RT Dissertation/Thesis
T1 Modificación de grafeno con cadenas de polisulfona e incorporación a matrices poliméricas. Evaluación de las propiedades y de la biocompatibilidad de los nanocomposites
A1 Peña Bahamonde, Janire
AB La presente tesis trata del estudio y diseño de nanocomposites de grafeno empleandocomo matrices poliméricas polisulfona y una mezcla de polímeros de polisulfona y resinaepoxi.En el diseño de estos nanocomposites juega un papel muy importante la interfase delnanomaterial; ya que una buena interacción entre la nanopartícula y la matriz en la regióninterfacial podría mejorar la estabilidad y despersabilidad de los nanorrefuerzos. Paraaumentar la compatibilidad con la matriz, se optó por modificar la superficie de grafenocon cadenas de polifulfona. La modificación superficial del nanorrefuerzo se realizómediante el método que se conoce como nitrene chemistry empleando dos estrategiassintéticas diferentes; permitiendo obtener cadenas de polímero ancladas con diferente pesomolecular (diferente longitud).La polisulfona es un polímero empleado generalmente en aplicaciones biomédicas ymedioambientales, por lo que además, se estudió la biocompatibilidad de losnanomateriales de rGO con cadenas de polisulfona. Para que un material seabiocompatible debe cumplir dos requisitos, por un lado que presente propiedadesantibacterianas, y además, que no presente citotoxicidad. El estudio realizado de labiocompatibilidad de nuestro nanomaterial muestra que este puede ser potencialmenteempleado en aplicaciones que requieran contacto directo con el ser humano, ofreciendoademás propiedades antibacterianas.La preparación de los nanocomposites de polisulfona tuvo lugar mediante la técnicade extrusión-inyección. Se prepararon nanocomposites con diferente carga denanomaterial, 0.1, 0.5, 1.0 y 3 % en peso de rGO y grafeno modificado con polisulfona. La dispersión del nanorrefuerzo presenta una notable importancia en las propiedades del xnanocomposite, por lo que previo al estudio de sus propiedades se analizó mediantereología, espectroscopía dieléctrica y técnicas microscópicas su dispersión en la matrizpolimérica. De los resultados obtenidos, todas las técnicas empleadas para el estudio de la dispersión concluyen que la modificación superficial con cadenas de polisulfona de mayor peso molecular ayuda a mejorar la dispersabilidad.Se estudiaron las propiedades mecánicas, térmicas y eléctricas de los nanocompostites, y además, se realizaron estudios de biodegradabilidad. Los resultadosmuestran que al aumentar la carga de nanorrefuerzo, mejoran significativamente suspropiedades térmicas y mecánicas, obteniéndose mejoras en los nanocompositesmodificados con cadenas largas de polisulfona. El estudio conformacional de las cadenas,concluye que las cadenas de mayor peso molecular se encuentran preferentemente enconformación semidiluida y además, se encuentran a una distancia lo suficientementealejadas unas de otras para que las cadenas de polisulfona de la matriz interpenetren en las cadenas de polisulfona ancladas a la superficie del rGO. Esta interpenetración ayuda amejorar y fortalecer la región interfacial, observándose en la mejora de las propiedades.Los estudios de biodegradabilidad muestran que este nanomaterial, a altos contenidos derGO, es altamente resistente a periodos largos de exposición en contacto con aguasresiduales industriales, debido a que sus propiedades iniciales se mantienen y además, escapaz de inhibir la formación de biofilms.Los nanorrefuerzos sintetizados fueron también embebidos en una mezcla depolímeros epoxi polisulfona, con el fin de obtener una morfología de fases invertidas. Sepretendía obtener esta morfología para introducir las láminas de grafeno preferentementeen los canales que forma la fase co-continua, para dar lugar a lo que se conoce comofenómeno de doble percolación. Los resultados del análisis de las propiedades estudiadasde estos nanocomposites muestran cómo el nanorrefuerzo modificado con cadenas depolisulfona ayuda a obtener la morfología deseada, obteniendo resultados satisfactorios en las propiedades mecánicas y térmicas estudiadas.
AB Polymer-matrix nanocomposites formed by incorporation of graphene sheets in polymermatrices have attracted enormous attention in various fields of science and engineering, due to the excellent properties of graphene sheets. Specifically, graphene has been used to improve the mechanical, thermal, electrical, and barrier properties of polymers. Graphenebased polymer nanocomposites have been employed for diverse applications in electronics, aerospace, automotive manufacturing, and green energy.Polysulfones (PSUs) are high-temperature thermoplastic polymers that exhibit greatchemical inertness, enhanced oxidative resistance, thermal and hydrolytic stability, as wellas high mechanical strength. Additionally, PSUs might be easily processed as a film andthus, they are good candidates for different applications, such as gas separation,hemodialysis, nano/ultra-filtration, adhesives for metal to metal bonds, membranes for fuel cells, drug delivery, or matrices for fiber reinforced composites.Reduced graphene oxide (rGO) is of particular interest, since functional groups on itssurface enhance its solubility in organic solvents and remarkably facilitate surfacemodification with organic molecules or polymers. The grafting of polymer brushesimproves the dispersion state and the polymer/graphene interfacial adhesion with thesubsequent increase in the nanocomposite properties. During the nanocomposite synthesis, both the rGO/polymer ratio and the molecular weight of the graft polymer play animportant role regarding rGO dispersion. This is because the behavior of polymer brushes is strongly determined by the polymer chain conformation. The grafting density and thecritical spacing between two neighboring chains determine the brush regime, i.e.mushroom, crossover, and brush-like regimes. Depending on the conformation of the vigraftedpolymer chains, the interactions with the polymer matrix may be improved.Another factor to be considered in order to enhance the interphase region innanocomposite materials is the preparation method of those. One of the objectives of thisthesis is improving some of these parameters to obtain better properties in the finalnanomaterial, studying the interphase of the system.The present dissertation reports, for the first time, the modification of reducedgraphene oxide nanosheets with polysulfone chains through two different synthetic routesvia nitrene chemistry. The PSU polymer was bonded to rGO at the end (rGO-PSU end) orrandomly along the PSU chain (rGO-PSU mid). These strategies allowed to obtainpolymer brushes with two different lengths on the surface. The resulting rGO-PSUsynthetic products were carefully characterized by Raman, FTIR, XPS, TEM, and TGA,evidencing the successful grafting of PSU onto rGO surfaces. The long-term stability ofthese nanosheets was also determined in common solvents.In addition, the biocompatibility of the nanoparticles was tested. This study involvedthe antimicrobial properties and cytotoxicity in human cells. The nanoparticles of modifiedand non-modified graphene were tested at different concentrations to determine the mosttoxic concentrations to both, Gram-positive (B. subtilis) and Gram-negative (E. coli K12)microorganisms. The results showed a reduction of 97% in the growth of B. subtilis afterthree hours exposure, for the polymer modified nanosheets. The results also demonstrated that rGO-PSU mid exhibited better antimicrobial properties due to its shorter polymerchains, which improves the contact of the microorganisms with the graphene surface.Furthermore, cytotoxicity in human cells was evaluated, showing no toxic effect even at thehighest concentration employed in antimicrobial properties.Unmodified and modified rGO with polysulfone brushes were included inpolysulfone and epoxy resin matrices to evaluate their properties. PSU nanocompositeswere prepared at four different percentages (up to 3 wt% rGO) by extrusion. The extrudedmaterial was further processed by injection molding to finally obtain specimens forevaluation of thermal, mechanical, electrical, and antimicrobial properties. Themorphology and microstructure of the prepared samples were examined by scanningelectron microscopy (SEM) and transmission electronic microscopy (TEM). Rheologicaland dielectric spectroscopy were employed to study the dispersion state of thenanocomposites, showing that nanocomposites with rGO-PSU end nanoparticles presentedbetter dispersion than non-modified graphene ones.The results indicated that the extrusion-injection procedure was an efficientpreparation method of the nanocomposites with good dispersion degrees of rGO in thematrix. Tensile test, dynamic mechanical thermal analysis (DMTA), and nanoindentationshowed an important improvement in the Young modulus respect to the neat polymer.The enhancement of mechanical properties was interpreted in terms of the dispersion andinterface modification of rGO. A theoretical study about the polymer brushesconformation at the interphase helped to understand the mechanical behavior. Thermalproperties of the nanocomposites were also analyzed, showing a moderate increase in thethermal stability.The antimicrobial properties of the prepared nanocomposites, with unmodifiedgraphene, were investigated in E. coli K12. Biofilm formation was studied by confocalmicroscopy. The antimicrobial properties of rGO were preserved in the nanocompositesand a decrease in the biofilm thickness was observed for the nanocomposites with 3 wt%rGO. A biodegradation study was also performed by exposure to industrial wastewater fornine days. The mechanical properties of the nanocomposites with high rGO content weremaintained and they exhibited antifouling properties. The results of this study showed thatthese materials may be employed in environmental field applications.Epoxy resins are widely used in many industry fields due to their inherent excellentthermal and mechanical properties. Nevertheless, in order to increase toughness and meethigh performance applications, they are modified with elastomers, thermoplastics, and all sorts of nanoparticles embedded on the epoxy network. Modification with highperformanceengineering thermoplastic modifiers, such as polysulfones, helps to improveepoxy resins toughness. Thermoplastics are usually partially miscible with epoxy resinprecursors at several temperatures and compositions, but as curing progress, the decreasein the entropy of mixing leads to a two-phase structure by reaction-induced phaseseparation (RIPS). Morphology and performance of epoxy/PSU blends has beenextensively studied. Several morphologies, such as sea-island, bicontinuous or doublephase,and nodular (phase-inverted) structures have been observed.In this work, rGO or rGO-PSU sheets, up to 1% by weight, have been incorporatedto an epoxy/PSU blend containing 20 wt% PSU by weight. The resulting epoxynanocomposites were characterized by differential scanning calorimetry (DSC), DMTA,and rheology. The morphology and microstructure of the prepared samples wereexamined by SEM. Phase-inverted morphologies (PSU as continuous phase) have been viiiobserved.Nanocomposites showed interesting morphology changes in the presence ofrGO-PSU end, which may be due to rGO nanosheets were preferently embedded anddispersed in PSU channels. The interest in this morphology lies in the possibility ofachieving the phenomena known as double threshold, introducing channels wheregraphene sheets are preferably located. Nanocomposites with PSU and rGO-PSU endnanoparticles showed also an improvement in the mechanical and thermal properties.In summary, nitrene chemistry was successfully applied to graft PSU onto rGOsheets. The synthetic strategy presented in this work demonstrates that modified graphenenanosheets can be easily obtained in high yields. The resulting nanomaterials have suitabledispersability and processability in organic solvents; and present improved antimicrobialbehavior and lower cytotoxicity compared to non-modified rGO.PSU matrix nanocomposites show an improvement in mechanical, thermal,antimicrobial, and degradability properties, and epoxy/PSU polymer blends modified withrGO exhibit noticeable morphology and mechanical changes.
YR 2017
FD 2017-03
LK https://hdl.handle.net/10016/25321
UL https://hdl.handle.net/10016/25321
LA spa
NO Mención Internacional en el título de doctor
DS e-Archivo
RD 1 sept. 2024