Nylon-6/montmorillonite material

A nanocomposite material is the combination of the nanosized ultrafine powders and the polymer matrix. In such materials, organic polymer generally is a continuous phase and the nanopartides form the dispersed phase, such as Bil3-nylon 11 nanocomposites and nylon-montmorillonite nanocomposites. In this century, nanocomposite materials have become one of the most advanced composite materials. 

Nylon-6. Nylon-6—clay nanometer composites using montmorillonite clay intercalated with 12-aminolauric acid have been produced (37,38). When mixed with S-caprolactam and polymerized at 100°C for 30 min, a nylon clay—hybrid (NCH) was produced. Transmission electron microscopy (tern) and x-ray diffraction of the NCH confirm both the intercalation and molecular level of mixing between the two phases. The benefits of such materials over ordinary nylon-6 or nonmolecularly mixed, clay-reinforced nylon-6 include increased heat distortion temperature, elastic modulus, tensile strength, and dynamic elastic modulus throughout the —150 to 250°C temperature range. 

Examples of the use of nanostructured materials for packaging applications have been given in Chaudhry et al. (2008) and references therein. One of the first market entries into the food packaging arena was polymer composites containing clay nanoparticles (montmorillonite). The natural nanolayer structure of the clay particles impart improved barrier properties to the clay-polymer composite material. Some of the polymers which have been used in these composites for production of packaging bottles and films include polyamides, polyethylene vinyl acetate, epoxy resins, nylons, and polyethylene terephthalate. 

A new composite material was introduced in 1987 with the discovery of a nylon-6/clay hybrid (NCH) [201]. The hybrid was prepared by the in situ thermal polymerization of s-caprolactam with 8% or less montmorillonite, the clay material containing 1-nm thick exfoliated aluminosilicate layers. It exhibited a truly nanometer-sized composite of nylon-6 and layered aluminosilicate. Figure 2.14 depicts conceptually the NCH synthesis and its fine structure. The NCH exhibited high modulus, high strength, and good gas-barrier properties. The unique and superior properties led to the commercialization of NCH. It has also created a new class of nanocomposites and worldwide interest. 

Additional specimens were prepared by melting and kneading sodium-type montmorillonite (unorganized type) and nylon 6 using a twin screw extruder at 250 °C for the purpose of comparing them with the specimens prepared as described above. This method of preparing specimens is commonly used when compounding particulate fillers with polymers. The composite material prepared in this way was called NCC (Nylon 6-Clay Composite), and the NCC was compared with the NCH. 

Exfoliated clay nanocomposites formed between organocation exchanged montmorillonites and thermoplastic Nylon-6 have recently been described by Toyota researchers (9-11). Clay exfoliation in the Nylon-6 matrix gave rise to greatly improved mechanical, thermal and rheological properties, mal g possible new materials applications of this polymer. However, it is relatively difficult to achieve complete exfoliation of smectite clays into a continuous polymer matrix, because of the strong electrostatic attraction between the silicate layers and the intergallery cations. 

The new class of polymer materials, organic- inorganic (clay) nanocomposites, was also reported as an excellent FR composition [234]. Nylon-6 clay nanocomposites, first developed by Toyota Central Research and Development Laboratories, are materials with unique properties. The nylon- 6 clay nanocomposites (clay mass fraction from 2%-70%) are synthesized by ring - opening polymerization of e-caprolactam in the presence of cation exchanged montmorillonite clay [235]. 

Inan, G. Patra, P.K. Kim, Y.K. Warner, S.B. Flame retardancy of laponite- and montmorillonite-based nylon 6 nanocomposites continuous nanophase and nanos-tructured materials. MRS Proc. 2004, 788L8.46. 

At this point in the discussion of the mechanical properties of montmorillonite-nylon 6 polymer nanocomposites, a review of the work carried out by the Toyota Central Research Development Labs, Inc. that initiated an explosion of research and development of polymer-montmorillonite nanocomposite technology in relation to the subsequent work found above is provided. A series of three articles appeared in the Journal of Materials Research in 1993 in issue number 5. 

Among the variety of inorganic solids e.g. silica, iron oxides, titanium dioxide, metals), clay minerals have recently attracted considerable attention. Indeed, polymer-clay nanocomposites (PCNs) have been the topic of extensive research worldwide since scientists at the Toyota Central Research laboratories reported 10 years ago that the incorporation of small amounts of montmorillonite (MMT) into nylon-6 resulted in a remarkable enhancement of the thermal and mechanical properties of the nanocomposite material. Whereas there has been a tremendous number of studies on the synthesis, properties and applications of polymer-clay nanocomposites in the recent literature, surprisingly only a small number of reports have dealt with emulsion polymerization. 

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