Nanofillers layered double hydroxides

This chapter reports the results of the literature that concerns the photooxidation of polymer nanocomposites. The published studies concern various polymers (PP, epoxy, ethylene-propylene-diene monomer (EPDM), PS, and so on) and different nanofillers such as organomontmorillonite or layered double hydroxides (LDH) were investigated. It is worthy to note that a specific attention was given to the interactions with various kinds of stabilizers and their efficiency to protect the polymer. One of the main objectives was to understand the influence of the nanofiller on the oxidation mechanism of the polymer and on the ageing of the nanocomposite material. Depending on the types of nanocomposite that were studied, the influence of several parameters such as morphology, processing conditions, and nature of the nanofiller was examined. 

Graphene-polymer nanocomposites share with other nanocomposites the characteristic of remarkable improvements in properties and percolation thresholds at very low filler contents. Although the majority of research has focused on polymer nanocomposites based on layered materials of natural origin, such as an MMT type of layered silicate compounds or synthetic clay (layered double hydroxide), the electrical and thermal conductivity of clay minerals are quite poor [177]. To overcome these shortcomings, carbon-based nanofillers, such as CB, carbon nanotubes, carbon nanofibers, and graphite have been introduced to the preparation of polymer nanocomposites. Among these, carbon nanotubes have proven to be very effective as conductive fillers. An important drawback of them as nanofillers is their high production costs, which... 

Nanofillers may be nanoclays, carbon nanotubes (single or multiwall) (CNTs), silica, layered double hydroxides (LDHs), metal oxides, etc., offering the promise of a variety of new composites, adhesives, coatings, and sealant materials with specific properties [32-37]. Among the fillers mentioned, nanoclays have attracted most of the academia and industry interest, due to their abrmdance as raw materials and to the fact that their dispersion in polymer matrices has been studied for decades [38]. In fact, there are three major polymer nanocomposites categories in terms of nanofiller type that are expected to compile the global nanocomposites market in 2011 nanoclay-reinforced (24%), metal oxide-reinforced (19%), and CNTs-reinforced (15%) ones [39-41]. 

Nanoclays can be categorized into cationic and anionic types. Cationic nanoclays are based on smectite clays. An example is montmorillonite (MMT), a hydrated Al, Mg silicate that may contain cations such as Na+ and Ca++ between the anionic layers. In contrast, anionic clays contain cationic layers and anions such as Cr and in the interlayer space. Typical examples include layered double hydroxides (LDH) and hydrotalcite (HT), a mostly synthetic hydrated magnesium and aluminum carbonate salt. Whereas MMT is commonly used as a nanofiller to improve thermal, mechanical, and barrier properties, LDHs have many attractive properties that lead to application as surfactant adsorbents, biohybrid materials, antacid food formulations, acid neutralizers, and active pharmaceutical ingredients excipients [37, 13, 28, 14, 35]. 

Layered double hydroxides (LDHs) are a different kind of layered crystalline filler for nanocomposite formation. Because they combine the flame retardant features of conventional metal hydroxide fillers (magnesium hydroxide and aluminum hydroxide) with those of layered silicate nanofillers (montmorillonite), LDHs are considered to be a new emerging class of nanofillers favorable for the preparation of flame retardant nanocomposites. In the present chapter, recent progress in the study of polymer/LDH flame retardant nanocomposites is reviewed. 

In this chapter we considered recent developments that have tried to increase the efficiency of infumescent system for polymeric materials using nanofillers, including organo-modified clays, layered double hydroxides, polyhedral silsesquioxane, and nanoparticles of silica as synergists. Intumescent nanocomposites exhibit superior flammability properties as well as enhancing properties, such as mechanical properties. 

At present, clays are by large the most investigated nanofillers in flame retar-dancy. In this chapter we focus on thermoset nanocomposites based on layered silicates and a lately emerging class of layered crystals known as layered double hydroxides G DHs). The use of polyhedral oligomeric silsesquioxanes and nanotubes nanocomposites is discussed in Chapter 10. The preparation of thermoset nanocomposites based on spherical nanosilica is also reported in the hterature. It is shown that while being heated in the nanocomposite, nanosilica, migrates to the surface of the material, due to the relatively low surface potential energy... 

In light of the issues with natural clays, one likely trend is an increase in the use of synthetic clays, such as fiuorinated synthetic mica, magadiite, and layered double hydroxides (LDH). This last clay, since it has the potential to release water under fire conditions [much like Mg(OH)2 or Al(OH)3], may find even more use in flame retardant applications. Cost issues and limited sources for synthetic clays will slow the adaptation of these materials, so most of the work will probably be seen in the patent or open literature. More work will be seen for nanocomposites containing nanofillers, such as carbon nanotubes and nanofibers, and these will probably also be combined with additional fiame retardants. 

Layered Double Hydroxides as Nanofillers of Composites and Nanocomposite Materials Based on Polyethylene... 

In the last few years, a large variety of organic and inorganic nanofillers of various shapes and sizes have been used to prepare SR nanocomposites. They can be classified into zero dimensional (OD), one dimensional (ID), two dimensional (2D) and three dimensional (3D) fillers. Recently, layered double hydroxides (LDHs) have also received more attention as new generation 2D nanofiller in the preparation of polymer nanocomposites with a lot of promise. 

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