Polyethylene/clay distribution

Iron catalysts [20-24] have been used to make polyethylene-clay nanocomposites where the polyethylene had very broad molecular weight distribution (MWD). Ziegler-Natta [25, 26], organo-chromium (Phillips) [27], and bis(imino)pyridine iron and cobalt catalysts [28] have also been used to make polyolefin-late transition metal catalysts [29, 30], capable of producing highly branched polyethylene from only ethylene and of promoting the copolymerization of ethylene with polar comonomers, have also been apphed to make polyolefin-clay nanocomposites. 

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. 

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. 

Maneshi et al. [62] compared in-situ polymerization using pristine montmorillo-nite and an organically modified clay (Cloisite 93A), and observed that, despite reaching near 100% supporting efficiencies for both clays, the organically modified clay produced clay-polyethylene nanocomposites with more uniform clay nanolayers distribution in the polymer matrix, supposedly because a more uniform catalyst distribution was obtained with the organoclay. 

The surface of printed paper has been examined through fully automated /xATR-FTIR mapping [464]. Compositional differences attributed to the printed ink, kaolinite, and cellulose distributions were revealed, which are not discemable in the visible. After spectral subtraction of the carbonate also DOP and an aromatic acrylate, both used in paper manufacturing, could be identified. Coles et al. [465] have compared /iFTIR and ATR-FTIR in the quantitative determination of fillers such as kaolin clay in polyethylene/vinyl acetate. Although ATR-FTIR is not as sensitive to kaolin as /xFTIR, the former provides a larger sampling area and more consistent results. ATR-FTIR is sometimes used for in-depth analysis. 

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