Nanofillers barrier properties, effects

With the advent of nanocomposites, notions about how to cost-effectively reinforce resins may change. As with fiber-filled PP, the issues of stiffness and strength vs. weight and cost could be key questions for nanocomposites, which require only low loadings (3%-5%) of nanofillers to maximize properties. Since resin makes up most of the balance of these composite systems, a cost-conscious user of a PP nanocomposite would likely seek to minimize product thickness. Otherwise, other value-adding properties of a nanofiller (such as charge dissipation, flame retardancy, or barrier properties) may also help it to compensate for its extra material and processing costs [8-12]. 

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. 

In recent years, lamellar nanofiUers have been established as the most important filler type for barrier and mechanical reinforcement. Dal Point et al. reported a novel nanocomposite series based on styrene-butadiene rubber (SBR latex) and alpha-zirconium phosphate (a-ZrP) lamellar nanofiUers. The use of surface modified nanofiUers improvement the mechanical properties. However, no modification of the gas barrier properties is observed. The addition of bis(triethoxysilylpropyl) tetrasulfide (TESPT) as coupUng agent in the system is discussed on the nanofiUer dispersion state and on the fiUer-matrix inteifacial bonding. Simultaneous use of modified nanofillers and TESPT coupling agent is found out with extraordinary reinforcing effects on both mechanical and gas barrier properties [123]. 

Slavutsky and Bertuzzi (2014) recently showed ceUulose nanociystals (C-NC) obtained from sugarcane bagasse. They formulated starch/C-NC composites and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/C-NC films have a lower affinity to water molecules than starch films. The same effect was observed in studies by Savadekar and Mhaske (2012). They studied the effect of C-NC incorporation on TPS matrix and found that the nanofillers addition improved their barrier and mechanical properties. 

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]. 

Finally, in the case of SSP of PA 66, when combining a phosphorus-containing antioxidant and day, reduced antioxidant catalytic performance was observed, which was ascribed to significant counteradions between them day hydrophilidty acted as a polycondensation water trap, hindering the escape of the by-product. The latter effect was also related to day barrier properties, while the occurrence of adsorption phenomena on the surface of the nanofillers was also assumed to reduce the catalytic performance of the antioxidant. ... 

Silicone rubber (SR) nanocomposites with different dimensional nanofillers like OD (nanosilica, POSS, metal nanoparticle), ID (CNT, CNF), 2D (layered silicate, LDH, graphene) and 3D (graphite), etc., have been effectively reviewed in the up-to-date research work presented in this chapter covering their synthetic method, nanostructure and properties. It is noted that the SR nanocomposites exhibited improved mechanical, thermal, gas barrier properties, reduced flammability and biological properties at very low loading of fillers. However, it is concluded that such improvement in properties is only observed when fillers are uniformly dispersed and interact with SR chains. 

Depending on the distribution of micro/nanofiller in the polymer matrix, the composites may be classified as microcomposites or nanocomposites. These two types of composites differ significantly with respect to their properties. The nanocomposites show improved properties compared to pure polymer or that of microcomposites. It started only back in 1990, when Toyota research group showed that the use of montmorillonite can improve the mechanical, thermal, and flame retardant properties of polymeric materials without hampering the optical translucency behaviour of the matrix. Since then, the majority of research has been focused in improving the physicochemical properties, e.g. mechanical, thermal, electrical, barrier etc. properties of polymer nanocomposites using cost effective and environmental friendly nanofillers with the aim of extending the applications of these materials in automotive, aerospace, construction, electronic, etc. as well as their day to day life use. The improvements in the majority of their properties have invariably been attributed... 

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