Resumo:
In the mechanical recycling of refrigerators, a significant challenge arises: the residue in powder form of rigid polyurethane (PUR), which is difficult to recycle, has high disposal costs, and represents a potential risk of environmental contamination. This study aims to explore an innovative solution: the production of a new rigid polyurethane foam from this residue, by combining it with a Methylene Diisocyanate (MDI) prepolymer and water as a foaming agent. A mixture design experiment (DOE) was adopted to optimize the apparent density, compression modulus, and water absorption of this new foam. Mass contents of PUR residue between 10% and 30% and water between 20% and 40% were investigated. Additionally, both the PUR residue and the produced foams were evaluated by Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The thermal behavior of all foams and PUR residue was similar, with an onset of degradation around 245°C and a glass transition at about 150°C. The produced foams have apparent densities ranging from 0.228 to 0.425 g/cm³ and compression moduli between 23 and 250 MPa. The DOE indicated that an ideal formulation should contain 50% MDI prepolymer. Foams with lower densities are produced with equal proportions of PUR residue and water (~25%), while foams with higher compression modulus contain less water (~20%) and more PUR residue (30%). Although there is still a need to test more formulations to improve and increase the reliability of the generated model, this study demonstrates the feasibility of producing a new foam using a challenging residue. The rigid polyurethane foams obtained have potential applications in the civil sector, in the refrigerator industry, or in more specialized applications, such as structural foams in sandwich panel cores.
