Features of Modelling the Kinetics of Extraction of Plasticisers from Polyvinyl Chloride

Approaches to Modelling the Kinetics of Extraction of Plasticisers from Polyvinyl Chloride

“…The extraction of plasticisers from PVC with liquids has a number of peculiar features by comparison with their evaporation (contact of the polymer with air) and migration (contact of the polymer with solid materials capable of absorbing the released ingredient). A specific feature of desorption of plasticisers from PVC is a reduction in the rate of the process after loss of a certain proportion of ingredient [1,2]. Under conditions of retention of the initial polymer-surrounding medium boundary, which is realised in the case of evaporation, migration, and partially during extraction, a cause of change in the desorption rate is the glass transition of the polymer with reduction in the plasticiser content.…”

“…The kinetic parameters include the coefficients of diffusion of the plasticisers in the PVC and the surrounding medium, and also the volatility of the plasticisers, which is used in equations for predicting the evaporation rate. In a number of cases, the equations of the mathematical models contain additional coefficients reflecting correction of these models when comparing experimental results and prediction, and the deviation of the content of plasticisers from equilibrium solubility in the polymer or surrounding medium [5][6][7].…”

“…For prediction of the kinetics of evaporation [5], extraction [6,7], and migration [8] of plasticisers, the authors substantiated the basic possibility of using the Calvert-Billingham mathematical model [4] developed for predicting the kinetics of evaporation of stabilisers from polyolefin films. The equation for predicting the kinetics of desorption of plasticisers from PVC with a diffusion limiting stage of the process has the form:…”

“…where τ i is the sorption time of a certain part of the ingredient, l is a parameter linking the film thickness (δ) and the conditions of its contact with the surrounding medium (with one-sided contact l = δ, with two-sided contact l = δ/2), D is the coefficient of diffusion of the plasticiser in the polymer, and a i is a coefficient whose magnitude depends on the specified ratio M τ /M 0 [4], which in explicit form does not enter equation (2).…”

“…The development of empirical models based on equation 1is connected with possible exclusion of the dependence of coefficient k on the experimental conditions. To this end, the dependence of coefficient k on the molecular weight of the plasticisers [6], their initial content, and the temperature of the surrounding medium [10], and also on the thickness of the PVC films and the conditions of their contact with the surrounding medium [10], was established.…”