Koranit Shlosman

The use of many pesticides in agricultural crop protection has been banned due to their harmful effects on health and the environment, leaving farmers with limited crop protection options. A natural nontoxic alternative is thymol (TY), the main component in thyme essential oil (EO), which is known to have pesticidal and anti‐mold properties. TY can be incorporated into plastic films, widely used in agricultural applications. However, its volatility and susceptibility to heat limits its use in polymeric systems. By encapsulating TY using natural biopolymer such as cellulose, TY can be protected during high‐temperature plastic processing, thus enabling to achieve an active plastic packaging. In this study, cellulose‐encapsulated TY was melt‐compounded with low‐density polyethylene (LDPE) and 100 μm‐thick films were fabricated and compared with similar compounds containing free TY. Scanning electron microscopy with energy dispersive X‐ray spectroscopy confirmed the presence of TY‐loaded particles and demonstrated that they had no significant effects on the LDPE matrix morphology. LDPE films containing encapsulated TY offered higher anti‐mold protection functionality to postharvest alfalfa plants, in comparison to films containing free TY. Fourier transform infrared spectroscopy supported by thermo gravimetric analysis further confirmed successful incorporation of TY‐loaded particles in the LDPE films. Taken together, the application range of EOs and their synthetic compounds such as TY, can be broadened by encapsulation with cellulose. Incorporation of cellulose‐encapsulated TY in plastic composites can serve as a useful natural alternative to toxic pesticides in agricultural applications.

Efforts to tap into the broad antimicrobial, insecticidal, and antioxidant activities of essential oils (EOs) are limited due to their strong odor and susceptibility to light and oxidation. Encapsulation of EOs and subsequent drying overcome these limitations and extend their applications. This study characterized freeze-dried (lyophilized) emulsions of eugenol (EU) and thymol (TY) EOs, encapsulated by chemically unmodified cellulose, a sustainable and low-cost resource. High-resolution scanning electron microscopy showed successful lyophilization. While the observed “flake-like” structure of the powders differed significantly from that of the emulsified microcapsules, useful properties were retained. Fourier transform infrared spectroscopy confirmed the presence of EOs in their corresponding powders and thermo-gravimetric analysis demonstrated high encapsulation efficiency (87–88%), improved thermal stability and resistance to evaporation, and slow EO release rates in comparison to their free forms. The lightweight and low-cost cellulose encapsulation, together with the results showing retained properties of the dried powder, enable the use of EOs in applications requiring high temperatures, such as EO incorporation into polymer films, that can be used to protect agricultural crops from microbial infections.

Essential oils (EOs) are volatile natural organic compounds, which possess pesticidal properties. However, they are vulnerable to heat and light, limiting their range of applications. Encapsulation of EOs is a useful approach to overcome some of these limitations. In this study, a novel emulsification technique is utilized for encapsulation of thymol (TY) and eugenol (EU) (EOs) within microcapsules with an unmodified cellulose shell. Use of low cost materials and processes can be beneficial in agricultural applications. In the encapsulation process, unmodified cellulose was dissolved in 7% aqueous NaOH at low temperature, regenerated to form a dispersion of cellulose hydrogels, which was rigorously mixed with the EOs by mechanical mixing followed by high-pressure homogenization (HPH). Cellulose:EO ratios of 1:1 and 1:8 utilizing homogenization pressures of 5000, 10,000 and 20,000 psi applied in a microfluidizer were studied. Light microscopy, high-resolution cryogenic scanning electron microscopy (cryo-SEM) and Fourier transform infrared spectroscopy (FTIR) revealed successful fabrication of EO-loaded capsules in size range of 1 to ~8 µm. Stability analyses showed highly stabilized oil in water (O/W) emulsions with instability index close to 0. The emulsions exhibited anti-mold activity in post-harvest alfalfa plants, with potency affected by the cellulose:EO ratio as well as the EO type; TY showed the highest anti-mold activity. Taken together, this study showed potential for anti-fungal activity of cellulose-encapsulated EOs in post-harvest hay.

This paper presents compression molding of peptide assemblies with low-density polyethylene (LDPE) for the robust production of antimicrobial polymeric films.