Nanoclays

Functional group that reacts with polymer, monomer, or oligomers 

Cellulose nanowhiskers (CNWs) have been obtained from a variety of matrices such as cotton [63], sisal [64], and coconut husk fibers [65]. Other alternative sources of cellulose nanofibrils includes naturally colored cotton, curaua (Ananas erecti-Jblius), and sugarcane bagasse have been successfully used to prepare nanowhiskers [66-69]. 

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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 ... 

The data provided by Toyota Research Group of Japan on polyamide-MMT nanocomposites indicate tensile strength improvements of approximately 40%-50% at 23°C and modulus improvement of about 70% at the same temperature. Heat distortion temperature has been shown to increase from 65°C for the unmodified polyamide to 152°C for the nanoclay-modified material, all the above having been achieved with just a 5% loading of MMT clay. Similar mechanical property improvements were presented for polymethyl methacrylate-clay hybrids [27]. 

Further data provided by Honeywell relating the polyamide-6 polymers confirm these trends in property [28]. In addition, further benefits of short/long glass fiber incorporation, together with nanoclay incorporation, are clearly revealed. 

One of the few disadvantages associated with nanoparticle incorporation concerns the loss of some properties. Some of the data presented have suggested that nanoclay modification of polymers such as polyamide could reduce impact performance [28]. Nanofillers are sometimes very matrix-specific. High cost of nanofillers prohibits their use. 

They have studied the properties of NR-epoxidized natural rubber (ENR) blend nanocomposites also. Vulcanization kinetics of natural mbber-based nanocomposite was also smdied. The effect of different nanoclays on the properties of NR-based nanocomposite was studied. The tensile properties of different nanocomposites are shown in Figure 2.7 [33]. 

This is a nonpolar rubber with very little unsamration. Nanoclays as well as nanotubes have been used to prepare nanocomposites of ethylene-propylene-diene monomer (EPDM) rubber. The work mostly covers the preparation and characterization of these nanocomposites. Different processing conditions, morphology, and mechanical properties have been smdied [61-64]. Acharya et al. [61] have prepared and characterized the EPDM-based organo-nanoclay composites by X-ray diffracto-gram (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy... 

The results suggest that the thermal stability improves with higher loading till 6 phr of nanoclay and this improvement is attributed to the barrier effect of the exfoliated and the intercalated nanoclay particles. 

This is another important and widely used polymer. Nanocomposites have been prepared based on this rubber mostly for flame-retardancy behavior. Blends with acrylic functional polymer and maleic anhydride-grafted ethylene vinyl acetate (EVA) have also been used both with nanoclays and carbon nanotubes to prepare nanocomposites [65-69]. 

ENGAGE is an ethylene-octene copolymer. Ray and Bhowmick [70] have prepared nanocomposites based on this copolymer. In this study, the nanoclay was modified in situ by polymerization of acrylate monomer inside the gallery gap of nanoclay. ENGAGE was then intercalated inside the increased gallery gap of the modified nanoclay. The nanocomposites prepared by this method have improved mechanical properties compared to that of the conventional counterparts. Preparation and properties of organically modified nanoclay and its nanocomposites with ethylene-octene copolymer were reported by Maiti et al. [71]. Excellent improvement in mechanical properties and storage modulus was noticed by the workers. The results were explained with the help of morphology, dispersion of the nanofiller, and its interaction with the mbber. 

FIGURE 2.9 X-ray diffractogram (XRD) spectra of unmodified and modified nanoclays and styrene-butadiene rubber (SBR)-based nanocomposites with styrene content of (a) 15% and 40% and (b) 23%. (From Sadhu, S. and Bhowmick, A.K., J. Polym. Set, Part B Polym. Phys., 42, 1573, 2(304. Courtesy of Wiley InterScience.)... 

Fluoroelastomer-based nanocomposites were prepared using various nanoclays and their different properties were studied [93-98]. 

The overall sorption value tends to decrease with the addition of the nanoclays. The decrease is maximum for the unmodified-clay-fiUed sample. As the ternperamre of swelling increases, the penetrant uptake increases in all the systems (Table 2.5). The rate of increase of solvent uptake is slower for the unmodified-clay-filled sample compared to the modified one. From Table 2.5 it can be seen that the values are higher for THE compared to MEK in every composite system. The higher sorption can be explained from the difference in solubility parameter of solvent and rubber (9 — 99 and polarity. The solubility parameter value of MEK, THE, and the mbber is 19.8, 18.6, and 14.8 MPa, respectively. This difference is lower (3.8 MPa ) in the case of THE than that of MEK (5.0 MPa ). 

They also established a model to predict the aspect ratio of nanoclays from the swelling smdies. They proposed the model in the following way [98]. 

Addition of layered nanoclays to a neat polymer restricts the permeability due to the following two phenomena ... 

The available area for diffusion will decrease as a result of impermeable nanoclays replacing the permeable polymer. 

When nanoclays are added to the system, we may assume that the clay layers are randomly placed in the matrix. The diffusion of the solvent will detour around the impermeable clay layers. Diffusion will be diverted to pass a clay platelet in every layer and, hence, the solvent must have to travel a longer path d in the filled system compared to that d( for the neat polymer. 

When a solvent diffuses across a neat polymer, it must travel the thickness of the sample (do). When the same solvent diffuses through a nanocomposite film with nanoclays, its path length is increased by the distance it must travel around each clay layer it strikes. According to Lan et al. [99] the path length of a gas molecule diffusing through an exfoliated nanocomposite is... 

The aspect ratio of the nanoclays in different samples has been calculated using Equation 2.11 and is reported in Table 2.6. 

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

Honeywell has also been active in developing a combined active-passive oxygen barrier system for polyamide-6 materials [201]. Passive barrier characteristics are provided by nanoclay particles incorporated via melt processing techniques, while active contribution comes from an oxygen-scavenging ingredient (undisclosed). Oxygen transmission results reveal substantial... 

Triton Systems and the U.S. Army [202] have conducted further work on barrier performance in a joint investigation. The requirement here is for a nonrefrigerated packaging system capable of maintaining food freshness for 3 years. Nanoclay polymer composites are currently showing considerable promise for this application. 

The ability of nanoclay incorporation to reduce solvent transmission through polymers such as polyamides has been demonstrated. Data provided by de Bievre and Nakamura [203] of UBE Industries reveal significant reductions in fuel transmission through poIyamide-6/66 polymers by incorporation of a nanoclay hller. As a result, considerable interest is now being shown in these materials as both fuel tank and fuel line components for cars. Of further interest, the reduced fuel transmission characteristics are accompanied by significant material cost reductions. 

B. de Bievre and K. Nakamura, UBE Europe. Polyamide Nanoclay Hybrids at UBE. Nanocomposites 2002. Conference Paper. January 2002. 

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]. 

Sonawane et al. [90] investigated the affect of ultrasound and nanoclay for the adsorption of phenol. Three types of nanoclay tetrabutyl ammonium chloride (TBAC), N-acetyl-N,N,N trimethyl ammonium bromide (CTAB) and hexadecyl trimethyl ammonium chloride (HDTMA), modified under sonication, were synthesized which showed healthier adsorption of phenol within only 10 min in waste water. The interlamellar spacing of all the three clay increased due to incorporation of long chain quaternary salts under cavitational effect. 

Sonawane S, Chaudhari P, Ghodke S, Ambade S, Gulig S, Mirikar A, Bane A (2008) Combined effect of ultrasound and nanoclay on adsorption of phenol. Ultrason Sonochem 15 1033-1037... 

Fig. 14.2 Transmission electron microscopy images of halloysite from Nanoclay and Technologies Inc. longitudinal and cross-sectional views (A, B) cross-section, and three different samples from supplies 2006-2007 (C-F).

Atlas Mining Corporation Nanoclay and Technology Division 1200 Silver City Road Eureka, UT 84628 USA... 

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