Unmodified montmorillonite

The morphology of rubber-based nanocomposites also seems to change in the presence of compounding ingredients [89, 90]. HNBR, when melt-compounded with organo-modified sodium montmorillonite clays (o-MMTs) prior to sulfur curing, resulted in the formation of nanocomposites with exfoliated or intercalated structures. In stark contrast, under similar conditions HNBR compounded with unmodified sodium montmorillonite clays (NA) formed microcomposites [90]. This was traced to its reactivity with the sulfur in the presence of amine-type organomodifiers. 

Figure 7 shows the representative bright field HRTEM images of nanocomposites of NR and unmodified montmorillonite (NR/NA) prepared by different processing and curing techniques. It is apparent that the methodology followed to prepare the nanocomposites by latex blending facilitates the formation of exfoliated clay structure, even with unmodified nanoclays. It has been reported in the literature that hydration of montmorillonite clay leads to extensive delamination and breakdown of silicate layers [94, 95]. It has also been shown that NA disperses fully into the individual layers in its dilute aqueous dispersion (clay concentration <10%)... 

Fig. 12 Stress-strain curves of a 19NBR, b 34NBR, c 50NBR, d BR, and e SBR and their nanocomposites with control unmodified (NA) and modified (o-MMT) montmorillonite clays...

The incorporation of unmodified and organically modified montmorillonite nanoclays (namely 15A and 30B) in chlorinated polyethylene (CPE) by the solution intercalation method and their influence on mechanical properties of the nanocomposites have been studied by Kar et al. [137]. The o-MMT-embedded nanocomposites show enhanced tensile strength and Young s modulus in comparison to the nanocomposites containing the unmodified nanoclay. They have shown from and XRD analyses that organically modified clay shows better dispersion in the CPE matrix. This has been further substantiated from FTIR analysis, which proves an interaction between the CPE matrix and the clay intercalates. 

On the other hand, Bhattacharya et al. have reported the plasticization effect of organically modified layered silicates on dynamic mechanical properties [13]. In this work, nanocomposites of SBR have been prepared using various nanofillers like modified and unmodified montmorillonite, SP, hectorite etc. It has been observed that the Tg shifts to lower temperature in all the nanocomposites, except for systems from hectorite and NA. This is due to the fact that clay layers form capillaries parallel to each other as they become oriented in a particular direction. Due to wall slippage of the unattached polymer through these capillaries, the Tg is lowered, which could be even more in the absence of organo-modifiers [13]. A similar type of plasticization effect is also noted in the case of the low... 

A mixture of benzaldehyde la (106 mg, 1 mmol) and 2-aminopyridine 3a (94 mg, 1 mmol) was irradiated in an unmodified household microwave oven for 1 min (at full power of 900 W) in the presence of montmorillonite K-10 clay (50 mg). After addition of benzyl isocyanide 2a (117 mg, 1 mmol), the reaction mixture was further irradiated successively (2 min) at 50% power level for a duration of 1 min followed by a cooling period of 1 min. The resulting product was dissolved in dichlorometliane (2x5 mL) and the clay was filtered off. The solvent was removed under reduced pressure and the crude product was purified either by crystallization or by passing it through a small bed of silica gel using EtOAc-hexane (1 4, v/v) as eluent to afford 4a. 

Freitas, A. F., M. F. Mendes, and G. L. V. Coelho. 2009. Thermodynamic study on the adsorption of some organic acids from aqueous solutions by unmodified and modified montmorillonite clays. Chem. Eng. Commun. 196 824—840. 

Natural, unmodified montmorillonite-Na (MMT-Na) has cation exchange capacity, typically 80-90 mequiv/100 g. Although some polymers, such as polyethylene oxide or polyvinylpyrrolidone, are of sufficient polarity to be able to directly exfoliate unmodified MMT-Na, organic modification of the layered clay is usually required to render the hydrophilic surface of the clay more hydrophobic and thus more compatible with most polymers, thereby improving the wettability and dispersibility of the clay in the polymer matrix. 

Botana et al. [50] have prepared polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, PHB and two commercial montmorillonites [MMT], unmodified and modified by melt-blending technique at 165°C. PHB/Na and PHB/ C30B were characterized by differential scanning calorimetry [DSC], polarized optical microscopy [POM], X-ray diffraction [XRD], transmission electron microscopy [TEM], mechanical properties, and burning behavior. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHB/Na,... 

Plasticizers used for TPS can also exfoliate clay during processing. Maksimov et al. [239] investigated an unmodified-montmorillonite (MMT)-filled... 

Mondragon et al. [250] used unmodified and modified natural mbber latex (uNRL and mNRL) to prepare thermoplastic starch/natural rubber/montmorillonite type clay (TPS/NR/Na+-MMT) nanocomposites by twin-screw extrusion. Transmission electron microscopy showed that clay nanoparticles were preferentially intercalated into the mbber phase. Elastic modulus and tensile strength of TPS/NR blends were dramatically improved as a result of mbber modification. Properties of blends were almost unaffected by the dispersion of the clay except for the TPS/ mNR blend loading 2 % MMT. This was attributed to the exfoliation of the MMT. 

Surface-modified and unmodified montmorillonite with doublelayered hydroxides can also be used as drug delivery vehicle. When antiinflammatory drug in layered double hydroxide is subjected to intercalation. 

Unmodified montmorillonite shows band at 3600 cm corresponding to Al-OH and Mg-OH groups (Figure 9.6). After silane modification, it shows bands between 3050-2700 cm due to the vibration of CH bonds introduced by the modifier. The high intensity of this absorption may be due to the covalent bonding of the modifier with the clay mineral and also it may be due to the interaction of the intercalated modifier with the water... 

Figure 9.6 FTIR spectra of (a) unmodified montmorillonite and (b) modified montmorillonite. Reprinted from [2] with permission from Elsevier.

On the other hand Abdallah et al. [22] showed that bentonites modified by alkyl and aryl based phosphonium salts in poly(ethylene terephthalate) exhibited better dispersion than those unmodified. In 2010 Gu [23] showed that montmorillonite modified Octadecylammonium improves dispersion in namral rubber/butadiene rubber nanocomposites. Have also been studied in terms of particle size of styrene-butadiene mbber (SBR) nanocomposites showed remarkable improvement in thermal stability their compared to that of the pure SBR. Was also demonstrated that the increase in particle size is not beneficial in improving the thermal stability [5]. 

Authors have reported the thermal degradation behaviour of polycaprolactone (PCL) bio-nanocomposites [47, 77]. A study by Chrissafis et al. [46] investigated the thermal behaviour of modified and unmodified nanocomposites on PCL. They revealed that both unmodified montmorillonite and multiwalled carbon nanombes inhibited the thermal degradation of the bio-nanocomposites. On the other hand, organically modified montmorillonite and nanosilica increased the rate of degradation of PCL bio-nanocomposites (Fig. 9). 

F. 9 Thermogravimetric analysis of siliea, modified and unmodified montmorillonite [46]. Copyright 2007. Reproduced by permission of Elsevier Seienee Ltd. 

Figure 8.5 TEM micrograph of unmodified montmorillonite dispersed in water.

Figure 8.5 shows the transmission electron microscopy (TEM) micrograph of the unmodified montmorillonite filler indicating the delaminated single layers. It... 

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