Superficial Modification in Recycled PET by Plasma Etching for Food Packaging S. A. Cruz, 1 M. Zanin, 2 P. A. P. Nascente, 2 M. A. Bica de Moraes 3 1 Centro de Engenharia, Modelagem e Cie ˆncias Sociais Aplicadas, Universidade Federal do ABC, Rua Santa Ade ´lia 166, CEP 09.210-170, Santo Andre ´, Brasil 2 Departamento de Engenharia de Materiais, Universidade Federal de Sa ˜o Carlos, Rod. Washington Luı ´s, Km 235, CEP 13565-905, Sa ˜o Carlos, Brasil 3 Instituto de Fı ´sica, Universidade Estadual de Campinas, Cidade Universita ´ria Zeferino Vaz, CEP 13083-970, Campinas, Brasil Received 27 December 2007; accepted 21 December 2008 DOI 10.1002/app.29958 Published online 26 October 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: An oxygen plasma treatment has been used to improve the adhesion of amorphous hydrogenated car- bon (a-C:H) films onto surfaces of recycled poly(ethylene terephthalate) (PET). Modifications produced by the oxygen plasma on the PET surface in chemical bonds and morphol- ogy were investigated by X-ray photoelectron spectroscopy and atomic force microscopy, respectively. Contact angle measurements were used to study the changes in the sur- face wettability. Adhesion of the a-C:H film onto the PET surface was investigated by the tape test method. It was observed that the improvement in film adhesion is in good correlation with the increase in surface roughness, due to plasma etching, and with the appearance of oxygen-related functional groups at the surface. The results of this study indicate that a-C:H-coated recycled PET can be used in food packaging. The a-C:H film could be used as a functional barrier to reduce or prevent migration of contaminants from the polymer to the package content. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2728–2733, 2010 Key words: PET; recycling; plasma; etching; adhesion; coating INTRODUCTION Amorphous hydrogenated carbon (a-C:H) films have been widely used as protective coatings in a variety of materials for applications such as gas barriers, gas separations membranes, 1,2 and ultimately as a func- tional barrier to avoid or reduce the migration of possible residual contaminants in packaging made by recycled polymers. 3 Poly(ethylene terephthalate) (PET) is one of the most applied materials used for bottle fabrication in the soft drinks market. The principal of PET application is in blow-molded packaging. Thus, it would be extremely useful if this material could be treated in such a way as to return it to a form suitable to its original purpose. However, restrictions still exist to the use of the recycled material in direct contact with food because of the possibility of contaminant migration. 4,5 This problem can be avoided using a functional barrier, which can be a layer of virgin material placed between the recycled polymer and the food. This layer could reduce the migration of possible residual contami- nants. 6 In general, the ability of functional barriers to prevent or reduce the migration of contaminants is dis- cussed in terms of models stipulated by the Food and Drugs Administration (FDA) of USA. 7 Cruz et al. 3 verified the feasibility of the use of recycled PET for food packaging employing an internal coating made from a-C:H film deposited by plasma-enhanced chemi- cal vapor deposition (PECVD) process. To verify the efficiency of the carbon layer as barrier for contami- nants, PET samples were deliberately contaminated with a series of surrogates using a FDA protocol. They concluded that the carbon-coated material increases the chemical resistance to a series of surrogates (chlo- roform, toluene, benzophenone, and lindane), which represents the behavior of different chemical families. The samples were analyzed using a solid-phase micro- extraction coupled to GC-MS. a-C:H films could be used as a functional barrier in food packaging. The films are usually applied by PECVD. However, bulges or cracks may appear in the films as a consequence of the high internal stress of these materials. As flaw formation benefits from poor adhe- sion, processes leading to the strong adhesion of the bar- rier coating onto the plastic package surface are a major concern. Fortunately, increases in the adhesion of a film onto a substrate can be improved by previous treatments of the substrate surface. In a polymer surface, the main modifications produced by plasma treatment are etching Journal of Applied Polymer Science, Vol. 115, 2728–2733 (2010) V V C 2009 Wiley Periodicals, Inc. Correspondence to: S. A. Cruz (sandra.cruz@ufabc.edu.br).