Jocelei Duarte

Effect of non-solvents used in the coagulation bath on morphology of PVDF membranes

The aim of this paper was to prepare a poly (vinylidene fluoride) (PVDF) membrane using different non-solvents in the coagulation bath for the phase inversion method. In order to increase the mechanical strength of membranes, facing the pressure of work, was used a macro-porous polyester support. The morphology and structure of the resulting membranes were evaluated by scanning electron microscopy, porosity measurements, water and 1-octanol uptake, contact angle, pure water flux, hydraulic permeability and hydraulic resistance. The morphology and pure water flux changed significantly using ethanol (symmetric membrane) and/or water (asymmetric membrane) as the non-solvent. The symmetric membrane presented a high hydrophobic surface (water contact angle ~136o) and a higher pure water flux and porosity than the asymmetric membrane, which presented a lower hydrophobicity surface (water contact angle ~90o). The morphologies obtained suggest different applications.

Characterization of Polyamide 66 membranes prepared by phase inversion using formic acid and hydrochloric acid such as solvents

The membranes properties prepared from water/formic acid (FA)/ polyamide 66 (PA66) and water/hydrochloric acid (HCl)/polyamide 66 (PA 66) systems has been studied. The different solvents interact distinctly with the polymer, affecting the membrane morphology. The asymmetric structure of the membranes showed a dense top layer and a porous sublayer. The membranes M-HCl prepared from HCl/PA 66 system showed a larger dense layer (around 23 μm) in compared to those prepared from FA/PA 66 system (M-FA) (around 10 μm). The membrane morphology was a determinant factor in results of water absorption, porosity and pure water flux. The lower thickness of dense layer in M-FA membranes resulted in a higher water absorption and, consequently, porosity, approximately 50%, compared with M-HCl membranes, approximately 15%. The same trend was observed to permeate flux, the lower thickness of dense layer higher pure water flux.

Preparation and Characterization of PA66/Alumina Composite Membrane

In this study, polymer/ceramic composite membranes were prepared and characterized. The polymer used was polyamide 66 (PA66) deposited by dip coating on the inner surface of α-alumina-based (Al2O3) microporous tube. A coating on the ceramic support surface and the formation of the selective layer was analyzed by scanning electron microscopy (SEM) in membranes with one (PA-1) and two layers (PA-2). The results of mercury porosimetry showed that the deposition of the polyamide layers decreases the average pore size. The PA-1 presented an average pore size of 0.35 μm, while the PA-2 presented two peaks of 0.18 and 0.56 μm. Both showed a superior performance than the ceramic support (pore diameter of 0.65 μm). Although, the permeate flux was higher with an impregnation membrane, the number of layers (one or two) just introduced a slight difference in pore statistical analysis. The order of rejection coefficient values for protein molecules is BSA > egg albumin > trypsin. The permeation tests showed that the composite membrane can be applied in ultrafiltration processes with MWCO of 69 kDa.

Caracterização de membranas assimétricas de acetato de celulose produzidas a partir do aproveitamento do resíduo da palha de milho para uso em ultrafiltração

Cellulose acetates (CA) with different degrees of acetylation were synthesized from cellulose extracted from corn stover. Membranes were prepared for the ultrafiltration process with pure polymers and blend form of CA utilizing a dioxane/acetone system. The membranes were characterized according to their transport properties. The blend form materials presented the best results for application in ultrafiltration experiments. M-TAC/DAC (corn stover triacetate and diacetate) and M-TAC/DAC-Rho (corn stover triacetate and Rhodia diacetate) presented rejection to egg albumin protein of 87.39% and 80.50%, respectively. Thus, MWCO of 45 kDa was determined for these materials.

A Dual-mode model interpretation of CO2/CH4 permeability in polysulfone membranes at low pressures

An asymmetric membrane of polysulfone (PSf) was synthesized by phase inversion method. Permeation experiments were carried out between 2 to 5 bar pressure, and at temperatures 20 to 45°C. The dense-selective layer of PSf membrane presents regular thickness (about 5 µm), and was not possible to observe the formation of macrovoids in porous layer. The CO2 permeability through membrane was 18.8 Barrer at 35°C and 2 bar pressure, and this relationship between the pressure and the CO2 permeability was described adequately by Dual-mode model. The absence of CH4 permeability at 2 and 3 bar pressure, qualifies the PSf membrane for gases separation with high selectivity in this range.

Behavior Classification Physical/ChemistryPA66/HC Binary System Utilized to ObtainSeparation Membranes

The dissolution of polymers in solvents is an interest area of polymers science and technology due to their applications in films and membranes. The starting point for the preparation of polymer membranes by phase inversion is having a thermodynamically stable solution. In this work, the thermodynamic behaviour of polyamide 66 (PA66) solutions in formic acid (FA) and in hydrochloric acid (HC), was studied to evaluate its physical/chemistry classification. The polymer systems may be divided into five classes (types), which incorporate polymer-low molecular liquid systems, ranging from true solutions to dispersions of polymers in liquids. The polyamide 66/formic acid (PA66/FA) binary system is considered a true solution. Several experiments were performed to verify if the polyamide 66/ hydrochloric acid (PA66/HC ) binary system has all characteristics of true solution. The analysis showed that the PA66/HC binary system presents all characteristics of true solution, including the final morphology of the membranes that are similar obtained membranes by PA66/FA binary system.