Structure melt intercalation

In order to prove the importance of the delaminated layer structure in the direct (melt) intercalation, the intercalation of stearic acid molecules into the clay galleries has been studied by premixing them with organoclay and then successfully incorporating this modified clay into the rubber matrix [59]. A schematic presentation of such modification of clay is given in Fig. 37. 

Figure 9 shows a typical temporal series XRD patterns, for a polystyrene Mw= 30,000 (PS30)/octadecyl-ammonium modified fluorohectorite (C18FH) mixture annealed in-situ at 160 °C in vacuum. Details regarding the data collection and analysis are presented in reference [ 12]. The width of the original unintercalated peak and the final intercalated peak appear to be similar, suggesting that the polystyrene melt intercalation does not drastically alter the coherence length or disrupt the layer structure of the silicate crystallites. 

FIGURE 5.90 Schematic presentation of two extremes of composite structures that can be obtained by polymer melt intercalation of layered silicates. The rectangular bars represent individual silicate layers (1 nm thick), (a) Single polymer layers intercalated in the silicate galleries, (b) Delamination (exfoliation) of layered silicates and dispersion in a continuous polymer matrix. (After Giannelis, E. R 1996. Adv. Mater., 8(1), 29. With permission.)... 

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. 

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

Layered siUcate/polypropylene nanocomposites were prepared by melt intercalation method. Homopolymers PP alone and maleic anhydride-grafted polypropylene (PPgMA) as a compatibiUzer were used as the matrix. Clay (Na montmorillonite, MMT) particles were used to obtain silicate nano-layers within the PP matrix. Structural modification of MMT... 

The synthesis of polymer nanocomposites is an integral aspect of polymer nanotechnology. By inserting the nanometric inorganic compounds, the properties of polymers improve and hence this has a lot of applications depending upon the inorganic material present in the polymers. The improvements obtained in day/PP nanocomposite structure can make this commercial thermoplastic polymer more suitable for automotive, construction and packaging applications. Different alkyl ammonium surfactants and compatibilizer was used to produce layered silicate/PP nanocomposites by the same melt intercalation technique. 

This system does not increase the carbon monoxide or soot produced during the combustion, as many commercial FRs do [233]. Other polymer silicate nanocomposites based on a variety of polymers, such as polystyrene, epoxy and polyesters, have been prepared recently by melt intercalation [236]. A direct synthesis of PVA-clay (hectorite) complexes in water solution (hydrothermal crystallization) was reported [237]. It was assumed that the driving force of this phenomenon, at least kinetically, can be described in terms of a simple diffusion reaction of polymers/monomers into clay-layered structures. 

Y. Ding, R. Xiong, S. Wang, and X. Zhang, Aggregative structure of the 1-octadecyl-3-methylimidazolium cation in the interlayer of montmorillonite and its effect of polypropylene melt intercalation. Journal of Polymer Science, Part B Polymer Physics, 45 (2007), 1252-9. 

P. Ding and B. J. Qu, Synthesis of exfoliated PP/LDH nanocomposites via melt-intercalation Structure, thermal properties, and photo-oxidative behavior in comparison with PP/MMT nanocomposites. Polymer Engineering and Science, 46 (2006), 1153-9. 

PVDF nanocomposites based on ammonium-, pyridinium-, imidazolium-, or phosphonium-modified MMT have been prepared by melt intercalation [57,64-73]. The influence of the modified clays on the morphologies and their consequence on the physical properties have been investigated. XRD and TEM analyses evidence different morphologies as a function of the nature of the surfactant. An exfoliated structure is obtained with ammonium-, pyridinium-, and imidazolium-treated MMT, while phosphonium IL-modified MMT leads to a partially exfoliated morphology. The mechanical properties of nanocomposites are higher than the neat PVDF. However, the influence of thermostable ILs on mechanical properties is limited. In fact, the storage modulus of the neat PVDF and the PVDF nanocomposites remains the same whatever be the nature of the IL intercalant. Nevertheless, the elongation at break increases (-1-175%) with 5wt.% of pyridinium-treated MMT compared to h-200% of strain at break obtained for ammonium-modified MMT. Recently,... 

These materials, unlike the other nanophase materials described in this chapter, are nano-sized in only one dimension and thereby act as nanoplatelets that sandwich polymer chains in composites. Mont-morillonite (MMT) is a well-characterized layered silicate that can be made hydrophobic through either ionic exchange or modification with organic surfactant molecules to aid in dispersion [5,23]. Polymer-layered silicates may be synthesized by exfoliation adsorption, in situ intercalative polymerization, and melt intercalation to yield three general types of polymer/clay nanocomposites. Intercalated structures are characterized as alternating polymer and siHcate layers in an ordered pattern with a periodic space between layers of a few nanometers [13], ExfoHated or delaminated structure occurs when silicate layers are uniformly distributed throughout the polymer matrix. In some cases, the polymer does not intercalate... 

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