Exfoliated nanocomposites Subject

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

On the other hand carbon nanotubes (CNT) have been the subject of extensive investigation due to their remarkable properties such as very high aspect ratio, excellent mechanical, electrical, optical and magnetic properties. To exploit the properties of carbon nanotubes, efficient exfoliation of the CNT bundles in the polymer matrix is a prerequisite. There are various methods aimed at efficient exfoliation of CNT either in polymer or solvent [7-10]. In addition, nanocomposites... 

It is generally accepted that appearance of stress overshoot at the beginning of steady shear is related to the accumulation of stress in the particle phase and its subsequent release due to the rupture of various particulate structures [90,97,106,116). The particle phase mainly consists of physically associated particle domains such as the soft particle clusters and localized network structures formed both by primary clay particles and the nanoscopic exfoliated clay layers [106]. When the nanocomposite melt is subjected to shearing, both the particle phase and the matrix phase respond according to their characteristic structural rigidities. The elastic modiflus of the par-... 

Barrier films of exfoliated clay-polymer composites have been a subject of considerable investigation with some commercial utility (e.g., barrier layer for termis balls).The thin exfoliated clay platelets dispersed in a polymer matrix present a tortuous diffusion path for gas molecules similar to that observed in Figure 12 for biaxially oriented polymer blends. The advantages of exfoliated clay modification for barrier properties are the retention of transparency and low cost. A novel approach utilizing nanocomposites involves dispersion of the exfoliated clay in a water emulsion or suspension and coating a desired substrate. This approach has been commercialized by IntMat for tennis balls, tires, and food packaging applications. For exceptional barrier properties, and where transparency is not required, metalized polymer films or aluminum foil polymer film laminates are usually employed. 

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