Joule effect self-heating of epoxy composites reinforced with graphitic nanofillers

Self-heating of conductive nanofilled resins due to the Joule effect is interesting for numerous applications, including computing, self-reparation, self-post-curing treatment of resins, fabrication of adhesive joints, de-icing coatings and so on. In this work, we study the effect of the nature and amount of graphitic nanofiller on the self-heating of epoxy composites. The addition of graphitic nanofillers induced an increase in the thermal conductivity of the epoxy resins, directly proportional to the nanofiller content. Percolation was not observed because of the heat transport through phonons. In contrast, the electrical conductivity curves present a clear percolation threshold, due to the necessity of an electrical percolation network. The electrical threshold is much lower for composites reinforced with carbon nanotubes (CNTs, 0.1 wt.%) than for the resin filled with graphene nanoplatelets (GNPs, 5 %). This fact is due to their very different specific areas. The composites filled with CNTs reach higher temperatures than the ones reinforced with GNPs, applying low electrical voltage because of their higher electrical conductivity. In contrast, the self-heating is more homogeneous for the GNP/epoxy resins due to their higher thermal conductivity. It was also confirmed that the self-heating is repetitive in several cycles, reaching the same temperature when the same voltage is applied

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 molecular architecture on the adsorption onto solid surfaces: comb-like polymers

The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control parameters in the study of the adsorption are the existence or absence on the molecular architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount depends on the architecture of the polymer chains (length of the PEG chains), on the polymer concentration and on the chemical nature of the main chain. The comparison of the thicknesses of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the water content of the layers that is intimately related to the grafting length. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but the entropic contributions as a result of the trapping of water in the layer structure are of fundamental importance

Influence of the molecular architecture on the secondary relaxations of Poly(styrene-co-methylmethacrylate) copolymers

The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control parameters in the study of the adsorption are the existence or absence on the molecular architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount depends on the architecture of the polymer chains (length of the PEG chains), on the polymer concentration and on the chemical nature of the main chain. The comparison of the thicknesses of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the water content of the layers that is intimately related to the grafting length. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but the entropic contributions as a result of the trapping of water in the layer structure are of fundamental importance

Nanocompuestos grafeno-nanotubos de carbono-epoxi influencia de la absorción de agua en las propiedades = Graphene-Carbon Carbon Nanotubes Thermoseting Epoxy Materials: Water Absortion Influence on their Properties

En este trabajo se presenta el efecto del envejecimiento hidrotérmico mediante inmersión en agua destilada, sobre varios materiales híbridos epoxi que incorporan nanotubos de carbono y/o nano-láminas de grafeno. Se han utilizado dos tipos de grafeno: grafeno funcionalizado con grupos amino (GNH2) y grafeno sin funcionalizar. En el caso del grafeno funcionalizado, durante el proceso de curado se produce la unión de dichas láminas al termoestable por formación de enlaces tipo covalente. El grafeno sin funcionalizar permite comprobar el efecto del uso del grafeno funcionalizado en estos materiales. Se ha realizado el estudio gravimétrico de la absorción isoterma de agua, así como y del efecto de la absorción de agua a saturación en las propiedades dinámico-mecánicas, mediante análisis térmico dinámico mecánico y sobre la conductividad eléctrica de los nano-compuestos. ----------ABSTRACT---------- This work presents the effect of hydrothermal aging in destilled water on several epoxy hybrid materials that have a certain amount of carbon nanotubes and/or graphene nanoplatelets. Two types of graphene nanoplatelests have been used: amino funtionalized graphene (GNH2) and non funtionalized graphene. When funtionalized graphene is used, covalent bonds between the graphene nanoplatelets and the epoxy matrix are expected to be formed over the curing proccess. Non functionalized graphene platelets are used to prove this effect. Gravimetric study of the absortion process has been done as well as the effect of the water absortion on the thermo-mechanical properties and the electric conductivity

Nanocompuestos grafeno-nanotubos de carbono-epoxi influencia de la absorción de agua en las propiedades = Graphene-Carbon Carbon Nanotubes Thermoseting Epoxy Materials: Water Absortion Influence on their Properties

En este trabajo se presenta el efecto del envejecimiento hidrotérmico mediante inmersión en agua destilada, sobre varios materiales híbridos epoxi que incorporan nanotubos de carbono y/o nano-láminas de grafeno. Se han utilizado dos tipos de grafeno: grafeno funcionalizado con grupos amino (GNH2) y grafeno sin funcionalizar. En el caso del grafeno funcionalizado, durante el proceso de curado se produce la unión de dichas láminas al termoestable por formación de enlaces tipo covalente. El grafeno sin funcionalizar permite comprobar el efecto del uso del grafeno funcionalizado en estos materiales. Se ha realizado el estudio gravimétrico de la absorción isoterma de agua, así como y del efecto de la absorción de agua a saturación en las propiedades dinámico-mecánicas, mediante análisis térmico dinámico mecánico y sobre la conductividad eléctrica de los nano-compuestos. ----------ABSTRACT---------- This work presents the effect of hydrothermal aging in destilled water on several epoxy hybrid materials that have a certain amount of carbon nanotubes and/or graphene nanoplatelets. Two types of graphene nanoplatelests have been used: amino funtionalized graphene (GNH2) and non funtionalized graphene. When funtionalized graphene is used, covalent bonds between the graphene nanoplatelets and the epoxy matrix are expected to be formed over the curing proccess. Non functionalized graphene platelets are used to prove this effect. Gravimetric study of the absortion process has been done as well as the effect of the water absortion on the thermo-mechanical properties and the electric conductivity

Efecto del contenido de entrecruzante y tipo de grafeno en las propiedades termo-mecánicas de nanocompuestos = Effect of the cross-linker content and type of graphene on the thermomechanical properties of nanocomposites

En este trabajo se estudia la influencia del tipo de grafeno (GNP) y de las diferentes proporciones agente entrecruzante (XB)-resina epoxi (LY), en las propiedades termo-mecánicas de nanocompuestos epoxi-grafeno (GNP). Se han preparado nanocompuestos epoxi/GNP utilizando dos tipos de grafenos diferentes: uno no funcionalizado (GNPn) y un grafeno amino funcionalizado (GNPNH2). El contenido de grafeno ha sido 6% y 10% en peso. Se han determinado las propiedades termo-mecánicas del termoestable LY-XB y de los nanocompuestos a través del análisis térmico mecánico dinámico y de ensayos a tracción en máquina universal de ensayos. El módulo de almacenamiento en la zona elastomérica y la temperatura de transición vítrea (Tg) del termoestable LY-XB y de los nanocompuestos presentan valores máximos para relaciones ligeramente ricas en amina. La adición de grafeno aumenta notablemente el módulo elástico de los nanocompuestos en comparación con el termoestable LY-XB, tanto en la zona vítrea (TTg). El termoestable LY-XB muestra la mejor resistencia y tenacidad para la relación estequiométrica XB/LY. Con la adición de grafeno se obtienen materiales más rígidos pero más frágiles. PRESENTADO EN: XII Congreso Nacional de Materiales Compuestos - MATCOMP 2017 Donostia / San Sebastián, 21, 22 y 23 Junio 2017 ----------ABSTRACT---------- In this paper we study the influence of the type of graphene (GNP) and the different ratios of the crosslinking agent (XB)-resin epoxy (LY) on the thermo-mechanical properties of epoxy-graphene nanocomposites (GNP). Epoxy/GNP nanocomposites have been prepared using two different types of graphene: one non-functionalized (GNPn) and one amino functionalized graphene (GNPNH2). The content of graphene has been 6% and 10% by weight. The thermo-mechanical properties of the LY-XB thermoset and the nanocomposites have been determined through dynamic mechanical thermal analysis and tensile tests in a universal testing machine. The glass transition temperature and the storage modulus in the elastomeric zone (T>Tg) of the thermoset LY-XB and the nanocomposites have maximum values for slightly rich amine content. The addition of graphene significantly increases the elastic modulus of the nanocomposites compared to the neat epoxy thermoset (LY-XB), both in the vitreous region (TTg). The thermoset LY-XB shows the best strength and toughness for the stoichiometric ratio XB/LY. The addition of graphene leads to more rigid but more fragile materials

Hydrothermal ageing of graphene/carbon nanotubes/epoxy hybrid nanocomposites

The hydrothermal ageing of hybrid nanocomposites formed by carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) incorporated into an epoxy matrix was studied. In order to avoid the weak interface, amine functionalized GNPs were used which are reactive with the epoxy matrix. The content of CNTs was 0.1 wt% and the GNPs content ranged from 5 to 12 wt%. The isothermal water absorption was measured until very long times (almost two years). Reduction of water absorption with the addition of either carbon nanotubes or graphene nanoplatelets has been found independently of the ageing time. The results can be described by a two-stage diffusion model with the first and second stages being diffusion and matrix relaxation controlled respectively. The obtained diffusion coefficient for the neat epoxy thermoset is higher than those of nanocomposites, which decreases with the increase of GNPs content. Theeffect of water absorbed on the dynamic-mechanical properties and on the electrical conductivity of the nanocomposites was analyzed. Whatever the temperature the storage modulus shows a continuous increase with the increase of the nanoparticles content, the effect of hydrothermal ageing is to decrease the modulus only in the glassy state (T < Tg). Water aged specimens show broadening of the tanδ peak related to the plasticization of the matrix. Tg of aged specimens coincides with the one of the unaged matrix, indicating that hydrothermal ageing does not produce noticeable matrix damage even after two years. Water aged specimens show similar electrical conductivity than unaged ones,which is another indication of no degradation of samples by water

Efecto del contenido de entrecruzante y tipo de grafeno en las propiedades termo-mecánicas de nanocompuestos = Effect of the cross-linker content and type of graphene on the thermomechanical properties of nanocomposites

En este trabajo se estudia la influencia del tipo de grafeno (GNP) y de las diferentes proporciones agente entrecruzante (XB)-resina epoxi (LY), en las propiedades termo-mecánicas de nanocompuestos epoxi-grafeno (GNP). Se han preparado nanocompuestos epoxi/GNP utilizando dos tipos de grafenos diferentes: uno no funcionalizado (GNPn) y un grafeno amino funcionalizado (GNPNH2). El contenido de grafeno ha sido 6% y 10% en peso. Se han determinado las propiedades termo-mecánicas del termoestable LY-XB y de los nanocompuestos a través del análisis térmico mecánico dinámico y de ensayos a tracción en máquina universal de ensayos. El módulo de almacenamiento en la zona elastomérica y la temperatura de transición vítrea (Tg) del termoestable LY-XB y de los nanocompuestos presentan valores máximos para relaciones ligeramente ricas en amina. La adición de grafeno aumenta notablemente el módulo elástico de los nanocompuestos en comparación con el termoestable LY-XB, tanto en la zona vítrea (TTg). El termoestable LY-XB muestra la mejor resistencia y tenacidad para la relación estequiométrica XB/LY. Con la adición de grafeno se obtienen materiales más rígidos pero más frágiles. PRESENTADO EN: XII Congreso Nacional de Materiales Compuestos - MATCOMP 2017 Donostia / San Sebastián, 21, 22 y 23 Junio 2017 ----------ABSTRACT---------- In this paper we study the influence of the type of graphene (GNP) and the different ratios of the crosslinking agent (XB)-resin epoxy (LY) on the thermo-mechanical properties of epoxy-graphene nanocomposites (GNP). Epoxy/GNP nanocomposites have been prepared using two different types of graphene: one non-functionalized (GNPn) and one amino functionalized graphene (GNPNH2). The content of graphene has been 6% and 10% by weight. The thermo-mechanical properties of the LY-XB thermoset and the nanocomposites have been determined through dynamic mechanical thermal analysis and tensile tests in a universal testing machine. The glass transition temperature and the storage modulus in the elastomeric zone (T>Tg) of the thermoset LY-XB and the nanocomposites have maximum values for slightly rich amine content. The addition of graphene significantly increases the elastic modulus of the nanocomposites compared to the neat epoxy thermoset (LY-XB), both in the vitreous region (TTg). The thermoset LY-XB shows the best strength and toughness for the stoichiometric ratio XB/LY. The addition of graphene leads to more rigid but more fragile materials

Epoxy Composites Reinforced with ZnO from Waste Alkaline Batteries

The zinc alkaline battery is one of the most popular sources of portable electrical energy, with more than 300,000 tons being consumed per year. Accordingly, it is critical to recycle its components. In this work, we propose the use of zinc oxide (ZnO) microparticles recovered from worn-out batteries as fillers of epoxy resins. These nanocomposites can be used as protective coatings or pigments and as structural composites with high thermal stability. The addition of ceramic nanofillers, such as ZnO or/and TiO2, could enhance the thermal and mechanical properties, and the hardness and hydrophobicity, of the epoxy resins, depending on several factors. Accordingly, different nanocomposites reinforced with recycled ZnO and commercial ZnO and TiO2 nanoparticles have been manufactured with different nanofiller contents. In addition to the different ceramic oxides, the morphology and size of fillers are different. Recycled ZnO are&ldquo;desert roses&rdquo; such as microparticles, commercial ZnO are rectangular parallelepipeds nanoparticles, and commercial TiO2 are smaller spherical nanoparticles. The addition of ceramic fillers produces a small increase of the glass transition temperature (&lt;2%), together with an enhancement of the barrier effect of the epoxy resin, reducing the water diffusion coefficient (&lt;21%), although the maximum water uptake remains constant. The nanocomposite water absorption is fully reversible by subsequent thermal treatment, recovering its initial thermomechanical behavior. The water angle contact (WCA) also increases (~12%) with the presence of ceramic particles, although the highest hydrophobicity (35%) is obtained when the epoxy resin reinforced with recycled flowerlike ZnO microparticles is etched with acid stearic and acetic acid, inducing the corrosion of the ZnO on the surface and therefore the increment of the surface roughness. The presence of desert rose ZnO particles enhances the de lotus effect