Non-isothermal cure and exfoliation of tri-functional epoxy-clay nanocomposites

The non-isothermal cure kinetics of polymer silicate layered nanocomposites based on a tri-functional epoxy resin has been investigated by differential scanning calorimetry. From an analysis of the kinetics as a function of the clay content, it can be concluded that the non-isothermal cure reaction can be considered to consist of four different processes: the reaction of epoxy groups with the diamine curing agent; an intra-gallery homopolymerisation reaction which occurs concurrently with the epoxy-amine reaction; and two extra-gallery homopolymerisation reactions, catalysed by the onium ion of the organically modified clay and by the tertiary amines resulting from the epoxy-amine reaction. The final nanostructure displays a similar quality of exfoliation as that observed for the isothermal cure of the same nanocomposite system. This implies that the intra-gallery reaction, which is responsible for the exfoliation, is not significantly inhibited by the extra-gallery epoxy-amine cross-linking reaction.Peer ReviewedPostprint (published version

A novel comparative study of different layered silicate clay types on exfoliation process and final nanostructure of trifunctional epoxy nanocomposites

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The effect of three different organically modified layered silicate clays (Nanomer I.30E, Cloisite 30B and Nanofil SE 3000) on the exfoliation process and on the thermal properties and nanostructure of cured trifunctional epoxy resin based nanocomposites was studied. Optical microscopy showed that the best and poorest qualities of clay distribution in the epoxy matrix were obtained with Nanofil SE 3000 and Nanomer I.30E, respectively. However, the isothermal differential scanning calorimetry scans show that, of the three systems, it is only the Nanomer clay that promotes intra-gallery reaction due to homopolymerisation, appearing as an initial rapid peak prior to the cross-linking reaction. This rapid intra-gallery reaction is not present in the curing curve for the Cloisite and Nanofil systems. This fact implies that the fully cured nanostructure of the Cloisite and Nanofil system is poorly exfoliated, which is confirmed by small angle X-ray scattering which shows a scattering peak for these systems at around 2.53°, corresponding to about 3.5 nm d-spacing.Peer ReviewedPostprint (author's final draft

The effect of melatonin on aerobic capacity and time of exhaustion during a sub-maximum activity in girl students of physical education

Background: Preservation and storage of muscle glycogen is the most important factor limiting the success of individuals in performing the following activities. It has been shown that melatonin supplementation before exercise can maintain glycogen stores. This study aimed to investigate the effect of melatonin consumption (6 mg) on the time of exhaustion during a submaximal-activity and also the maximum oxygen consumption during an increasing activity in physical education girl students of Shahid Chamran University of Ahvaz. Materials and Methods: In this clinical trial study, 13 girls with the mean age of 21.5±1.29 years, the mean weight of 58.36±2.69 kg and vo2max 39.08±4.17 mg/kg/min were participated and received melatonin (6 mg) and placebo (starch capsules) in two complementary steps. Supplements were administered acutely 30 minutes before the exercise. Each test was repeated in placebo and supplement conditions. To ensure the elimination of exercise and supplement impact, the interval of 5 to 7 days was considered between the two tests. The sub-maximal and progressive protocols respectively included running below the maximum intensity (70 of the heart rate reserve) to exhaustion and the Bruce's test on the treadmill. Results: The results showed that consumption of 6 mg melatonin significantly increased the time to reach exhaustion (P=0.01) and the maximum oxygen consumption (P=0.002). Conclusion: It appears that trained girls can use 6 mg of melatonin supplement 30 minutes before starting the exercise to improve endurance performance and aerobic capacity

Comparison of the nanostructure and mechanical performance of highly exfoliated epoxy-clay nanocomposites prepared by three different protocols

Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methylamine complex, BF3·MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF3·MEA into the clay galleries of nanocomposites containing 2 wt% MMT.Peer ReviewedPostprint (published version

Highly exfoliated nanostructure in trifunctional epoxy/clay nanocomposites using boron trifluoride as initiator

Epoxy/clay nanocomposites based upon a trifunctional epoxy resin, triglycidyl p-amino phenol (TGAP), have been prepared by intercalating an initiator of cationic homopolymerization, a boron trifluoride monoethylamine (BF3·MEA) complex, into the montmorillonite clay galleries before the addition of the TGAP and the curing agent, 4,4-diamino diphenyl sulfone (DDS), and effecting the isothermal curing reaction. The BF3·MEA enhances the intragallery cationic homopolymerization reaction, which occurs before the extragallery cross-linking reaction of the TGAP with the DDS, and which hence contributes positively to the mechanism of exfoliation of the clay. The effects of isothermal cure temperature and of BF3·MEA content have been studied, in respect of both the reaction kinetics, monitored by differential scanning calorimetry, and the nanostructure, as identified by small-angle X-ray scattering and transmission electron microscopy. It is shown that the use of BF3·MEA in this way as an initiator of intragallery homopolymerization significantly improves the degree of exfoliation in the cured nanocomposites.The authors are grateful to Huntsman Corporation for the epoxy resin and curing agent. This work was supported financially by MINECO Project MAT2011-27039-C03 and the Generalitat de Catalunya (2009-SGR-1512). FS is grateful for a grant from the Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR), FI-DGR 2011 and XF-F acknowledges the contract JCI-2010-06187.Peer ReviewedPostprint (author's final draft

Study of the exfoliation process in epoxy-clay nanocomposites

Cured epoxy resins are highly cross-linked polymers which are increasingly important in high performance engineering field due to the stiffness, high strength, heat resistance and solvent resistance. However one major drawback is their poor resistance to impact and crack initiation. Consequently, there is a need to improve the toughness while maintaining desirable properties. Various approaches were suggested for improving the toughness including the addition of silicate layered clay. The aim of this investigation is to develop the exfoliation process in the epoxy-silicate layered nanocomposites. It is generally considered that, in order to maximize the degree of exfoliation, the intra-gallery reaction, which is associated to the epoxy homopolymerization reaction between clay galleries, should occur before the extra-gallery reaction, which is related to the cross-linking reaction between epoxy groups and amines, hence for enhancement the rate of intra-gallery reaction, these different possibilities were considered to improve the exfoliation degree in cured nanocomposites as follow: 1. Select suitable cure temperature and curing program, 2. Pre-conditiong the epoxy/clay mixture 3. Incorporation of the cationic initiator in clay galleries 4. Addition of the hyperbranched polymer to epoxy/clay mixture 5. Select the appropriate type of silicate layered clay In support of these statements, TGAP (Araldite MY0510) as tri-functional epoxy resin, montmorillonite (Nanomer I.30E, MMT) as silicate layered clay and diamino diphenyl sulphone (Aradur 976-1, DDS) as curing agent were chosen as experimental system to study the influence of these strategies on improvement of the final nanostructure. The curing behavior and the thermal properties of epoxy silicate layered nanocomposites which is prepared based on the above procedures were separately examined with differential scanning calorimetry (DSC and TOPEM) and Thermogravimetric analysis (TGA) and also the fully cured nanostructure in each case is characterized by transition electron microscopy (TEM) and the x-ray scattering (SAXS) and moreover, the mechanical properties are studied by dynamic mechanical analysis (DMA), impact test and scanning electron Microscopy (SEM). Although in each case we obtained the intersecting results which are presented in our papers, the real goal is to fabricate the highly exfoliated nanostructure which is obtained from the first three procedures. Among these three procedures, it is difficult to decide which one is more effective on the exfoliation process based on the TEM images which shows the small part of the nanostructure. Therefore, the mechanical properties such as modulus, impact test and fracture surface which display the behavior of the whole nanostructure are helpful tools to compare the degree of exfoliation between these cases. As results, the mechanical properties measurements suggested that incorporation of the cationic initiator is the best protocol to achieve the highly exfoliated epoxy/clay nanocompositesResinas epoxi curados son polímeros reticulados altamente que son cada vez más importante en el campo de la ingeniería de alto rendimiento debido a la rigidez, alta resistencia, resistencia al calor y resistencia a los disolventes. Sin embargo, una desventaja importante es su pobre resistencia al impacto ya la iniciación de grietas. En consecuencia, hay una necesidad de mejorar la tenacidad a la vez que mantiene propiedades deseables. Se han sugerido varios enfoques para mejorar la tenacidad incluyendo la adición de silicato arcilla estratificada. El objetivo de esta investigación es desarrollar el proceso de exfoliación de las capas de nanocompuestos - epoxi silicato. Es generalmente se considera que, con el fin de maximizar el grado de exfoliación, la reacción intra - galería, que se asocia a la reacción de homopolimerización epoxi entre galerías de arcilla, debe ocurrir antes de la reacción adicional - galería, que está relacionada con la reacción de reticulación entre los grupos epoxi y aminas, por lo tanto, para la mejora de la velocidad de reacción dentro de la galería, estos se consideraron diferentes posibilidades para mejorar el grado de exfoliación en nanocompuestos curados de la siguiente: 1. Seleccionar temperatura de curado adecuado y el programa de curado 2. Pre- conditiong la mezcla epoxi / arcilla 3. Incorporación del iniciador catiónico en galerías de arcilla 4. La adición del polímero hiperramificado de epoxi / mezcla de arcilla 5. Seleccione el tipo apropiado de arcilla en capas de silicato. En apoyo de estas afirmaciones, TGAP (Araldite MY0510) como la resina epoxi trifuncional, montmorillonita (Nanomer I.30E, MMT) como silicato en capas de arcilla y diamino difenil sulfona (Aradur 976-1, DDS) como agente de curado fueron elegidos como experimentales sistema para estudiar la influencia de estas estrategias en la mejora de la nanoestructura definitiva el comportamiento de curado y las propiedades térmicas de silicato de nanocompuestos epoxi en capas que se presenta de acuerdo a la procedimientos anteriores se examinaron por separado con calorimetría diferencial de barrido (DSC y TOPEM) y el análisis termogravimétrico (TGA) y también la nanoestructura completamente curado en cada caso se caracteriza por la transición de electrones microscopía (TEM) y la dispersión de rayos x ( SAXS ) y, además, las propiedades mecánicas son estudiados por dinámico análisis mecánico (DMA), la prueba de impacto y microscopía electrónica de barrido (SEM). Aunque en cada caso se obtuvo la intersección de los resultados que se presentan en nuestros papeles, el verdadero objetivo es fabricar la nanoestructura muy exfoliada que se obtiene a partir de los tres primeros procedimientos. Entre estos tres procedimientos, es difícil decidir cuál es el más eficaz en el proceso de exfoliación a base de las imágenes de TEM que muestra la pequeña parte de la nanoestructura. Por lo tanto, las propiedades mecánicas tales como el módulo, prueba de impacto y la superficie de fractura que muestran el comportamiento de toda la nanoestructura son herramientas útiles para comparar el grado de exfoliación entre estos casos. Como resultados, las propiedades mecánicas mediciones sugirieron que incorporación del iniciador catiónico es el mejor protocolo para alcanzar los nanocompuestos epoxi / arcilla altamente exfoliadas

A novel comparative study of different layered silicate clay types on exfoliation process and final nanostructure of trifunctional epoxy nanocomposites

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The effect of three different organically modified layered silicate clays (Nanomer I.30E, Cloisite 30B and Nanofil SE 3000) on the exfoliation process and on the thermal properties and nanostructure of cured trifunctional epoxy resin based nanocomposites was studied. Optical microscopy showed that the best and poorest qualities of clay distribution in the epoxy matrix were obtained with Nanofil SE 3000 and Nanomer I.30E, respectively. However, the isothermal differential scanning calorimetry scans show that, of the three systems, it is only the Nanomer clay that promotes intra-gallery reaction due to homopolymerisation, appearing as an initial rapid peak prior to the cross-linking reaction. This rapid intra-gallery reaction is not present in the curing curve for the Cloisite and Nanofil systems. This fact implies that the fully cured nanostructure of the Cloisite and Nanofil system is poorly exfoliated, which is confirmed by small angle X-ray scattering which shows a scattering peak for these systems at around 2.53°, corresponding to about 3.5 nm d-spacing.Peer Reviewe

The effect of melatonin on aerobic capacity and time of exhaustion during a sub-maximum activity in girl students of physical education

Background: Preservation and storage of muscle glycogen is the most important factor limiting the success of individuals in performing the following activities. It has been shown that melatonin supplementation before exercise can maintain glycogen stores. This study aimed to investigate the effect of melatonin consumption (6 mg) on the time of exhaustion during a submaximal-activity and also the maximum oxygen consumption during an increasing activity in physical education girl students of Shahid Chamran University of Ahvaz. Materials and Methods: In this clinical trial study, 13 girls with the mean age of 21.5±1.29 years, the mean weight of 58.36±2.69 kg and vo2max 39.08±4.17 mg/kg/min were participated and received melatonin (6 mg) and placebo (starch capsules) in two complementary steps. Supplements were administered acutely 30 minutes before the exercise. Each test was repeated in placebo and supplement conditions. To ensure the elimination of exercise and supplement impact, the interval of 5 to 7 days was considered between the two tests. The sub-maximal and progressive protocols respectively included running below the maximum intensity (70% of the heart rate reserve) to exhaustion and the Bruce's test on the treadmill. Results: The results showed that consumption of 6 mg melatonin significantly increased the time to reach exhaustion (P=0.01) and the maximum oxygen consumption (P=0.002). Conclusion: It appears that trained girls can use 6 mg of melatonin supplement 30 minutes before starting the exercise to improve endurance performance and aerobic capacity

Non-isothermal cure and exfoliation of tri-functional epoxy-clay nanocomposites

The non-isothermal cure kinetics of polymer silicate layered nanocomposites based on a tri-functional epoxy resin has been investigated by differential scanning calorimetry. From an analysis of the kinetics as a function of the clay content, it can be concluded that the non-isothermal cure reaction can be considered to consist of four different processes: the reaction of epoxy groups with the diamine curing agent; an intra-gallery homopolymerisation reaction which occurs concurrently with the epoxy-amine reaction; and two extra-gallery homopolymerisation reactions, catalysed by the onium ion of the organically modified clay and by the tertiary amines resulting from the epoxy-amine reaction. The final nanostructure displays a similar quality of exfoliation as that observed for the isothermal cure of the same nanocomposite system. This implies that the intra-gallery reaction, which is responsible for the exfoliation, is not significantly inhibited by the extra-gallery epoxy-amine cross-linking reaction.Peer Reviewe

Radiative Gaunt factors

SIGLEAvailable from British Library Document Supply Centre- DSC:4672.262(JET-P--86/06) / BLDSC - British Library Document Supply CentreGBUnited Kingdo