Cristina Cardoso Pereira

New insights in the removal of diluted volatile organic compounds from dilute aqueous solution by pervaporation process

The present work aimed the mass transfer investigation in the removal of organic contaminants from water by the pervaporation process. The terpolymer ethene-propene-diene (EPDM) was used as the selective elastomer. Two classes of model organic solutes were chosen: chlorinated hydrocarbons (trichloroethylene, dichloromethane and trichloromethane) and aromatic ones (toluene, phenol and aniline). Pervaporation tests were carried out using dense and composite membranes with different thickness, solute concentrations and feed flow velocities at room temperature. The liquid boundary layer resistance (i.e., concentration polarization phenomenon) was observed for all solutes. The resistance-in-series model was used to determine liquid and polymer phase resistances. The results obtained indicate that the model would be better written considering the chemical potential gradient as driving force, in order to take into account affinity between water and the organic solutes, as well as their interactions with the polymer selective layer. The rational activity coefficients of the solutes in the polymer phase were determined by inverse gas chromatography (IGC) and related to the mass transfer coefficient in the polymer phase.

Membranes obtained by simultaneous casting of two polymer solutions

Abstract Simultaneous casting of two polymer solutions allows formation of each membrane layer by different concepts. However, mass transfer between the polymer solutions increases the complexity of the involved phenomena. In the present work, it was investigated the simultaneous casting of two different polymer solutions to form the top and support layers of the membrane, respectively. Polyetherimide and polyethersulfone were used as base polymers. In order to form the support layer, it was used as a polymer solution composed of Lewis acid:base complex (adipic acid — Lewis acid, and n-methyl-2-pyrrolidone — Lewis base), and another composed of a macromolecular additive (polyvinylpyrrolidone). In order to form the top layer, different polymer solutions composed of a volatile component tetrahydrofuran (THF) were used. The velocity of precipitation of the polymer solutions and the morphology of the membranes were characterized by light transmission measurements and scanning electron microscopy (SEM), respectively. The morphology of the resulting membranes were also compared with the membranes obtained by single casting of each polymer solution. The results mainly showed that adhesion of the membrane layers seemed to occur when there was sufficient time for the solutions to interpenetrate through each other. This was probably favored when the region close to the interface of the solutions remains stable for a longer period. The presence of polyvinylpyrrolidone seemed also to favor adhesion between the layers.

Spinning process variables and polymer solution effects in the die-swell phenomenon during hollow fiber membranes formation

During hollow fiber spinning many variables are involved whose effects are still not completely clear. However, its understanding is of great interest because the control of these variables may originate membranes with the desired morphologies and physical properties. In this work, the phase inversion process induced by the immersion precipitation technique was applied to prepare hollow fibers membranes. It was verified that some of the variables involved, can promote a visco-elastic polymer solution expansion, called die-swell phenomenon, which is undesired since it may lead to low reproducibility of the permeation properties. The effects of the distance between spinneret and precipitation bath, the bore liquid composition, and the polymer solution composition were analyzed and discussed in order to avoid this phenomenon. According to the results, it was verified that the parameters investigated might promote a delay precipitation, which restrained the visco-elastic expansion.

Evaluation of biodegradable polymer conduits – poly(l-lactic acid) – for guiding sciatic nerve regeneration in mice

Polymeric biomaterials are often used for stimulating nerve regeneration. Among different conduits, poly(lactide acid) - PLA polymer is considered to be a good substrate due to its biocompatibility and resorbable characteristics. This polymer is an aliphatic polyester which has been mostly used in biomedical application. It is an organic compound with low allergenic potential, low toxicity, high biocompatibility and predictable kinetics of degradation. In this study we fabricated and evaluated a PLA microporous hollow fiber as a conduit for its ability to bridge a nerve gap in a mouse sciatic nerve injury model. The PLA conduit was prepared from a polymer solution, throughout extrusion technique. The left sciatic nerve of C57BL/6 mouse was transected and the nerve stumps were placed into a resorbable PLA (PLA group) or a PCL conduit (PCL group), n=5 each group. We have also used another group in which the nerves were repaired by autograft (autograft group, n=5). Motor function was analyzed according to sciatic functional index (SFI). After 56days, the regenerated nerves were processed for light and electron microscopy and morphometric analyses were performed. A quantitative analysis of regenerated nerves showed significant increase in the number of myelinated fibers and blood vessels in animals that received PLA conduit. The PLA group exhibited better overall tissue organization compared to other groups. Presenting well-organized bundles, many regenerating clusters composed of preserved nerve fibers surrounded by layers of compacted perineurium-like cells. Also the SFI revealed a significant improvement in functional recovery. This work suggests that PLA conduits are suitable substrate for cell survival and it provides an effective strategy to be used to support axonal growth becoming a potential alternative to autograft.