Casting solutions, formulation

In the case of cellulose acetate (CA) casting dopes the solution structurization is mainly due to hydrogen bonding between polymer molecules and additives (swelling agents) in the solution. Therefore, a choice of a proper additive is an important step in the casting dope formulation. 

The above set of rules - though accurately descriptive of earlier casting procedures - has led to serious misconceptions pertaining to the formation of anisotropic membranes, and therefore, misconceptions in the formulation of new polymeric casting solutions. It is evident that the polymer solution concentration progressively increases at the surface layer during the evaporation period, and... 

Asymmetric Membrane Preparation. The preparation of the as5Tnmetric membranes was done in a fashion similar to the "classical" technique referred to below, although the casting solutions often deviated from the "classical" formulations. In all cases, a solution of polymer plus at least two other components was cast on a glass plate with a doctor s knife set at a thickness of 15 mils (0.381 mm). After a brief evaporation period the membrane was gelled in a non-solvent bath. Finally, the membrane was thoroughly washed in distilled, deionized water. 

The present chapter is devoted exclusively to an analysis of the problems of isotopically mixed solvents. It will not concern itself, except in passing, with the measurement and interpretation of solvent effects on equilibrium and rate constants due to the isotopic change from pure H20 to pure D20. The aim is to show to what extent measurements of this type are of practical utility, especially as a tool in the investigation of reaction mechanisms. For this reason, the development of theory is mainly directed towards compromise solutions of a complex problem, i.e. solutions which enable the theory to be tested and applied but lay no claim to being theoretically unassailable. The guiding principle has been to cast the formulation in terms of parameters or types of measurement which are either known or at least known to be feasible. 

Formulation of Casting Solutions. Once a polymer has been selected, the next step is formulation of the casting dope. This includes finding solvents, swelling agents, and non solvents, and making a formula for the proportion of the different substances. The solubility parameters are of a certain help, but still it is mainly trial and error through lots of experiments which leads to the result. 

Clear, water-soluble, oU-and grease-resistant films of moderate strength can be cast from hydroxyethylceUulose solutions. Elexible, nontacky, heat-sealable packaging films and sheets can be produced from hydroxypropylceUulose by conventional extmsion techniques. Both gums can be used in the formulation of coatings, and both can be used to form edible films and coatings. 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

Phenolics Elastomers Powder, solutions Excellent thermal stability to over 300 F generally, and over 400 F in special formulations. Broad choice of resins. May be cast or compression, transfer, or injection molded. Precision potentiometers, RF connectors, heating panels. 

Films of PATE were cast on copper plated circuit boards. Typical solutions contain from 8% to 17% PATTE solids and 0.02% Flourad FC 135 surfactant. No other additives, such as adhesion promoters, sensitizers, viscosity modifiers or stabilizers, were employed in the formulations. Films of 0.001 to 0.008 inches wet film thickness were cast on abrasively cleaned circuit boards and then oven dried for 5 minutes at 105 °C. Thus, in each case the... 

The structural variations of Novolak resins also influence how well they mix or form solid solutions with a dissolution inhibitor when resist films are cast onto substrates. This is a crucial problem for resist formulation. Usually, cresol-formaldehyde Novolak resins mix well with photoactive compounds like a... 

Crystalline BaTi03prepared by hydrolysis of the alkoxide solutions in the form of dispersion without drying was successfully used to make a ceramic slip formulation, which was then cast as a ceramic green body for microcapacitors 1 to 50 pm thick. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

Table 13.6 shows the characteristics and properties of supported and nonsupported high-molecular-weight epoxy resins cast from solvent solution. A crosslinked and uncrosslinked formulation using the same high-molecular-weight epoxy is shown for comparison. 

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