Predicting the conformity of packaging materials - THESIS

Plastic materials contain additives, which are not fixed in the polymer matrix and may migrate into food. European Directive 2002/72 introduced the possibility of demonstrating the food contact suitability of these materials using predictive approaches, the application of which is limited by the availability of formulation and physico-chemical data. This work aims to adapt and develop rapid analytical approaches for identifying and quantifying the major substances contained in plastics, and to develop a generic approach for predicting partition coefficients between polymers and food simulants. Conventional solvent extraction and HPLC-UVDEDL and GPC-FID quantification methods were compared for four model HDPE and PS formulations. A rapid deconvolution method for infrared spectra of HDPE extracts was developed to identify and quantify additives. A predictive model of activity coefficients in PE and simulants is proposed. The enthalpic and non-configurational entropic contributions are evaluated by sampling pairwise contact energies. It is shown that the configurational entropic contribution is essential for describing the affinity of large molecules in polar simulants or simulants not made up of small molecules. Decision trees combining experimental and model approaches are finally discussed in the logic of compliance demonstration and health monitoring.

Plastic packagings are formulated with additives, which can migrate from materials into foodstuffs. According to European directive 2002/72/EC, the ability of plastic materials to be used in contact with food can be demonstrated using modelling tools. Their use is however limited due to availability of some data, like the formulation of materials and partition coefficients of substances between plastics and food. On the one hand this work aims to develop the ability of laboratories to identify and quantify the main substances in plastic materials, and on the other hand it aims to develop a new method to predict partition coefficients between polymers and food simulants. Four formulations of both HDPE and PS were chosen and used during the work. Standard extraction- methods and quantification methods using HPLC-UV-ELSD and GC-FID were compared. A new deconvolution process applied on infrared spectra of extracts was developed to identify and quantify additives contained in HDPE. Activity coefficients in both phases were approximated through a generalized off-lattice Flory-Huggins formulation applied to plastic materials and to liquids simulant of food products. Potential contact energies were calculated with an atomistic semi-empirical forcefield. The simulations demonstrated that plastic additives have a significant chemical affinity, related to the significant contribution of the positional entropy, for liquids consisting in small molecules. Finally, decision trees, which combine both experimental and modelling approaches to demonstrate the compliance of plastic materials, were discussed.