Greener Nanocomposite Polyurethane Foam Based on Sustainable Polyol and Natural Fillers: Investigation of Chemico-Physical and Mechanical Properties

Abstract

Nowadays, the chemical industry is looking for sustainable chemicals to synthesize nanocomposite bio-based polyurethane foams, PUs, with the aim to replace the conventional petrochemical precursors. Some possibilities to increase the environmental sustainability in the synthesis of nanocomposite PUs include the use of chemicals and additives derived from renewable sources (such as vegetable oils or biomass wastes), which comprise increasingly wider base raw materials. Generally, sustainable PUs exhibit chemico-physical, mechanical and functional properties, which are not comparable with those of PUs produced from petrochemical precursors. In order to enhance the performances, as well as the bio-based aspect, the addition in the polyurethane formulation of renewable or natural fillers can be considered. Among these, walnut shells and cellulose are very popular wood-based waste, and due to their chemical composition, carbohydrate, protein and/or fatty acid, can be used as reactive fillers in the synthesis of Pus. Diatomite, as a natural inorganic nanoporous filler, can also be evaluated to improve mechanical and thermal insulation properties of rigid PUs. In this respect, sustainable nanocomposite rigid PU foams are synthesized by using a cardanol-based Mannich polyol, MDI (Methylene diphenyl isocyanate) as an isocyanate source, catalysts and surfactant to regulate the polymerization and blowing reactions, H2O as a sustainable blowing agent and a suitable amount (5 wt%) of ultramilled walnut shell, cellulose and diatomite as filler. The effect of these fillers on the chemico-physical, morphological, mechanical and functional performances on PU foams has been analyzed.

Upgrading Sustainable Polyurethane Foam Based on Greener Polyols: Succinic-Based Polyol and Mannich-Based Polyol

“…The morphology of polyurethane foams and the corresponding surface cell diameter distribution are reported in Figure 7. As observed, the pristine PS0 exhibited a somewhat homogeneous cell distribution (diameters ranging from 100 to 450 µm) with a closed cells structure [7,26,37] typical of a rigid polyurethane foam [6,7,24,26]. By adding the bS, a change in morphology was observed.…”

“…This means that the macromolecular structure of PS5 and PS7 was less constrained [36] as compared with the structure of the PS3 system. Furthermore, in the PS3 and PS5 spectra, vibration peaks correlating to the urea linkages were also observed (see the spectra in Figure 6) [7,35].…”

“…The higher thermal stability of bM, due to the presence of the aromatic species, induces a profound effect on the stability of the derived polyurethane foams [17]. Figure 6 reports the FTIR spectra related to the PS3, PS5 and PS7 samples (the FTIR spectrum of PS0 is reported in de Luca Bossa et al [7]), with the focus in the main characteristic region of urethane groups (2000-800 cm −1 ). The absence of the signal related to the asymmetric stretching of free NCO group (~2270 cm −1 , data not reported for brevity), in all the spectra, confirms the occurrence of the polyurethane reaction as well described elsewhere [4,7,9,14].…”

“…The FTIR analysis was conducted on bM polyol and synthesized bS polyol, and the spectra are reported in Figure 3. By observing the FTIR spectra, it was observed for the bS spectrum that the main characteristic peaks related to the OH stretching vibration around 3300 cm −1 , the carbonyl absorption peak at 1711 cm −1 (higher than C=O of bM due to its higher quantity in the polymeric structure) and the stretching vibration C-O-C at 1153 cm −1 , both ascribed to the polyester polyol [5,7,8,14]. Conversely, bM polyol shows the OH and C=O absorption peaks (see the spectrum in Figure 3), the double peaks around 1100-1000 cm −1 belong to the C-O-C ether groups of Mannich polyol and the C-N and aromatic vibration peaks at 1254 cm −1 and 1490 cm −1 wavenumber, respectively [18,[28][29][30].…”

“…Figure 6 reports the FTIR spectra related to the PS3, PS5 and PS7 samples (the FTIR spectrum of PS0 is reported in de Luca Bossa et al [7]), with the focus in the main characteristic region of urethane groups (2000-800 cm −1 ). The absence of the signal related to the asymmetric stretching of free NCO group (~2270 cm −1 , data not reported for brevity), in all the spectra, confirms the occurrence of the polyurethane reaction as well described elsewhere [4,7,9,14]. The peak at 1705 cm −1 assigned to the characteristic stretching vibration of C=O hydrogen-bonded urethane units was observed for PS3.…”