Preparation and characterization of chitosan/polyacrylic acid/copper nanocomposites and their impact on onion production.

Chitosan nanoparticles (CS-NPs) and chitosan/polyacrylic acid hydrogel nanoparticles (CS/PAA-HNPs) were obtained by ionic gelation with tripolyphosphate anions and copolymerization of CS with acrylic acid (AA), respectively. The prepared NPs were loaded by different concentrations of copper (1, 2 and 3% with respect to CS) to obtain chitosan/copper nanocomposites (CS/Cu-NCs) and chitosan/polyacrylic acid/copper hydrogel nanocomposites (CS/PAA/Cu-HNCs). The prepared NPs and their NCs were characterized by different techniques. The swelling properties and copper release from CS/Cu-NCs and CS/PAA/Cu-HNCs were evaluated. The antibacterial activity of the prepared samples against bacteria (e.g., Staphylococcus aureus and Pseudomonas aeruginosa), fungi, and yeast were investigated. The results displayed that the copper release, as well as the swelling percentage of CS/PAA/Cu-HNCs, were higher than that of CS/Cu-NCs. Furthermore, the impact of using CuSO4, CS/Cu-NCs, and CS/PAA/Cu-HNCs as a different source of copper on chlorophyll content, vegetative growth, minerals content, and the yield of onion plants during two seasons 2016 and 2017 were studied. It was found that the yield, plant growth, and nutrient content of onion bulbs were improved using CS/PAA-HNPs, which was loaded with 75 ppm copper, as foliar spray for onion plants.