Fillers and Nanofillers

Vulcanized NR is widely used as a polymeric matrix due to its particular capacity to disperse fillers and nanofillers in concentrations greater than 100 parts per hundred of rubber (phr). It is interesting to note the NR capacity of disperse various kinds of fillers, regardless of the existence of chemieal or physical interactions between matrix and filler. 

Blends are classified as either thermodynamically miscible or immiscible, with the latter dominating. However, imposition of a flow affects the thermodynamic equilibrium and it may enhance the miscibiUty of immiscible blends or vice-versa - there is an interrelation between rheology and thermodynamics. Similarly, flow affects the degree of deformation of the dispersed phase, thus in immiscible blends there are other interrelations between rheology and morphology, which affect the blend performance. To the complexity of polymer alloys and blends (PAB) behavior one must add the incorporation of soUds, either in the form of filler and nanofiller particles or by simple factofblendingtwocomponents with widely differenttransitiontemperatures. 

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... 

The authors [1] studied kinetics of poly (amic acid) (PAA) solid-state imidization both in the presence of nanofiller (layered silicate Na+-montmorillonite) and without it. It was found, that temperature imidization 1] raising in range 423-523 K and nanofiller contents Wc increase in range 0-7 phr result to essential imidization kinetics changes expressed by two aspects by essential increase of reaction rate (reaction rate constant of first order k increases about on two order) and by raising of conversion (imidization) limiting degree Q im from about 0,25 for imidization reaction without filler at 7 i=423 K up to 1,0 at Na -montmorillonite content 7... 

The kinetics of solid state imidization of PAA, synthesized from 4,4 -oxydianilinc and pylomellitic dianhydride, both without filler and with addition of 2 and 5 weight % Na+-montmorillonite [1], The nanofiller is processed by solution of P-phenylenediamine in HC1 and then washed with de-ionized water to ensure a complete removal of chloride ions. The conversion (imidization) degree Q was determined as a function of reaction duration t with the aim of Fourier transformation of IR-spectra bands 726 and 1014 cm 1. The samples for IR studies were prepared by spin-coating of mixture PAA/Na+-montmorillonite solution in N,N-dimethylacetamide on KBr disks. Then the KBr disks were dried in vacuum at 303 K for 48 h. It was shown, that the used in paper [1] method gives exfoliated nanocomposites. The other details of polyimide/Na+-montmorillonite nanocomposites synthesis and studies in paper [1] were cited. The solid state imidization process was made at four temperatures 7 423, 473, 503 and 523 K. 

Mineral fillers and additives aluminium trihydrate (ATH), magnesium hydroxide and boron derivates are the best known but tin derivates, ammonium salts, molybdenum derivates and magnesium sulphate heptahydrate are used to varying extents and nanofillers are developing. 

The lowering of die swell values has a direct consequence on the improvement of processability. It is apparent that the processability improves with the incorporation of the unmodified and the modified nanofillers. Figure lOa-c show the SEM micrographs of the surface of the extrudates at a particular shear rate of 61.2 s 1 for the unfilled and the nanoclay-filled 23SBR systems. The surface smoothness increases on addition of the unmodified filler, and further improves with the incorporation of the modified filler. This has been again attributed to the improved rubber-clay interaction in the exfoliated nanocomposites. 

Also, the loss in available surface area due to overlapping and aggregation is quite substantial in the case of nanofiller. As illustrated in Fig. 41, the loss is directly dependent on the interparticle distance between the fillers and, hence, also on the filler loading. Introduction of these two terms into the IAF in the form of the correlation length between the nanoparticles (J ) and the filler volume fraction ( ), respectively, mitigates the problem. 

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. 

Fillers and reinforcing fibers 7 and 8 Engineering-type applications for POs (especially PP and TPO), more interest in sustainable fillers and fibers Greater use of cellulose-based fiber reinforcements, of long-glass fiber reinforcement, and of nanofillers and specially fillers... 

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. 

Composites are engineered materials that contain two or more constituents with different properties that remain distinct from one another within the structure. POCs are a subset of the larger polymer composites group. The increased synthesis of POCs with different additives is necessary to satisfy the industrial demand that cannot be fulfilled by pure polymers. Additive materials can be classified as micro-and nanofillers depending on the applications of the composites. The fillers may be further subdivided as natural (plant fibers) or synthetic (glass fibers, CNT, etc.), different shapes (long or short length), flaky, fibrous, and spherical or disk-like [6]. The conventional addition of filler materials lowers the cost and improves the... 

In case of other fillers, the nanofillers can introduce new functionality into the polymer, e.g. electrical conductivity in case of carbon based nanoparticles, barrier properties in case of platelet like nanofillers (nanoclay, expanded graphite), enhancement of mechanical properties, enhanced flame retardancy, and many others. 

In addition, by scaling the filler size to the nanometer scale, it has been shown that novel material properties can be obtained. Nanoscaled fillers are those having at least one dimension in the range of nanometers (< 100 nm) [3]. When the dimensions of the reinforcement approach the nanometer scale, a number of effects make the properties of the corresponding composites different from those of composites reinforced with micro-scaled fillers. The major influencing factors of the properties of nanocomposites are nanofiller dispersion, dimensions, volume fractions, nature of the matrix material, interfacial properties between filler and matrix, and manufacturing process [4]. 

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]. 

The mechanical performances of polymer nanocomposites are influenced not only by several factors such as properties and amounts of the constituent phases (matrix and nanofiller), nanoparticle dispersion, morphology, and orientation, the matrix-filler interactions but also by the degree of crystallinity and crystalline phases of the polymer, as described... 

NR composites and nanocomposites can be fabricated by three main techniques, namely latex compounding, solution mixing and melt blending. A variety of nanofillers, such as carbon black, silica, carbon nanotubes, graphene, calcium carbonate, organomodified clay, reclaimed rubber powder, recycled poly(ethylene terephthalate) powder, cellulose whiskers, starch nanocrystals, etc. have been used to reinforce NR composites and nanocomposites over the past two decades. In this chapter, we discuss the preparation and properties of NR composites and nanocomposites from the viewpoint of nanofillers. We divide nanofillers into four different types conventional fillers, natural fillers, metal or compound fillers and hybrid fillers, and the following discussion is based on this classification. 

Recently, there has been much interest in the effect of filler sizes in polymer composites. In this review, the effect of macro- and nanofillers such as palm ash, wood flour, CNTs, organoclay on mechanical properties of NR composites are discussed. 

Polymer composites can be classified according to their particle size. Macro-filled composites contain filler particle size more than 10 pm. Midsize fillers are less than 10 pm and more than 1 pm while nanofillers have a particle size less than 1 pm and more than 0.1 pm. The micro-filled composite contains filler particle size less than 0.1 pm. The macrofiller generally is non-reinforcing filler and generally used for cost reduction particularly. 

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