Cosolvencia de polímeros : dimensiones y solvatación del PMMA

Tesis - Universidad Complutense de Madrid, 1982.Depto. de Química FísicaFac. de Ciencias QuímicasTRUEProQuestpu

Thermal behavior os thermosetting resing reinforced with carbon nanotubes and graphene nanoplatelets

In this work, we study the effect of the addition of GNP and CNT in an epoxy matrix. The influence of the content added of these nanofillers on the glass transition temperature and degradation temperature is analysed. Moreover, the thermal conductivity of these nanocomposites is determined

Comportamiento Mecánico de Poliéster Insaturado Modificados con Poli(ε-Caprolactona) Reforzadas con Monmorillonita C30B

La dispersión de nanopartículas en el seno de una matriz polimérica es la base para la fabricación de los materiales denominados nanocompuestos. Una de las categorías de nanocompuestos que ha merecido especial atención en la última década es aquella en la que el nanorrefuerzo pertenece a la categoría de los silicatos laminares. Las propiedades únicas de estos materiales derivan del tamaño nanométrico de las partículas de silicato y de la elevada superficie de contacto polímero-nanosilicato que es posible alcanzar. En este trabajo se han preparado nanocompuestos fabricados con un nanosilicato laminar Cloisita 30B (C30B) perteneciente a la categoría de las montmorillonitas, orgánicamente modificada para favorecer su interacción con la matriz polimérica. Como matriz polimérica se ha utilizado una resina de poliéster de tipo isoftálico curada (UP) que ha sido modificada mediante la adición de un termoplástico, en concreto, poli (ε-caprolactona) (PCL) de dos pesos moleculares diferentes. La intención de la investigación es comparar el comportamiento de estos sistemas con el de sus análogos no reforzados, evaluando la influencia del nanorrefuerzo en el comportamiento mecánico y termomecánico

Dielectric and dynamic mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: polystyrene-b-poly(t-butylacrylate)

A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich- and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the α-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the α-relaxation, the relaxation map for the β-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the β-relaxations have a more local character than the α-ones. The width of the α-relaxation increases with T for all the samples, and it is slightly larger for the copolymers. The intensity of the α-relaxation is larger (between 3 and 4 times) for the homopolymer. Considering the molecular weights of the PtBa blocks, this effect has to be ascribed to the existence of frozen amorphous PtBa due to the existence of the glassy PS domains in the microphase separated copolymers. Molecular Dynamic Simulations (MDSs) for different sequences of the polymers under study were carried out. The conformational analysis was carried out between 1000 and 1700 K. The analysis of the variation of angles 1 and 2 of the ester group of PtBa points out the existence of a correlation between the conformational changes of the side group of the polymer chains and their relaxational behaviour

Efecto del grafeno en las propiedades mecánicas de adhesivos de base epoxi

En este trabajo se estudia la influencia del tipo de grafeno y su contenido en las propiedades mecánicas y adhesivas de adhesivos de base epoxídica. Se han utilizado dos tipos de grafeno: sin funcionalizar y funcionalizado. El grafeno funcionalizado contiene grupos amina que son reactivos con el prepolímero epoxi. Se han seleccionado dos tipos de grafeno no funcionalizado que difieren en las dimensiones de las nanoláminas. El módulo de Young, la deformación a la rotura, resistencia mecánica y tenacidad a 22ºC se han determinado en todos los nanocompuestos epoxi/grafeno. La resistencia mecánica de uniones adhesivas en solape sencillo con sustrato de aluminio se ha obtenido para los tres tipos de adhesivos

Preparation and characterization of polyester resin-layered silicate containing reactive groups

Polymer nanocomposites, specifically nanoclay-reinforced polymers, have attracted great interest as matrix materials for high temperature composite applications. Nanocomposites require relatively low dispersant loads to achieve significant property enhancements. These enhancements are mainly a consequence of the interfacial effects that result from dispersing the silicate nanolayers in the polymer matrix and the high in-plane strength, stiffness and aspect ratio of the lamellar nanoparticles. The montmorillonite (MMT) clay, modified with organic onium ions with long alkyl chains as Cloisites, has been widely used to obtain nanocomposites. The presence of reactive groups in organic onium ions can form chemical bonds with the polymer matrix which favours a very high exfoliation degree of the clay platelets in the nanocomposite (1,2

Rubber modified epoxy resins cured with piperidine

Glass transition temperatures (Tᵍ) of epoxy resins, diglycidyl ether of bisphenol-A cured with piperidine, have been measured by differential scanning calorimetry and dynamic mechanical thermal analysis in order to follow the curing process. Optimum cure conditions have been established as 3% PP at 120°C. Tᵍs of the neat epoxy system and those modified with 5 and 16% of a carboxyl-terminated reactive rubber copolymer of butadiene and acrylonitrile (CTBN) have been determined as a function of the cure time. Addition of 5% of CTBN does not modify the process, but the higher CTBN content accelerates the initial stage. Tᵍs after long cure times (Tᵍx) are lower for the modified systems than for the neat, showing that CTBN is not fully segregated. The amounts of CTBN dissolved in the epoxy crosslinked network have been estimated.The authors thank Dr A. J. Kinloch for advice in this investigation. We are grateful to CIBAGEIGY for kindly providing the samples. Financial support by the Comisión de lnvestigación Científica y Técnica is acknowledged (89/0435)

X-Ray Diffraction, Calorimetric and Dielectric Relaxation Study of the Amorphous and Smectic States of a Main Chain Liquid Crystalline Polymer

Los polímeros cristales líquidos (LCP) son sistemas complejos que forman mesofases que presentan orden orientacional y polímeros amorfos. Con frecuencia, el estado amorfo isotrópico no puede ser estudiado debido a la rápida formación de mesofases. En este trabajo se ha sintetizado y estudiado un nuevo LCP: poli(trietilenglicol metil p, p '-bibenzoato), PTEMeB. Este polímero presenta una formación de mesofase bastante lenta haciendo posible estudiar de forma independiente tanto los estados amorfo y de cristal líquidos. La estructura y las transiciones de fase del PTEMeB han sido investigados por calorimetría (DSC), con MAXS / WAXS con temperatura variable que emplean radiación de sincrotrón y con difracción de rayos X. Estos estudios han mostrado la existencia de dos transiciones vítreas, relacionadas con las fases amorfa y cristal líquido. Se ha realizado un estudio de relajación dieléctrica en amplios intervalos de temperatura y presión. Se ha encontrado que la transición vítrea dinámica de la fase amorfa es más lenta que la del cristal líquido. El estudio de la relajación ? nos ha permitido seguir la formación isoterma de la mesofase a presión atmosférica. Además, con el estudio el comportamiento dinámico a alta presión se ha encontrado que se produce la formación rápida de la mesofase inducida por cambios bruscos de presión. Liquid crystalline polymers (LCPs) are complex systems that include features of both orientationally ordered mesophases and amorphous polymers. Frequently, the isotropic amorphous state cannot be studied due to the rapid mesophase formation. Here, a new main chain LCP, poly(triethyleneglycol methyl p,p'-bibenzoate), PTEMeB, has been synthesized. It shows a rather slow mesophase formation making possible to study independently both the amorphous and the liquid crystalline states. The structure and phase transitions of PTEMeB have been investigated by calorimetry, variable-temperature MAXS/WAXS employing synchrotron radiation, and X-ray diffraction in oriented fibers. These experiments have pointed out the presence of two glass transitions, related to the amorphous or to the liquid crystal phases. Additionally, the mesophase seems to be a coexistence of orthogonal and tilted smectic phases. A dielectric relaxation study of PTEMeB over broad ranges of temperature and pressure has been performed. The dynamic glass transition turns out to be slower for the amorphous state than for the liquid crystal. Monitoring of the α relaxation has allowed us to follow the isothermal mesophase formation at atmospheric pressure. Additionally, the dynamical behavior at high pressures has pointed out the fast formation of the mesophase induced by sudden pressure changes

Influence of the epoxy/amine stoichiometry on the thermomechanical properties of nanocomposites based on high Tg epoxy and organophilic clays.

In layered silicate-epoxy nanocomposites organic modification of the silicates makes them compatible with the epoxy which intercalates into the clay galleries. The effect of clay dispersion on epoxies of high Tg is not clear. Decreases of the epoxy Tg have been frequently reported. The presence of clay may cause stoichiometry imbalances that conduces to the formation of imperfect network

Propiedades de nanocompuestos de matriz termoestable con nuevos organosilicatos laminares

En este trabajo se han preparado nanocompuestos de matriz polímero termoestable del tipo poliéster insaturado y epoxídica utilizando como refuerzo nanosilicatos laminares que se han modificado específicamente para mejorar la interacción con la matriz. En concreto se han modificado montmorillonitas con cationes orgánicos reactivos con la matriz de poliéster insaturado. Asimismo se han silanizado montmorillonitas comerciales orgánicamente modificadas con el objetivo de formar enlaces químicos con la matriz epoxídica. En ambos nanocompuestos se han estudiado las propiedades termo- mecánicas pudiendo comprobar la efectividad de los nuevos organosilicatos