit the migration data to a diffusion model. BO films significantly reduced the migration rate compared with thin films, with reductions of 29% and 41% for BO-PBS and BO-PBSA, respectively, due to the increased degree of molecular crystallinity. Higher ethanol content increased the quantity of substance diffusing from plastic film. PBS and PBSA are more suitable for packaging hydrophilic foods than alcoholic beverages. PBS exhibited a lower migration rate than PBSA due to its more rigid polymer matrix. Remarkably, BO-films exhibited 31% and 41% lower diffusion coefficients (D) compared with thin films, but significantly higher partition coefficients (K_P,F) by 44% and 267% for BO-PBS and BO-PBSA, respectively. This suggests a stronger affinity of migrant for BO film matrix. However, at 70°C, PBSA films may be hydrolyzed with a high ethanol, resulting in an inadequate diffusion model. The diffusion–reaction concept should be implemented for a better fit. These findings provide valuable insights for selecting appropriate packaging materials and predicting migration under diverse conditions, ultimately promoting consumer safety.     

Octanol/water partition coefficients of ionic liquids

BACKGROUND: Room temperature ionic liquids (ILs) are attractive alternatives to environmentally unfriendly volatile organic solvents. Partitioning is one of the most important and fundamental properties of a chemical, and the octanol/water partition coefficient is widely used to measure the tendency of a chemical to cross biological membranes. However, there is very limited information on the concentration dependence of the partition coefficients of ILs. This study investigated the octanol/water partitioning of 1‐butyl‐3‐methylimidazolium ([bmim]) ILs containing either hexafluorophosphate ([PF₆]) or bis[(trifluoromethyl)sulfonyl]amide ([Tf₂N]) over a wide range of IL concentrations of three to five orders of magnitude. RESULTS: It was found that the apparent partition coefficients of the ILs increased with increasing IL concentration. A model based on the ionic nature of ILs was proposed to explain this behaviour, and the results showed a good fit with the experimental data. The intrinsic partition coefficients and dissociation constants of the ILs were determined using the equations from the proposed model. The differences in the intrinsic partition parameter values between the two ILs showed a good correlation with other physicochemical properties. CONCLUSIONS: The present study clearly shows that the octanol/water partition coefficients of ILs increase with increasing IL concentration owing to the formation of ion pairs. By using the proposed partition model, it was possible to determine the intrinsic partition coefficients of ILs, and it was found that the apparent partition coefficients of ILs converge to the intrinsic partition coefficients of the ionic species and ion pairs of ILs with decreasing and increasing IL concentration respectively. Copyright © 2008 Society of Chemical Industry     

纸塑复合包装材料纸中化学物迁移预测模型

基于一维Fick扩散理论,考虑了纸和塑料涂层界面处的分配系数及纸和塑料涂层中不同的扩散系数,建立了迁移预测模型,得到了其解析解。分析了各参数如分配系数、扩散系数、纸中化学污染物初始浓度和量纲1时间对迁移行为的影响。结果表明,随纸塑界面处分配系数k_CP的增大,从纸中迁移入功能阻隔层塑料中的化学污染物量和通过功能阻隔层塑料迁移进入食品中的化学污染物量明显增多;塑料中扩散系数D_C的变化显著影响了塑料和食品中化学污染物的量,而纸中扩散系数D_P的改变对迁移的影响不显著。     

Permeation of molecules through different polymeric membranes

Permeation of molecules through the membranes plays an important role in immobilized cell systems. Permeation of molecules like glucose and bovine albumin serum was studied through chitosan, polyvinyl alcohol, and polyvinyl acetate membranes using a flow cell made of two detachable compartments. Permeation of molecules through chitosan, polyvinyl alcohol, and polyvinyl acetate membranes increases with decrease in hydrophobic characteristics of the membrane. Permeation of molecules also show its dependency on the molecular weight of the solute. Distribution coefficient of glucose and bovine serum albumin in these polymeric membranes measured by equilibration technique indicates that permeation of molecules through these membranes follows pore type mechanism. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3469–3472, 1999     

A novel fluorescence technique for measurements of additive migration from polymers

Diffusion coefficients for two antioxidants N,N′-diphenyl-p-phenylene-diamine (DPPD) and 2,5-di(-5-tert-butyl-2-benzoxazolyl)thiophene (Uvitex OB) have been measured by extraction from a low density polyethylene film into 1-propanol at 22°C. Extraction was carried out in a special cuvet-equipped vessel which excludes oxygen during extraction and permits direct fluorescence monitoring of the extraction solvent. Oxygen exclusion eliminates errors due to fluorescence quenching and antioxidant oxidation and allows precise measurement of the diffusion coefficient.     

蛋白质分子在聚丙烯酰胺凝胶中扩散和分配特性的研究

利用凝胶内溶质分子向缓冲溶液中扩散的方法,测定了溶菌酶、β－乳球蛋白、卵清蛋白、牛血清白蛋白和γ－球蛋白５种蛋白在聚丙烯酰胺凝胶中的有效扩散系数和分配系数,研究了单体质量浓度、交联度和蛋白分子粒径等因素的影响,讨论了聚丙烯酰胺凝胶中蛋白分子的扩散和分配机制,发现不能用Ｏｇｓｔｏｎ理论解释聚丙烯酰胺凝胶中蛋白分子的扩散和分配特性     

Molecular organogels. Soft matter comprised of low-molecular-mass organic gelators and organic liquids

This Account presents recent advances in understanding how and why dilute solutions/sols of low-molecular-mass organic gelators (LMOGs) undergo microscopic phase separation to form self-assembled fibrillar networks in molecular organogels. Concepts are illustrated structurally at the subnanometer (molecular) to several millimeter (bulk) length scales and dynamically over time scales that follow the assembly of supersaturated solutions/sols into gel phases. Examples include both structurally complicated (ALSmolecules with aromatic, linking, and steroidal groups) and simple (n-alkanes or n-alkanes along whose chains a hetero-group has been inserted) LMOGs in a wide range of organic liquids.     

Sorption and migration of organic liquids in poly(ethylene terephthalate)

Sorption kinetics of organic liquids in amorphous poly(ethylene terephthalate) (APET) and biaxially oriented PET (BPET) were determined at 34°C. With heptane and 1,2 propanediol, no sorption or swelling was observed. Estimated diffusion coefficients based on analysis from pseudo-Fickian sorption data are 3.7 ± 1.0 × 10⁻⁹ cm²/sec for toluene sorption in APET, 12.7 ± 4.1 × 10⁻⁹ cm²/sec for benzyl alcohol in APET, 0.44 ± 0.4 × 10⁻⁹ cm²/sec for toluene in BPET, and 0.33 ± 0.4 × 10⁻⁹ cm²/sec for benzyl alcohol in BPET. Weight gain of sorbed APET samples at equilibrium was 11.4 ± 0.1% in toluene and 21.7 ± 0.8% in benzyl alcohol. BPET weight gain at equilibrium was 9.5 ± 0.1% in toluene and 13.5 ± 0.2% in benzyl alcohol. Subsequent migration of sorbed toluene from APET samples into water at 34°C was measured by gas chromatography. Migration from toluene-sorbed APET films sandwiched between virgin APET layers was two orders of magnitude less than from sorbed films placed directly in water.     

Water diffusion into transcrystalline layers on polypropylene

The diffusion constant of water through transcrystalline surface layers on isotactic polypropylene (i‐PP) is reported. A suitable experimental technique was developed, based on sorption or desorption measurements. The accompanying change in sample weight is detected by the corresponding change in mechanical resonance frequency. The facility allows investigation of the diffusion current parallel to as well as perpendicular to the sample surface. Tests with commercial polyethylene films revealed that reproducibility and reliability are better than 6%. The samples were prepared as thin films in which the transcrystallinity was controlled by use of several substrate materials and different thermal conditions during solidification of the melt. The water diffusion constant of finely spherulitic i‐PP turned out to be 15.9 μm²/s; whereas the values for transcrystalline material amounted to 19.6 μm²/s parallel and between 12 and 10 μm²/s perpendicular to the film surface, depending on the actual supermolecular structure. These results are discussed with respect to the underlying transcrystalline texture and the texture of the amorphous percolation network. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3275–3285, 1999     

气体在水中的分子动力学模拟

采用分子动力学（ＭＤ）模拟的方法在常温及工业应用背景条件下对ＣＨ４、ＮＨ３、ＣＯ２、Ｏ２这些气体在水中的结构及扩散情形进行了研究。ＭＤ模拟可以为这些涉及到气体在水中的工业应用情形的机理提供分子水平的解释,同时ＭＤ模拟还可为一些不易实验测定扩散性质的体系提供工程初步设计和过程开发所需的数据。     

离子液体中的相互作用对硝基苯扩散系数的影响

应用紫外吸收光谱法和循环伏安法研究了离子液体中的相互作用及对离子液体中硝基苯的扩散系数的影响。结果表明,硝基苯的紫外光谱受离子液体EMimBF₄(1-甲基-3-乙基咪唑四氟硼酸盐)与其相互作用的影响,硝基的吸收峰红移,210 nm以下的末端吸收消失,而苯环的吸收基本不变;离子液体与硝基苯之间的作用主要发生在硝基上。在离子液体中电还原,硝基苯的扩散系数受硝基苯与离子液体、水与离子液体的相互作用的影响。同一离子液体中,随硝基苯浓度增加,扩散系数减小。相同硝基苯浓度时,不同离子液体的咪唑阳离子侧链越长扩散系数越小,但扩散系数减小得越缓慢;同一离子液体中,随着水浓度增加,硝基苯扩散系数增大;不同离子液体中,咪唑侧链越长,随着水的浓度增加,硝基苯扩散系数增加越快。     

低温低浊河网水的有机高分子助凝处理研究

用不同特征黏度的聚二甲基二烯丙基氯化铵(PDM)与聚合氯化铝(PAC)、两种市售无机复合聚铝分别复合,用以改进无机混凝剂对低温低浊微污染河网水的混凝脱浊效果。考察了无机混凝剂的种类及其与PDM的复合配比对低温低浊微污染河网水脱浊效果的影响。结果表明,对温度为7～10℃,浊度为4.5～8NTU的低温低浊河网水,在与实际生产相近的混凝搅拌强度下,要达到2NTU左右的出水余浊标准,PAC、复合聚铝1、复合聚铝2分别需4.0、3.5、2.8mg/L的投加量。而用特征黏度分别为0.52、1.47、2.46 dL/g的PDM配制的、无机复合聚铝与PDM复合质量比为20:1、10:1、5:1的复合混凝剂PAC/PDM、复合聚铝1/PDM、复合聚铝2/PDM,比单独使用同种无机混凝剂,分别约能减少10%～25%、8.6%～28.6%、7.1%～28.6%的无机药剂投加量,无机复合聚铝与PDM复合比例越低、PDM特征黏度越高,复合混凝剂脱浊效果越好。因此,PDM对低温低浊河网水具有明显的强化混凝脱浊效果。     

Mass transfer from spherical particles and reservoirs into quiescent liquids

A continuous weighing technique was developed for measuring urea transfer (carbamide, a fertilizer) from a single opening on a coated sphere in a stagnant liquid. Urea release was determined from the changes of the particle weight with time. Mass transfer coefficients for Rayleigh numbers from 1.8 × 10⁷ to 6.8 × 10¹⁰ were measured and compared with those for uncoated urea spheres and literature data. For the opening oriented vertically upward in water, natural convection enhanced the transfer rate by 1.8 times compared to that for urea diffusion only. In other opening orientations (45°, 90°, 135° and 180° to the vertical), natural convection provided the major mechanism for the release. A model for urea diffusion was also developed. It agrees well with experimental data.