Exfoliation epoxy nanocomposites

FIG. 10 Compressive (a) yield strength and (b) moduli for the pristine epoxy polymer and the exfoliated epoxy-clay nanocomposites prepared from three different kinds of organomontmorillonites. (From Ref. 40.)... 

Fig. 15 X-ray traces of epoxy nanocomposites - intermediate cure temperaturesshow best exfoliation (the cure cycles are indicated above the traces) [58]...

A number of other strategies to manipulate epoxy nanocomposite formation have been discussed in the literature. Chin et al. [45] have investigated the influence of the stoichiometric resin/hardener ratio on exfoliation of a MPDA/DCEBA/octadecylammonium montmorillonite using in situ small-angle X-ray scattering. It was found that resin cure with under-stoichiometric amounts of MPDA and the homopolymerization of DCEBA without any hard-... 

Recent work on highly intercalated and ordered exfoliated glassy epoxy nanocomposites [118] found that the neat epoxy systems generally absorb more water than the nanocomposites. A monotonic decrease in water sorption with increasing clay concentration, however, was not observed. In con-... 

Lan T, WangZ, Shi H, PinnavaiaTJ (1995) Clay-epoxy nanocomposites relationships between reinforcement properties and the extend of clay layer exfoliation, in Polimeric Materials - Science and Engineering. Proceedings of the ACS Division of... 

Biobased epoxy nanocomposites can be reinforced with organo montmorillonite clay and carbon fibers obtained from poly(acryl-onitrile) (45). To get the organically modified clay into the glassy biobased epoxy networks, a sonication technique was used. In this way, clay nanoplatelets were obtained that were homogeneously dispersed and completely exfoliated in the matrix. 

Recently, exfoliated layered silicate-epoxy nanocomposites have been prepared from the diglycidyl ether of bisphenol-A and nadic methyl anhydride (12). The dynamic storage modulus of the nanocomposite containing 4 vol %... 

The model illustrated in Figure 2 summarizes the overall mechanism for formation of epoxy polymer - clay nanocomposites. Upon solvation of the organoclay by the epoxide monomers, the gallery cations reorient from their initial monolayer, lateral bilayer, or inclined paraffin structure to a perpendicular orientation with epoxy molecules inserted between the onium ions. A related reorientation of alkylammonium ions has been observed previously for e-caprolactam intercalated clay intermediates formed in the synthesis of Nylon-6 -exfoliated clay nanocomposites (9). Thus, the ability of the onium ion chains to reorient into a vertical position in order to optimize solvation interactions with the monomer may be a general prerequisite for pre-loading the clay galleries with sufficient monomer to achieve layer exfoliation upon intragallery polymerization. 

Figure 3. X-ray diffraction patterns of CH3(CH2)i5NH3+-montmorillonite in different physical states (A) pristine clay, (B) Epon-828 solvated clay, (C) exfoliated clay in a mPDA-cured epoxy nanocomposite.

Epoxy-clay nanocomposites were studied extensively, but only ordered exfoliated nanocomposites were reported with in situ polymerization. Two recent works showed that disordered and highly exfoliated epoxy-clay nanocomposites can be prepared using an exfoliation-adsorption process." In this method the organo-modified clay is first dispersed in a solvent. It is well known that due to the weak forces that stack the layers together, layered silicates can easily be swelled and eventually delaminated in an adequate solvent. The polymer then adsorbs onto the delaminated sheets, and when the solvent is evaporated, a highly disordered structure is obtained before starting the standard in situ polymerization. 

Chen, B. Liu, J. Chen, H. Wu, J. Synthesis of disordered and highly exfoliated epoxy/clay nanocomposites using organoclay with catalytic function via acetone-clay slurry method. Chem. Mater. 2004, 16, 4864-4866. 

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