Modelization of matter transfers between plasticized PVC and liquids in case of a maximum for liquid‐time curves

Abstract

SynopsisWhen plasticized PVC and liquids are contacted with each other, as in liquid and packaging, some matter transfer may occur. The phenomenon is complicated, and no analytic solution can be found. A simultaneous transfer of the liquid into and plasticizer out from the PVC mass takes place with concentrationdependent diffusivities. Very often, liquid concentrationtime curves have a maximum, when the rate of transfer is higher for the liquid than for the plasticizer at the beginning of the contact. Another application of short tests has been obtained with success in this hard case. A new model using short test data has been developed. It takes into account not only the diffusion of both liquids through the PVC, but also matter transfers through the liquid-PVC interface with a coefficient of matter transfer, as well as the data corresponding to the equilibrium. Some information of interest is given by way of the materials transferred through PVC faces, and the profile of concentration through the PVC for the liquid and plasticizer.

Transport phenomena into and out of plasticized PVC sheets: The influence of sample history

“…On the other hand, no considerable plasticization effect should be expected from the liquid medium penetrated if separation of the latter in a second phase O C C U~S .~ A great amount of research work has been oriented in establishing and solving the corresponding implications of the diffusion mathematics due to the complexity of the total behavior, but the general applicability of some of the models proposed remains limited. Nevertheless, simple migration models are often proposed, based on Fick's law with constant diffusion coefficients, simple boundary conditions, negligible relaxation effects, and constant polymer volume.35 Thus, in agreement with previous studies on migration phenomena, [10][11][12]14,16,18,19,[21][22][23][24] the following well-known Fickian approximation for short times is considered MS,/MS, = 2 ( D t /~l~)~/~ (1) where MS, denotes the total amount diffused (of plasticizer migrated or liquid counterdiffused) at time t, MS, the corresponding quantity after infinite time, and D the diffusion coefficient. The PVC specimens are considered as plane sheets having a thickness 21.…”

“…'~-~~ It is evident, however, that the prior sorption and thermal history does not affect next sorption cycles in rubbery polymer systems due to their rapid response to changes in ambient ~o n d i t i o n s .~~~~~,~~ Previous efforts on history include the investigation of concentration profiles in two-stage plasticizer migration experiments to prove that extraction results in surface-depleted concentration profiles. 16 In both stages the liquid environment employed was n -heptane, which, however, readily diffuses into the PVC.14 In our studies paraffin oil is used instead for the stage of the initial desorption ("first stage"). Paraffin oil comprises a high viscosity medium for which counterdiffusion effects are safely excluded, as experimentally proved in previous paper^.…”

Absorption and Desorption of Water in a Wood Beam, Below and Beyond the Fiber Saturation Point, with Three-Dimensional Diffusion

“…The sample is parallelepipedic with square cross-section; the diagonals of this are directed along two principal axes (tangential and radial). Each principal diffusivity is determined by using the short test method used previously in many cases (Taverdet and Vergnaud 1984;Taverdet and Vergnaud 1986;Droin-Josserand etal. 1988), and a thin sheet of wood protected in such a way that only the transport through the thickness can take place.The rate of evaporation is obtained from the kinetics of desorption, at the beginning of the process when the water concentration is known and uniform.…”

Safety and quality of plastic food contact materials. Optimization of extraction time and extraction yield, based on arithmetic rules derived from mathematical description of diffusion. Application to control strategies

“…The relative time required for a given extraction yield (M F,t /M F,∞ ) can be calculated from equation (4), assuming that samples are parallelepipeds of dimensions L, L 1 , L 2 . Equation (6) was also used for comparison.…”

“…4,5 A numerical model is necessary to take each fact into account. The process of release of contaminants out of a polymer into a liquid can be simplified by considering only their diffusion through the polymer thickness.…”