Quaternary ammonium salts organoclays

Another significant use for dialkyl dimethyl quaternary ammonium salts and alkylhenzyl dimethyl ammonium salts is in preparing organoclays for use as drilling muds, paint thickeners, and lubricants. 

Chang et al. incorporated hexadecylamine, dodecyltrimethyl ammonium bromide, and quaternary ammonium salt-modified MMT clays in PLA films at 0-10% [w/w) MMT levels, based on wet casting method, using Al,Al-dimethylacetamlde as a solvent. They observed that there was an optimal loading of organoclay [ 3-... 

The preparation of organoclays is fairly standard. A slurry of purified smectites in water is made up and stirred to maintain good agitation. A quaternary ammonium salt is then added to this stirring slurry. After the exchange, the organoclay is filtered and dried. A number of process adjustments and improvements have been patented, mostly concerned with improving the efficiency or consistency of the finished product. 

The biggest difference involved in describing an organoclay is the type of quaternary ammonium salt(s) used to prepare it. Although most commercial products are made from three types of quaternaries, namely dimethyldi(hydrogenated tallow)ammonium chloride, dimethylbenzyl(hydrogenated allow)ammonium chloride, and methylbenzyldi(hydrogenated tallow)ammo-nium chloride, many other quaternaries have been used and described in the patent literature. 

FIGURE 17.3 Dependence of cell size and cell density of PLA (NatureWorks 3000D, Cargill Dow) and PLA nanocomposites on the concentration of organically modified layered silicates (organoclay Cloisites 30B, Southern Clay Products, Inc., Texas) [42]. Cloisite 30B is the montmorillonite modified with methyl, tallow (-65% C18, -30% C16, -5% C14), and bis-2-hydroxy ethyl quaternary ammonium salt. 

However, it was suggested that if the residual anions could be completely removed from the organoclays, the primary degradation pathway would switch to an elimination-type mechanism [16]. The Hofmann elimination of ammonium compounds was most probably the source of additional amounts of vinyl-type unsaturation found in melt-processed OMMT-PE relative to both the polymer control and the Na+MMT-PE samples [28]. On the other hand, the presence of alkenes was also explained by three possible routes of decomposition (i) pyrolysis of alkanes derived from the major component of the organic part, i.e., hydrogenated tallow (HT) (ii) pyrolysis of the tallow (unsaturated fatty acids used for the preparation of the quaternary ammonium salt) and (iii) decarboxylation of RCOO and RCO radicals [17, 29]. 

A typical polymer-modified organoclay for the preparation of PS nanocomposites could be a PS polymer with some cationic sites to be attached to the clay surface. Polystyryl quaternary ammonium salts (PSQAS) were synthesized via three different polymerization routes anionic polymerization (AP), free radical co-polymerization (CP), and chloromethy-lation of polystyrene (CM) [67] (Table 3.6). TGA results indicated that CP-PSQAS and CM-PSQAS were thermally stable, because the C-C bonds in aromatics are much stronger than those in aliphatic compounds. The polystyryl-modified clays exhibited intercalated or partially exfoliated structures. 

To improve their dispersibility, clays could be modified with organic surfactants, which are typically the quaternary ammonium salts of long fatty acid chains. These surfactants decrease the surface tension of the aluminosilicate particulates, which in turn reduces the endothermal enthalpy of mixing. Many organophilic nanoclays or organoclays, therefore, have already been studied, and some of their products are already marketed on an industrial scale (Matsuda et al., 2012 Park et al., 2002 Turri, Alborghetti, and Levi, 2008). 

Quaternary alkylammonium salts or alkylamines are the cationic surfactants most commonly used in the modification of layered silicates. They are synthesized by complete alkylation of ammonia or amines. Many efforts have been made to produce ammonium surfactants to improve the affinity between the clay mineral and the polymer [3]. Ammonium organoclays undergo thermal degradation at temperatures below or comparable to the melt-processing temperatures of many polymers. 

The onset temperature of decomposition of alkyl quaternary ammonium-modified montmorillonite, in nonoxidative thermal degradation, is about 180°C. Initial degradation of the surfactant follows either a Hoftnann elimination or an Sn2 nucleophilic substitution mechanism. Both mechanisms can affect the performance of high-processing-temperature nanocomposites and, in general, the thermal stability and combustion behavior of nanocomposites. In particular, Hofmann elimination generates acidic sites on the layered silicate that can act as a protonic acid catalyst on polymer decomposition. " Imidazolium and phosphonium salts exhibit improved thermal stability compared to ammonium salts.Alkylimidazolium salt-modified layered silicates were used successfully to prepare organoclays that exhibit an onset of decomposition temperature up to 392°C. 

Organomontmorillonites are prepared by exchanging tetra alkyl quaternary ammonium ions onto the surface of the clay. The existing counterion of the montmorillonite is a metal ion (sodium, potassium, etc.). The positive charged quat displaces the positively charged metal ion to produce the organoclay and the metal halide salt (sodium chloride, potassium chloride, etc.). The salt is washed away from the organoclay... 

Ammonium ILs Currently, an intensive research is done on the modification of layered silicates by several varieties of modifiers associated with chloride and bromide anions [18,19]. The alkylammonium salts derived from the complete alkylation of amine are the most used ILs to prepare organoclays. The main role of quaternary alkylammonium is to lower the surface energy of the modified clays and to increase the basal spacing, that is, to allow the diffusion of the polymer between... 

In addition to ammonium quaternary salts, other surfactants are also mentioned in the literature as an organomodifler in organoclays. Nonionic surfactants, which are linear alcohol ethoxylate, with low toxicity and potential for biodegradation are used to prepare organomontmorillonite (Shen, 2001). Furthermore, clays can also be modified with biomolecules, such as proteins, enzymes, amino acids, peptides, and so forth. 

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