Revalorization of Macadamia nutshell residue as a filler in eco-friendly castor polyol-based polyurethane foam

The use of lignocellulosic fibers as fillers in polymer matrices has aroused the interest of the scientific community and industrial sectors. In Brazil, the high macadamia consumption has generated a significant amount of residues that are incorrectly discharged. Thus, the revalorization of macadamia residues (MR) as filler in castor oil-based polyurethane (PU) foams with different particle sizes (28 and 35 mesh) and filler contents (5-20%wt) was evaluated. The MR, neat PU, and their biocomposites were characterized by Spectroscopy Fourier-transform infrared spectroscopy (FTIR), Optical microscopy (OM), Scanning electron microscopy (SEM), apparent density, contact angle, water adsorption experiments, X-Ray diffraction analysis (XRD), Thermogravimetry (TGA), and mechanical tests. The insertion of MR in the PU matrix provided a nucleating effect producing greater density foams and smaller pore sizes compared to neat PU. Specimens of higher MR contents were highlighted. These biocomposites presented a good hydrophobic character, a low water permeation, and a strong interaction between MR/PU, resulting in biocomposites of good thermal stability and compressive strength. Regarding the statistical study, it was observed that the different MR sizes induced the formation of small pores statistically distinct. Besides, the largest particle (28 mesh) provided better mechanical performance. Therefore, MR as filler in PU foams is a sustainable alternative for the development of materials with several applications.