Polyethylene/clay exfoliation

Jin, Y.-H., Park, H.-J., Im, S.-S., Kwak, S.-Y, and Kwak, S. 2002. Polyethylene/clay nanocomposite by in situ exfoliation of montmorillonite during Ziegler-Natta polymerization of ethylene. Macromolecular Rapid Communications 23 135-140. 

Transmission electron microscopy (TEM) is the main technique to detect intercalation and exfoliation for polymer-clay nanocomposites. Polyethylene-clay nanocomposites samples with poor (Figure 3.13a) and good (Figure 3.13b) exfoliation are shown in Figure 3.13 [62]. Uniform exfoliation and distribution of clay nanolayers is obtained by in-situ polymerization only when ethylene is polymerized with a metallocene supported on the organoclay in this case. 

Gopakumar, T.G., Lee, J.A., Kontopoulou, M. etal. (2002) Influence of clay exfoliation on the physical properties of montmorillonite/polyethylene composites. Polymer, 43, 5483. 

Keywords Montoraorillonite polyethylene nano composites, CPN, clay exfoliation, nanocomposites formulation, thermal stabihty, barrier propoerties, mechanical behaviour... 

Solution blending Polar as well as nonpolar solvents can be used in this method. The polymer is solubilized in a proper solvent and then mixed with the filler dispersion. In solution, the chains are well separated and easily enter the galleries or the layers of the fillers. After the clay gets dispersed and exfoliated, the solvent is evaporated usually under vacuum. High-density polyethylene [24], polyimide (PI) [25], and nematic hquid crystal [26] polymers have been synthesized by this method. The schematic presentation is given in Scheme 2.2. 

The formulation of skin cleansing products with exfoliating benefits has been subject of several patents. The materials claimed to provide exfoliation in these products include sugars, inorganic salts, calcite [31] and silica, clays, polymeric materials such as polyethylene powders [32], and crushed seed powders from walnut, apricot kernel, and almond. 

There are two basic types of nanocomposites, in which particles are intercalated or exfoliated. In an intercalated composite the nanodispersed filler still consists of ordered structures of smaller individual particles, packed into intercalated structures. Exfoliated particles are those dispersed into practically individual units, randomly distributed in the composite. Layered silicates, such as montmorillonite clays or organoclays, can be used in nanocomposites. Because clays are hydrophilic and polyolefines are hydrophobic, it is not easy to make a nanocomposite based on polyethylene or polypropylene because of their natural incompatibility. 

Natural, unmodified montmorillonite-Na (MMT-Na) has cation exchange capacity, typically 80-90 mequiv/100 g. Although some polymers, such as polyethylene oxide or polyvinylpyrrolidone, are of sufficient polarity to be able to directly exfoliate unmodified MMT-Na, organic modification of the layered clay is usually required to render the hydrophilic surface of the clay more hydrophobic and thus more compatible with most polymers, thereby improving the wettability and dispersibility of the clay in the polymer matrix. 

Mainil, M., Alexandre, M., Monteverde, R, and Dubois, P. 2006. Polyethylene organo-clay nanocomposites The role of the interface chemistry on the extent of clay intercalation/exfoliation. Journal of Nanoscience and Nanotechnology 6 337-344. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

Recently, Moad et al. [288,289] designed and prepared novel copolymer intercalant/dis-persant/exfoliant systems that are effective with unmodified clays at low levels (<20% with respect to clay), can be combined with commercial PP and clay in a conventional melt-mixing process, and do not require the use of additional compatibilizers. PP-clay nanocomposites prepared by direct melt mixing using unmodified MMX clays and a copolymer additive added at a level of only 1 wt.% with respect to PP for 5wt.% clay Authors investigated the following two classes of dispersants (1) polyethylene oxide-based nonionic surfactants... 

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