Revalorização dos resíduos provenientes da casca de noz macadâmia como enchimento em compósito de poliuretano derivado do óleo de mamona

Abstract

The use of agro-industrial residues as filler in polymer matrices has aroused the interest of the scientific community and industrial sectors due to the manufacture of composite materials with excellent morphological, thermal, and mechanical properties. In Brazil, the high consumption of macadamia has generated a significant amount of waste that is incorrectly released into the environment. Thus, the present study proposed the revaluation of macadamia residues (RM) as a filler in castor oil-based polyurethane (PU) foams. Different particle sizes (28 and 35 mesh) and filler contents (5-20% m/m) were evaluated. RM, pure PU, and their composites were characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Apparent Density, Water Absorption, Contact Angle, Fourier Transformed Infrared Spectroscopy (FTIR), Thermogravimetry (TGA), X-Ray diffractometry (XRD), Mechanical Properties and the evaluation of environmental aging. According to the morphological analysis of the composites, the insertion of MR in the polyurethane matrix provides a nucleating effect, producing foams with higher density and smaller pore sizes compared to pure PU. A sample with higher MR content has a smaller pore size. Due to this morphology, the composite presents a good hydrophobic character and a low permeability to water. In line with this, the Infrared Spectroscopy analysis shows strong interactions between MR/PU, and this characteristic results in composites with good thermal stability and resistance to compression. Regarding the granulometry (particle size) of the RM, it is observed that the composites with macadamia residue (RM) of 28 mesh, present better mechanical performances. In addition, the assessment of natural environmental aging carried out over a period of 12 months shows changes in properties such as apparent density generated by the degradation of oxidation processes, photodegradation, and hydrolytic processes arising from factors such as UV radiation, temperature variation, and humidity present in the environment at the which samples are exposed. However, the degrading effect of aging is mitigated due to the addition of macadamia nut shell waste (especially between 5 to 20% MR). The study shows that MR in the PU foam matrix results in a protective effect in the degradative process, preventing property loss or structural alteration in PU foams. Therefore, MR as a reinforcement in PU foams is a sustainable alternative for the development of materials with different applications, including civil construction areas, as a weather protection material.