Essential oils are environmentally friendly candidates for antimicrobial smart packaging systems. Encapsulation is needed to reduce their volatility and achieve controlled release. Within this study, the essential oil of Cymbopogon citratus (citronella oil) was microencapsulated and applied in pressure-sensitive antimicrobial functional coatings on papers for secondary packaging. Two microencapsulation methods were used: complex coacervation of gelatine with carboxymethylcellulose or with gum arabic, and in situ polymerization of melamine-formaldehyde prepolymers with a polyacrylic acid modifier. Minimum inhibitory concentrations of citronella oil microcapsules were determined for Bacillus subtilis (B. subtilis), Escherichia coli (B. subtilis), Pseudomonas aeruginosa (P. aeruginosa) and Saccharomyces cerevisiae (S. cerevisiae). Microcapsule suspensions were coated on papers for flexible packaging, 2 and 30 g/m2, and mechanically activated in the weight pulling test. A novel method on agar plates in sealed Petri dishes was developed to evaluate the antimicrobial activity of released citronella vapours on E. coli and S. cerevisiae. The results showed that both microencapsulation methods were successful and resulted in a container type single-core microcapsules. In situ microcapsule suspensions had better paper coating properties and were selected for industrial settings. The antimicrobial activity of 2 g/m2 coatings was not detected; however, the antimicrobial activity of 30 g/m2 partially activated coated papers was confirmed. The product enabled a prolonged use with the gradual release of citronella oil at multiple exposures of functional papers to pressure, e.g., by a human hand during product handling.

Water-based dispersion adhesives consist of a solid adhesive dispersed in an aqueous phase. These adhesives contain water-soluble additives such as surfactants, emulsifiers, and protective colloids, which act as links between the solid adhesive particles and the aqueous phase. They prevent the adhesive particles from sticking together and separating during storage. During drying, these additives evaporate or are absorbed into the adhesive. Polyvinyl acetate (PVAc) and polyvinyl alcohol (PVOH) are further examples of ethylene copolymers. PVAc is used as an emulsion adhesive for production of bags, sacks and cartons. Recently there have been some preliminary investigations concerning the addition of nanocellulose as adhesion improver. Nanocellulose is a term that refers to nanostructured cellulose. It can be either cellulose nanocrystal (CNC or NCC), cellulose nanofibres (CNF) also called nanofibrillated cellulose (NFC), or bacterial nanocellulose, which refers to nanostructured cellulose produced by bacteria. CNF is a material consisting of nanofibrillated cellulose fibrils with a high aspect ratio (length to width ratio). In this study, we tested the adhesion strength of two PVAc adhesives by adding 0,5, 1 and 2% [wt.%] of two types of nanocellulose to two commercial adhesives. The adhesive was applied to the cardboard with a rod coater. To test the influence of temperature, we varied the mixture at two different temperatures (23 and 45°C). The adhered samples were tested for z-direction tensile strength (according to ISO 15754:2009) and T-peel test (ASTM D1876-08) on a mechanical testing device. The results showed no significant improvement in adhesion strength compared to pure adhesive, indicating that further optimization of the adhesive mixture and testing procedure is required.