Crystallization of the Nanocomposites

Diaminodecane and 1,10-decanedicarboxylic acid were polyconden-sated in the presence of an organophihc clay to polymerize a nylon 1012 clay nano composite [27]. X-ray diffraction and TEM observations revealed that the clay layers were exfoliated and uniformly dispersed in nylon 1012. The speed of crystallization of the nanocomposite increased compared with nylon 1012. Furthermore, the tensile strength and the elastic modulus in tension were improved, and the amount of absorbed water was decreased through the improvement of the barrier characteristics. 

Presence of montmorillonite produces another example of morphological changes. The morphology of crystals of the nanocomposite is different from that of matrix polymer - polyamid 1212. Poly-amid 1212 processed withont montmorillonite has large spherocrystals, while the sphemlites of the nanocomposite are fine and nniform becanse crystals grow on the snrface of the silicate layers and cannot grow as freely as in the pure polyamid 1212. ... 

The graphene platelets play a role of effective nucleating agents for PBT a-phase crystals and accelerate the overall crystallization of the nanocomposites. ... 

Analyzing the different results obtained in the literature, it is possible to observe that the effect of adding nanocellulose in PHA matrix depends on the volume of added reinforcement, which may increase or decrease the thermal stability, melting temperatures and crystallization of the nanocomposites. 

Nd-Fe-B and Pr-Fe-B nanocomposites are rare-earth deficient with respect to the R2Fei4B stoichiometry. The soft phase which is formed is Fe3B or a-Fe. The control of the soft grain size is crucial to preserve a significant coercivity. This can be obtained by crystallisation of amorphous ribbons. The annealing temperature must be high enough to allow crystallization of the... 

The crystal structure of the nanocomposites was studied with XRD and DSC. The XRD spectra in Figure 5 shows the effect of alkyl chain length on the different crystal structure formation in the skin (Figure 5a) and at the core (Figure 5b) of the nanocomposites. By observing the diffraction pattern of the injection moulded test bars core (Figure 5b) between 10 and 40°, the relative content of amorphous material and a and y crystals in the polymer matrix can be determined. The peak at 24.6° corresponds to the y crystal structure and the peaks at 23.7° and 27.3° to the ai and a2 crystal in nylon 6 respectively. As reported in previous literature (16-18) the peak at 21.4° corresponds to the amorphous content in the matrix, but it is not prominent in Figure 5b Contrary to this literature however, the a and y peaks are not located at the same 20 values... 

This structural information can also help explain changes observed in the mechanical properties of the nanocomposites. As the amorphous content of the samples decreases from UM to dPC and the material becomes more crystalline, the nanocomposites become stronger. Also in the core of the injection moulded test bars where slow cooling is prevalent, the more stable a structure appears to form readily. As the y crystal structure is said to be more ductile than the a, it would be expected that the tensile strength of materials containing mostly a crystals, like DdPC-OdPC, to be much stronger than those with high levels of y crystal in the core. So not only is the increase in modulus due to the reinforcement provided by the clay layers and increase in crystallinity, but also the reduction in y crystal content. 

The above polyolefin copolymers have also been used to prepare conventional composites and nanocomposites. However, similar to the case of polymer blends, not too many studies have been reported thus far. Recently, Kelarakis et al. (49) have mixed 10 wt% of surface-modified carbon nanofiber (MCNF) with propylene-ethylene random copolymer (propylene 84.3%). The MCNF acted as a nucleating agent for crystallization of the a-form of PP in the matrix. During deformation at room temperature, strain-induced crystallization took place, while the transformation from the 7-phase to a-phase also occurred for both unfilled and 10 wt% MCNF-filled samples. The tensile strength of the filled material was consistently higher than that of pure copolymer. These results are illustrated in Fig. 8.27. 

Figure 9.13. A twisted-nematic iiquid crystal display (LCD) equipped with a poly(ethylene)-silver nanocomposite that had been annealed at 180°C for 15 hr and subsequently drawn as described in the text. The drawing axis of the nanocomposite is oriented paraiiei to the poiarizer in the left image and perpendicular in the right image. See coior insert.

Indicating the better compatibility between the modified clay and the PHB matrix. An increase in the crystallization temperature and a decrease in spherulites size were observed for PHB/C30B nanocomposites. The intercalation/exfoliation, observed by TEM and XRD patterns were correlated with the higher moduli of the nanocomposites. They have also observed that the burning behavior of PHB/C30B was influenced by the aggregation of the clay mineral particles. 

Variations in the preparation of nanocomposites have now been investigated extensively. Liu et al. [202] proposed the preparation of nylon-6/clay nanocomposites by a melt-intercalation process. They reported that the crystal structure and crystallization behaviors of the nanocomposites were different from those of nylon-6. The properties of the nanocomposites were superior to nylon-6 in terms of the heat-distortion temperature, strength, and modulus without sacrificing their impact strength. This is attributed to the nanoscale effects and the strong interaction between the nylon-6 matrix and the clay interface. More recently, nanocomposites of nylon-10,10 and clay were prepared by melt intercalation using a twin-screw extruder [203]. The mechanical properties of the nanocomposites were better than those of the pure nylon-10,10. 

Nam et al. [44] studied the detailed crystallization behavior and morphology of pure PLA and one representative PLA/C18-MMT nanocomposites. They concluded that the overall crystallization rate of neat PLA increases after nanocomposite preparation with C18-MMT. These behaviors indicate dispersed MMT particles act as a nucleating agent for PLA crystallization in the nanocomposites. Lee and co-workers ([45]) who investigated the thermal and mechanical characteristics of PLA nanocomposite scaffold, reported that the recrystallization temperature (Tc) of quenched PLA and its nanocomposite systems decreased by the addition of MMT clay. The nanosized layered MMT platelets provide large surface area due to their small size and thus it is reasonable to consider that the MMT particles could act as effective nucleating sites of PLA crystallization. The increased nucleating sites are likely to facilitate the PLA crystallization process in the nanocomposite systems. 

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. 

Multilayers of PS colloidal crystals assembled on the electrode surface were also used as the template for electropolymerization of aniline. Nanoporous or nanocomposite films of PANl may be produced with or without the removal of the PS template. Better stability and reproducibility of the nanocomposite film have been observed than the nanoporous PANl film. The reason for this was the PS nanoparticles enable the PANl/PS composite film to maintain its morphology, since the nanoporous PANl film may suffer from collapse or shrinkage. Insulating pol3mier nanoparticles can also be electrochemically codeposited into the CP matrix by grafting their surfaces with reactive moieties,i.e., a PPy-PEG-PLA nanocomposite film can be prepared. [PEG-PLA poly(l-ethoxyethylglycidyl ether)-block-poly(L-lactide) copol5mier]. 

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