Production of castor oil-based polyurethane resin composites reinforced with coconut husk fibres

In recent years, coconut tree cultivation has intensified worldwide. Therefore, it is necessary to analyse the agribusiness of coconut residues and the environmental impacts that its waste can cause to slow degradation of approximately eight years. Considering this and knowing that coconut is a highly reusable product, the aim of the present study was to investigate the physical, mechanical and microstructural properties of castor oil-based polyurethane resin composites, reinforced with different contents coconuts husk fibres. The coconut husk fibres were characterized according to chemical composition, basic density, pH and surface SEM images. The composites with dimensions of (200 x 200 x 3 mm) were produced by hand lay-up, in which the resin was mixed at magnetic shaking in a beaker at 150 rpm for 5 min under vacuum with the coconut husk fibres. Then, the mixture was placed in a mould and pressed at 1 MPa at room temperature. Four different compositions were tested: 30, 50, 65 and 75% coconut husk fibres. Specimens were obtained from the composites to perform tensile tests, determine the bulk density and water absorption, as well as visualize the matrix-reinforcement interface using SEM. The results showed no significant differences between the compositions for water absorption, bulk density and modulus of elasticity (MOE) obtained in the tensile tests. The tensile strength of the composites tended to increase as greater amounts of coconut husk fibres were added to the matrix. The averages were around 4.39 to 5.64 MPa for composites with 30 and 75% fibres, respectively. The photomicrographs obtained using SEM indicated detachment between the matrix and the reinforcement, which may be attributed to the high levels of extractives (19.78%) present in the fibres. The tests showed the viability of replacing polymer with fibres, in levels of up to 75%.