Biodegradable and Active Mulch Films: Hydrolyzed Lemon Peel Waste and Low Methoxyl Pectin Blends with Incorporated Biochar and Neem Essential Oil

Water-based biopolymer solutions capable of forming a protective layer when sprayed onto the soil represent a groundbreaking step toward eco-friendly mulching. Low methoxyl pectin (LMP) can cross-link with calcium cations naturally present in the soil. Therefore, LMP-based bioplastics were prepared here to assess their potential use as mulches. Lemon peel (LP), a common pectin source, was hydrolyzed and mixed with LMP in aqueous solutions in ratios of 1:3, 1:1, and 3:1. In all the formulations, polyglycerol-3 was used as plasticizer at a concentration of 30 wt % with respect to LMP + LP. Subsequently, films were produced by casting and cross-linking with anhydrous CaCl₂. The incorporation of hydrolyzed lemon peel (hLP) produced a further plasticizing effect on the LMP films. The formulation of 1:1 ratio of LMP/hLP presented the best mechanical properties and was selected to prepare active mulch films. For that, neem essential oil (NEO) was added to the films at 0.5 and 1.5 wt % concentrations, in the form of nanoemulsion, to provide insecticidal activity, and 5 or 10 wt.% lemon peel biochar (LPB) particles were added to obtain opaque materials and reduce light transmission to prevent the weed growth. The characterization of the mulch films demonstrated that NEO did not affect the film properties significantly, but LPB reduced their mechanical resistance and water vapor barrier, mainly when added at 10 wt %. When LPB was incorporated at 5 wt % concentration, the developed composites presented mechanical properties acceptable for mulching. Tested materials showed fast biodegradability in soil, considering 50% weight loss during the first week of the experiment.