Unmodified clays

Maiti and Bhowmick reported exciting results that a polar matrix like fluoroelastomer (Viton B-50) was able to exfoliate unmodified clay (Cloisite NA ) as well as the modified one (Cloisite 20A) [93]. They studied morphology, mechanical, dynamic mechanical and swelling properties of fluoroelastomer nanocomposites. The unmodified-clay-filled systems showed better properties than the modified ones (Table 2.3). 

For example, the increment in maximum stress over the neat polymer is 100% and 53% in the case of the unmodified- and the modified-clay-fiUed samples, respectively. The extraordinary results obtained with the unmodified clays were explained with the help of thermodynamics and surface energetics. They explained it as follows. 

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 ). 

The influence of clay and modified clay on the physical properties of the CR vulcanizates at 5 phr filler concentration is given in Table 5. As is obvious, the modulus values (stresses at 100%, 200% and 300% elongation) increase in all cases after filler loading. Again, the extent of improvement depends on the nature of the nanofillers. In the case of unmodified clay, the increase in 100% and 300% modulus is more with LDH, whereas MMT shows similar enhancement as that observed with... 

At room temperature, the storage modulus is increased about fivefold in OMMT-filled vulcanizates. The increment of this value in CR-OLDH is much smaller, whereas unmodified clays give hardly any change at room temperature. 

The nanocomposites prepared using modified clay are referred to as oPC, dPC, DdPC, TdPC, HdPC and OdPC denoting increasing alkyl chain length of 8, 10, 12, 14, 16 and 18 respectively and is shown in Table 1. As a reference, a nanocomposite with unmodified clay was also used and denoted UM. 

It is clear from Figure 5a that the sample containing unmodified clay has both crystalline and amorphous content present in the composite, as do the oPC and dPC samples. A small peak is noticed at 21.8° for the DdPC sample but this disappears completely for the remaining nanocomposites. This indicates that as the length of the alkyl chain increases, the amount of amorphous material forming in the composite decreases, producing a more uniform y-type crystal... 

Recently, Moad et al. [288,289] designed and prepared novel copolymer intercalant/dis-persant/exfoliant systems that are effective with unmodified clays at low levels (<20% with respect to clay), can be combined with commercial PP and clay in a conventional melt-mixing process, and do not require the use of additional compatibilizers. PP-clay nanocomposites prepared by direct melt mixing using unmodified MMX clays and a copolymer additive added at a level of only 1 wt.% with respect to PP for 5wt.% clay Authors investigated the following two classes of dispersants (1) polyethylene oxide-based nonionic surfactants... 

A Fourier transform infrared spectrophotometer (FTIR, model-IR Prestige-21, Schimadzu Corporation, Japan) was used for the structural determination of functional groups and compounds. The FTIR spectra of modified and unmodified clay in the solid state using potassium bromide (KBr) as a reference material were recorded by diffuse reflectance spectroscopy (DRS technique). This technique consists of preparation of sample by mixing about 0.5 mg of powder sample with 50 mg of high-purity infrared-grade KBr powder (Aldrich). The KBr was previously oven dried to reduce the interference of water. The spectra were recorded in the wave number range of 4000—400 cm with a resolution of 4 cm and 20 scans were carried for each sample in transmittance mode. 

The most important argument for the siUcate layers intercalation by protonated adducts was revealed by XRD analysis, which gives the value of the basal distance between silicate layers as shown in Fig. 3. From Fig. 3, one may observe that the basal distance of modified montmorillonite is always higher than of unmodified clay. The modification directed that aU the new protonated adducts were successively intercalated between the silicate layers during the cationic exchange process. 

Similar studies were carried out with polyethylene, which is also a nonpolar polymer with limited affinity toward unmodified clays. Stoeffier et al. [41] used clays modified with... 

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