No abstract

Currently, the use of composites to replace parts made only with plastics has been gradually employed. The advantages of these composites are low cost, high availability of raw materials and good physical and mechanical properties. Thus, this work aimed at producing and characterizing composites produced with coconut fibre reinforced polyurethane matrices. The coconut fibres were studied as to their chemical constituents, aspect ratio, bulk density, pH, tensile properties, and surface SEM images. The composites were prepared using the hand lay-up process and four different concentrations of coconut fibre were evaluated: 30, 40, 50, and 60%. The composites were assessed as for water absorption after 20 days of immersion, bulk density, impact IZOD, tensile tests, and visualize the matrix-reinforcement interface using SEM. The electron micrographs showed a great deal of impurities on the surface of coconut fibres, such as greases, waxes, and gums, due to the high amount of extraction material (19.78%), which damages the adherence of the polymer onto the coconut fibre and, as observed, cause detachment between the reinforcement and the matrix. The tensile strength of the composites tended to increase as greater amounts of coconut fibres were added to the matrix. The averages were around 6.51 to 6.72 MPa for composites with 30 and 60% fibres, respectively. Therefore, coconut fibres can be considered as an alternative to synthetic fibres commonly used in composites, and they can be used at a ratio of 60% without prejudicing the properties of the composites, making them lighter and cheaper.

Urease (EC 3.5.1.5) activity is one of the processes that most contributes to urea loss by ammonia volatilization in agriculture. The present study describes the capacity of polyphenols extracted from barbatimão tree bark (Stryphnodendron adstringens (Mart.) Coville) on inhibiting the urease enzyme extracted from Canavalia ensiformis (L.) DC. Fourier transform infrared spectroscopy (FTIR) coupled to an attenuated total reflection (ATR) accessory was chosen to determine the enzymatic kinetics. This spectroscopic technique is used to perform more sustainable enzyme kinetic studies due to the decreased use of chemicals, including highly toxic reagents. The inhibition capacity of the polyphenols was compared with N-(n-butyl)­thiophosphoric triamide (NBPT). The reactions occurred in 20 mM potassium phosphate buffer, pH 7.2, and the crude urease extract was used. The maximum intensity of asymmetric stretching of the bicarbonate functional group at 1361 cm–1 was measured to study the kinetics of urease. The kinetic constants V max and K m were determined by nonlinear fitting with the Michaelis–Menten model. The data obtained showed the strong potential of polyphenols from bark to be used as urease inhibitors on fertilizers in soil, decreasing the use of chemical reagents exogenous to the environment, such as NBPT.