## 1 Introduction  
In recent decades much effort has been devoted to the use of polymer nanocomposites in food packaging industrial products [1]. Nanocomposites are multiphase materials where at least one dimension of the phases smaller than 100 nm [2]. Nanocomposites exhibit improved optical, thermal, barrier, and mechanical performance compared to the corresponding characteristics of conventional composites.  
Polystyrene (PS) is one of the most widely used thermoplastic polymers in various industrial applications, including food packaging. Due to its high stiffness, strength, durability, good thermal properties, low moisture absorption, transparency, light density, convenience of processing and moulding, and low cost, this polymer is widely used as a food packaging material [3, 4, 5, 6].  
Among various nanoparticles [7] which are used as reinforcements for polymer nanocomposites, montmorillonite (Mt) has been extensively used in industrial applications because it is a naturally abundant clay mineral and biodegradable material, and it has unique structure and properties. PS/clay nanocomposites have been widely studied over the last several decades [8, 9]. According to researchers, two main synthesis routes compose the mixing process of the inorganic Mt nanoclay with the hydrophobic PS matrix. The first is the modification of the Mt surface with organic surfactants [10; 11] and the second is the hydrophilic modification of the PS surface with compatibilizers such as co-maleic anhydride [12; 13].  
In the last few years, nanoclays have been suggested as ideal nanocarriers for bioactive compounds such as essential oils (EOs) [14; 15; 16]. According to later research findings, the EOs have antioxidant, antimicrobial, and aromatic properties and are promising candidates to replace synthetic additives and materials in chemoactive packaging which could cause adverse health effects [17; 18]. Such novel EO@clay nanostructures can be easily loaded to polymer [19; 20] or biopolymer [21; 22; 23; 24] matrixes in order to develop a novel and promising active food packaging film. Such films are expected to exhibit enhanced mechanical and barrier properties due to the presence of the nanoclay. Moreover, the presence of the EOs is expected to provide aroma properties and controllable antioxidant activity [19; 25; 26; 27]. Recently, a Na-montmorillonite clay (NaMt) and a commercial organically modified montmorillonite clay (OrgMt) were modified with thyme oil (TO), Oregano oil (OO), and Basil oil (BO) and used in a process for the development of low-density polyethylene active packaging films [19]. One of the results of this study was that even after six months of incubation, both EO@NaMt-based and EO@OrgMt-based films exhibited enhanced water/oxygen barrier properties and controllable and sustained antioxidant activity.  
In this work, the OO@NaMt and OO@OrgMt hybrid nanostructures, which in a previous work exhibited the highest antioxidant activity [19], were loaded in polystyrene (PS) and polystyrene co-maleic anhydride (PS-coMA) matrixes for the development of active flavouring packaging films via a co-extrusion moulding process. The obtained PSOO@NaMt, PSco-mAOO@NaMt, and PSOO@OrgMt nanocomposite films were morphologically characterized via XRD analysis and FTIR spectrometry. The packaging performance of obtained films was evaluated via tensile properties, thermomechanical (DMA) studies, water, and oxygen barrier properties, antioxidant, and antimicrobial activity tests. Specific goals of this work are the efficiency of nanoclay type and polystyrene type in the development of polystyrene/montmorillonite/oregano oil active antioxidant/flavouring packaging films.