Polymers swelling and dissolution

The mechanisms of drug release from dextran matrix occur in the early stage by polymer swelling, and the tablet thickness increases. Soon thereafter, polymer (and drug) dissolution starts occurring. The polymer dissolves because of chain disentanglement. Thus, there is a slow diminution of the thickness because of erosion until, finally, the tablet disappears (time > 480min). 

In this chapter, we present results of the testing of a broad spectrum of polymers in carbon dioxide over a range of temperatures and pressures and evaluation of the effect of the high pressure carbon dioxide on the chemical/physical properties of materials tested. The testing was performed in a static manner with four controlled variables, namely temperature, pressure, treatment time and decompression time. The evaluation of the interaction of high pressure carbon dioxide with polymers included sorption and swelling behavior, solubility issue, plasticization and crystallization, and mechanical properties. The results of these evaluations are discussed in three sections Sorption, Swelling and Dissolution of Carbon Dioxide in Polymers at Elevated Pressure, Thermal Properties, and Mechanical Properties. ... 

SORPTION, SWELLING AND DISSOLUTION OF CARBON DIOXIDE IN POLYMERS AT ELEVATED PRESSURE... 

The sorption of carbon dioxide can result in swelling and/or dissolution of a polymer. The extent of either/or both swelling and dissolution depends on the solubility of carbon dioxide in the polymer and/or the solubility of the polymers in carbon dioxide. When the system pressure is reduced, absorbed carbon dioxide may nucleate into bubbles and cause the formation of foam, or small defects in the polymer structure that may significantly alter the mechanical properties of the material. In addition, carbon dioxide can extract the plasticizer, if present, in the polymer and thus cause embrittlement. In this chapter, we address such solubility issues. 

Yih-o Tu, "Miltiphase Stefan Problem Describing the Swelling and Dissolution of Glassy Polymer", IBM Symposium on Mathematics and Computation, October 6-7, 1976. Yorktown Heights, N.Y. 

Borgquist, P., Kitchner, A., Piculell, L., Larsson, A., Axelsson, A., 2006. A model for the drug release from a polymer matrix tablet — effects of swelling and dissolution. Journal of Controlled Release 113, 216—225. 

Swelling and dissolution of polymers are due to the same factors. The tendency toward swelling is opposed by a reaction force arising from the network formed by cross-linking. It is assumed that crystalline regions play roles of cross-linkages [88]. 

Chemical structure and the polarity determine dissolution of polymers. If the bonds in polymer and solvent are similar, then the energy of interaetion between homogeneous and heterogeneous moleeules is nearly identieal whieh faeilitates solubility of polymer. If the chemical structure of polymer and solvent moleeule differ greatly in polarity, then swelling and dissolution does not happen. It is refleeted in an empirieal rule that like dissolves like . 

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