Dispersion of clay

Adhesives for paper tubes, paperboard, cormgated paperboard, and laminated fiber board are made from dispersions of clays suspended with fully hydrolyzed poly(vinyl alcohol). Addition of boric acid improves wet tack and reduces penetration into porous surfaces (312,313). The tackified grades have higher solution viscosity than unmodified PVA and must be maintained at pH 4.6—4.9 for optimum wet adhesion. 

Inhibited Muds—Dispersed Systems. These are water-base drilling muds that repress the hydration and dispersion of clays. There are essentially four types of inhibited muds lime muds (high pH), gypsum muds (low pH), seawater muds (unsaturated saltwater muds, low pH), and saturated saltwater muds (low pH). 

Seawater muds are commonly used on offshore locations, which eliminate the necessity of transporting large quantities of freshwater to the drilling location. The other advantage of seawater muds is their inhibition to the hydration and dispersion of clays, because of the salt concentration in seawater. The typical composition of seawater is presented in Table 4-48 most of the hardness of seawater is due to magnesium. 

At high electrolyte concentrations of the soil solution, the double layer is compressed so that clay remains flocculated. A decrease in ion concentration, e.g. as a result of dilution by percolating rain water, can result in dispersion of clay and collapse of aggregates. If the exchange complex is dominated by polyvalent ions, the double layer may remain narrow even at low electrolyte concentrations and consequently aggregates remain intact (FAO, 2001). 

Soil-pH may influence both the concentrations of ions in the soil solution and the charge characteristics of the clay. Dispersion of clays is thus, to some extent, a pH-dependent process. At soil-pH(H2o,i i) values below 5, the aluminum concentration of the soil solution is normally sufficiently high to keep clay flocculated (Al3+ is preferentially adsorbed over divalent and monovalent ions in the soil solution). Between pH 5.5 and 7.0, the content of exchangeable aluminum is low . If concentrations of divalent ions are low, clay can disperse. At still higher pH values, divalent bases will normally keep the clay flocculated unless there is a strong dominance ofNa+-ions in the soil solution. 

Choudhury et al. [86] have studied the effect of polymer-solvent and clay-solvent interaction on the mechanical properties of the HNBR/sepiolite nanocomposites. They chose nine different sets of solvent composition and found that chloroform/methyl ethyl ketone (Qi/MEK) (i.e., HNBR dissolved in Ch and sepio-lite dissolved in MEK) is the best solvent combination for improvement in mechanical properties. XRD, AFM, , and UV-vis spectroscopy studies show that the dispersion of clay is best in the Ch/MEK solvent combination and hence polymer-filler interaction is also the highest. images shown in Fig. 14a, b clearly elucidate the aforementioned phenomena. Consequently, the tensile strength and modulus are found to be higher (5.89 MPa and 1.50 MPa, respectively) for the Ch/MEK system due to the minimum difference in interaction parameter of HNBR-solvent (xab) and sepiolite-solvent (Xcd)- Choudhury et al. have also studied the effect of different nanoclays [NA, , 15A, and sepiolite (SP)] and nanosilica (Aerosil 300) on the mechanical properties of HNBR [36]. The tensile... 

It has been found that the HNBR/SP nanocomposite provides the best thermal and mechanical properties when HNBR is dissolved in Ch and SP is dispersed in MEK. XRD, AFM,TEM, and optical transmittance studies show that the dispersion of clay is best in the Ch/MEK solvent combination and, hence, polymer-filler interaction is also highest in this system. Thus, rather than implying that the solvent selection directly affects the physical properties of the nanocomposite, solvent acts on the properties through its influence on the developed morphology. 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

XRD is easily used but does not directly provide the dispersion information while TEM is an expensive and difficult method to use. With TEM, however, direct information, although qualitative, about the dispersion of clay (and other nanoadditives) in the matrix polymer can be obtained. The XRD method is usually used together with the TEM technique to characterize the morphology of the resulting PCNs. Attempts have been made to quantify the information that has been obtained through TEM technique,78 but it seems to be not so successful in current practice, particularly for describing the dispersion of clays. 

The presence of compatibilizer helped in improving dispersion of clay in PP as shown in Figure 24.5 and the dispersion improved with the increase in compatibilizer level (Figure 24.5b-d).13 However, the clays were not exfoliated or intercalated, but dispersed at nanolevel as shown by TEM... 

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

Duquesnoy, J.A. Thibault, F. Tanguy, P.A. Dispersion of clay suspensions at high solids content. Private communication, 1995, MacMillan Bloedel, British Columbia. 

The relationship between lEPs and mechanical properties of dispersions of clay minerals is more complex than for oxides. Specific results for bentonites can be found in [394] (Tables 3.1317, 3.1318, and 3.1321). Eor kaolin, tlie maximum in the yield stress was at pH 5.3, while the potential was negative at pH > 4. This lack of coincidence of the IEP and the maximum in the yield stress is due to different charges of faces and edges [1019]. 

Surfactants may not only stabilize system against coagulation, but may have an opposite effect, i.e. cause destabilization in cases when the surfactant adsorption proceeds against the polarity equalization rule (Chapter III,2), e.g., during chemisorption of surfactants from aqueous medium on a hydrophilic surface. For example, small additives of cationic surfactants cause coagulation of aqueous dispersions of clays and other silicates due to hydrophobization at T< rmax. Further increase in surfactant concentration results in the formation of a second (hydrophilizing) adsorption layer and leads to an increased... 

D. J. Cebula, R. K. Thomas, and J. W. White, Small angle neutron scattering from dilute aqueous dispersions of clay, J.C.S. Faraday /, 76 314 (1980). 

Increased water solubility in the range of 50-100% hydrolysis, controlling flocculation/ dispersion of clay,... 

One kind of nanometer-size reinforcement is the montmo-rillonite, which is a layered silicate whose interlayer ions can be exchanged by organ-ions in order to produce an increment in the interlayer spacing (dooi3 snd to improve the polymer/clay compatibility. These improvements allow the dispersion of clay platelets to be easier [49]. 

Maiti and co-workers [43] investigated the effect of organic modifiers of various chain lengths in different types of clays, smectite, MMT, and mica on the degree of dispersion of clay in PLA. They observed that the nanocomposites of MMT and mica are intercalated and well-ordered compared to smectite. The... 

Class C—emulsions of various organic substances, increasing the electrostatic attraction and introducing ultra-fine particles to cement paste. The following compounds, among many others, are in this group acryl emulsions and water dispersions of clay. 

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