Aldo Bottino

The formation of microporous polyvinylidene difluoride membranes by phase separation

Abstract Microporous polyvinylidene fluoride (PVDF) membranes were prepared by casting and coagulating solutions of the polymer in eight different solvents. The membranes were characterized by scanning electron microscope observations, water content measurements and water permeability tests. The possible correlations between the resulting membrane characteristics and the properties of both the polymer-solvent solutions and the solvent-nonsolvent systems are extensively discussed. The analysis indicates that most of the correlations suggested or adopted in the literature do not hold for PVDF membranes, whereas the transport properties of the solvent-nonsolvent system seem to affect significantly the final membrane structure and the resulting performances in separation processes.

Preparation and characterization of novel porous PVDF-ZrO2 composite membranes☆

Poly(vinylidene) fluoride (PVDF)-ZrO2 composite membranes were prepared by casting and immersion into a water bath of ternary suspensions obtained by adding additional amounts of ZrO2 particles to PVDF solutions. Methods to obtain an intimate dispersion of the inorganic particles in the PVDF solutions were developed. A large variety of supported and unsupported membranes were prepared by varying some of the preparative parameters such as: the PVDF solvent (N-methyl-2-pyrrolidone or triethylphosphate), the total concentration and the PVDF/ ZrO2 ratio in the ternary dispersion. Membranes were also cast from a binary solution of PVDF and solvent for comparison purposes. All the obtained membranes were characterized by scanning electron microscope observations and ultrafiltration tests. The effect of the above-mentioned preparative parameters on the structure, flux and dextran retention properties of the membranes is discussed.

Characterization of PVDF membranes by vibrational spectroscopy

Abstract In order to investigate the effectiveness of vibrational spectroscopy in the characterization of polymeric membranes, several poly(vinylidene fluoride) (PVDF) membranes with different porous structures were prepared by the phase inversion process using different casting solvents. An accurate analysis of the Fourier transform Raman (FT-Raman) and the Fourier transform infrared (FTIR) spectra was performed for each sample and the scanning electron microscopy (SEM) results were noted. To highlight the specific problems related to porosity and surface roughness in the acquisition of spectra by different sampling techniques, the attenuated total reflection (ATR) and photoacoustic spectroscopy (PAS) spectra were compared with corresponding spectra obtained from dense films. A detailed analysis of these spectra highlighted their ability in determining the differences in the polymer structure between the two membrane sides. This indicates that (considering the results given by all the different techniques) thorough qualitative membrane characterization can generally be achieved. Moreover, the good quality spectra of the PVDF membrane provide information on a portion of material which depends on its structure, highlighting the usefulness of FTIR-PAS in studying porous materials which, as a rule, give low quality infrared spectra when other sampling techniques are used. However, the complex and inhomogeneous structure of these materials can make quantitative analysis more, or less, difficult.

Preparation and properties of novel organic–inorganic porous membranes

This paper deals with the preparation and characterization of novel organic–inorganic composite membranes formed by fine silica particles uniformly dispersed in the porous matrix of poly(vinylidene fluoride). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments, burst pressure tests and scanning electron microscope (SEM) observations. Spectroscopic (FTIR-ATR, FT-Raman) and calorimetric (DSC) measurements were also carried out in order to investigate interactions between membrane components. Supported membranes were finally prepared and their ultrafiltration performance was compared with that of unsupported ones.

High performance ultrafiltration membranes cast from LiCl doped solutions

Abstract This paper deals with the preparation and properties of ultrafiltration polyvinylidene fluoride based membranes obtained by casting and gelation of ternary solutions of polyvinylidene fluoride, solvent and LiCl as an appropriate inorganic salt additive. The membranes were tested in a laboratory scale pilot plant. Flux and rejection were evaluated as functions of the type of solvent and the amount of inorganic salt added. The influence of these latter variables on the morphology and mechanical properties of the membranes was also investigated. The role of LiCl on the properties and the mechanism of membrane formation is discussed.

Poly(vinylidene fluoride) with improved functionalization for membrane production

Abstract Poly(vinylidene fluoride) (PVDF) was modified by chemical treatments in order to obtain a functionalized polymer suitable for the preparation of ultrafiltration membranes with improved hydrophilicity and fouling resistance. Membranes obtained from the modified polymer as well as from the unmodified one were characterized through pure water permeability measurements and ultrafiltration tests with a dilute solution of skim milk. The fouling tendency of the membranes was measured from the relative reduction in water permeability before and after ultrafiltration. Dense films were also prepared and characterized through contact angle measurement in order to obtain a preliminary evaluation of the hydrophobicity. Vibrational spectroscopy (FT-IR and FT-Raman) techniques were effectively used to investigate the functionalities introduced by the chemical treatments.

Water treatment for drinking purpose: ceramic microfiltration application

Conventional treatment of raw water for the municipal supply of drinking water may include chemical addition, coagulation, flocculation, sedimentation, filtration and disinfection, usually with chlorine. The reason for a larger use of membrane filtration systems, such as microfiltration and ultrafiltration, in this field, is mainly due for example to the ability of the membrane to remove pathogenic microorganisms as well as to control the disinfection by-products (DBPs) precursor. In this paper the use of microfiltration ceramic membranes for the treatment of raw water drawn from a lake located near Genoa is studied. The behaviour of permeate flux as a function of operating variables such as temperature, transmembrane pressure, and test duration is analysed. Membrane retention towards particles, microorganisms, algae and DBPs precursor is also investigated.

Casting and performance of polyvinylidene fluoride based membranes

Abstract The investigation of factors governing membrane preparation is of paramount importance in order to understand the formation of the membrane and its behaviour under test conditions. A large amount of fundamental work on membrane formation has been carried out on cellulose acetate membranes, but less information is available for other polymers. The purpose of the present work is to provide a better understanding of the parameters governing the formation of polyvinylidene fluoride membranes. The parameters controlling the casting process have been investigated in some detail.

Permoporometric study on ultrafiltration membranes

Abstract Skin layer porosity of ultrafiltration membranes was evaluated by an instrument based on the combined bubble pressure and solvent permeability methods. Nuclepore membranes were first tested for calibration and reproducibility purposes. Measurements were then carried out both on membranes prepared in our labs and an commercial ones. Porosity results are discussed in relation to membrane preparation variables as well as to phenomena controlling membrane performance during ultrafiltration application.

Preparation and characterization of polysulfone-polyvinylpyrrolidone based membranes.

Abstract Microporous polysulfone membranes were prepared from casting solutions of polysulfone, solvent and polyvinylpyrrolidone as additive. The membranes were characterized by scanning electron microscope observations, porosity measurements and ultrafiltration tests. The effect of polyvinylpyrrolidone and its molecular weight on the viscosity of the casting solutions and the properties of the membranes is discussed.