Cyclic olefin polymer as a novel membrane material for membrane distillation applications

A first attempt was made to prepare cyclic olefin polymer/copolymer (COP/COC) flat-sheet porous membranes by the well-known non-solvent induced phase separation method. In this study, two solvents (chloroform and 1,2,4-trichlorobenzene), different additives (polyvinylpyrrolidone, PVP, polyethylene glycol, PEG400, polyethylene oxide, PEO, and Sorbitan monooleate, Span 80) and coagulants (acetone and 70/30 wt% acetone/water mixture) were employed. The prepared membranes were characterized in terms of the thickness (70-85 mu m), porosity (-50-80%), liquid entry pressure (1.16-4.55 bar), water contact angle (similar to 86 degrees - 111 degrees), mean pore size (158-265 nm), mechanical properties (tensile strength: 0.74-5.51 MPa, elongation at break: 3.34%-7.94% and Young's modulus: 29-237 MPa), morphological and topographical characteristics. Short-term direct contact membrane distillation (DCMD) tests showed maximum permeate fluxes of 20 kg m(-2) h(-1) and 15 kg m(-2) h(-1) when using as feed distilled water and 30 g/L sodium chloride aqueous solution, respectively, with a high salt separation factor (99.99%). Long-term DCMD tests of some selected membranes carried out during 24-50 h showed that the membranes prepared with PEG additive exhibited more stable DCMD performance. In general, it was proved that COP can be successfully used as a novel polymer candidate in membrane distillation (MD) applications

Patients’ Opinions about Knowing Their Risk for Depression and What to Do about It. The PredictD-Qualitative Study

[Background] The predictD study developed and validated a risk algorithm for predicting the onset of major depression in primary care. We aimed to explore the opinion of patients about knowing their risk for depression and the values and criteria upon which these opinions are based. [Methods] A maximum variation sample of patients was taken, stratified by city, age, gender, immigrant status, socio-economic status and lifetime depression. The study participants were 52 patients belonging to 13 urban health centres in seven different cities around Spain. Seven Focus Groups (FGs) were given held with primary care patients, one for each of the seven participating cities. [Results] The results showed that patients generally welcomed knowing their risk for depression. Furthermore, in light of available evidence several patients proposed potential changes in their lifestyles to prevent depression. Patients generally preferred to ask their General Practitioners (GPs) for advice, though mental health specialists were also mentioned. They suggested that GPs undertake interventions tailored to each patient, from a “patient-centred” approach, with certain communication skills, and giving advice to help patients cope with the knowledge that they are at risk of becoming depressed. [Conclusions] Patients are pleased to be informed about their risk for depression. We detected certain beliefs, attitudes, values, expectations and behaviour among the patients that were potentially useful for future primary prevention programmes on depression.This work was supported by grants from the Andalusian Council of Health [grant reference: 2008/0195][www.juntadeandalucia.es/fundacionprogres​oysalud]; the Department of Health of the Basque Government [grant reference: 2008/111021][www.osakidetza.euskadi.net]; the Spanish Network of Primary Care Research “redIAPP” (RD06/0018), the “Aragón group” (RD06/0018/0020), the “Sant Joan de Deu group” (RD07/0018/0017), “Bizkaya group” (RD07/0018/0018), “Castilla-León group” (RD07/0018/0027) and the “SAMSERAP group” (RD06/0018/0039 and CTS-587) [www.rediapp.org]

Effects of mixed solvents on the structural morphology and membrane distillation performance of PVDF-HFP hollow fiber membranes

Está depositada la versión postprint del artículoPoly(vinylidene fluoride-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique, maintaining all the parameters the same except the solvent used to prepare the polymer solution. Different solvents namely, single N,N-dimethyl acetamide (DMAC) and different mixed solvents, DMAC and trimethyl phosphate (TMP) as well as N,N-dimethyl formamide (DMF) and TMP were employed. The relative affinity of the PVDF-HFP and the solvent(s) and the thermodynamic and kinetic aspects responsible for membrane formation were investigated and related with the structure of the prepared hollow fiber membranes. The structural and morphological properties of the hollow fiber membranes as well as the necessary parameters to be known for a membrane proposed for direct contact membrane distillation (DCMD) were studied by different characterization techniques. It was observed that an increase of TMP ratio in the solvents mixture resulted in a decrease of the finger-like structure of the external layer, an increase of the pore sizes of the hollow fibers and the DCMD permeate flux enhancement as consequence. When changing DMAC by DMF a thicker hollow fiber membrane was obtained and the DCMD was decreased due partly to the formation of macro-voids in the middle layer of the hollow fiber membrane.Ministerio de Ciencia e Innovación (España)Ministerio de Educación, Cultura y Deporte (España)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Effects of PVDF-HFP concentration on membrane distillation performance and structural morphology of hollow fiber membranes

Poly(vinylidene fluoride-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different copolymer concentrations in the dope solutions ranging from 17 to 24 wt.%. All the spinning parameters were maintained constant except the copolymer concentration. The morphological properties of the hollow fiber membranes were studied in terms of scanning electron microscopy (SEM), atomic force microscopy (AFM) and void volume fraction. The effects of PVDF-HFP content in the spinning solutions were also studied by measuring the water entry pressure and direct contact membrane distillation (DCMD) permeate flux of the hollow fiber membranes. An increase in the copolymer concentration of the spinning solution resulted in a decrease in the precipitation rate and a transition of the cross-section structure from a finger-type structure to a sponge-type structure. Pore size, nodule size and roughness parameters of both the internal and external hollow fiber surfaces were determined by AFM. It was observed that the pore size decreased in both the internal and external surfaces of the hollow fiber membranes with increasing the copolymer concentration and reached a minimum value at the outer surface for PVDF-HFP concentrations greater than 20 wt.%. Water entry pressure values were decreased whereas both the void volume fraction and the DCMD permeate flux increased with decreasing the copolymer concentration

Preparation and characterization of PVDF-HFP copolymer hollow fiber membranes for membrane distillation

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were prepared by the dry/wet spinning technique at different copolymer concentrations from 17 to 24 wt%. All the spinning parameters were kept constant except the copolymer concentration. The temperature of both the internal and external coagulants was maintained at 40 degrees C. The effects of the copolymer concentration on the morphological properties of the hollow fibers were studied in terms of external and internal diameter and scanning electron microscopy (SEM). It was found that the thickness of all tested hollow fibers did not change significantly. An evolution of the cross-section structure with the increase of the copolymer concentration was detected. The cross-section of the hollow fiber prepared with the lowest copolymer concentration exhibited a finger-like structure in both the external and internal layers disappearing in the internal layer as the copolymer concentration increases. Finally, a spongelike structure is formed through all cross-section of the hollow fiber prepared with the highest concentration. This may be explained based on the decrease of the coagulation rate with the increase of the copolymer concentration in the dope solution

Fomento del uso de software libre de tipo científico en estudios de ciencias

Incidencias en la creación de una base de dato online de software científico de uso gratuito para alumnos de las titulaciones de la Facultada de Física

Morphological design of alumina hollow fiber membranes for desalination by air gap membrane distillation

Está depositada la versión postprint del artículoAlumina hollow fiber membranes were prepared by the phase inversion technique under different spinning conditions in order to induce various types of structural morphologies. In the membrane fabrication process, the studied parameters were the polymer concentration in the inorganic suspension and its flow rate, the gap distance, the bore liquid, the outer coagulant composition and their flow rates. After sintering, the hollow fibers were chemically modified by grafting (1H,1H,2H,2H-perfluorodecyltriethoxysilane) rendering them hydrophobic for their use in membrane distillation (MD) process. The effects of the membrane morphology on the obtained MD membrane characteristics and on air gap membrane distillation (AGMD) desalination performance were studied in order to figure out the most promising structure for MD. The suitability of alumina hollow fibers for AGMD was confirmed by various membrane characterization techniques. In general, the membranes prepared with lower polymer concentration in the inorganic suspension exhibited higher AGMD performance (i.e. higher permeate flux with a smaller flux reduction factor and a good salt rejection factor). Among all prepared hollow fiber membranes prepared in this study, the one with the largest micro-channel structure exhibited the best AGMD performance, even better than all hydrophobic ceramic membranes used so far in desalination by AGMD and DCMD.Ministerio de Economía y Competitividad (MINECO)Ministerio de Educación, Cultura y Deporte (MECD)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Hollow fiber spinning experimental design and analysis of defects for fabrication of optimized membranes for membrane distillation

A fractional factorial design and a steepest ascent method were applied for possible fabrication of hollow fibers by the dry/wet spinning technique. Seven spinning factors were taken into account. Different concentrations of the copolymer poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP with 400,000 g/mol molecular weight and the additive polyethylene glycol. PEG with 10,000 g/mol molecular weight were dissolved in N,N-dimethyl acetamide, DMAC. The developed approach permits localization of the region of experimentation, defect-free spinning conditions, to produce hollow fibers. The obtained hollow fiber membranes were characterized by scanning electron microscopy and atomic force microscopy. Penetration liquid in membrane pores and porosity were also determined. Finally the membranes were tested for desalination by direct contact membrane distillation. An optimal hollow fiber membrane was finally fabricated using the determined optimum spinning conditions: a copolymer concentration of 20% w/w, a PEG concentration of 6% w/w, an air gap length of 25 cm, an internal/external coagulation temperature of 37.5 degrees C, an internal coagulant flow rate of 19 ml/min, a pressure of 0.3 bar and free falling. This membrane exhibits the highest performance index and the greatest global desirability (i.e. high permeate flux and salt rejection factor)

Water desalination by membrane distillation using PVDF-HFP hollow fiber membranes

Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different polyethylene glycol (PEG) concentrations as non-solvent additive in the dope solution. Two different PEG concentrations (3 and 5 wt.%). The morphology and structural characteristics of the hollow fiber membranes were studied by means of optical microscopy, scanning electron microscopy, atomic force microscopy (AFM) and void volume fraction. The experimental permeate flux and the salt (NaCl) rejection factor were determined using direct contact membrane distillation (DCMD) process. An increase of the PEG content in the spinning solution resulted in a faster coagulation of the PVDF-HFP copolymer and a transition of the cross-section internal layer structure from a sponge-type structure to a finger-type structure. Pore size, nodule size and roughness parameters of both the internal and external hollow fiber surfaces were determined by AFM. It was observed that both the pore size and roughness of the internal surface of the hollow fibers enhanced with increasing the PEG concentration, whereas no change was observed at the outer surface. The void volume fraction increased with the increase of the PEG content in the spinning solution resulting in a higher DCMD flux and a smaller salt rejection factor

Structural and performance studies of poly(vinyl chloride) hollow fiber membranes prepared at different air gap lengths

Poly(vinyl chloride) hollow fiber membranes were prepared by the dry/wet and wet/wet spinning technique at different air gap lengths keeping all other spinning parameters constants. Mean pore size, pore size distribution and mean roughness of both the internal and external surfaces of the hollow fibers were determined by atomic force microscopy. Cross-sectional structure was studied by scanning electron microscopy. Ultrafiltration experiments of pure water and aqueous solutions of different solutes having different molecular weights (bovine serum albumin, polyethylene glycol and polyvinyl pyrrolidone) were carried out. It was found that the inner and outer diameters of the PVC fiber membranes decreased with the increase of the air gap distance due to the gravitational force effect. The hollow fiber membranes prepared without and with air gap distances up to 7 cm exhibited a quite symmetric cross-structure consisting of four layers, two small finger-like structure layers at both edges of the hollow fibers and two larger finger-like voids mixed with macrovoids layers in the middle of the cross-section. The outer-middle layer thickness decreased when the air gap distance was increased to 10 cm and disappeared from the cross-section of the hollow membranes prepared with higher air gap lengths than 15 cm. For all dry/wet spun PVC hollow fibers, the outer pore size and the pure water permeation flux both increased with the increase of the air gap distance. In contrast, the solute separation factor decreased with the air gap distance. This was related to the pore size of the external surface of the PVC hollow fibers