Equilibrium swelling in binary solvents

Vasiliy V. Tereshatov, Valery Yu. Senichev Institute of Technical Chemistry E.Ya. Denisyuk Institute of Continuous Media Mechanics Ural Branch of Russian Academy of Sciences, Perm, Russia 

Depending on the purposes and operating eonditions of polymer material processing, the opposite demands to solubility of low-moleeular-mass liquids in polymers exist. The produets of polymer materials designed for use in eontact with solvents should be stable against relative adsorption of these liquids. On the eontrary, the well dissolving polymer solvents are necessary to produce the polymer films. The indispensable condition of creation of the plasticized polymer systems (for example, rubbers) is the high thermodynamic compatibility of plasticizers with the polymer basis of material. 

it immediately follows the statement of the problem of regulation of thermodynamic compatibility of polymers with low-molecular-mass liquids in a wide range of its concentration in polymer material. The problem of compatibility of crosslinked elastomers with mixed plasticizers and volatile solvents is thus of special interest. 

Depending on ratios between solubility parameters of the solvent 1, 5i, of the solvent 2, and polymer, solvents can be distinguished as symmetric liquids and non-sym-metric ones. The non-symmetric liquids are defined as a mixture of two solvents of variable composition, solubility parameters 8, and 8 which are larger or smaller than solubility parameter of polymer ( 8 2, 8,). The symmetric liquid (SL) with relation to 

1 -toluene-acetone, 2-eyelohexane-acetone, 3-heptane-acetone. [Adapted, by permission, from V. V. Tereshatov, M. I. Balashova, A. I. Gemuev, Prediction and regulating of properties of polymeric materials, Ural Branch of AS USSR Press, Sverdlovsk, 1989, p. 3.] 

Depending on ratios between solubility parameters of the solvent 1,8i, of the solvent 2, and polymer, solvents can be distinguished as symmetric liquids and non-sym- 

07 kmol/m ] and crosslinked elastomer of butadiene-nitrile rubber = 19 (MJ/m ) , (yJVo)x = 005 kmoEm ]. 

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If the Xi23 value is considered as a criterion of existence of a maximum of equilibrium swelling of polymer in the mixed solvent, a maximum of Q should correspond to the minimum of %i23. For practical use of Eq. [6.2.2] it is necessary to know parameters 5 13,5 23, and Xn- The values X13 and X23 can be determined by the Flory-Rehner equation, with data on swelling of a crosslinked elastomer in individual solvents 1 and 2. The evaluation of the Xn value can be carried out with use of results of the experimental evaluation of vapor pressure, viscosity and other characteristics of a binary mixture. ... 

F or the high accuracy of the analysis of binary solvent composition, a volatile solvent, hexane, was used as a component of SL in most experiments. Following the attainment of equilibrium swelling, the samples were taken out of SL and held in air until the full evaporation of hexane, that was controlled by constant mass of sample. A content of a nonvolatile component of SL in elastomer was determined by the difference between the amount of liq-... 

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