Effect of an Organo-Modified Montmorillonite on the Barrier Properties of PET Nanocomposites Using a Polyester Ionomer as a Compatibilizing Agent

© 2017 Materials Research. 2017; 20(3): 826-834 DOI: http://dx.doi.org/10.1590/1980-5373-MR-2016-0751 Effect of an Organo-Modified Montmorillonite on the Barrier Properties of PET Nanocomposites Using a Polyester Ionomer as a Compatibilizing Agent Suel Eric Vidottia*, Anne Cristine Chinellatoa, Guo-Hua Hub, Luiz Antonio Pessanc Centro de Engenharia, Modelagem e Ciências Sociais Aplicadas, Universidade Federal do ABC (CECS/UFABC), Avenida dos Estados, 5001, Bloco A, Torre 1, sala 618, Bairro Santa Terezinha, CEP: 09210-580, Santo André, SP, Brazil b Laboratoire Réactions et Génie des Procédés (CNRS UMR 7274), Ecole Nationale Supérieure des Industries Chimiques (LRGP/ENSIC), Université de Lorraine, 1 rue Grandville, BP 20451, Nancy F-54001, France c Departamento de Engenharia de Materiais, Universidade Federal de São Carlos (DEMa/UFSCar), Via Washington Luiz, km 235, P. O. Box 676, 13565-905 São Carlos, SP, Brazil a Received: October 04, 2016; Revised: March 15, 2017; Accepted: April 21, 2017 Poly(ethylene terephthalate)/organically modified montmorillonite (PET/o-Mt) nanocomposites were prepared via melt intercalation in a twin-screw extruder using a polyester ionomer (PETi) as compatibilizer. The o-Mt content used was 0, 1, 3 or 5 wt% and the compatibilizer/o-Mt mass ratio was 0/1, 1/1 or 3/1. The main objective was to study the effects of the addition of o-Mt and compatibilizer on the barrier properties of PET/o-Mt nanocomposites. The nanocomposites showed a significant reduction in CO2 permeability of up to 50% when compared to the neat PET, without significant change in the CO2 solubility revealing the importance of the diffusional path imputed by the organoclay on the overall permeation process. Water vapor permeability was reduced for all nanocomposites, achieving up to 30% reduction for the nanocomposite containing a compatibilizer/o-Mt mass ratio of 1/1. Overall, the nanocomposite containing 5 wt% of organoclay and compatibilizer/o-Mt mass ratio of 1/1 showed the best barrier properties. Keywords: PET nanocomposite, Organoclay, Polyester ionomer compatibilizer, Barrier properties, Permeability 1. Introduction The use of nano-scale fillers has led to the development of polymer nanocomposites and has provided a potential alternative to conventional polymer composites. Polymerlayered silicate nanocomposites prepared with an organically modified montmorillonite (o-Mt) are of increasing interest for packaging applications. These nanocomposites show improved mechanical and barrier properties compared to the corresponding neat polymer matrix and conventional composites due to the nano-scale reinforcement and the tortuous diffusion path caused by the high aspect ratio of aluminosilicate layers1-5. In order to maximize these benefits it is necessary to achieve a high level of organoclay exfoliation, uniform distribution and appropriate orientation of clay platelets6-9. Among various processes, the following two are considered as being commercially attractive for preparing layered silicate based polymer nanocomposites: in situ polymerization and melt compounding10,11. The second one is especially appealing because classical melt compounding equipment and standard processing conditions can be used. Depending on the nature of the components used (layered * e-mail: silicate, organic modifier, polymer matrix and compatibilizer) and preparation process, three main types of composites may be obtained: conventional composite and intercalated or exfoliated nanocomposites10. In conventional composites, the polymer is unable to intercalate silicate layers. Thus its properties are not very different from that of traditional microcomposites. Intercalated nanocomposites show a well-ordered multilayered structure (alternating polymer and inorganic layers) in which polymer chains are inserted into the interlayer spaces between individual silicate layers. Exfoliated nanocomposites are achieved when individual silicate layers are completely separated and uniformly distributed in the polymer matrix10. Properties of intercalated and exfoliated nanocomposites are usually significantly improved compared to conventional composites or the neat polymer. However, it is not always possible to reach an intercalated or exfoliated state of dispersion of layered silicate particles by melt compounding12. Optimal mixing conditions and adequate surface treatment of silicates should be applied to prepare exfoliated nanocomposites12-16. The use of polymers containing polar functional groups and/or ionomers as compatibilizers also promotes the dispersion of silicates and may lead to intercalated and/or exfoliated nanocomposites17-21. Effect of an Organo-Modified Montmorillonite on the Barrier Properties of PET Nanocomposites Using a Polyester Ionomer as a Compatibilizing Agent The gas permeation in a homogeneous polymer matrix is governed by a mechanism of diffusion and solubility. The diffusion coefficient (D) describes the kinetic aspect of the transport whereas the solubility coefficient (S) reflects the penetrant/polymer affinity and the thermodynamic aspect of the transport. In the case of a Fickian transport, the permeability coefficient (P) can be expressed by22: P = D.S (1) 827 This work was concerned with the preparation of poly(ethylene terephthalate)/organically modified montmorillonite (PET/oMT) nanocomposites via melt compounding, using a polyester ionomer as compatibilizer. The main objective was to study the effects of the concentrations of o-MT and compatibilizer on the barrier properties of these nanocomposites. 2. Experimental 2.1. Materials A similar model has been considered to describe the gas transport properties of composites in which impermeable fillers are dispersed in a polymer matrix. Assuming that the filler does not absorb or conduct the penetrant, the local polymer matrix is not affected by the presence of the filler and the polymer/filler interactions are sufficiently strong enough to avoid void formation at the interfaces, the gas solubility in the composite can be expressed as23: S = S 0 (1 - z) (2) where S0 is the penetrant solubility coefficient in the pure polymer matrix and ϕ is the volumetric fraction of particles dispersed in the matrix. In this approximation, the penetrant solubility does not depend on the morphological features of the phases. However, the diffusion process of the penetrant is more complex. The particles act as impenetrable barriers so that the penetrant must follow an elongated (or tortuous) path in order to diffuse through the composite24. The diffusion rate of the penetrant is slowed down and can be expressed as: D = D 0 /x (3) where D0 is the diffusion coefficient in the neat polymer, D the apparent diffusion coefficient in the nanocomposites and τ the tortuosity. For semi-crystalline polymers the permeation process is even more complex. Semi-crystalline polymers are discussed as materials consisting of two phases, namely th (...truncated)