Clays as nanofillers

Until recently this has been a minor topic, with a small use of organic amines to treat clays and related materials. The growing interest in the use of organo-clays as nanofillers is creating what may become a significant market opportunity for this type of modifier. More details will be found in Chapter 10. 

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... 

Table 24.5 Characteristics of several clays used as nanofillers...

This chapter reviews the use of the sepiolite/palygorskite group of clays as a nanofiller for polymer nanocomposites. Sepiolite and palygorskite are characterized by a needle-like or fiber-like shape. This peculiar shape offers unique advantages in terms of mechanical reinforcement while, at the same time, it allows to study the effect of the nanofiller s shape on the final composite properties. The importance of the nanofiller shape for the composite properties is analyzed in Section 12.2, introducing the rationale of the whole chapter. After a general description of needle-like nanoclays in Section 12.3, the chapter develops into a main part (Section 12.4), reviewing the preparation methods and physical properties of polyolefin/needle-like clay nanocomposites. 

Fillers such as CaCOs, clay, etc. with average particle size in the range 01 to 100 nm may be defined as nanofillers. Unlike traditional fillers, mainly used for cost reduction, nanofillers are performance-enhancing fillers used in relatively small amounts (5 10%) in order to provide substantial improvements in physical and other properties. Nanosized particles (average diameter around 40 nm) form a very fine and homogeneous distributed system in polymer matrix. As compared to micron size filler particles the nanosized filler particles are able to occupy substantially greater number of sites in the polymer matrix. 

From a mineralogical point of view, the term clay encompass a group of minerals (clay minerals) mainly composed of phyllosilicates, whose physicochemical properties depend on their structure and particle size, which is very small (in the nanometre range in at least one of their dimensions). For the particular application of clay materials as nanofillers for the synthesis of nanocomposites, the only interesting clay minerals present in clays are the phyllosilicates, any other clay mineral being an impurity for this purpose. Therefore, from now on, although clay and phyllosilicate are not strictly synonyms, both terms will be equally used. 

In short, this innovative procedure has opened an easy pathway for the use of CNTs in aqueous media without the use of surfactants or commonly applied oxidative treatments responsible for extensively damaging the CNT outer walls, allowing an alternative preparation of fibrous clay materials provided with conducting properties and of great interest as nanofillers for diverse polymeric matrices. 

Alcantara ACS, Aranda P, Darder M, Ruiz-Hitzky E (2011) Zein-clay biohybiids as nanofillers of alginate based bionanocomposites. Abstr Pap Am Chem Soc 241 114—115... 

As a matrix polymer HDPE with melt flow index of approx. 1.0 g/10 min and crystallinity degree K of 0.72, determined by samples density, manufactured by firm Himtsman LLC, was used. As nanofiller organoclay Na -montmorillonite of indrrs-trial production of mark Cloisite 15, supphed by firm Southern Clay (USA), was used. A maleine anhydride (MA) was applied as a coupling agent. Conventional signs and composition of nano composites HDPE/MMT are listed in Table 14.1 [3]. 

The presence of silica NPs assembled to fibrous clays could be of interest for their use as nanofillers in polymers reinforcement Preliminary attempts in the use of silica-sepiolite nanoarchitectures, as well as the intermediate silica-organosepiolite materials, as nanofillers of epoxy resins show a moderate mechanical improvement [57,74], Further modifications of the silica NPs assembled to sepiolite could produce organic-inorganic hybrids that can be considered as promising new functional materials for diverse applications, from sensing devices to polymer reinforcement. 

The use of nanoclays, mainly montmorillonite family, as nanofillers for sol-gel silica coatings has been extensively used in the content range from 0.5 up to 5wt% [75]. Every hybrid matrbc-nanoclay composite is unique and the properties depend on (i) hybrid matrix and clay material, (ii) composition, and (Mi) fabrication route of the nanocomposite. 

Figure 9.27 shows the TEM micrograph of the cell wall foamed at 100 °C under 28 MPa. Interestingly, the grown cells with a diameter of 200 nm are localized along the dispersed nano-clay particles in the cell wall. In other words, the dispersed nanofiller particles act as nucleating sites for cell formation and the cell growth occurs on... 

---