Polymer dissolution is a necessary step in many of the polymer processing methods, such as blending, separation, coating, casting, etc.
SOLVENT POWER:
The usual problem of polymer engineering is a selection of proper solvent(s) for a given polymer. This selection implies that the solvent must form with polymer a thermodynamically stable mixture in the whole range of concentrations and temperatures. Such choice is facilitated by use of numerical criterion of a solvent power. Solvent power might be taken from the thermodynamic treatment (for example, a change of Gibbs free energy or chemical potentials of mixing of polymer with solvent), but these criteria depend not only on the solvent properties but also on polymer structure and its concentration. For this reason, various
approaches were proposed to estimate solvent power.
? Kauri-butanol value, KB: is used for evaluation of dissolving ability of hydrocarbon solvents. It is obtained by titration of a standard Kauri resin solution (20 wt% in 1-butanol) with the solvent until a cloud point is reached (for example, when it becomes impossible to read a text through the solution). The amount of the solvent used for titration is taken as KB
value. The relationship between KB and solubility parameter, ?, fits the following empirical dependence:
? Dilution ratio, DR: is the volume of a solvent added to a given solution that causes precipitation of the dissolved resin. This ratio can characterize the compatibility of a diluent with a resin solution in primary solvent. When compatibility is high, more diluent can be added.
DR depends on the polymer concentration. With polymer concentration increasing, DR increases as well.
?Aniline point, AP: is the temperature of a phase separation of aniline in a given solvent.
AP is a critical temperature of the aniline - solvent system. AP can be related to KB value using the following equations:
AP depends on the number of carbon atoms in the hydrocarbon molecule. AP is useful for describing complex aromatic solvents.
?The solvent power can also be presented as a sum of factors that promote solubility or decrease it:
where:
H: a factor characterizing the presence of active sites of opposite nature in solvent and polymer that can lead to formation of hydrogen bond between polymer and solvent
B: a factor related to the difference in sizes of solute and solvent molecules
A: a factor characterizing solute melting.
C :a factor of the self-association between solvent molecules
D :a factor characterizing the change of nonspecific cohesion forces in the course of transfer of the polymer molecule into solution.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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