Torrefied banana tree fiber pellets having embedded urea for agricultural use Diogenes S. Dias 2 • Marisa S. Crespi 2 • Lilian D. M. Torquato 2 • Marcelo Kobelnik 1 • Clovis A. Ribeiro 2 Received: 8 June 2016 / Accepted: 9 December 2016 Ó Akade´miai Kiado´, Budapest, Hungary 2017 Abstract Banana tree fibers (BF) torrefied in the absence of air and residence time of 60 min at temperatures between 180 and 600  C were evaluated for its agglutina- tion power when converted to pellets. The agglutination power was estimated as aqueous media residence time, being the most resistant pellets the ones obtained from 180 to 300  C. The agglutination power was also evaluated for pellets samples containing from 10 to 90% (w/w) urea. BF torrefied with or without urea have been assessed by thermogravimetry (TG) and differential thermogravimetry (DTG), indicating increased stability on torrefaction tem- perature and the growth of urea. TG/DTG curves were also used to assess the kinetics of release of urea with time in aqueous by analyzing the residue of biochar BF. Kinetics of release was investigated using a semi-empirical model, known as the power law or the Korsmeyer–Peppas model, C t =C inf ¼ kt n . The value found for n lies between 0.5 and 1.0 indicating that urea release mechanism tends to non- Fickian diffusion or anomalous transport. FTIR spectra showed the weak interaction between urea and biochar. Keywords Banana tree fibers  Torrefaction  Biochar  TG/DTG curves  Urea fertilizer release Introduction Despite the fight against hunger around the world, it remains very high, and it is estimated that at least 795 million people or one in nine do not have enough food to be healthy and active life [1]. It must increase the food production to remedy the hunger, and therefore, new agricultural frontiers must be explored or intensify already cultivable [2]. In 2009, the FAO, the Food and Agriculture Organization of the United Nations warned of the need to increase by 70% to global food production by 2050 [3–5]. Therefore, there is a growing need in the use of fertilizers for soil improvement and increase in agricultural produc- tion by area. Among the fertilizers used in agriculture, urea is the one with the greatest problems because of its insta- bility, occurring nitrogen loss by volatilization and the enzymatic hydrolysis or ions leaching to the soil solution. The plants do not exploit more than 67% of urea applied to the soil. The technology for fertilizers confronts an ongoing challenge to improve their products or increase the effi- ciency of existing ones, especially nitrogen, due to its environmental impacts. Therefore, there is much research in the direction to increase effectiveness in the use of urea, employing features such as nitrification and urease inhibi- tors. Further research goes toward cover the fertilizer with various materials, such as sulfur and polymers to control their release to the soil. The coating or encapsulation of the fertilizer should serve as a protective layer, but which does not interfere with the availability to plants, being released gradually. The slow or controlled release fertilizers are called ‘‘smart fertilizer’’. For ‘‘smart fertilizer’’, controlled release is known to release rate with time and the ones with the slow release is dependent on soil and climatic condi- tions [6–10]. It is known that the Amazonian soil in Brazil is sandy, loamy and low in nutrients, but this same region & Clovis A. Ribeiro ribeiroc@iq.unesp.br 1 University Center North Paulista-UNORP, Sa˜o Jose´ do Rio Preto, SP, Brazil 2 Analytical Chemistry Department, Sa˜o Paulo State University IQ/UNESP, Professor Francisco Degni Street 55, Araraquara 14800-060, Brazil 123 J Therm Anal Calorim DOI 10.1007/s10973-016-6049-7