Polymeric matrix nanofillers

One more aspect of the model, concerns the determination of parameter b, which characterizes interfacial adhesion at the nanofiller - polymeric matrix level. The condition b = was accepted for the value of (Fig. 4.1), but this parameter can also be estimated more precisely according to Eq. (4.6) and Eq. (4.7), using experimental values E, E and (p. An independent estimation of the interfacial adhesion level for the nanocomposites studied, can be obtained with the aid of parameter A, determined according to the equation ... 

However, in both cases - thermoplastics and thermosets - the equipment and the processes need to be adapted to the nanosized fillers. The most crucial point in the production of polymer-nanofiller dispersions is the proper separation of the CNTs from each other, the deagglomeration of agglomerates, and their coupling to the polymeric matrix material. For this purpose, dispersion aids, stabilizers, and compatibilizers, used for other filler particles, need to be adapted in many cases specifically for nanosized fillers with their different surface treatments for the different matrix materials. This is a very complicated issue, and makes a close co-operation between the different scientific disciplines necessary [1]. 

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

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]. 

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. 

The synthetic mbber is widely used, this type of elastomer have important properties and numerous application due to stability. These properties are favored when the synthetic mbber is reinforced with organic nanoparticle as carbon nanombes, nanofibers, graphene, and fuUerene, among other [78-80]. These may or may not be modified nanofiUers surface for subsequent incorporation in the matrix, promoting greater interaction between inorganic nanofillers and polymeric matrix, thus improving the thermal stability of the nanocomposite etc. [81, 82]. 

The mechanical properties of PA-based polymers can also be enhanced through the incorporation of inorganic micro- and nanofillers such as silica nanoparticles. Thus, the maximum value of stress at yield point (72 MPa) was observed in hybrid materials containing 10 wt% silica and the maximum stress at break point increased up to 66 MPa in PA-sUica hybrids containing 20 wt% silica (compared with 44 MPa for the silica-free PA system). Also, the tensile modulus was found to increase up to 2.59 GPa upon incorporation of 10 wt% silica within the polymeric matrix [268]. 

The surface of hydrophilic nanofillers is usually functionalized (modified) so as to promote a homogeneous dispersion throughout the polymer, and to enhance interactions within the polymeric matrix, resulting in improved... 

Nanocomposites are a relatively new class of hybrid materials characterized by an ultra fine dispersion of nanofillers into a polymeric matrix. As the result of this dispersion, these materials possess unique properties, behaving much diflferentiy than conventional composites or microcomposites, and offering new technological and economical opportunities. The first studies on nanocomposites were carried out in 1961, when Blumstein performed the polymerization of vinyl monomer intercalated into montmorillonite structure. Since then, clay-based polymer nanocomposites have emerged as a new class of materials and attracted considerable interest and investment in research and development worldwide (Schaefer and Justice 2007). 

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]. 

Reynaud, E. Jouen, T. Gauthier, C. Vigier, G. Varlet, J. Nanofillers in polymeric matrix a study on silica reinforced PA6. Polymer 2001, 42, 8759-8768. 

Reynaud E, Jouen T, Gauthier C, Vigier G, Varlet J (2001) Nanofillers in polymeric matrix a study on silica reinforced pa6. Polymer 42 8759 Scheiner S (1997) Hydrogen bonding a theoretical perspective. Oxford University Press, New York... 

Analysis of the thermal properties of nanoreinforcement, matrix and also of the nanocomposites is important to determine their processing temperature range and to analyze the effect of nanofiller addition on the thermal properties of the polymeric matrix [21]. 

Up to now we considered pol5meric fiiactals behavior in Euclidean spaces only (for the most often realized in practice case fractals structure formation can occur in fractal spaces as well (fractal lattices in case of computer simulation), that influences essentially on polymeric fractals dimension value. This problem represents not only purely theoretical interest, but gives important practical applications. So, in case of polymer composites it has been shown [45] that particles (aggregates of particles) of filler form bulk network, having fractal dimension, changing within the wide enough limits. In its turn, this network defines composite polymer matrix structure, characterized by its fractal dimension polymer material properties. And on the contrary, the absence in particulate-filled polymer nanocomposites of such network results in polymer matrix structure invariability at nanofiller contents variation and its fractal dimension remains constant and equal to this parameter for matrix polymer [46]. 

Mechanical Properties Chen et al. [2007] smdied the dynamic mechanical properties of films prepared by the solution casting method of PHBHV reinforced with HAp. The results indicated that at 75°C the storage tensile modulus of the polymer matrix, E , almost doubled by incorporation of 30 wt% HAp. The decrease in tan S was attributed to the hindrance of polymeric segment mobility by the nanofiller. Polyamide-69 has been reinforced with up to 10 wt% HAp [Sender et al., 2007]. The DMA results have pointed out an enhancement of the mechanical properties as a function of HAp content up to 5 wt% above this limit they deteriorated, probably due to the HAp agglomeration. 

---