Carbon based nanofillers

The carbon-based nanofillers are mainly layered graphite, nanotube, and nanofibers. Graphite is an allotrope of carbon, the stmcture of which consists of graphene layers stacked along the c-axis in a staggered array [1], Figure 4.1 shows the layered structure of graphite flakes. 

The effects of carbon-based nanofillers of EG, MWCNTs, and CNFs on the AC conductivity and dielectric constant of elastomeric grade EVA (50% vinyl acetate content) at a particular frequency of 12 Hz, are shown in Fig. 29a, b [194]. EVA-EG, EVA-T, and EVA-F represent EVA-based nanocomposites reinforced with EG, MWCNT, and CNF respectively. 

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... 

Strength). The nanosized particles most commonly used in PU foams are clearly silicate-layered nanoclays, and particularly unmodified or organically modified montmorillonite (MMT), though others have also been considered, such as carbon-based nanofillers (carbon nanotubes and nanofibers, and more recently graphene), nanosilica, or cellulose-based nanofillers. 

Owing to the particular high transport properties of carbon-based nanofillers, a great number of recent publications have considered the incorporation of these nanofillers into flexible PU foams, as opposed to silicate-layered nanoclays, which are mainly added as mechanical reinforcements and for that reason are almost only considered for rigid PU foams. The addition of carbon-based nanofillers comes from the interest in developing new functional flexible foams, for instance with improved piezoresistivity properties. 

Bernal, M. M., I. Molenberg, S. Estravis, M. A. Rodrfguez-Perez, I. Huynen, M. A. L6pez-Manchado, and R. Verdejo. 2012. Comparing the effect of carbon-based nanofillers on the physical properties of flexible polyurethane foams. J. Mater. ScL 47 5673-5679. 

A brief account of each of the carbon-based nanofillers discussing the structural morphology and production techniques is presented in the following sections. Typical properties of the aforementioned carbon-based nanofillers are listed in Table 8.1. 

Table 8.5 EMI SE properties of polymer nanocomposites with carbon based nanofillers... 

Due to the recent development in nanotechnology, TLCPs are usually compounded with nanoparticles to form particulate composites to enhance their properties, such as barrier properties, electrical properties, mechanical properties and thermal properties. Carbon-based nanofillers such as carbon nanotube (CNT), graphene and graphene oxide are the most common fillers used for the TLCP matrices (Cheng et al. 2012). 

Recent works in liquid crystalline polymer science, also emphasises more on the use of Thermotropic Liquid Crystalline Polymers (TLCPs) for development of nanocomposites using different nanofillers (Cheng et al. 2012). A discussion has already been made on this in the foregoing discussions. Carbon based nanofillers are more promising in this regards. 

---