Design of modified plastic surfaces for antimicrobial applications: Impact of ionizing radiation on the physical and mechanical properties of polypropylene

Surface modification of polypropylene (PP) sheets was carried out by radiation induced graft polymer- ization of hydrophilic functional molecules such as N,N-dimethylacrylamide (DMA) and [2-methacry- loyloxy)ethyl] trimethylammonium chloride, which is a quaternary ammonium salt (QAS). Polypropylene sheets were activated prior to the grafting reaction by using electron beam radiation. The changes in morphology, crystallinity and tensile parameters like deformation and stress at yield and deformation at break of PP after irradiation were investigated. The results showed that a minor crystalline reorganization takes place during the irradiation of PP at 100 kGy. The grafting has been observed to be strongly dependent on the monomer dilution in the reaction medium. After grafting of QAS (40%) and DMA (20%) it was possible to develop highly hydrophilic surfaces (water contact angle comprised between 30 and 411). The surfaces of virgin, irradiated and grafted PP were studied using polarized optical microscopy (POM) and scanning electron microscopy (SEM). Spherical particles (i.e. polystyrene or silica beads) adhering to the modified samples were studied according to the surface parameters. Adhesion tests confirmed the strong influence of substrate type (mainly hydrophilicity and roughness) and to a lesser extent underlined the role of electrostatic interactions for the design of plastic surfaces for antimicrobial applications

Thermodynamics of migration in polymers: Can contamination from materials in contact be predicted, controlled and possibly avoided?

The contamination from materials is coined as “migration” and refers to a combination of various mass transfer mechanisms under thermodynamic control: molecular or mutual diffusion, sorption and desorption phenomena linear with concentration or not. The contamination pathways are particularly complicated when they involve several components or steps and strong interactions between materials and the medium in contact. They have been studied and mathematically described with two possible purposes: i) simplified approaches with a goal of overestimating the real contamination and ii) more sophisticated approaches to optimize the design of polymer materials, packaging materials or to redesign plastic additives with lower migration risk and toxicological hazard (e.g. plasticizers, surfactant, etc.). The simplified descriptions use conventional Fick equations and proper partition rules to enable decision making – Is the contamination acceptable or not? – without requiring a perfect understanding of underlying phenomena. The approach has been chosen in EU to regulate food contact materials and is used somehow for food contact notifications in US. It has been applied to the diffusion in various polymers and is currently under extension for elastomers and varnishes. A rigorous formulation using a probabilistic resolution of transport equations provides a justification of such intuitive assumptions while minimizing both contamination levels and adverse risks (i.e. discarding falsely a good material). These theoretical results demonstrated that migration in closed systems by materials was obeying to prescribed statistical laws and that it could be managed robustly through conventional risk assessment approaches [1]. Special methodologies have been recently developed to cover the whole supply chain [2]. More sophisticated approaches seek relationships between the chemical structures of contaminants and polymers and their mass transfer properties. Several calculation procedures have been proposed and tested over the last decades including semi-empirical models, models derived from molecular thermodynamics and brute force molecular simulation [3,4]. An overview of current capabilities of prediction based on the sole chemical structure is presented. Among the most effective techniques, generalized Flory-Huggins approximations at atomistic scale enable tailored calculation of partition coefficients (or equivalently excess-chemical potentials) with reasonable accuracy for almost any contaminant, polymer or co-polymer and media in contact [5-9]. Similar breakthroughs have been proposed for diffusion coefficients based on a generalized free-volume theory [10] and solute classification [11]. Experimental and theoretical results demonstrate that adding flexible segments and symmetry axes close to the center-of-mass in additives could reduce diffusion coefficients of several magnitude orders and accordingly migration. When no data are available on the initial compositions or the identity of possible migrants, rapid deconvolution techniques have been shown to be effective for plastic materials [12,13]

The ubiquitous issue of cross-mass transfer: applications to single-use systems

The leaching of chemicals by materials has been integrated into risk management procedures of many sectors where hygiene and safety are important, including food, medical, pharmaceutical, and biotechnological applications. The approaches focus on direct contact and do not usually address the risk of cross-mass transfer of chemicals from one item or object to another and finally to the contacting phase (e.g., culture medium, biological fluids). Overpackaging systems, as well as secondary or ternary containers, are potentially large reservoirs of non-intentionally added substances (NIAS), which can affect the final risk of contamination. This study provides a comprehensive description of the cross-mass transfer phenomena for single-use bags along the chain of value and the methodology to evaluate them numerically on laminated and assembled systems. The methodology is validated on the risk of migration i) of -caprolactam originating from the polyamide 6 internal layer of the overpackaging and ii) of nine surrogate migrants with various volatilities and polarities. The effects of imperfect contacts between items and of an air gap between them are particularly discussed and interpreted as a cutoff distance depending on the considered substance. A probabilistic description is suggested to define conservative safety-margins required to manage cross-contamination and NIAS in routine

Practical guidelines on the application of migration modelling for the estimation of specific migration

The aim of this practical guidance document is to assist the users of the described diffusion models to predict conservative, upper bound specific migration values from plastic food contact materials for compliance purposes. Explanatory guidance tables and practical examples of migration modelling are provided. This document is an updated version of the report "Estimation of specific migration by generally recognised diffusion models in support of EU Directive 2002/72/EC" (Simoneau, 2010) concerning the current legal basis (Regulation (EU) No 10/2011) and the use of migration models for the estimation of specific migration from plastic multi-layers. This document represents the current validity of the models based on constant periodical evaluations of new experimental migration data performed by the Task Force on Migration Modelling chaired by the Directorate General Joint Research Centre of the European Commission on behalf of Directorate General Health and Consumers. The members of the Task Force are R. Brandsch, C. Dequatre, E.J. Hoekstra, P. Mercea, M.R. Milana, A. Schäfer, C. Simoneau, A. Störmer, X. Trier and O. Vitrac.JRC.I.1-Chemical Assessment and Testin

The fate of food packaging substances: cross-contaminations, migrations…a main challenge for the 21st century

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La sécurité des emballages alimentaires en question

National audienceReady-to-eat food and our unstructured diets have resulted in the widespread use of food packaging. The toxicity of the substances is not the only issue with regard to the risks of chemical contamination posed by packaging materials. Our knowledge of the phenomena which lead to food contamination raises further questions.Le prêt-à-manger et l’alimentation déstructurée ont imposé l’usage généralisé des emballages alimentaires. La toxicité des substances n’est pas la seule à être mise en cause dans les risques de contamination chimique que font courir les matériaux des emballages. Notre connaissance des phénomènes qui conduisent à la contamination des aliments est également impliquée

Migration modeling related to food contact materials: present and future

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