Studying the diffusion of erucamide in linear low density polyethylene films using FTIR microspectroscopy

Surface modifying additives such as slip agents, antistatic agents, and antifogging agents are commonly used to tailor the surface properties of polymer products. These additives exude to the film surfaces due to incompatibility of the additive and polymer, surface-energy differences, or morphological differences between the surface and bulk regions of a film. An optimal amount of an additive is desired at the surface for superior performance over the intended use-time. This research focused on prediction of bulk-to-surface segregation and the distribution of a surface-modifying additive across the thickness of a polymer film. Mass-sorption experiments demonstrated that the diffusion of a slip agent, erucamide, in linear low density polyethylene (LLDPE) films was Fickian. The diffusivity of erucamide in LLDPE was measured using mass-sorption and observed to have an Arrhenius dependence on temperature. Diffusion-out, or additive diffusion from the bulk to the surfaces of a film, was studied experimentally at 35;The diffusion-out process was modeled using Fickian diffusion equations with unsteady state, accumulation-type boundary conditions that account for the observed build-up of additive at the film surfaces. The important parameters in the model are the diffusivity of additive in the polymer and a surface parameter that depends on the additive-polymer compatibility and on the surface energetics. The model predicts time-dependent additive concentration profiles across the film thickness, the time required for the system to attain equilibrium, and the surface concentration at equilibrium. The model also predicts the equilibrium partitioning of the additive between the surface and bulk regions of the film. The model parameters were obtained from independent measurements and then used in the model to predict concentration profiles, which matched the experimental data reasonably well, especially in the bulk of the film. Suggestions have been made to improve the model predictions by accounting for an additional resistance to the mass transfer process at the film surfaces.