Polyurethane Composites Synthesized Using Natural Oil-Based Polyols and Sisal Fibers

Elastomeric polyurethanes were prepared from a reference polyurethane system modified with biobased polyols synthesized using rapeseed or palm oils. The reference material was modified by replacement of the commercial polyol by 10% of biopolyols and also by addition of sisal fibers up to 5 wt%. The higher functionality of the biopolyols increased the crosslinking density of the networks and this was reflected by an increase in hardness and a decrease in water absorption. The effect of the sisal fibers mainly improved the mechanical and thermomechanical properties of the system with rapeseed oil because of good dispersion and strong fiber-matrix interaction. The system containing palm oil polyol corresponded to an initial formulation of high viscosity and, consequently, the resulting composites presented lower densities than the theoretically expected ones. These results are associated with fiber dispersion problems in the initial reactive mixture.