Sorption and Swelling of Polymers

Variations in the thomal properties (v and vi from above) and the mechanical properties (vii from above) for polymaic materials are discussed sq arately in Sec. 3. This section details our results on sorption and swelling of polymers by carbon dioxide and the dissolution characteristics of various polymeric materials under a variety of conditions. A comparison will be shown for wdght change data of twenty different polymers that have been treated in both sub- and supercritical carbon dioxide at seven different conditions. These results are discussed in general to isolate important factors which affect the weight change (and possibly dimensions) of polymers. 

RUI Ruiz-Alsop, R.N., Mueller, P.A., Richards, J.R., Kao, C.-P.C., and Brown, G.G., Simultaneous in-situ measurement of sorption and swelling of polymers in gases and supercritical fluids, J. Polym. Sci. PartB Polym. Phys., 49, 574, 2011. 

BON Bonavoglia, B., Storti, G., Morbidelli, M., Rajendran, A., and Mazotti, M., Sorption and swelling of semicrystalline polymers in supercritical CO2, J. Polym. Sci. Part B Polym. Phys., 44, 1531, 2006. 

Guadagno, T. and S.G. Kazarian, High-pressure C02-expanded solvents Simultaneous measurement of C02 sorption and swelling of liquid polymers with in-situ near-IR spectroscopy. Journal of Physical Chemistry B, 2004. 108(37) p. 13995-13999. 

Reprinted with permission from Kni R, Storti G, Mazzotti M, Tai H, Shakesheff KM, Howdle SM. Sorption and swelling of poly(DL-lactic acid) and poly(lactic-co-glycolic acid) in supercritical CO2 an experimental and modeling study. J Polym Sci Part B Polym Phys 2008 46 483—96. Copyright 2008 Wiley Periodicals, Inc. 

Eikerling, M. and Berg, P. 2011. Poroelectroelastic theory of water sorption and swelling in polymer electrolyte membranes. 7(13), 5976-5990. 

In order to account for the well known sorption and swelling properties of polymer ion exchangers, Helfferich s model [427] is frequently used for liquid phase reactions. According to this, the pore liquid of the resin, where the reaction occurs, is treated as a homogeneous system and the reactant is assumed to be distributed according to a distribution coefficient... 

H. Rave, R. Staudt, J.U. Keller Measurement of sorption and swelling behaviour of polymer/C02 systems by a combined oscillometric-gravimetric method. Proeedings. of P3AC2, Brisbane, May 14-18, 2000, World Scientific, Singapore 2000. 

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. ... 

Potential interactions of a supercritical fluid with a polymeric material may include the following (i) sorption of carbon dioxide by polymers (ii) swelling of polymers by carbon dioxide (Hi) dissolution of polymers in carbon dioxide (iv) dissolution of carbon dioxide in polymers (v) plasticization and decrease of the glass transition... 

B Singh et al, Metal ion sorption and swelling studies of psyllium and acrylic acid based hydrogels , Carbohydrate Polymers, 2006 64 50-56. 

The diffusion and permeabihty are closely interconnected with the solubility of a polymer. The permeation of the permeants through polymeric membrane film occurs in three stages (1) Sorption includes the initial adsorption, absorption, penetration, and dispersal of penetrant into the voids of the polymer membrane surface and cluster formation. The distribution of permeant in the membrane may depend on penetrant size, concentration, temperature, and swelling of the matrix as well as on time. The extent to which permeant molecules are sorbed and their mode of sorption in the polymer depends upon the enthalpy and entropy of permeant-polymer mixing, i.e., upon the activity of the permeant within the polymer at equilibrium. When both polymer-permeant and permeant-permeant interactions are weak relative to polymer-polymer interactions, i.e., dilute solution occurs, Henry s law is obeyed. The solubihty coefficient S is a constant independent of sorbed concentration at a given temperature. (2) Diffusion includes the transfer of the penetrant through the polymer membrane which depends on penetrant concentration that leads to a plasticization effect, penetrant size and shape, polymer Tg, time, and temperature. The diffusion coefficient is determined by Pick s first law of diffusion. (3) Desorption includes release of the penetrant from the opposite side of the membrane face. 

The slope change apparent in both experimental and calculated data corresponds to the transition from gas to denser supercritical state taking place for CO2 at about 75 bar. The dependence of sorption and swelling behavior on the copolymer composition is highly nonlinear, confirming the need of reliable models and parameter values to design the polymer treatment in a proper way. 

The theory of bundle formation in the section Aggregation Prenomena in Solutions of Charged Polymers provides sizes, as well as electrostatic and elastic properties of ionomer bundles. The theory of water sorption and swelling, described in this section, gives a statistical distribution of pore size and local stress in pores. The merging point of both theories is a theory of fracture formation in charged polymer... 

In membrane research, Michael has developed a poroelectroelastic theory of water sorption and swelling together with Peter Berg (NTNU Trondheim). It rationalizes the impact of external conditions, statistical distribution of anionic head groups, and microscopic elastic properties of the polymer on water sorption and swelling. This work has opened up an intriguing research area the study of internal mechanical stresses in charged elastic media, induced by water sorption. 

To study the C02-induced plasticization, different techniques can be applied, for example, gas sorption and polymer swelling [26, 27] in-situ FTIR spectroscopy [28, 29], NMR spectroscopy [30], and dynamic light scattering [31]. Two new techniques for simultaneous sorption and swelling measurement have been proposed, based on detection of the volume change of the polymer sample measured by mercury displacement [32], and on gravimetric measurement [33], respectively. 

In the case of moderate interactions of carbon dioxide with the polymer, substantial levels of sorption and swelling can occur. The swelling of the polymer significantly enhances diffusivities of solutes in the polymer matrix, allowing for rapid extraction, impregnation, shaping, and blending processes. Extraction applications include removal of residual monomers, solvents, and catalysts [84, 85]. An impor-... 

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