Bio-based polyurethanes and composites from passion fruit oil methyl esters and coconut husk fibers

The present work describes a route to produce cost-effective and bio-based polyurethane (PU) composites from passion fruit oil (PFO) methyl esters (BIPFO) and coconut husk fibers. Fourier transform infrared spectroscopy (FTIR) and solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopies suggest that the macromolecular structure of the BIPFO-based PUs (PUBIPFO) consist of a mixture of polyurethane and polyurea, with the former being the major phase. Thermogravimetric analysis (TGA) indicates that the highest thermal stability is achieved for an optimized composite produced with isocyanate to hydroxyl ratio ([NCO]/[OH]) of 1.5 and a fiber loading of 15 wt%. In addition, dynamic mechanical analysis shows that the glass-transition temperatures (T_g) of the PUBIPFO shifts from 42°C to 56°C and finally to 66°C when varying the [NCO]/[OH] ratio from 1.5 to 1.8, and to 2.0, respectively. Despite the poor fiber-matrix interaction revealed by scanning electron microscopy (SEM), a five-fold increase is observed in the storage modulus, from 27 MPa to 133 MPa, after addition of the fibers to the plain PUBIPFO, confirming the reinforcement effect of the coconut husk fibers. The inexpensiveness and environmentally friendly features of PFO and coconut husk fibers allied to their ability to produce PU composites with enhanced thermal and mechanical properties make them very interesting materials.