Layered silicate organoclay

Nanoparticles or nanofillers are collective terms for modified layered silicates (organoclay), graphite nanoflakes, carbon nanotubes, and a number of materials dispersed in the polymer matrix, when the particles size is in order of nanometers (one thousands of micron), or tens of nanometers. A plastic filled with nanoparticles, typically in the range of 2-10% (w/w) is called a nanocomposite. 

FIGURE 17.3 Dependence of cell size and cell density of PLA (NatureWorks 3000D, Cargill Dow) and PLA nanocomposites on the concentration of organically modified layered silicates (organoclay Cloisites 30B, Southern Clay Products, Inc., Texas) [42]. Cloisite 30B is the montmorillonite modified with methyl, tallow (-65% C18, -30% C16, -5% C14), and bis-2-hydroxy ethyl quaternary ammonium salt. 

As it has been shown above (see the Eqs. (15.7) and (15.15)), the nanocluster relative fraction increasing results to polymers elasticity modulus enhancement similarly to nanofiller contents enhancement in artificial nanocomposites. Therefore, the necessity of quantitative description and subsequent comparison of reinforcement degree for the two indicated above nanocomposites classes appears. The authors of Ref. [58, 59] fulfilled the comparative analysis of reinforcement degree by nanoclusters and by layered silicate (organoclay) for polyarylate and nanocomposite epoxy poly-mer/Na" —montmorillonite [60], accordingly. 

The compatibilisation between starch and aliphatic polyesters can be promoted either by the processing conditions and/or by the presence of compatibilisers between starch and aliphatic polyesters. Examples of preferred compatibilisers are amylose/EVOH V-type complexes and starch-grafted polyesters as well as chain extenders such as diisocyanates, epoxides, and layered silicate organoclay [134, 135]. These types of materials are characterised by excellent compostability, mechanical properties and reduced sensitivity to water. 

Layered silicate (organoclay) TMOS TEOS ETEOS... 

Sodium montmorillonite (Wyoming, prepared at Siid-Chemie Ag, Moos-burg, Germany, diameter < 2 pim) was used for the preparation of the liquid crystal/layered silicate organoclay. Prior to the addition of the liquid crystalline mixtine, the mineral was stored under saturated water vapor. After 4 days the adsorbed water amount was 22 wt%. This water content makes possible the incorporation of liquid crystalline components between the silicate lamellae. 

Das et al. [89] observed that both sulfur and peroxide vulcanizations of NBR filled with organoclay lead to intercalated-exfoliated structures of the layered silicate. They also reported that the use of excess stearic acid could lead to exfoliation of the clay layers in NBR when cured with sulfur. 

S-SBR, and organoclay it can be assumed that the surface silanol groups of the layered silicates react with the carboxyl groups of the XNBR and, thus, direct rubber-filler bonds are formed. In this way, the high elongation properties can be explained. 

It is also interesting to look into the chemical interactions of organoclay (QUAT-modified MMT) with functionally polar rubbers like XNBR, CR, and their mutual blend. The role of layered silicate on the curing process of CR/XNBR blends was investigated through the study of curing kinetics, mechanical properties, WAXS, and DMA [74]. 

Compositions of EVA with 5phr of crude or purified CNTs (MWNTs), 2.5 phr of each CNTs and organomodified layered silicate (dimethyl distearyl ammonium) were tested using the cone calorimeter80-81 at 35 kW/m2. It was found that crude CNTs were as effective in the reduction of PHRR as purified CNTs. A synergistic effect for flame retardancy between CNTs and organoclays was observed. Moreover, the residues revealed a reduction in the crack density for the sample with CNTs and organoclay. 

The most commonly studied polymer nanocomposites are clay-based nanocomposites, mainly with montmorillonite (MMt) as layered silicate filler (Scheme 15.12). Upon incorporation of organomodihed clays (organoclays) into a polymer matrix, two nanomorphologies (Scheme 15.13) can be obtained, either intercalation of the polymer chain in between the clay platelets keeping the stacking of the sheets, or exfoliation of the clay platelets with a disordered dispersion of the inorganic sheets in the polymer. 

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. 

The field of intercalation chemistry in layered silicates is huge. It includes many types of intercalates, and a large variety of host structures that can be modified before intercalation by various exchange reactions. Organoclays, for example, represent a family of compounds resulting from the introduction of organic cations by ion exchange and which also allow intercalation. 

The pol5mier nanocomposite field has been studied heavily in the past decade. However, polymier nanocomposite technology has been around for quite some time in the form of latex paints, carbon-black filled tires, and other pol5mier systems filled with nanoscale particles. However, the nanoscale interface nature of these materials was not truly understood and elucidated until recently [2 7]. Today, there are excellent works that cover the entire field of polymer nanocomposite research, including applications, with a wide range of nanofillers such as layered silicates (clays), carbon nanotubes/nanofibers, colloidal oxides, double-layered hydroxides, quantum dots, nanocrystalline metals, and so on. The majority of the research conducted to date has been with organically treated, layered silicates or organoclays. 

Maiti, R, Yamada, K., Okamoto, M. et al. (2002) New polylactide/layered silicate nanocomposites Role of organoclays. Chemistry of Materials, 14, 4654 661. 

Fig.7 TEM of DETDA cured DGEBA octadecyl ammonium modified layered silicate nanocomposite containing 7.5 wt % organoclay...

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