Fillers Including Nanofillers

Particulate fillers such as calcium carbonate, carbon black, silica, talc, sawdust, woodflour, slate dust and chopped cotton were originally used in the early plastics as cost-cutting additives, because their cost by weight was lower than that of polymers. One filler manufactmer has recently pubhshed figures suggesting that the addition of 20% of calcium carbonate to a polyolefin polymer can reduce the polymer cost on a weight basis by about 5.7%. The assumption was that the filler costs just over a quarter as much (per tonne) as the polymer. 

All the physical and mechanical properties are altered at the same time when a filler is added, and the extent of the change depends on particle size and geometry. Chemical resistance may be affected (calcium carbonate is attacked by mineral acids) and weathering behaviour can alter. 

Some fillers perform valuable specialist functions and some are discussed in other sections of this report. One example is aluminium trihydroxide (ATH), discussed under the heading of Flame Retardants and Smoke Suppressants, rather than Fillers. Carbon black has several roles, improving polymer conductivity, electrostatic dissipation and UV stabihsation. Antimony trioxide is a flame retardant synergist. 

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Different monomers may be copolymerized to modify the properties of thermoplastics. For the same purpose, homo- and copolymers are frequently mixed with other substances, including other polymers, various fillers, and nanofillers. The presence of comonomers in macromolecules, as well as interactions between macromolecules in miscible blends, can affect both crystallization and morphology of the polymeric material. Interfaces and the confinement of polymer chains within a finite volume influence the solidification and morphology of immiscible polymer blends and polymer-based composites. They are also of special importance in ultra-thin polymer layers where the thickness is comparable to or smaller than the lamellar crystal thickness itself... 

Although certain fillers and reinforcements including layered silicates, other nanofillers, or natural fibers possess special characteristics, the effect of these four factors is imiversal and valid for all particulate filled materials. 

Although many kinds of fillers and fibers have been added to POs over the years, and new ones continue to be developed, the sections below cover the most used and most commercially important materials. These fillers and fibers continue to draw the greatest efforts from industry and academia for further development and improvement. Some newer kinds, such as nanofillers and plant-based fibers, are included here mainly because of their potential future importance. As in other chapters of this book, here the focus is more on materials that can be added in a typical compounding operation or "at the press"—rather than modifiers that are added more upstream by the resin producer, or hybrid combinations of materials, such as glass-mat composites or laminates, where the reinforcing material is not added during screw processing. 

NanofiUers are often added to enhance one or more of the properties of polymers. Inactive fillers or extenders raise the quantity and lower the cost price, while active fillers bring about targeted improvements in certain mechanical or physical properties. Common nanofillers include calcium carbonate, ceramic nanofiUers, carbon black, carbon nanotubes (CNTs), carbon... 

Broadband dielectric spectroscopy is a powerful tool to investigate polymeric systems (see [38]) including polymer-based nanocomposites with different nanofillers like silica [39], polyhedral oligomeric silsesquioxane (POSS) [40-42], and layered silica systems [43-47] just to mention a few. Recently, this method was applied to study the behavior of nanocomposites based on polyethylene and Al-Mg LDH (AlMg-LDH) [48]. The properties of nanocomposites are related to the small size of the filler and its dispersion on the nanometer scale. Besides this, the interfacial area between the nanoparticles and the matrix is crucial for the properties of nanocomposites. Because of the high surface-to-volume ratio of the nanoparticles, the volume fraction of the interfacial area is high. For polyolefin systems, this interfacial area might be accessible by dielectric spectroscopy because polyolefins are nonpolar and, therefore, the polymeric matrix is dielectrically invisible [48]. 

As can be seen an important aspect in material development is to achieve good combination of properties. The performance of a composite material depends on several factors including formulation, dispersion of fiUer in the polymer matrix and adhesion between the filler and the matrix. The properties of nanocomposites depend on the type of nanofiller used and its interaction with the polymer matrix. 

Electrical properties Electrical properties of polymers include several electrical characteristics that are commonly associated with dielectric and conductivity properties. Electrical properties of nanofilled polymers are expected to be different when the fillers get to the nanoscale for several reasons. First, quantum effects begin to become important because the electrical properties of nanoparticles can change compared with the bulk. Second, as the particle size decreases, the interparticle spacing decreases for the same volume fraction. Therefore percolation can occur at lower volume fractions. In addition, the rate of resistivity decrease is lower than in micrometer-scale fillers. This is probably due to the large interfacial area and high interfacial resistance. 

Recentiy, a new class of organic-inorganic hybrid materials based on the ultra incorporation of nano-sized fillers (nanofillers) into a polymer matrix has been investigated. Nanotechnology is the aptitude to work on a scale of about 1-100 nm in order to understand, create, characterize and use material structure, devices, and system with unique properties derived from their base on the nanostructures. Nanocomposites could exhibit exclusive modifications in their properties, compared with conventional composites in terms of physical properties, including gas barrier, flammability resistance, thermal and environmental stability, solvent uptake, and rate of biodegradability of biodegradable (Chivrac et al. 2009). 

At the present time, important nanofillers include certain nanoclays (montmorillonite, hydrotalcite in platelet form), nanofibers (single- and multiple-wall carbon nanotubes), and nanosized particulate metal oxides. Several technological advances will undoubtedly contribute to additional growth in the usage of these fillers. Examples of such advances include [45]... 

The final properties of the cellulose nanofibers-based nanocomposites depend not only on the aspect ratio (1/d), but also on the mechanical and percolation effects [4, 24]. The developed studies have shown that the tensile properties and transparency of the nanocomposites increase with the aspect ratio of the cellulose nanowhiskers [25,26]. In addition [27], the tensile properties also depend on the orientation of the cellulose nanofibers inside the polymeric matrix, making critical the processing conditions. However, other authors [26] showed that filler orientation and distribution play an important role in the aspect ratio. The maximum enhancement in properties of the composites takes place for the adequate quantity of filler in the matrix, where the particles can form a continuous structure known as percolation threshold [28]. The improvement of the properties of nanocomposites compared with the neat matrix is also related with the dispersion of filler within the matrix. The compatibility between the selected matrix and the nanofiller is another important factor to be taken into accoxmt [29]. The high polarity of cellulose surface leads to certain problems when added to nonpolar polymer matrices including weak interfacial compatibility, poor water barrier properties and aggregation of fiber by hydrogen bondings [4, 30]. 

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