Biodegradable starch sachets reinforced with montmorillonite for packing ZnO nanoparticles: solubility and Zn2+ ions release

Agriculture's importance in human lives and the economy has directed studies to improve crop production. An essential challenge for improving fertilizer efficacy is reducing losses due to leaching and increasing the nutrients supplies. In this context, biodegradable sachets stand out as internal packaging instead of direct insertion into the polymer matrix, facilitating the system processing and making it easier to adapt the soil's nutritional quantity. Thus, the present work aimed to increase the zinc oxide (ZnO) solubility by obtaining nanoparticles using top-down and bottom-up approaches and packaging them in montmorillonite (MMT) reinforced starch sachets. The different diameters and forms of the ZnO nanoparticles were evaluated to understand the solubility dependence on these parameters. In this way, the top-down process was performed for the attritor milling method allowing the nanoparticles with about 71 nm average diameter and greater homogeneity than the commercial one (approximately 174 nm). The milled ZnO nanoparticles presented better solubility than those synthesized bottom-up processes and the commercial ones, reaching a 90 to 100% solubility plateau in 48 h. Concerning starch sachets, the 1% MMT (w w − 1 ) insertion in the polymeric matrix promoted increased water vapor barrier and mechanical properties, improving the tensile strength. In the solubility test for nanoparticulate ZnO packed in sachets, similar behaviors to free ZnO were observed due to the high affinity of the starch matrix with water. Therefore, starch sachet systems with improved properties from the MMT reinforcement insertion showed as an alternative source of Zn 2+ ions to minimize losses during application.