Glass transition temperature epoxy nanocomposites

Figure 2.16. Enhancement of (a) decomposition temperature as well as (b) glass transition temperature as a function of filler content in epoxy nanocomposites. Reproduced from reference 51 with permission from American Chemical Society.

Fig. 18 Glass transition temperature, Tg, of highly crosslinked epoxy nanocomposite systems. The resin systems are diethyltoluene diamine cured octadecylammonium modified layered silicate DGEBA, TGAP and TGDDM [63]...

Figure 9.27 shows the influence of nano-clay incorporation on storage modulus of the epoxy nanocomposites. The increase in percentage of nano-clay in epoxy resin increases the storage modulus up to a certain weight fraction of nano-clay, above which it decreases the modulus, but it is still above the value of neat epoxy matrix. The loss modulus curve shows the variation of glass transition temperature with respect to nanoclay incorporation and the maximum value of glass transition temperature is noted for the clay content of 3 wt% [31]. 

Studies by Becker et al. reveal that the glass transition temperature (T of the nanocomposites decreases gradually with the rise in clay concentration for all the epoxy systems irrespective of the functionality of the epoxy resin [32]. A lot of factors may contribute to such a decrease in glass transition temperature. Certain studies show significant improvement in T on the incorporation of clay platelets [85-86]. Interestingly some studies s ow a decrease in values on clay incorporation [87-88]. The following factors maybe responsible for the decrease in glass transition temperature [32] ... 

The thermal history during curing dramatically affects the glass transition temperature Tg for fully cured DGEBA system differences up to 30°C in Tg where observed. This effect is much more relevant than the one due to the presence of layered silicate and/or the variation in its level of dispersion in epoxy nanocomposites. ... 

In the early work on epoxy nanocomposites it was reported " that flexible resin systems with a low glass transition temperature showed greater improvement in mechanical properties upon forming nanocomposites, than those systems exhibiting higher glass transitions. A summary of improvement in mechanical properties of epoxy nanocomposites in both the rubbery and the glassy state is reported in this section. 

The depression of the final hmiting fictive temperatures of polycyanurate networks under nanoscale constraint observed in the current study corroborates that the BMDC monomer does penetrate into the nanopores instead of acting as fillers, because the glass transition temperature of the polymer is not expected to be affected when the particles are in micron size as seen in the nanocomposites of epoxy/silica [13] and PMMA/alumina... 

---