Layered Silicate Nanocomposites Based on Various High-Functionality Epoxy Resins:  The Influence of Cure Temperature on Morphology, Mechanical Properties, and Free Volume

Abstract

This paper investigates the relationship between cure temperature, morphology, and mechanical properties of di-, tri-, and tetrafunctional high-performance, epoxy layered-silicate nanocomposites. Wide-angle X-ray analysis (XRD) was carried out at different stages of cure to monitor organoclay exfoliation kinetics. It was found that some (small) degree of conversion was required to obtain significant intercalation. The nanocomposite morphology was also probed using transmission electron microscopy, XRD, and positron annihilation lifetime spectroscopy. The bifunctional DGEBA resin gave better exfoliation than the resins of higher functionalities. This is attributed to better catalysis of the intragallery reaction by the organo-ions which reside within the galleries. Higher cure temperatures were also found to improve clay delamination and simultaneously increased toughness and modulus in case of the DGEBA-and TGAP-based materials. Free volume properties did not vary significantly between resins or with cure temperature and generally followed the rule of mixtures, although there was a suggestion that the presence of clay leads to increased free volume. This was consistent with decreased glass transition temperatures upon addition of layered silicate, ascribed to disruption, and decreased cross-link density in interfacial regions of clay and epoxy matrix.

Investigation of free volume, interfacial, and toughening behavior for cyanate ester/bentonite nanocomposites by positron annihilation

“…As mentioned above, our results are remarkably different from the results observed in other polymer nanocomposites, especially the intensity of o ‐Ps lifetime and free volume fraction 24–26. For example, in the case of linear polymer/clay nanocomposites, the mean size of free volume holes does not vary significantly, and the concentration of free volume holes and the free volume fraction obviously decreases with the increase of the content of filler 24, 26.…”

Investigation of free volume, interfacial, and toughening behavior for cyanate ester/bentonite nanocomposites by positron annihilation

“…As mentioned above, our results are remarkably different from the results observed in other polymer nanocomposites, especially the intensity of o ‐Ps lifetime and free volume fraction 24–26. For example, in the case of linear polymer/clay nanocomposites, the mean size of free volume holes does not vary significantly, and the concentration of free volume holes and the free volume fraction obviously decreases with the increase of the content of filler 24, 26.…”

Influence of the isothermal cure temperature on the nanostructure and thermal properties of an epoxy layered silicate nanocomposite

“…The values of T g found earlier for the TGAP/DDS system without clay, again with a 1:0.9 molar ratio of epoxy:DDS, are 252.9 and 256.5°C for isothermal cure at 120 and at 150°C, respectively . The present results therefore indicate a systematic decrease in T g as the clay content increases, as has often been observed in epoxy polymer layered silicate (PLS) systems . There are two plausible explanations for these observations.…”

Nanocomposites Derived from a Low-Color Aromatic Polyimide (CP2) and Amine-Functionalized Vapor-Grown Carbon Nanofibers: In Situ Polymerization and Characterization

“…Watson et al also observed T g decreases with addition of CNTs and VGCNF into polyimides . Similar results have been observed when nanoclay and bentonite were blended with epoxies and cyanate ester, respectively, where the free volume fractions increased with the contents of nanoclay and bentonite. The T g 's of the resulting nanocomposites decreased accordingly in most occasions.…”

Investigation of free volume, interfacial, and toughening behavior for cyanate ester/bentonite nanocomposites by positron annihilation

“…As mentioned above, our results are remarkably different from the results observed in other polymer nanocomposites, especially the intensity of o ‐Ps lifetime and free volume fraction 24–26. For example, in the case of linear polymer/clay nanocomposites, the mean size of free volume holes does not vary significantly, and the concentration of free volume holes and the free volume fraction obviously decreases with the increase of the content of filler 24, 26.…”

Influence of the isothermal cure temperature on the nanostructure and thermal properties of an epoxy layered silicate nanocomposite

“…The values of T g found earlier for the TGAP/DDS system without clay, again with a 1:0.9 molar ratio of epoxy:DDS, are 252.9 and 256.5°C for isothermal cure at 120 and at 150°C, respectively . The present results therefore indicate a systematic decrease in T g as the clay content increases, as has often been observed in epoxy polymer layered silicate (PLS) systems . There are two plausible explanations for these observations.…”

Nanocomposites Derived from a Low-Color Aromatic Polyimide (CP2) and Amine-Functionalized Vapor-Grown Carbon Nanofibers: In Situ Polymerization and Characterization

“…Watson et al also observed T g decreases with addition of CNTs and VGCNF into polyimides . Similar results have been observed when nanoclay and bentonite were blended with epoxies and cyanate ester, respectively, where the free volume fractions increased with the contents of nanoclay and bentonite. The T g 's of the resulting nanocomposites decreased accordingly in most occasions.…”

Investigation of free volume, interfacial, and toughening behavior for cyanate ester/bentonite nanocomposites by positron annihilation

“…As mentioned above, our results are remarkably different from the results observed in other polymer nanocomposites, especially the intensity of o ‐Ps lifetime and free volume fraction 24–26. For example, in the case of linear polymer/clay nanocomposites, the mean size of free volume holes does not vary significantly, and the concentration of free volume holes and the free volume fraction obviously decreases with the increase of the content of filler 24, 26.…”

Influence of the isothermal cure temperature on the nanostructure and thermal properties of an epoxy layered silicate nanocomposite

“…The values of T g found earlier for the TGAP/DDS system without clay, again with a 1:0.9 molar ratio of epoxy:DDS, are 252.9 and 256.5°C for isothermal cure at 120 and at 150°C, respectively . The present results therefore indicate a systematic decrease in T g as the clay content increases, as has often been observed in epoxy polymer layered silicate (PLS) systems . There are two plausible explanations for these observations.…”

Nanocomposites Derived from a Low-Color Aromatic Polyimide (CP2) and Amine-Functionalized Vapor-Grown Carbon Nanofibers: In Situ Polymerization and Characterization

“…Watson et al also observed T g decreases with addition of CNTs and VGCNF into polyimides . Similar results have been observed when nanoclay and bentonite were blended with epoxies and cyanate ester, respectively, where the free volume fractions increased with the contents of nanoclay and bentonite. The T g 's of the resulting nanocomposites decreased accordingly in most occasions.…”