Effect of functionalizing sawdust as a reinforcement in two types of renewable polyurethane

In this work, composites were prepared in polyurethane (PU) matrices with sawdust fibers at levels of 10, 20 and 30%. The PU was obtained using polyols, castor oil and wood tar pitch (bio-pitch), reacted with a polymeric 4,4′-diphenylmethane diisocyanate (MDI), in a ratio NCO/OH = 1:1, catalyzed by dibutyltin dilaurate. Two groups of composites were formulated: materials synthesized only with polyol castor oil (PU 0%), and those obtained with 25% bio-pitch and 75% castor oil (PU 25%). The sawdust fibers were previously modified by mercerization, followed by benzylation or reaction with toluene diisocyanate (TDI). The changes were confirmed by infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetry (TG), X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The addition of bio-pitch to the matrix caused an increase in its porosity and a decrease in density. The sawdust showed good adhesion to the matrix containing bio-pitch, which was confirmed by the increase in the mechanical properties of its composites. The water absorption results showed that the matrix composites containing bio-pitch are more hydrophobic, with greater intercrossing, which corroborates the evaluation of good fiber–matrix interaction. Vegetable pitch seems to behave as a coupling agent between the fiber and the matrix, presenting itself as a suitable polyol for the synthesis of composites from renewable sources.