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Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 142-146
Plasticizer Migration from Plasticized Poly(viny1 chloride) into Liquids. Effect of Several Parameters on the Transfer Djelloul Messadi, Jean-Louls Taverdet, and Jean-Maurlce Vergnaud + Laboratory of Industrial Chemistry, U.E.R. of Sciences, 23, r. du Docteur Paul Michelon, 42023 Saint-€t/enneC&ex, France
The migration of dioctyl phthalate as plasticizer was studied from PVC (poly(viny1chloride)) into several liquids such as methanol, n -heptane, benzyl alcohol, ethanolic solutions in water, and peanut oil. Diffusion coefficients were measured by considering a nonsteady-state phenomenon for different plasticizer concentrations. The importance of the following parameters was pointed out: plasticizer concentration, temperature, and kind of liquid. Diffusivity was found to vary with the temperature for all the liquids according to Arrhenius' law except for n-heptane, whose transfer did not depend on the temperature. A simultaneous transfer of liquid into PVC and of plasticizer from PVC into liquid was pointed out especially for benzyl alcohol as the liquid. I n this case the amount of liquid transferred into PVC increased at the beginning of the immersion, reached a maximum, and then decreased. The profile of the plasticizer concentration developed inside the PVC was determined at different times.
Introduction PVC plays an important role in the plastics industry. In most plastics producing countries, PVC is the leading plastic material. In others, for instance the USA and Japan, it is second only to polyethylene. The greater part of PVC is used as soft or plasticized PVC, and PVC applications consume approximately 80% of the total production of plasticizer. In most applications, a plasticized PVC is in contact with some kind of surrounding medium: gas, liquid, or solid. Under these conditions, the plasticizer may stay in place, or it may migrate to the surrounding media with the following results: (1) a loss of plasticizer and considerable change in mechanical properties of the PVC; (2) the surrounding medium is contaminated by the plasticizer or by other additives. This contamination was found to be a serious problem in liquid foods (Haesen and Schwarze, 1978; Woggon L id Kohler, 1967; Vom Bruck et al., 1971; Figge, 1972,197ti; Gilbert, 1976; Leimgruber, 1974; Koros and Hopfenberg, 1979), drugs, cosmetics, and pure chemicals (Kampouris, 1975a,b; Troparevsky et al., 1976). A large part of the literature in this field is generally based on short time tests and pure products used as simulants for commercial materials. For instance, n-heptane is recommended as simulant for fatty oils by the Food and Drug Administration. Possible factors which affect the migration process can be classified (Messadi and Vergnaud, 1980; 1981a,b) in relation to: (i) the polymer, i.e., molecular weight; (ii) the plasticizer, nature and amount; the plasticization process and the homogeneity of the compound; (iii) the surrounding media, i.e., nature, compatibility with the plasticizer, and effect on polymer; and (iv) the conditions of the test, Le., time and temperature. In the present work (Vergnaud et al., 1981b), the mathematics was of significance, and the following parameters were studied. (1)The mathematical treatment is of significance and several equations have been tested. ( 2 ) The stirring of the liquid plays an important role a t the beginning of the transfer. (3) There is a dependence of the kind of liquid on the transfer of plasticizer into the liquid (and vice versa). (4)There is an influence of other parameters such as temperature, time, and percentage of plasticizer in the PVC. Theoretical Section Plasticized PVC disks were soaked in the liquid, and the plasticizer transfer took place from the PVC into the liquid 0196-4321/83/ 1222-0142$01.50/0
by a two-step process, as described recently (Messadi and Vergnaud, 1980; 1981a,b): (1)a plasticizer transfer in the PVC itself by internal diffusion; It was studied by assuming a non-steady state phenomenon; (2) a plasticizer transfer through the PVC-liquid interface from the solid into the liquid, and diffusion of plasticizer in the liquid. The following assumptions were made: (i) The problem was treated as a non-steady-state phenomenon, and the transfer was described by Fick's laws. (ii) The diffusivity D of plasticizer was considered to be independent with the concentration. (iii) PVC disks were considered as plane sheets having a thickness of 21. The plane sheets of PVC were so thin that all the diffusing substance effectively entered through the plane faces and a negligible amount through the edges. The diffusion equation in one dimension reduced to
where C was the plasticizer concentration at time t and the abscissa x was taken along the thickness of PVC disk. 1. Case of an Infinite Volume of Liquid. The initial conditions were t=O;-l
