Conservação da viabilidade de sementes de Senna macranthera por meio de recobrimento

Abstract

For the process of coating in spouted bed, the physical characteristics of the particles to be coated, the formulation of coating suspension and the operating conditions such as the air flow, the pressure of atomization, the flow of suspension, the air temperature and the mass of solids are important parameters that influence the process performance. In the case of seeds, coating can be applied to facilitate handling, transporting and sowing, to protect the seeds against insects and for the conservation of species to environmental preservation. In this work the process of coating of forest seeds of Senna macranthera species in spouted bed was studied and analysis of the physiological quality of covered and in nature seeds during storage were performed. The seeds of this species have tegument dormancy, which hinders the germination due to impermeability of the tegument. The breaking of dormancy in seeds of forest species aims to increase the percentage of seed germination and to uniform the seedling emergence; however, these seeds cannot maintain their viability for long periods and the storage becomes unworkable without dormancy. The first stage of this work involved the physical characterization of the seeds, the definition of operating conditions for the coating process and the development of the formulation of the coating suspension. Then, the seeds underwent to tegument dormancy break by immersion in sulfuric acid before being coated with the polymer suspension developed. The coated seeds and the control (in nature seeds) were stored in conventional refrigerator at a temperature of 5 ºC.The storage period was of 380 days. The results of physical characterization of the seeds in nature were: Sauter diameter of 3.4 mm, sphericity of 0.52, dynamic angle of repose of 10 º, porosity of 1.81 %, weight of thousand seeds of 41.05 g and real, apparent and volumetric densities equal to 1397.2, 1371.9 and 884.4 kg/m³, respectively. For the coated seeds the following values were obtained: Sauter diameter of 3.7 mm, sphericity of 0.69, dynamic angle of repose of 35 º, porosity of 4.30 %, weight of thousand seeds of 50.52 g and real, apparent and volumetric densities equal to 1397.2, 1337.2 and 795.1 kg/m³, respectively. Operating conditions were defined as: suspension flow of 2 ml/min, atomization pressure of 2 psig, inlet air temperature of 70 ºC and load of seeds of 450 g. The formulated suspension was composed of: Eudragit FS 30D ® , triethyl citrate, magnesium stearate, titanium dioxide, talc, pink pigment and water. Scanning electron microscope images of the seeds before and after coating were analyzed.Adsorption isotherms at 25 ºC were determined for the coated and in nature seeds using the dynamic method. The results were adjusted using five models of sorption isotherms: GAB, xi Caurie, Oswin, Peleg and Smith. For the seeds in nature, the best fit was obtained with the model of Peleg (R² = 0.998), whereas for the coated seeds the best fit was obtained with the model of Smith (R² = 0.981). During the storage, three ...