Essential oils as natural root?repellent herbicides for drip irrigation systems
The increasing use of synthetic herbicides in agriculture creates severe ecological and environmental threats. Several essential oils (EOs) (Thymol, Carvacrol, Cinnamaldehyde, and Eugenol) were investigated as natural herbicides, and their potential use as a substitute for synthetic and toxic chemicals for preventing roots intrusion in subsurface drip irrigation systems. To overcome their high volatility and to increase their thermal stability during processing, multiphase hybrid blends based on polymer/nanoclays (NCs) were prepared, enabling control of the EOs migration rate from the final active film. Germination experiments on mash bean seeds in open and closed systems have been conducted to evaluate the EOs efficacy as germination inhibitors. The amount of EO remaining in the films, after processing and for varying timepoints, was determined by UV–Vis spectroscopy through extraction. From these two experiment's results, we identified Thymol as the most effective herbicide. The effects of polymers/Thymol affinity and organoclay polarity were investigated to achieve a slow?release effect. Linear low?density polyethylene/polyamide 6 system showed better efficiency compared to the linear low?density polyethylene in retaining Thymol during processing due to the thermodynamic affinity of the polyamide 6 phase with Thymol. NCs have been found to be nuclear foci during the first thermal process to obtain smaller highly surface voids allowing better absorption of the Thymol during the second thermal processing. NC Cloisite 15A showed better dispersion in the polymer matrix and improved chemical affinity between the nanocomposite and the Thymol. As a result, Thymol's desorption was delayed and a controlled release was obtained. Eventually, it was concluded that Thymol could be a natural and environmentally friendly alternative to the synthetic herbicides and use as root?repellent agent.