Solubility of additives

For chemical stabilization and optimization of polymer properties for specific applications, additives must be introduced into the pure polymer. Such additives include antioxidants, UV stabilizers, thermal stabilizers, chemical stabilizers, nucleating agents, plasticizers, and processing aids. Depending on the application, additives are present in a homogeneous or phase-separated form. The level of solubility of additives in the polymer is important. 

The solubility of low molecular weight compounds in polymer matrices is a very important topic. The level of solubility strongly depends on the molecular structure of the additives compared to the polymer. Mineral additives do not dissolve in polymers. The level of miscibility of low molecular weight compounds depends on characteristics such as differences of polarity and of solubility parameters, when this approach is appropriate. 

Insoluble additives may nucleate polymer crystallization, while high concentrations of insoluble additives may restrict crystallization. Soluble additives at low concentrations should not affect the crystallinity of the polymer. High concentration levels of an additive may change the properties of the polymer by accident or by design. 

Antioxidants, antiozonants, light stabilizers, heat stabilizers, accelerators, etc., are generally polar compounds and have little affinity for non-polar polymers such as polyolefins. 

In Table 4.1, the solubility of various low molecular weight compounds in polymers is summarized. The situation is very different from oil-extended rubber (Section 3.10) or plasticized polyvinyl chloride (Section 3.11). The level of miscibility of polar additives in non-polar polyolefins is quite small. 

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Capillary Temperature Protein conformation and solubility are affected by the temperature of the solution. As described above, focused proteins may tend to precipitate during the CIEF process as they become highly concentrated at their pi with low concentration of salt ions. The temperature of the capillary can be manipulated to increase their solubility, but it should not be too high as protein denaturahon may occur. Higher temperature is used mainly in combination with other solubilizing agents, and temperature may be used to increase the solubility of additives such as urea rather than the solubility of the proteins. 

Some examples of ternary alloy precursors are also shown. Their general properties were examined and their microstructures were directly observed by transmission electron microscopy. Thus, catalysts synthesized from multi-system alloys had high solubility of additional elements into a major element, and might be expected to work as new catalysts. 

Effects of additives. The results are summarized In Figure 2 in terms of water solubility of additive solvent and membrane performance evaluated with 0.2% ovalbumlne aqueous solution. The water flux rises very steeply from zero to 8.8xl0 ml/mln.m In correspondence with Increase In the water solubility of additive solvent from 1 to 4 g/dl. Contrary to the fact that the water flux curve has a plateau for the additive water solubility larger than 4 g/dl, the ovalbumlne permeation values for some water mis-slble additive solvents are undesirably higher than those for additive solvents, of which water solubility Is in the rang,e from 4 to 20 g/dl. 

Figure 3 Illustrates that membrane thickness Increases consistently with water solubility of additive solvents.

Figure 2. Relationship between membrane performance and water solubility of additive solvents (O, 0J solubility of additive solvents in water fA, ik) solubility of water in additive solvents. Water flux is normalized to the staridard value of 8.8 X 10 mL/min m and ovalubumine permeation is normalized to the standard...

Solution Studies. The solubility of additives within an optical fiber coating material is of prime importance since particulates can damage the surface of the glass (14) in addition to causing pinholes or tears in the coating. Solubility data for a number of commercial stabilizers are summarized in Table I. The most soluble stabilizers in the acrylate diluent are monomeric materials, particularly those with long alkyl chains. 

Each of the above processes offers some advantages over the other, in terms of sulfate conversion, solubility of additives, or formation of unwanted insoluble salts. The smelter will select the process most suitable according to circumstances. 

The useful lifetime of a polyolefin corresponds essentially to the end of the oxidation induction time. In stabilised materials this may be determined either by the time at which the stabiliser has been chemically consumed or that at which it has been lost from the sample by evaporation or extraction. We have developed a model to describe these additive loss processes but it requires a knowledge of the diffusion rates and solubilities of additives in polymer (11, 12). 

There are matty reasons to be concerned about the solubility of additives in plasticizers, including ... 

It was noted previously that emulsions and foams are related by the fact that each represents a physical state in which one fluid phase is finely dispersed in a second phase, and that the state of dispersion and the long-term stability (persistence) normally is dependent on the composition of the system. In emulsions, each phase is a hquid so that such factors as mutual solubiUty and the solubility of additives in each phase must be considered. In foams, the dispersed phase is a gas so that problems of solubility are less critical, although as will be seen, the transfer of the dispersed gas from one bubble to another or out into the adjacent atmosphere is important. 

Krivoguz, Y. M., Pesetskii, S. S., Jurkowski, B., and Olkhov, Y. A. 2001. Solubility of additives Grafting of itaconic acid onto LDPE by reactive extrusion. II. Effect of stabilizers. 

In many applications it is of prime importance that plasticizer and polymer be completely miscible at the molecular level. Thermodynamic criteria for the solubility of additives in polymers are the same as those given for simple liquid mixtures [2-6]. When two liquid substances form a stable solution, classical thermodynamics shows that the free enthalpy of mixing, AG , is negative [7]. Furthermore, one can write... 

The selection of stabilizers for the various polyamides depends on processing temperature and the decomposition temperature of the stabilizers. The concentration of end groups should also be considered because they influence the solubility of additives in the molten polymer [14]. 

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