Nanocomposites based on cellulose acetate, a commercial organoclay (Cloisite30B), triethyl citrate and variable content of antimicrobial agents (thymol and cinnamaldehyde), were obtained using a solution casting technique. The properties of the nanocomposites were evaluated using X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mechanical (modulus of elasticity, tensile strength and elongation at break), scanning electronic microscopy, global migration and microbiological testing. A reduction of glass transition (T g ), melting temperature (T m ) and melting enthalpy (ΔH m ) was also observed when the content of thymol and cinnamaldehyde was increased in the cellulose acetate nanocomposites. In contrast, thermal stability, mechanical performance and morphology of material did not show important differences when the content was modified. Results of global migration were dependent of the kind of simulant used. Finally, the antimicrobial activity was dependent of the essential oil used and its content inside the nanocomposite. An important effect of organoclay on the antimicrobial activity was also observed. a Calculated from Bragg's Law. b Determined from second scan. c Calculated from ΔH f (100% crystalline) = 58.8 J/g. 153 CELLULOSE NANOCOMPOSITES WITH ANTIMICROBIAL ACTIVITY a Obtained from the first derivative of the TGA curve. 155 CELLULOSE NANOCOMPOSITES WITH ANTIMICROBIAL ACTIVITY Mean values with the same letter in each column indicate no statistically significant differences (p < 0.05) according to analysis of variance and Fisher LSD test. 156 F. RODRIGUEZ ET AL. 44. Valero M, Francés E. Synergistic bactericidal effect of carvacrol, cinnamaldehyde or thymol and refrigeration to inhibit Bacillus cereus in carrot broth. Food Microbiology 2006; 23: 68-73. 45. Nigmatullin N, Gao F, Konovalova V. Polymer-layered silicate nanocomposites in the design of antimicrobial materials. Journal of Materials Science 2008; 43: 5728-5733. 46. Rodríguez FJ, Coloma A, Galotto MJ, Guarda A, Bruna J. Effect of organoclay content and molecular weight on cellulose acetate nanocomposite properties. 3 rd International Conference on Bidegradable and Biobased Polymers. BIOPOL 2011.

Nanocomposites based on biopolymers have been recognised as potential materials for the development of new ecofriendly food packaging. In addition, if these materials incorporate active substances in their structure, the potential applications are much higher. Therefore, this work was oriented to develop nanocomposites with antimicrobial activity based on cellulose acetate (CA), a commercial organoclay Cloisite30B (C30B), thymol (T) as natural antimicrobial component and tri-ethyl citrate (TEC) as plasticiser. Nanocomposites were prepared by a solvent casting method and consisted of 5% (w/w) of C30B, 5% (w/w) of TEC and variable content of T (0%, 0.5% and 2% w/w). To evaluate the effect of C30B into the CA matrix, CA films without this organoclay but with T were also prepared. All nanocomposites showed the intercalation of CA into the organoclay structure; furthermore this intercalation was favoured when 2% (w/w) of T was added to the nanocomposite. In spite of the observed intercalation, the presence of C30B inside the CA matrices increased the opacity of the films significantly. On the other hand, T showed a plasticiser effect on the thermal properties of CA nanocomposites decreasing glass transition, melting temperature and melting enthalpy. The presence of T in CA nanocomposites also allowed the control de Listeria innocua growth when these materials were placed in contact with this Gram-positive bacterium. Interestingly, antimicrobial activity was increased with the presence of C30B. Finally, studies on T release showed that the clay structure inside the CA matrix did not affect its release rate; however, this nanofiller affected the partition coefficient KP/FS which was higher to CA nanocomposites films than in CA films without organoclay. The results obtained in the present study are really promising to be applied in the manufacture of food packaging materials.