Characterization of Poly(ε-caprolactone)-Based Nanocomposites Containing Hydroxytyrosol for Active Food Packaging Ana Beltra ́ n, † Artur J. M. Valente, ‡ Alfonso Jime ́ nez, † and Marı ́ a Carmen Garrigó s* ,† † Analytical Chemistry, Nutrition & Food Sciences Department, University of Alicante, 03080 Alicante, Spain ‡ Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal ABSTRACT: Antioxidant nanobiocomposites based on poly(ε-caprolactone) (PCL) were prepared by incorporating hydroxytyrosol (HT) and a commercial montmorillonite, Cloisite30B (C30B), at different concentrations. A full structural, thermal, mechanical, and functional characterization of the developed nanobiocomposites was carried out. The presence of the nanoclay and HT increased PCL crystallinity, whereas some decrease in thermal stability was observed. TEM analyses corroborated the good dispersion of C30B into the PCL macromolecular structure as already asserted by XRD tests, because no large aggregates were observed. A reduction in oxygen permeability and an increase in elastic modulus were obtained for films containing the nanoclay. Finally, the presence of the nanoclay produced a decrease in the HT release from films due to some interaction between HT and C30B. Results proved that these nanobiocomposites can be an interesting and environmentally friendly alternative for active food packaging applications with antioxidant performance. KEYWORDS: poly(ε-caprolactone), hydroxytyrosol, nanobiocomposites, characterization, active packaging ■ INTRODUCTION Biodegradable and/or biobased polymers show a number of properties adequate to different applications, including food packaging, automotive, and biomedical fields. 1 Most of these materials have properties comparable to many petroleum-based plastics and are readily biodegradable, making them an attractive potential alternative to reduce the environmental problems induced by the accumulation of plastic waste. 2 Among biodegradable polymers, aliphatic polyesters, such as poly(ε-caprolactone) (PCL), are now commercially available offering an interesting alternative to conventional thermo- plastics. PCL can be synthesized either by ring-opening polymerization (ROP) of the monomer, ε-caprolactone, with a variety of anionic, cationic and coordination catalysts or via free radical ROP of 2-methylene-1-3-dioxepane. 3 PCL is a semicrystalline polymer with a high degree of crystallinity, reaching 69%, 4 but with this value decreasing at higher molar masses. The good solubility of PCL in some common solvents, low melting point (59-64 °C), and exceptional blend- compatibility has raised some interest for the extensive research on potential applications of PCL. 3 However, some drawbacks in using PCL as polymer matrix should be taken into account, particularly its poor thermal and mechanical resistance and limited gas barrier properties. In this sense, PCL commercial uses are currently tempered by its high water solubility, high hydrophilicity, brittleness, low heat distortion temperature, high gas permeability, and low melt viscosity. 5 The use of PCL formulations in food packaging applications has been recently evaluated by several authors. In fact, the main current commercial application of PCL is in the manufacture of biodegradable bottles and compostable bags. 6 Martinez-Abad et al. suggested that the combination of cold storage with PCL incorporating ciannamaldehyde, as a natural biocide, could be suitable for the controlled diffusion of this agent extending the shelf life of packaged food products. 7 Antimicrobial nano- composites of PCL with thymol were also developed by Sa ́ nchez-Garci ́ a et al. 8 On the other hand, Perez-Masia ́ et al. 9 used PCL to encapsulate dodecane developing coating materials with energy storage capacity in refrigeration conditions. Blends of chitosan and poly-(ε-caprolactone) for food packaging applications with good tensile strength and low water vapor permeability were studied by Swapna et al., 10 concluding that fruits and vegetables packaged in PCL films were expected to extend their storage life. In order to improve PCL properties, the incorporation of nanoclays into this matrix is attracting some interest. It is known that the addition of montmorillonites (MMT) in contents lower than 10 wt % to polymer matrices leads to remarkable increases in rigidity (elastic modulus), thermal stability, and barrier to gases and vapors. 1 This strategy will be explored in this study to limit the current PCL disadvantages in food packaging applications. In the last years, several authors have worked on the preparation and characterization of PCL-based nanocompo- sites. 11-13 Pantoustier et al. 14 used the in situ intercalative polymerization method and compared the properties of nanocomposites prepared with both pristine MMT and after modification with amino-dodecanoic acid. Fukushima et al. developed nanocomposites of PCL with MMT and sepiolite showing a good dispersion level of clays within the polymer matrix as well as thermomechanical improvement in the resulting nanocomposites. 15 An additional functionality recently proposed for nano- composites is the controlled release of active substances embedded in food packaging materials. 1 Active packaging is Received: November 14, 2013 Revised: February 17, 2014 Accepted: February 19, 2014 Published: February 19, 2014 Article pubs.acs.org/JAFC © 2014 American Chemical Society 2244 dx.doi.org/10.1021/jf405111a | J. Agric. Food Chem. 2014, 62, 2244-2252