Nanoclay fillers

Problem Nanoclay fillers interact negatively with standard heat stabilizers. 

In addition to particle breakup, the coalescence process may be affected as well. It has been speculated that exfoliated clay platelets or well-dispersed nanoparticles may hinder particle coalescence by acting as physical barriers [19,22]. Furthermore, it has been suggested that an immobilized layer, consisting of the inorganic nanoparticles and bound polymer, forms around the droplets of the dispersed phase [50]. The reduced mobility of the confined polymer chains that are bound to the fillers likely causes a decrease in the drainage rate of the thin film separating two droplets [44]. If this is the case, this phenomenon should be dependent on filler concentration this is shown in Figure 2.8, which shows the effect of nanoclay fillers on the dispersed particle size of a 70/30 maleated EPR/PP blend [19]. 

Unitika Ltd. of Osaka, Japan has developed a hydrolysis-resistant polylactic acid which, when combined with a nanoclay filler, is said to have sufficiently good mechanical and thermal properties to be targeted at computer, electronic and automotive parts. 

Nanoclay filler-PLA Solvent casting + compression molding [79 1]... 

S. Lietz, J.-L. Yang, E. Bosch, J. K. W. Sandler, Z. Zhang, and V. Altstadt, Improvement of the mechanical properties and creep resistance of SBS block copolymers by nanoclay fillers. Macromolecular Materials and Engineering, 292 (2007), 23-32. 

Rashmi, Renukappa NM, Ranganathaiah C, Shivakumar KN (2011) Montmorillonite nanoclay filler effects on electrical conductivity, thermal and mechanical properties of epoxy-based nanocomposites. Polym Eng Sci 51 1827—1836... 

Figure 9.8 Nanoclay filler structures. (Reproduced from Hussain, F, jojjati, M., Okamoto, M. et al. (2006) Review article polymer-matrix nanocomposites, processing, manufacturing, and application an overview, j. Compos. Mater., 40, 1511-1575. Copyright (2006) Sahe Publications.)...

Therefore, many studies have attempted to alleviate the worsened mechanical and thermal properties through the inclusion of fillers. Several kinds of fillers used in research have included nanoclay fillers (Haq et al., 2008 Zhang et al., 2013 Swain et al., 2012 Albayrak et al., 2013), microfiber celluloses (Shibata and Nakai, 2010 Bitinis et al., 2013 Pandey et al., 2013), and basaltic fibers (Torres et al., 2013). Compared to other fillers, nanoclay fillers have gained great popularity due to their attractive platelet-like nanostructures. The unique structure and property of nanoclay fillers have resulted in the manufacture of numerous polymer/clay nanocomposites as reviewed by Alexander and Dubois (2000). 

Nanoclay fillers are categorized as platelet-like nanoclays or layered silicates and tubular nanoclays in terms of filler shape. With the configuration of two tetrahedral sheets of silicate and a sheet layer of octahedral alumina, platelet-like nanoclays or phyllosilicates are formed, which include smectite, mica, vermiculite, and chlorite. In particular, smectite clays are widely employed with further subcategories of MMT, saponite, hectorite, and nontronite. The typical MMT clays are regarded as one of the most effective nanofillers used in polymer/clay nanocomposites due to their low material cost and easy intercalation and modification (Triantafillidis et al., 2002). On the other hand, the fundamental structure of tubular nanoclays contains an aluminum hydroxide layer and a silicate hydroxide layer. They are also known as dio-ctahedral minerals with two different types of halloysite nanotubes (HNTs) and imo-golite nanotubes (INTs). Notwithstanding their material role as clay minerals, these two types of tubular nanoclays resemble the hollow tubular structure of carbon nanotubes (CNTs). In this section, three different types of clay nanofillers, namely MMTs, HNTs, and INTs are reviewed in detail along with the development of clay modification. 

To achieve improved dispersibUity of nanoclay fillers within polymer systems, three familiar methods are commonly used, namely, melt intercalation, solution intercalation, and in situ polymerization. The melt-intercalation method is based on the melting point of polymer matrices and is applied by annealing above the melting point of the polymer (Reddy et al., 2013). This method has been chosen by industrial sectors to produce polymer/clay nanocomposites. However, it is not apphcable to the fabrication of biobased polymer/clay nanocomposites based on thermosetting materials such as epoxy and polyester due to their high viscosities (Wypych and Satyanarayana, 2005 Wang et al., 2014). Therefore, the fabrication of biobased thermosetting polymer/clay nanocomposites is mainly based on solution intercalation or in sim polymerization. 

Abdulhadi A, Al-J uhani A A. The effect of OH-modified nanoclays fillers on the compatibility and properties of polypropylene/poly (ethylene oxide) blends. Arab J Sci Eng 2013 38 1929-37. 

Figure 11.4 Wide-Angle XRD traces of a series of model sUoxane elastomers filled with varying levels of an organically-modified nanoclay filler. The solid, dashed, circle, triangle and square lines represent the XRD traces of the clay powder and the elastomer filled with 0-8% nanoclay. The conspicuous lack of any diffraction peaks in the filled elastomers is evidence of the effective exfoliation of the clay filler within the polymer. Reprinted with permission from [9] Copyright Elsevier (2008).

Thorough study of nanocomposites has revealed clearly that nanoclays can provide certain advantages in properties in comparison to their conventional filler counterparts. Properties which have been shown to undergo substantial improvements include ... 

Effects of nanoclay and silica in mbber matrices have been discussed in earlier chapters. Recently, several other nanofillers have been investigated and have shown a lot of promise. All these fillers have not been investigated on rubbers extensively, although they have great potential to do so in the days to come. In this chapter, we have compiled the current research on mbber nanocomposites having nanofillers other than nanoclay and nanosilica. Further, this chapter provides a snapshot of the current experimental and theoretical tools being used to advance our understanding of mbber nanocomposites. 

Carbon black is reinforced in polymer and mbber engineering as filler since many decades. Automotive and tmck tires are the best examples of exploitation of carbon black in mbber components. Wu and Wang [28] studied that the interaction between carbon black and mbber macromolecules is better than that of nanoclay and mbber macromolecules, the bound mbber content of SBR-clay nanocompound with 30 phr is still of high interest. This could be ascribed to the huge surface area of clay dispersed at nanometer level and the largest aspect ratio of silicate layers, which result in the increased silicate layer networking [29-32]. 

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. 

In addition, Maiti and Bhowmick [93] also used fluoroelastomers having different microstructure and viscosity (Viton B-50, Viton B-600, Viton A-200, and VTR-8550). Viton is a terpolymer of vinylidene fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). Even with the addition of only 4 phr of clay in Viton B-50, the tensile strength and modulus improved by 30-96% and 80-134%, respectively, depending on the nature of the nanoclays. The better polymer-filler interaction in the case of NA clay and the fluoroelastomers has... 

Choudhury et al. [86] have studied the effect of polymer-solvent and clay-solvent interaction on the mechanical properties of the HNBR/sepiolite nanocomposites. They chose nine different sets of solvent composition and found that chloroform/methyl ethyl ketone (Qi/MEK) (i.e., HNBR dissolved in Ch and sepio-lite dissolved in MEK) is the best solvent combination for improvement in mechanical properties. XRD, AFM, , and UV-vis spectroscopy studies show that the dispersion of clay is best in the Ch/MEK solvent combination and hence polymer-filler interaction is also the highest. images shown in Fig. 14a, b clearly elucidate the aforementioned phenomena. Consequently, the tensile strength and modulus are found to be higher (5.89 MPa and 1.50 MPa, respectively) for the Ch/MEK system due to the minimum difference in interaction parameter of HNBR-solvent (xab) and sepiolite-solvent (Xcd)- Choudhury et al. have also studied the effect of different nanoclays [NA, , 15A, and sepiolite (SP)] and nanosilica (Aerosil 300) on the mechanical properties of HNBR [36]. The tensile... 

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

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