Estudos preliminares da liberação controlada de sulfato de amônio recoberto com poliuretano à base de lignina do endocarpo do coco seco para o uso como fertilizante agricola

Abstract

Polyurethanes are highly versatile materials synthesized from an isocyanate and a polyol, which have unique characteristics, such as low density, low thermal conductivity and moisture permeability, high strength to weight ratio and high dimensional stability, allowing them to be used to manufacture various kinds of higher added value materials such as flexible foams, adhesives, coatings, sealants, elastomers and binders. Due to the concern for the environment, the search for more biodegradable materials has grown. The coconut agroindustry is responsible for the large stacking of the dry coconut endocarp in the landfills, which has caused several environmental problems. Dry coconut is rich in lignocellulosic biomass. Lignin is one of the most abundant biopolymers in nature, and has a three-dimensional amorphous structure formed by three types of monolignols. These characteristics make lignin a strong candidate to replace polyols in polyurethane synthesis, even partially. Controlled Release Fertilizers (CRFs) are every kind of highly biodegradable material capable of coating fertilizers to efficiently obtain a controlled release of the nutrient. The use of lignin-based polyurethanes as a coating for controlled release of fertilizers is due to the following characteristics, degree of crosslinking, permeability to water and high biodegradability. The lignin was extracted from the coconut dried endocarp by the organosolv method. Polyurethanes were synthesized using toluene diisocyanate (TDI) and two polyols: lignin and polyethylene glycol (PEG 400). To obtain CRF, ammonium sulfate (NH4)2SO4 was added to the polyurethane synthesis. For characterizing, tests were carried out to obtain the gel content (% gel content) and swelling ratio (% S), using Fourier Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM) techniques. The kinetics of the nutrients controlled release was determined by UV-Vis spectrophotometry. According to the analysis, the polyurethanes had satisfactory results in terms of porosity, gel content, swelling ratio, surface morphology and ability to release the (NH4)2SO4 in a controlled manner, demonstrating that the methodology developed in this work is viable and that field trials can already be initiated.