Nylon 6, clay gallery

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. 

A novel compounding technique was developed to synthesize nylon 6 in a clay gallery by modifying the clay surface and intercalating monomers into the gallery. The organophilic material used in diis technique must satisfy the following three requirements ... 

The first nanocomposite prepared by Toyota Group of Japan was based on nylon 6. In situ polymerization of caprolactum inside the gallery of 5% MMT resulted in the first nylon 6-clay nanocomposite. Besides nylon, polypropylene (PP) is probably the most thoroughly investigated system. Excepting the study of the various properties, theoretical aspects and simulations have also... 

Exfoliation of MMT in the polymer matrix has been shown to occur through a process called slurry compounding, in which the MMT swells in water and then is mixed with Nylon-6 under extrusion [86]. Other techniques include the addition of MMT to water and the subsequent replacement of water by alcohol or acetone with further addition of a silane agent to modify the clay and make it compatible with the polymer matrix [87-89]. Intercalated nanocomposites were also obtained by slurry compounding introducing an epoxy monomer in the hydrated MMT galleries [90]. 

Fig. 17.24 TEM micrographs of nylon 6/organoclay/EOR-g-MA (76/4/20) ternary nanocomposite showing (a) submicron and nano-voids which are associated with intra-gallery delamination of some organoclay layers (note that the section is not selectively stained in order to clearly reveal delaminations of clay layers), (b) cavitation of EOR-g-MA particles which preferentially starts from the larger particles as indicated by arrows, and (c) extensive matrix shear yielding at the arrested crack tip which in turn causes the EOR-g-MA particles and delaminated clay layers to collapse within the matrix. A schematic of the arrested crack tip illustrating different locations from where TEM micrographs (a-c) were taken is also shown. Note that the schematic is not to scale (Lim et al. 2010)...

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