Eco-friendly polyurethane foams based on castor polyol reinforced with acai residues for building insulation

The search for environmental sustainability has stimulated the construction sector to look for natural materials with an ecological footprint, high strength/weight ratio, and better thermal and mechanical properties. Besides those properties, water absorption studies are necessary to reach these requirements. This research proposes to evaluate changes in the visual appearance, density, chemical structure, morphology, water absorption, porosity, and thermal and mechanical properties in castor oil-based polyurethane reinforced with acai waste (5-20 wt%). Results exposed that the addition of fiber to the PU reduced the pore size due to the increased cross-link density of PU foams caused by incorporating additional fiber groups, reacting with isocyanate groups. Also, the fibers were hydrogen bonded to the PU molecular chains via the interaction between the O-H of the fibers and the N-H of the PU foam. The water absorption of the biocomposites increased with time and with fiber loading; however, it did not surpass pure PU. The fiber addition improved crystallinity and hydrophobicity. The compressive strength presented a decreasing trend, while, for the impact test, an increase was observed proportionally to the acai residue content. Thus, the developed biocomposites can be a possibility for alternative eco-efficient building insulators.