Quaternary ammonium-modified montmorillonite

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. 

In the UPR-based nanocomposites, the styrene monomer was replaced with the polar hydroxypropyl acrylate [224]. X-ray and mechanical test data indicated that mixing of the components for an extended period of time is essential to improve the physical properties of nanocomposites in the UP/Cloisite 6A system. This phenomenon was attributed to the high polarity of hydroxypropyl acrylate which may disturb the preintercalation of UPR into the galleries of montmorillonite. The UPRs with a styrene monomer were used in dispersions with polymerizable quaternary ammonium-modified montmorillonite [225]. An increase in tensile and impact strength and heat resistance (Table 29) was found when 2-5 wt % organophiHc montmorillonite was added. 

To decrease the induction period, DMCs have been combined with quaternary ammonium salts, montmorillonite clays modified with quaternary ammonium salts, or imidazolium ionic liquids [10,12,13]. Such additives were found to decrease the induction period by acting as nucleophiles in the catalytic cycles. As such, these compounds (1) facilitate the formation and activation of the zinc-monomer bond and (2) make the zinc-monomer bonds more active for polymerization, and/or they stabilize the polymerization centers and prevent their decomposition [10,13]. 

The presence of an organophilic clay increases the catalyst activity (10). Suitable clays include montmorillonite, hectorite, mica, etc. For example, Lucentite is a trioctylmonomethylammonium salt-treated synthetic hectorite. The clays are modified with quaternary ammonium compounds. The clays are heat treated prior to their use in the polymerization process. Further, the incorporated clay can improve the performance of the UHMWPE or function as filler. 

A detailed study of the interaction of hydrocarbons with cetyl trimethyl ammonium bromide modified montmorillonite has been done using Raman spectroscopy [82]. The quaternary salt was observed to be in a liquid-like state and it was concluded that interaction of organic compounds in this system is best classified as absorption. 

Montmorillonite clay modified with a quaternary ammonium salt... 

Another class of siloxane surface active agents is that of cationic siufactants, which usually contain amine groups (Scheme 10) and are widely used in cosmetic products, especially as hair softeners and conditioners [54]. A quaternary ammonium chloride has been used to modify montmorillonite, in order to obtain nanocomposites with polymethylsilsesquioxane [104]. 

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. 

Boron oxide particles were incorporated to silicone rubber-based mixes containing fumed silica (reinforcing filler) and reference mineral fillers - aluminum hydroxide, wollastonite, calcined kaolin, mica (phlogipite) and surface modified montmorillonite with dimethyl-dihydrogenatedtal-low quaternary ammonium salt. Acidic character of boron oxide, which can disturb the peroxide curing process, was compensated by addition of magnesium oxide. The influence of boron oxide particles on properties of composites was determined and mechanism of their ceramization process studied. 

Vulcanization kinetics of the composites vulcanization are very similar regardless refractory filler type, excluding the mix containing surface modified montmorillonite (M-MMT) (Table 8.2). In its case values of torque were significantly lower than for other samples minimum (M j ), optimum (M ) and maximum (M ) torque values, respectively, from 14 to 27%, from 34 to 40% and from 35 to 41%. This effect can by explained by plasticization of silicone matrix by quaternary ammonium salt present in M-MMT. Also values of scorch (tp2) and vulcanization (t ) time... 

In our recent publications [4, 5] we discussed results concerning ion and molecule mobility in cationic montmorillonite film modified electrodes hydrophobized with aliphatic and aromatic quaternary ammonium compounds. We also described experiences with independent measurements by electrochemical and radiochemical methods on transport processes in humate containing montmorillonite and bentonite thin layers [6]. We interpreted the results as consequences of changes in structure which lead to changes in porosity and ditfu-sional transport [7, 8, 9]. The present paper approaches the role of film thickness, and the kinetics of the swelling of films (porodine xerogels) at different levels of hydrophobization, and also the kinetics of the penetration and release of probe molecules. 

Figure 4.4 X-ray diffraction of aUcylimidazolium montmorillonite (MMT) and the respective melt-processed nanocomposites with PET (Left) XRD curves for hexadecylimidazolium MMT and its nanocomposites with copolymer-PET. (Right) XRD curves of MMT organically modified with dimethyl-tallow-2-ethylhexyl quaternary ammonium [2MTL8-anunon-MMT] and with hexadecylimidazolium [CieHss-imidaz-MMT] and their respective nanocomposites with homopolymer-PET.

Table 6.1 includes typical quaternary ammonium salts used as organic modifiers in commercial montmorillonite nanoclays, which are to be primarily dispersed in nonpolar matrices. Figure 6.5 shows that hydrotalcite platelets of nanodimensions present a much smaller degree of agglomeration than the MMT particles. 

A commercially available organoclay based on a layered silicate (montmorillonite modified by dimethyldistearylammonium cation exchange) was used. The content of the quaternary ammonium compound was 38 wt%. Octadecylamine-modified montmorillonite is used to study the thermal stability of organoclay. 

Structure-property relationships in crosslinked polyester-clay nanocomposites, prepared by dispersing methyl tallow bis-2-hydroxyethyl quaternary ammonium chloride-modified montmorillonite in prepromoted polyester resin and subsequently crosslinking using the methylethylketone peroxide initiator at room temperature and at several clay concentrations, were analyzed by X-ray diffraction combined with Transmission Electron Microscopy (TEM), thermal (TGA) and dynamic mechanical analyses as well as by the determination of mechanical and optical properties [158]. In all cases the formation of a nanocomposite and the morphology of a dispersion of intercalated/exfoHated aggregates of clay sheets in the resin matrix were confirmed (Fig. 17). hi the absence of reflection irrespective of clay concentration in the scattering curves for all the polyester-clay nanocomposites was ascertained. 

TCN - montmorillonite modified with 25-30 wt% dimethyl, dihydrogenatedtallow, quaternary ammonium salt 2M2HT where HT is hydrogenated tallow ( 65% CIS, 30% C16, 5%C14) (Nanoclay, USA),... 

Montmorillonite modified with a quaternary ammonium salt (Cloisite SOB) was purchased from Southern Clay Products Inc. Texas, USA. Cloisite 30A was dried for 6 h at 90°C in a thermal vacuum chamber. Poly(ethylene oxide) Mw 3000 g/mol, was dried in a vacuum oven (under lower pressure) at 90 C for 30 min before use. 4,4 -Methylenebis(cyclohexyl isocyanate) (HMDI), 1,4-butanediol (B), 1,2,3-propanetriol (G), triethanolamine (T), acetone were used without purification. All these materials were purchased from Sigma-Aldrich Co. 

Several successful strategies are available in the literature [14] that increase the thermal stability of organic molecules. Full utilization of these strategies for the preparation of surface treatments of layered silicates with enhanced thermal stability for the development of polymer-clay nanocomposites has yet to be realized. An example of an effective strategy is the utilization of quaternary ammonium and phosphonium functional polystyrene as a surface treatment for montmorillonite that is employed to prepare polymer-clay nanocomposites [15]. TGA indicated a significant increase in the thermal stability of the organoclay and the polymer-clay nanocomposite. Imidazolium functional surface modifier for montmorillonite demonstrated a significant increase in the thermal stability of ABS terpolymer-clay nanocomposite when compared to the pure polymer and polymer-clay nanocomposites where the surface modification of the montmorillonite was produced with traditional quats [16]. These experiments were via TGA measurements. 

---