With platelet-type fillers

Performance of High-Barrier Resins with Platelet-Type Fillers... 

There are basically only three types of platelet-type fillers which can be considered for use in thin barrier films. These are aluminum flake, mica and talc (Table II). Other types of platelets, such as glass, stainless steel or brass flakes and certain aluminum silicate minerals, such as kaolin clay, are either too large in particle size or have too low an aspect ratio to be useful. With these three... 

The strength values of composites containing short fiber or platelet-type fillers are lower than those of their counterparts with continuous reinforcements. 

In some platelet-type fillers such as talc and mica, the platelets can align with the streamlines at higher shear rates, and the viscosity increase is less than that predicted by the above equation (see Chapter 2). 

In the past decade, clay-based polymer nanocomposites have attracted considerable attention from the research field and in various applications. This is due to the capacity of clay to improve nanocomposite properties and the strong synergistic effects between the polymer and the silicate platelets on both a molecular and nanometric scale [2,3], Polymer-clay nanocomposites have several advantages (a) they are lighter in weight than the same polymers filled with other types of fillers (b) they have enhanced flame retardance and thermal stability and (c) they exhibit enhanced barrier properties. This chapter focuses on the polymer clay-based nanocomposites, their background, specific characteristics, synthesis, applications and advantages over the other composites. 

Nowadays, ordered inorganic/organic PNs with a finely tuned structure have displaced a lot of traditional composite materials in a variety of applications because the intimate interactions between components can provide enhancement of the bulk polymer properties (i.e., mechanical and barrier properties, thermal stabihty, flame retardancy, and abrasion resistance). The reinforcing nanoparticle/ polymer adhesion is of primarily importance, as it tunes the final properties of the nanocomposite. Polymer/clay nanocomposites (PCNs) meet this demand due to the platelet-type dispersion of the clay filler in the organic matrix [1]. 

During initial studies, blends of several types of ethylene vinyl alcohol copolymers were made with all three types of platelet fillers, aluminum flake, mica and talc. Blend loadings were from 9 to 33 wt % filler. Thin films, 1 to 2 mils in thickness, were melt pressed from these composites and used to measure oxygen and water permeation rates. 

Clay is another common material of wide ranging properties. Like all fillers, just because one grade or type does not perform satisfactorily does not mean that all grades will fail. Some time with your vendor s technical department can pay off here in finding inexpensive filler with unique value to your application. Clay is becoming important in some nanocomposites because it can be exfoliated into nanothin platelets. 

Nanoclay fillers are categorized as platelet-like nanoclays or layered silicates and tubular nanoclays in terms of filler shape. With the configuration of two tetrahedral sheets of silicate and a sheet layer of octahedral alumina, platelet-like nanoclays or phyllosilicates are formed, which include smectite, mica, vermiculite, and chlorite. In particular, smectite clays are widely employed with further subcategories of MMT, saponite, hectorite, and nontronite. The typical MMT clays are regarded as one of the most effective nanofillers used in polymer/clay nanocomposites due to their low material cost and easy intercalation and modification (Triantafillidis et al., 2002). On the other hand, the fundamental structure of tubular nanoclays contains an aluminum hydroxide layer and a silicate hydroxide layer. They are also known as dio-ctahedral minerals with two different types of halloysite nanotubes (HNTs) and imo-golite nanotubes (INTs). Notwithstanding their material role as clay minerals, these two types of tubular nanoclays resemble the hollow tubular structure of carbon nanotubes (CNTs). In this section, three different types of clay nanofillers, namely MMTs, HNTs, and INTs are reviewed in detail along with the development of clay modification. 

To achieve a lower percolation threshold and a high conductivity, more than one type of filler with different dimensions can be used to prepare CPCs, such as zero-dimensional atomic clusters (e.g., nano-carbon black, and silica), ID rod-like nanofiller (e.g., carbon nanotubes, and silver nanowires), and 2D layered nanofiller (e.g., clay platelets, and graphene) [ 106-110]. In fact, because of their differences in shape and element component, each nanoparticle has its own unique ability. Positive synergistic effects of these nanoparticles on improving the electrical and other properties of polymer matrix are expected. 

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