Characterization of morphology controlled polyethersulfone hollow fiber membranes by the addition of polyethylene glycol to the dope and bore liquid solution

The preparation of polyethersulfone (PES) hollow fiber membranes has been studied using N-methylpyrrolidone (NMP) as solvent, polyethylene glycol 400 (PEG 400) as weak nonsolvent and water as strong nonsolvent. When PEG 400 is used as polymeric additive to the spinning dope the viscosity of the PES solution is strongly enhanced. Furthermore, it was observed that PEG 400 could be added to the solution in large amounts without causing phase separation (NMP/PEG ratio 1:9, PES concentration approximately 11 wt.%). Membranes prepared from a solution containing a NMP/PEG ratio of 1:1 results in higher fluxes than when a ratio of 1:4 is used. Similar fluxes were obtained for PES concentrations of 16 and 20 wt.%. Looking at the fiber cross-section it became clear that macrovoid formation could not be suppressed by the addition of PEG 400 alone, not even at concentrations as high as 38 wt.%. Only when relatively large amounts of water were added to the dope solution macrovoids disappeared and nice spongy structures were obtained. Variation of the bore liquid composition using the components NMP, PEG 400 and water showed to be a powerful method to control the pore size of the bore surface. Pores of 5–28 nm were obtained in combination with high pure water fluxes; e.g. a membrane with pores of 7 nm had a pure water flux of 940 l/(m2 h bar) and showed 100% BSA retention. When an air gap larger than 10 mm was applied the shell surface contained relatively large pores. Spinning directly in water (airgap=0) resulted in shell side pores of 8–10 nm, while an air gap of 10 mm resulted in pore sizes of 40–54 nm

Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 m have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent

Selectivity as a function of membrane thickness: gas separation and pervaporation

In this article, the pervaporation selectivity as a function of the membrane thickness is studied for the dehydration of acetic acid. From this study, it appeared that the selectivity of polysulfone (PSF), poly(vinyl chloride) (PVC), and polyacrylonitrile (PAN) decreases with decreasing membrane thickness, below a limiting value of about 15 m. However, in the case of gas separation, the selectivity of PSF membranes is independent of the membrane thickness. This phenomenon could not be explained by a difference in membrane morphology, sorption resistance, thermodynamic interaction, or coupling. It is believed that the decrease in selectivity for thin membranes has to be attributed to defects induced during pervaporation. These defects, crazes (and cracks), result from a reduced value of the critical strain, due to sorption of acetic acid/water and stresses between the polymer chains, due to a concentration gradient across the membrane

Novel thin film polymer foaming technique for low and ultra low-k dielectrics

The results presented show a novel route for the preparation of thin ultra-low-k polymer films based on commercial and "non-exotic" (non-expensive) polyimide by a foaming technique. Dependent on the glass transition temperature of the polyimide mechanically and thermally stable (> 300 °C) films having porosities of ca. 40 % and k-values below 2.0 are formed. A further reduction into the ultra low k region may be accomplished by tailoring the shape of the pores from spherical into disc-like void

Poly(vinyl chloride) polyacrylonitrile composite membranes for the dehydration of acetic acid

Composite membranes have been prepared consisting of a poly(vinyl chloride) (PVC) top layer on either a dense polyacrylonitrile (PAN) layer (bi-layer membrane) or a porous PAN support layer (normal composite membrane) and studied with respect to the dehydration of acetic acid. Especially, the influence of the surface porosity of the porous support layer on the selectivity and flux was studied and it was shown that the lower the surface porosity the higher the selectivity of the composite membrane, especially at high acetic acid concentrations in the feed. From the results it can be concluded that the support material does contribute to the selectivity. Despite the low surface porosity relatively high fluxes could be obtained. Using a feed composition of 80/20 wt.% acetic acid/water at 80°C selectivities of 182¿274 and fluxes of 0.56¿0.74 kg/m2-hr were obtained, and with a feed composition of 98/2 acetic acid/water selectivities of 206¿318 and fluxes of 0.14¿0.15 kg/m2-hr were obtained

Controlled drug delivery through tailor-made blend polymeric membranes

In this work, we prepare tailor-made membranes by blending sulfonated poly(ether ether ketone) (S-PEEK) and poly(ether sulfone) (PES) polymers, at various ratios. Timolol (TM) is used as a model drug for the investigation of the controlled delivery through these membranes and their application to a transdermal TM patch is discusse

The matching conditions of controlled Lagrangians and IDA-passivity based control

This paper discusses the matching conditions resulting from the controlled Lagrangians method and the interconnection and damping assignment passivity based control (IDA-PBC) method. Both methods have been presented recently in the literature as means to stabilize a desired equilibrium point of an Euler±Lagrange, respectively Hamiltonian, system. In the context of mechanical systems with symmetry, the original controlled Lagrangians method is reviewed, and an interpretation of the matching assumptions in terms of the matching of kinetic and potential energy is given. Secondly, both methods are applied to the general class of underactuated mechanical systems and it is shown that the controlled Lagrangians method is contained in the IDA-PBC method. The $\lambda$-method as described in recent papers for the controlled Lagrangians method, transforming the matching conditions (a set of non-linear PDEs) into a set of linear PDEs, is discussed. The method is used to transform the matching conditions obtained in the IDA-PBC method into a set of quadratic and linear PDEs. Finally, the extra freedom obtained in the IDA-PBC method (with respect to the controlled Lagrangians method) is used to discuss the integrability of the closed-loop system. Explicit conditions are derived under which the closed-loop Hamiltonian system is integrable, leading to the introduction of gyroscopic terms