Preparação e caracterização de espuma rígida de poliuretano com casca de laranja visando à remoção de bisfenol A em meio aquoso

Abstract

Polyurethane (PU) foams comprise a significant portion of the synthetic polymers produced worldwide. Likewise, agricultural waste can represent massive by-products from food industry operations. Research indicates that polyurethane foams and agricultural residues can be combined to improve the ability to remove contaminants in aqueous media and promote the economy of petrochemical reagents. This work aimed to prepare and characterize pieces of rigid polyurethane foams with orange peels and assess the material’s capacity to remove the contaminant Bisphenol-A (BPA) in an aqueous medium. For the synthesis of the foams, diphenylmethane diisocyanate (MDI) and polyester-type formulated polyol were used. Samples containing orange peel (CL) were produced in the proportions of 7% (PUCS7), 10% (PUCS10), and 14% (PUCS14), replacing (m/m) the polyol. The characterization of samples of precursor reagents, orange peel, and PU foams was performed using Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA) and scanning electron microscopy (SEM), and X-ray diffraction (XRD). In the infrared spectrum of CL samples, characteristic bands of lignocellulosic materials were identified at 3285 cm-1 (O–H groups), 2919 cm-1 (C–H bonds in CH2 groups) and 1733 cm-1 (C=O). For PU and compositions, characteristic bands were found at 3278 cm-1 (NH), 1710 (C=O) and 1593 cm-1 (NH2), bands also present in the PUCS7 sample. MEV analyzes demonstrated that the progressive addition of CL load altered the foam morphology. The TGA analysis revealed that the decomposition of the foams occurs in one step after the loss of water and that the addition of CL to the foams increased the temperature at which mass loss occurs by 85% (T85), with an alteration in the thermal stability upon the addition of CL. Regarding the BPA removal, it was verified that the adsorption capacity in the equilibrium of the foams with 7% of peels (PUCS7) was equal to that of the pure PU samples. The adsorptive capacity for the composition with 10% bark (PUCS10) was lower than for pure PU and PUCS7. The PU and PUCS7 samples reached equilibrium after 48 hours of contact and the PUCS10 samples reached equilibrium after 36 hours of testing. As for the adsorption kinetics models applied, the pseudo-second order was the one that best fitted the graph. In contrast, the pseudo-first order demonstrated the calculated adsorptive capacity closer to that obtained experimentally. The addition of CL did not enhance the removal of the contaminant; however, it can be used to replace part of the petrochemical polyol needed in the formulation without compromising the capacity to remove the pollutant, which can mean savings in raw materials in the production of polyurethanes and representing a positive impact for the industry, since the production of rigid polyurethane foams in the world is in the order of tons; therefore reagents of the same order of magnitude are consumed; promoting a 7% economy of polyol represents a breakthrough in the area of circular economy and Green Chemistry.