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.

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

“…It transpires that the first reaction, which takes place within the clay galleries and promotes the exfoliation of the clay, is enhanced at higher cure temperature, and hence higher isothermal cure temperatures give rise to increased exfoliation in the cured nanocomposite. This result is in agreement with the observations of Becker et al [21], who concluded that higher cure temperatures were found to improve clay delamination, as well as increasing the toughness and modulus in the case of both DGEBA-and TGAP-based materials. In order to further clarify the process of exfoliation in these TGAP-based systems, the goal of the present paper is to investigate the non-isothermal (dynamic) cure behaviour of the same system for comparison with the isothermal cure behaviour, to obtain the kinetic parameters and activation energy, and to analyse the quality of the final nanostructure.…”

“…Most of the studies of the cure reaction of epoxy PLS nanocomposites have concentrated on the iso -thermal or non-isothermal cure of bi-functional epoxy resin systems, typically diglycidyl ether of bisphenol-A (DGEBA); for example, only reference 13 of those cited immediately above (references 8 to 20) does not use DGEBA. Considerably less attention has been paid to the isothermal and/or non-isothermal cure behaviour of PLS nanocomposites based upon high-functionality epoxy resins, though there are exceptions, such as the study of triand tetra-functional epoxy resin systems [21] and our own earlier investigations of a tri-functional epoxy resin nanocomposite system based upon triglycidyl p-amino phenol (TGAP) [22,23]. Strangely, Becker et al [21] found that the DGEBA resin resulted in better exfoliation than for the resins of higher functionality, which is exactly contrary to our own experience.…”

“…Considerably less attention has been paid to the isothermal and/or non-isothermal cure behaviour of PLS nanocomposites based upon high-functionality epoxy resins, though there are exceptions, such as the study of triand tetra-functional epoxy resin systems [21] and our own earlier investigations of a tri-functional epoxy resin nanocomposite system based upon triglycidyl p-amino phenol (TGAP) [22,23]. Strangely, Becker et al [21] found that the DGEBA resin resulted in better exfoliation than for the resins of higher functionality, which is exactly contrary to our own experience. We found that, in the isothermal cure of TGAP-based nanocomposites, two distinct reactions occurred: the first of these reactions was very rapid and could be associated with the homopolymerisation reaction of the resin within the clay galleries, while the second reaction represented the cross-linking reaction of the TGAP with the curing agent, diaminodiphenyl sulphone (DDS) [22].…”

Control of the block copolymer morphology in templated epoxy thermosets

“…A similar structure has been observed in layered block copolymer-silicate nanocomposites. [32][33][34] The diameter of the rod-like structures was relatively consistent at 30 nm. The PEO-PE block copolymer has a low molecular weight, M nPEO-PE ¼ 1400 g/mol, with an estimated end-to-end distance of 156 Å , based on exclusion volume and monomer unit lengths given by Almdal et al 35 Thus, the rodlike structures were not simply produced by extended PEO blocks at the outer shell and the PE blocks in the core; a more complex structure must have formed.…”

Bio-based epoxy clay nanocomposites

“…In tandem, a range of different mixing procedures, including ultrasonic mixing and high shear mixing, have been used to produce epoxy / clay nanocomposites [3]. Most of these efforts at nanocomposite formation utilize solvents [4] and / or high temperature processing [5] to obtain clay dispersion in the epoxy-amine matrix.…”