Solvency reduction

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

The floe rupture model may also be used to explain the maximum observed in versus temperature (figure 5). According to equation (4) Tg = f (< > H) Eg, where f(2H) is the collision frequency term. Although Eg increases with increase of temperature, f(< > H) is a decreasing function of temperature as a result of decrease of solvency of the dispersing medium which leads to the contraction of the adsorbed layer (13). The increase of Eg with increase of temperature initially outweighs any reduction of f (< > H), but at higher temperatures, the reduction in f (4> j ) as a result of chain contraction may exceed the increase in Eg and this results in reduction in the measured Tg. 

It is worth mentioning that there are some solvents that combine good solvency power with coordinating properties. The most salient example is 1,2-dimethoxyethane as a solvent in the reduction of organic acceptors by alkali metals. The acceptors transform into anion-radicals, and alkali metals into their cations. These cations are bound in chelates with 1,2-dimethoxyethane, and the one-electron reduction of the acceptors becomes more energy advantageous. 

Figure 6 The main broad avenues of nanoparticle production. Comminution or size reduction (say by high-pressure homogenization or critical solution technology), precipitation methods by salting out or other solvency changes in solutions of drag-polymers mixtures and molecular assembly of amphipathic components. Methods are listed in Table 2.

Figure 8.6 Influence of reduction In solvency on the energy-distance curve.

The influence of temperature on adsorption is shown in Figure 17.6. The amount of adsorption was shown to increase with increase of temperature, due to the poorer solvency of the medium for the PEO chains. The PEO chains become less hydrated at higher temperatures, and the reduction in solubility of the polymer enhances adsorption. 

Neville and Hunter [6] studied the flocculation of poly(methylmethacrylate) (PMMA) latex stabilised with poly(ethylene oxide) (PEO). Flocculation was induced by the addition of electrolyte and/or an increase in temperature. Figure 21.12 shows the variation of with increase of temperature at constant electrolyte concentration. In the figure, it can be seen that increased with increases of temperature, reaching a maximum at the critical flocculation temperature (CFT), and then decreased with further increase in temperature. The initial increase was due to the flocculation of the latex with increase of temperature, as the result of a reduction in solvency of the PEO chains with the increase in temperature. The... 

Meanwhile, an increase in the sahnity of the dispersed medium leads to a reduction in the attractive electrostatic interactions. In addition, sahnity drastically affects the solvency of the thermally sensitive polymers, as mentioned above. An increase in the electrolyte concentration... 

Figure 5.2 presents a similar plot for a poly(methyl methacrylate) latex sterically stabilized in n-heptane by poly(12-hydroxystearic acid). In this instance, however, the reduction in the solvency of the dispersion medium for the stabilizing moieties was achieved by adding a miscible nonsolvent (specifically ethanol) to the dispersion medium (Napper, 1968a). Flocculation was again accompanied by an abrupt increase in turbidity when a certain volume fraction of ethanol was added to the ra-heptane. In this instance, it was possible to observe the slow flocculation of the latex particles (i.e. flocculation apparently in the presence of a small repulsive potential energy barrier at a rate slower than that predicted by Smoluchowski, 1917). It is, however, usually diflicult to detect such slow flocculation because of the sharpness of the transition from stability to flocculation for stericaUy stabilized dispersions. 

Decades of research in polymer drag reduction have shown that the effects of variables such as polymer molecular structure, flexibility, molecular weight, concentration, and solvency are important. They are described below along with polymer mechanical degradation. 

Uses Solvent for automotive retinishes, industrial coatings, maintenance coatings, traffic marking, aerosol wood furniture coatings Features Exc. solvency fast vise, reduction cost effective potential HAPs delisting... 

The effect of temperature on the adsorption isotherms for both copolymers on the larger latex particles D = 867) is shown in Figure 16.7. In both cases, adsorption increases with increase of temperature from 20 to 40°C. This is due to the reduction of solvency of the medium for the side chains with increasing temperature. Increase in the x parameter (with increase of temperature) results in an increase in polymer adsorption. 

Propyl and isopropyl acetates are used as solvents for printing inks, lacquers, plastics, and resins. These solvents afford excellent solvency for nitrocellulose and other cellulose derivatives. The use of /i-propyl acetate as a nitrocellulose lacquer thinner allows maximum viscosity reduction, good flow properties, and good blush resistance. Other uses for the two propyl acetates include as a solvent in other resin coatings, adhesives, and organic syntheses. 

SURFADONE LP surfactants are unique, multifunctional nonionic surfactants. Both of these surfactants combine the ability to complex many polar materials with excellent wetting, surface tension reduction and solvency. Applications include personal care, specialty cleaner and agricultural formulations. 

These products are characterized by superior wetting (especially LP-100), surface tension reduction and solvency. The intrinsic multifunctionality often enables the SURFADONE nonionios to replace several additive surfactants. The ability of the pyrrolidone ring to complex polar materials allows SURFADONE LP surfactants to be used to alter the solubility, vapor pressure or irritation potential of various classes of materials such as phenolics. 

Meanwhile, an increase in the salinity of the dispersed medium leads to a reduction in the attractive electrostatic interactions. In addition, salinity drastically affects the solvency of the thermally sensitive polymers, as mentioned earlier. An increase in the electrolyte concentration leads to an increase in the Flory-Huggins [42] interactions parameter between the polymer and water, resulting in reduced poly(A-alkylacrylamide) solvency. Consequently, the amount of nucleic acids adsorbed onto the cationic poly(NIPAM) microgel particles was reduced, as has been widely reported for the... 

To study the effect of solvency on adsorption, measurements were carried out as a function of temperature [30] and addition of electrolyte (Kd or Na2S04) [31]. Increasing temperature and/or addition of electrolyte reduces the solvency of the medium for the PVA chains (due to break down of the hydrogen bonds between the vinyl alcohol units and water). Figure 5.11 shows the adsorption isotherms for PVA with M = 65100 as a function of temperature. This shows a systematic increase of adsorption with rising temperature, i.e. with reduction of solvency (increase in x), as expected from theory. The results obtained in the presence of electrolyte are shown in Figures 5.12 and 5.13. In both cases, addition of electrolyte increases adsorption of PVA, again due to the reduction of solvency of the medium for the chains. 

Fig. 7.32. Influence of reduction in solvency on the energy-distance curves for sterically stabilised dispersions.

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