Influence of different organoclays on the curing, morphology, and dynamic mechanical properties of an epoxy adhesive

The thermal, mechanical, and adhesive properties of nanoclay-modified adhesives were investigated. Two organically modified montmorillonites: Cloisite 93A (C93A) and Nanomer I.30E (I.30E) were used as reinforcement of an epoxy adhesive. C93A and I.30E are modified with tertiary and primary alkyl ammonium cations, respectively. The aim was to study the influence of the organoclays on the curing, and on the mechanical and adhesive properties of the nanocomposites. A specific goal was to compare their behavior with that of Cloisite30B/epoxy and Cloisite15A/ epoxy nanocomposites that we have previously studied. Both C30B and C15A are modified with quaternary alkyl ammonium cations. Differential scanning calorimetry results showed that the clays accelerate the curing reaction, an effect that is related to the chemical structure of the ammonium cations. The three Cloisite/nanocomposites showed intercalated clay structures,the interlayer distance was independent of the clay content. The I.30E/epoxy nanocomposites presented exfoliated structure due to the catalytic effect of the organic modifier. Clay-epoxy nanocompo-sites showed lower glass transition temperature (Tg) and higher values of storage modulus than neat epoxy thermoset, with no significant differences between exfoliated or intercalated nanocom-posites. The shear strength of aluminum joints using clay/epoxy adhesives was lower than with the neat epoxy adhesive. The wáter aging was less damaging for joints with I.30E/epoxy adhesive

Ternary nanocomposites: curing, morphology and mechanical properties of epoxy/thermoplastic/organoclay systems

The influence of two organically modified montmorillonites on the curing, morphology and mechanical properties of epoxy/poly(vinyl acetate)/organoclay ternary nanocomposites was studied. The organoclays and poly(vinyl acetate) (PVAc) provoked contrary effects on the epoxy curing reaction. Ternary nanocomposites developed different morphologies depending on the PVAc content, that were similar to those observed in the epoxy/PVAc binary blends. The organoclays were only located in the epoxy phase independently of the morphology. All nanocomposites showed intercalated structures with similar clay interlayer distances. Both PVAC and organoclays lowered the Tg of the epoxy phase, the presence of clays did not influence the Tg of the PVAc phase. The addition of the organoclays to the epoxy improved stiffness but lowered ductility while the adition of PVAc improved toughness although reduced stiffness of epoxy thermoset. Ternary nanocomposites exhibited optimal properties that combine the favourable effects of the clay and the thermoplastic

Cure behavior and mechanical properties of graphene/epoxy nanocomposites

In this work we study the curing process of an epoxy resin reinforced with graphene nanoplatelets and the thermal and mechanical properties of the obtained nanocomposites, in order to clarify the effect of GNPs on these properties

Storage stability of SBS/sulfur modified bitumens at high temperature: influence of bitumen composition and structure

Polymer modified bitumens, PMBs, are usually prepared at high temperature and subsequently stored for a period of time, also at high temperature. The stability of PMBs, in these conditions, has a decisive influence in order to obtain the adequate performances for practical applications. In this article the attention is focused in the analysis of the factors that determine the stability of styrene–butadiene–styrene copolymer (SBS)/sulfur modified bitumens when the mixtures are maintained at high temperature. Bitumens from different crude oil sources were used to prepare SBS/sulfur modified bitumens. Changes in the values of viscosity, softening point, as well as in the morphology of PMB samples, stored at 160 °C, were related to the bitumen chemical composition and to the amount of asphaltene micelles present in the neat bitumen used in their preparation El trabajo se centra en el estudio de la influencia de la estructura /composición del betún sobre la compatibilidad del sistema betún/SBS. Cuatro betunes provenientes de dos crudos distintos se seleccionaron y sus mezclas se utilizaron para preparar betunes modificados con contenidos de SBS del 3% en pes

Influence of graphene nanoplatelets on curing and mechanical properties of graphene/epoxy nanocomposites.

The influence of graphene nanoplatelets (GNPs) on the curing of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) and cross-linked with 4,4′ diaminodiphenylmethane (DDM) was studied. Dynamic mechanical properties and tensile properties of the corresponding graphene/epoxy nanocomposites were obtained. Two compositions 1 and 5 mass% of GNPs were studied. The cross-linking reaction of the epoxy resin is accelerated in dispersions with 5 mass% GNPs. In the presence of GNPs, the curing reaction becomes less exothermic, obtaining less perfect epoxy networks compared to neat epoxy (DGEBA–DDM) thermoset. Accordingly, the glass transition temperatures (Tg) of the nanocomposites are lower than that of the neat epoxy thermoset. This effect is not detected for low content of graphene (1 mass%). Protocol of curing having two isothermal steps leads to more perfect networks than the dynamic curing in the DSC. The Tg reduction is minimized in the samples cured through two isothermal steps. The storage moduli of the nanocomposite containing 5 mass% graphene, both in the glassy (T Tg) states, are higher than the ones of neat epoxy thermoset, being most pronounced this effect at T > Tg. Tensile tests confirmed the higher elastic moduli of the nanocomposites; however, a decrease in strain at break and tensile strength was observed for the nanocomposite containing 5 mass% of GNPs. This brittle behavior is consistent with the morphology of the samples studied by scanning electron microscopy

Efecto combinado de grafeno y nanotubos de carbono en las propiedades de las resinas dopadas

En este trabajo se estudia la eficiencia de la adición de nanorrefuerzos grafíticos para la mejora de las propiedades de resinas epoxídicas. Para ello, se han obtenido dispersiones de nanotubos de carbono y nanoplaquetas de grafeno en resinas termoestables de calidad aeronáutica. Se ha confirmado que la adición de bajos contenidos de nanotubos aumenta la temperatura de transición vítrea de las resinas y su conductividad eléctrica, mientras que el grafeno aporta un interesante aumento de la conductividad térmica. Es por ello que se concluye que ambos refuerzos son complementarios e inducen mejoras del material en diferentes propiedades

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

Influencia de nanoláminas de grafeno en el curado y propiedades mecánicas de nanocompuestos grafeno/epoxi

En el presente trabajo se estudia la influencia de nanoláminas de grafeno en el proceso de curado de una resina epoxi constituida por diglicidiléter del bisfenol A (DGEBA) entrecruzada con 4,4´- diamino difenil metano (DDM). Además se han determinado las propiedades dinámico-mecánicas y las propiedades derivadas de los ensayos de tracción de los nanocompuestos grafeno/epoxi obtenidos. La presencia de nanoláminas de grafeno (5% en peso) acelera la reacción de reticulación del pre-polímero epoxídico y disminuye la exotermia de reacción, obteniendo termoestables epoxi formados por redes menos perfectas en comparación con el termoestable epoxi puro (DGEBA-DDM), lo que es coherente con las temperaturas de transición vítrea (Tg) de los nanocompuestos que son inferiores a la del termoestable epoxi puro. Este efecto no se detecta para bajos contenidos en grafeno. El módulo de almacenamiento de los nanocompuestos (5% de grafeno) tanto en la zona vítrea (T Tg) es superior al del termoestable epoxi puro siendo el efecto más acusado a T > Tg. Los ensayos a tracción a 22ºC confirman el mayor módulo elástico de los nanocompuestos, sin embargo se observa una disminución de la deformación a rotura y de la resistencia a tracción para nanocompuestos con contenido 5% de grafeno respecto al termoestable epoxi puro

Nanocompuestos de grafeno amino-funcionalizado/epoxi: curado y propiedades dinámico mecánicas

En el presente trabajo se estudia la influencia de las nanoláminas de grafeno amino funcionalizadas (GNP-NH2) en el proceso de curado de una resina epoxi de interés aeronáutico. Asimismo, se estudian las propiedades dinámico-mecánicas de los nanocompuestos GNP-NH2/epoxi. El comportamiento de estos nanocompuestos se compara con el de nanocompuestos reforzados con grafeno sin modificar (GNP/epoxi). Se ha podido concluir que la estructura del termoestable formado es sensible al método de curado. Que la presencia de GNP-NH2 acelera la reacción de curado. Los nanocompuestos GNP-NH2/epoxi presentan aumentos de módulo elástico muy superiores a los nanocompuestos GNP/epoxi. Se han obtenido curvas maestras módulo elástico-frecuencia mostrando los nanocompuestos un comportamiento complej