Intercalation tactoids

Here, on the contrary, the two schemes depict profoundly different situations with respect to solvent-clay interactions. In Figure 3.1, a clay dispersion comprising solvent-intercalated tactoids is considered, whereas complete exfoliation of the organoclay is assumed in... 

TEM analyses showed that melt-compounded EAA/M2(HT)2 composites have homogeneous dispersion of thin intercalated tactoids with several individual silicate platelets... 

In Figure 2 we present TEM images with different magnification which designate the presence of intercalated tactoids (A) and apparently exfoliated monolayers (B) coexisting in the nanocomposite structure. The intercalated structures are characterized by a parallel registry that gives rise to the XRD reflection of Fig. 1. 

Figure 2.TEM photos with different magnification of PP-MAPP-Cloisite 20A where A - stacks of layers (intercalated tactoids), B - exfoliated monolayers...

The WAX method therefore appears to be a poor one for quantifying the level of exfoliation. It has, however, the utility of confirming a lack of exfoliation or the presence of intercalated tactoids. This can be enhanced by the method of sample preparation utilized. In the melt, smectite clays have a strong tendency to orient parallel to flow lines. If the X-ray... 

In Fig. 13.5, the TEM of PCN materials with 5wt% clay loading (CLMA5) reveals that the nanocomposite displays a mixed nanomorphology. Individual silicate layers, along with two and three-layer stacks, are found to be exfoliated in the PMMA matrix. In addition, some larger intercalated tactoids can also be... 

The tensile stress-strain curves of neat epoxy and epoxy nanocomposite systems with three different levels of exfoliation are shown in Fig. 2. The addition of 2.0 vol% of poorly exfoliated, i.e., mostly intercalated, a-ZrP nanoplatelets into the epoxy matrix improves the tensile modulus by a mere 8%, and reduces strength and elongation-at-break by 30% and 50%, respectively. These large drops in strength and elongation-at-break are possibly caused by the intercalated tactoids which may act as defects to deteriorate the properties of the epoxy matrix. 

Ogata et al. (1997) first prepared PLA/ organoclay (OMMT) blends by dissolving the polymer in hot chloroform in the presence of dimethyl distearyl ammonium modified MMT (2Ci8MMT). XRD results show that the silicate layers forming the day could not be intercalated in the PLA/MMT blends, prepared by the solvent-cast method. Thus, the clay existed in the form of tactoids, consisting several stacked silicate monolayers. 

These tactoids are responsible for the particular geometrical structures formation in the blends, which leads to the formation of superstructures in the thickness of the blended film. The Young s modulus of the hybrid is increased by this kind of structural feature. After that, the preparation of intercalated PLA/ OMMT nano-composites with much improved mechanical and thermal properties was reported by Bandyopadhyay et al. (1999). 

Conventional composites in conventional composites, the clay tactoids exist in their original aggregated states with no intercalation of the polymer matrix into the clay lamellae. 

The Eq. (55) was received for nanocomposites polymer/organoclay with oiganoclay intercalated structure and its application in the given case proves to be correct by organoclay packets (tactoids) (N > ) availability, that is a typical sign of Na -montmorillonite intercalated stmcture [56]. For nanocomposites PBT/MMT value is varied within the limits of 1.5-16.6 within the range of W=l lO mass. % [70]. 

Li et al. [2003] postulated that the storage modulus of CPNCs, G, is a sum of three contributions these of the polymer matrix (G ), the confinement in the intercalated stacks (G c), and the interparticle frictional interactions between tactoids (G ) ... 

Lu and Xiao [72] studied the structure and properties of nanocomposites made from CMKGM and MMT. TEM showed that MMT dispersion in CMKGM was mainly in the intercalated state and depended on the CMKGM/MMT weight ratio. At 5 wt% MMT, most MMT layers existed as tactoids however, some intercalation was seen. At 15 wt% MMT, there were still some tactoids, exfoliation was observed a little in some parts, MMT layers were separated by ultrathin CMKGM, and intercalation was seen clearly. Pure MMT had a sharp XRD peak at 29 = 7.1°, corresponding to a basal spacing of 1.25 nm. All diffraction peaks of... 

Pluta [49] studied the structure and properties of PLA/MMT nanocomposites and showed an effective enhancement of MMT dispersion with prolongation of the blending time (from 6 to 30 min). They stressed that this was possible due to strong interaction between PLA-MMT and shearing forces during melt compounding. The nanostructure was induced by the intercalation followed by tactoids formation and exfoliation of MMT, as confirmed by TEM analysis and XRD. The studies performed also clearly revealed the influence of MMT s dispersion in the PLA matrix on the physical properties of the nanocomposites formed as the improved MMT s dispersion (at their constant concentration) had increased the thermal stability of the nanocomposites under oxidative and nonoxidative conditions was improved with MMT s dispersion. Besides that, the crystallization ability of PLA also improved with incorporation of MMT. 

Fig. 5. Schematic of the hierarchy of clay structures in polypropylene nanocomposites of mixed morphology. Clay tactoids and exfoliated platelets comprise the mesoscale morphology. The internal intercalation structure of clay tactoids is determined by the compatibilizer and compounding conditions. (View this art in color at www.dekker.co...

Fracture toughness, always important in composites and adhesives, remains an important issue, as does a better understanding of the relative importance of intercalation/exfoliation and the influence of their size-scale (micron vs. nanometer). Indeed, the effect of the size-scale of materials from individual layers to tactoids to clusters to larger clay clumps, many of which seem to exist simultaneously in a sample, is still not fully understood or able to be independently manipulated. The ability to make full use of the anisotropy of the clays in thermoset components Ijy appropriate processing techniques also is of interest. likewise, the ability to usefully add greater concentrations of clay in certain applications for particular property balances (as opposed to widely-used 3-5 wt %) may also allow a greater range of properties. 

Figure 1.15 Schematic representation of formation of polymer-based CMP systems viz. (a) conventional bulk CMP (tactoid), (b) intercalated NCs, and(c) exfoliated NCs, via physical mixing (dry/solution phase mixing or melt compounding) and in-situ polymerization routes.

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