Performance of Thyme Oil@Na-Montmorillonite and Thyme Oil@Organo-Modified Montmorillonite Nanostructures on the Development of Melt-Extruded Poly-L-lactic Acid Antioxidant Active Packaging Films.

Aris E Giannakas,Eleni Kollia,Anastasios Karakassides,Constantinos E Salmas,Maria Baikousi,Dimitrios Moschovas,Areti Leontiou,Vasiliki Tsigkou,Charalampos Proestos,Apostolos Avgeropoulos

doi:10.3390/molecules27041231

Abstract

Today, the use of natural biodegradable materials in the production processes is more and more adopted by industry to achieve cyclic economy targets and to improve environmental and human health indexes. Active packaging is the latest trend for food preservation. In this work, nanostructures were prepared by incorporation of thyme oil with natural natrium-montmorillonite and organo-montmorillonite with two different techniques, direct impregnation and the green evaporation–adsorption process. Such nanostructures were mixed with poly-L-lactic-acid for the first time via an extrusion molding process to develop a new packaging film. Comparisons of morphological, mechanical, and other basic properties for food packaging were carried out via XRD, FTIR, TG, SEM/EDS, oxygen and water vapor permeation, and antimicrobial and antioxidant activity for the first time. Results showed that poly-L-lactic-acid could be modified with clays and essential oils to produce improved active packaging films. The final product exhibits food odor prevention characteristics and shelf-life extension capabilities, and it could be used for active packaging. The films based on OrgMt clay seems to be more promising, while the thyme oil addition improves their behavior as active packaging. The PLLA/3%TO@OrgMt and PLLA/5%TO@OrgMt films were qualified between the tested samples as the most promising materials for this purpose.

Highlights

Today, green and circular economies favor the development of nanocomposite packaging materials from renewable source-based biodegradable plastics or biopolymers [1]
The basal space peak of PLLA/1OrgMt, PLLA/3OrgMt, and PLLA/5OrgMt film was at 2theta, 2.55◦, 2.59◦, and 2.64◦, respectively, while the basal space peak of all PLLA/1O@organomodified montmorillonite (OrgMt), PLLA/3TO@OrgMt, and PLLA/5TO@OrgMt films was at around 2theta = 2.53◦. These results indicated the formation of an intercalated nanostructure in all cases, and the boost that thyme oil (TO) molecules provided to PLLA chains to insert in the OrgMt clay interlayer space
Characterization techniques indicated that the interplay and compatibility between PLLA chains and clay platelets was more intense in the case of the intercalated OrgMt clay compared to that of the partially exfoliated NaMt clay

Summary

Introduction

Green and circular economies favor the development of nanocomposite packaging materials from renewable source-based biodegradable plastics or biopolymers [1]. Polylactides or poly(lactic acid) (PLA) is one of the most promising materials between the renewable source-based biodegradable plastics since it is thermoplastic, biodegradable, and biocompatible and exhibits high-strength, high-modulus, and good processability [2,3,4,5]. PLA is a linear aliphatic thermoplastic polyester produced either by the polycondensation of lactic acid or by the ring-opening polymerization of lactide. Lactide is a cyclic dimer prepared by the controlled depolymerization of lactic acid, which is obtained from the fermentation of renewable sugar feedstock, such as corn or sugar beets. Polymerization of a racemic of L-lactides leads to the synthesis of poly-L-lactide (PLLA). Since production cost has been lowered by new technologies and large-scale production, the application of PLA has been extended to materials for packaging applications [3,4,5,6]

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Conclusion