Active antimicrobial packaging is a promising form of active packaging that can kill or inhibit microorganism growth in order to maintain product quality and safety. One of the most common approaches is based on the release of volatile antimicrobial agents from the packaging material such as essential oils. Due to their highly volatile nature, the challenge is to preserve the essential oils during the high-temperature melt processing of the polymer, while maintaining high antimicrobial activity for a desired shelf life. This study suggests a new approach in order to achieve this goal. Antimicrobial active films are developed based on low-density polyethylene (LDPE), organo-modified montmorillonite clays (MMT) and carvacrol (used as an essential oil model). In order to minimize carvacrol loss throughout the polymer compounding, a pre-compounding step is developed in which clay/carvacrol hybrids are produced. The hybrids exhibit a significant increase in the d-spacing of clay and enhanced thermal stability. The resulting LDPE/(clay/carvacrol) films exhibit superior and prolonged antibacterial activity against Escherichia coli and Listeria innocua, while polymer compounded with pure carvacrol loses the antibacterial properties within days. The films also present an excellent antifungal activity against Alternaria alternata, used as a model plant pathogenic fungus. Furthermore, infrared spectroscopy analysis of the LDPE/(clay/carvacrol) system displayed significantly higher carvacrol content in the film as well as a slower out-diffusion of the carvacrol molecules in comparison to LDPE/carvacrol films. Thus, these new films have a high potential for antimicrobial food packaging applications due to their longlasting and broad-spectrum antimicrobial efficacy.

Over the past decade there is an immense effort to develop antimicrobial packaging systems, which incorporates natural biopreservatives, such as essential oils (EOs). The highly volatile nature of EOs, which is advantageous for their efficient diffusion and mode of action, presents a major obstacle for their incorporation with polyolefins via conventional high-temperature melt compounding and processing. This study presents a new approach to use organo-modified montmorillonite (MMT) clays, as active carriers for carvacrol (used as a model EO), aiming to minimize its loss throughout the polymer compounding. Different MMT clays are pretreated with carvacrol, resulting in the oil molecules intercalation in between the clay galleries and enhanced carvacrol thermal stability. These hybrids are incorporated within low-density polyethylene (LDPE) and the resulting films are characterized in terms of their nanostructure, thermal properties, and antimicrobial activity. The LDPE/(clay/carvacrol) nanocomposites exhibit excellent and prolonged antimicrobial activity against E. coli bacteria, while LDPE/carvacrol films loss their antimicrobial functions within several days. The superior antimicrobial behavior is ascribed to the significantly higher carvacrol content and its enhanced thermal stability within the films.

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