Preparación y caracterización de nuevos materiales nanocompuestos termoplásticos
- Autores: Jorge Teno Díaz
- Directores de la Tesis: Francisco Javier González Benito (dir. tes.)
- Lectura: En la Universidad Carlos III de Madrid ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: José Ramón Isasi Allica (presid.), Dušan K Božanić (secret.), José Maria Lagaron Caballero (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de Madrid
- Materias:
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- Resumen
In the present doctoral thesis, different polymer-based systems were designed, prepared and characterized, both pure polymers and polymer matrix nanocomposites. The method of preparation was named "Solution Blow Spinning" (SBS). The production throughout SBS of the materials, was carried out employing a commercial airbrush and home-made SBS equipment. Due to this fabrication process, materials were obtained in the form of films, made up of randomly arranged fibers, with diameters lower than 5 μm. For each system, the process conditions of SBS were optimized in order to obtain fine fibers and in the case of nanocomposites, ensure a good dispersion of the nanoparticles inside the polymer. The materials used were selected for their good properties in relation to their possible applications within the field of biomedicine and the food packaging industry. The polymers selected were the following; polyvinylidene fluoride, PVDF, polysulfone, PSF, polyethylene oxide, PEO, poly (ethylene-co-vinyl acetate) with 25% by weight of the comonomer vinyl acetate, EVA25 and poly (ethylene-co-vinyl acetate) with 40% by weight of the vinyl acetate comonomer, EVA40. On the other hand, the nanoparticles used to prepare the nanocomposite materials were TiO2 (100 nm), Cu (70 nm) and Ag (30-50 nm).
The first SBS studies were carried out using an airbrush. Specifically, the systems studied were based on PSF and PVDF filled with TiO2 nanoparticles, where different percentages of filler (0%, 1%, 2%, 5% and 10% by weight) were studied. These materials were characterized, studying the morphology at nanoscale, roughness, contact angles, and surface free energy. Also, the influence of the nanoparticles content in the bacteria adhesion was evaluated for each system. The DH5 E. Coli bacteria adhesion was studied on the surface of PSF-TiO2 materials by simple inspection using scanning electron microscopy (SEM). Obtained results indicated that the hydrophobicity and roughness promoted by the fabrication process and the presence of the filler, have a certain relationship with the reduction of the bacteria adhesion. On the other hand, the studies of cell adhesion of Streptococcus Mutans (S. Mutans) on the surfaces of PVDF-TiO2 system, indicated that there is a dependence between specific interactions of bacteria and the polar groups on the materials surfaces.
Using the home-made SBS equipment, different polymers were used in order to evaluate various processing conditions. The first work using this device was with EVA25. Here, the influence of the polymer concentration in the solution subjected to SBS (1%, 2%, 5%, 7 % and 10 %wt) in the final topography and morphology was studied. Then, the adhesion of DH5 E. Coli as a function of samples topography was evaluated. Thus, roughness measurement was carried out from the 3D surface image built from SEM images. In that work a correlation between roughness promoted by the morphology and the bacteria adhesion was found. It can be concluded, that surface heterogeneities at microscale, as well as the specific interactions at nanoscale, can greatly modify antibacterial action.
In order to obtain submicrometric fibers with higher homogeneity, in terms of morphology, within different polymeric systems, further investigations were done. In particular, PVDF and EVA40 were chosen to optimize the formation of fibers with the SBS equipment designed for this thesis. However, the preparation of PEO fibers were optimized using an airbrush. The conclusion of this work was that gas pressure, feed rate and working distance have a great influence in the fiber production, fiber diameters, and fiber diameters distribution.
Finally, from these results, a study of the system based on EVA40 filled with copper nanoparticles EVA40-Cu was carried out. The effect of the presence of different amounts of copper nanoparticles (0%, 1%, 3% and 6% by weight of Cu) on the properties of the polymer was studied. In addition, the bactericide effect of the copper nanoparticles inside the nanocomposite was evaluated with DH5 E. Coli bacteria. On the other hand, a cytotoxicity study was carried out with human epithelial cells HaCat. From this work it was possible to deduce that the copper particles are located inside and along the fibers. In the materials under study, a small effect is observed, as to see a significant bactericidal effect the Cu nanoparticles should have been located primarily on the surface of the fibers. Regarding the cytotoxicity test, materials do not seem to be toxic, but they produce a delay in the cell proliferation.
To conclude, a brief characterization study based in EVA40 filled with silver nanoparticles EVA40-Ag was done, aiming to observe the possible effect different silver nanoparticle concentration (0%, 1%, 2%, 3% y 6% wt.) could have on the matrix. It was concluded, that this kind of filler does not produce significant changes (structural, morphological, and thermo-mechanical behavior) in the EVA polymer.
