Reactivity of Aliphatic and Phenolic Hydroxyl Groups in Kraft Lignin towards 4,4′ MDI |
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| Authors: | Leonardo Dalseno Antonino Júlia Rocha Gouveia Rogrio Ramos de Sousa Júnior Guilherme Elias Saltarelli Garcia Luara Carneiro Gobbo Lara Basílio Tavares Demetrio Jackson dos Santos |
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| Institution: | 1.Nanoscience and Advanced Materials Graduate Program (PPG-Nano), Federal University of ABC (UFABC), Santo André 09210-580, Brazil; (L.D.A.); (J.R.G.); (R.R.d.S.J.); (G.E.S.G.); (L.C.G.); (L.B.T.);2.Materials Engineering Graduate Program (PPG-Nano), Federal University of ABC (UFABC), Santo André 09210-580, Brazil |
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| Abstract: | Several efforts have been dedicated to the development of lignin-based polyurethanes (PU) in recent years. The low and heterogeneous reactivity of lignin hydroxyl groups towards diisocyanates, arising from their highly complex chemical structure, limits the application of this biopolymer in PU synthesis. Besides the well-known differences in the reactivity of aliphatic and aromatic hydroxyl groups, experimental work in which the reactivity of both types of hydroxyl, especially the aromatic ones present in syringyl (S-unit), guaiacyl (G-unit), and p-hydroxyphenyl (H-unit) building units are considered and compared, is still lacking in the literature. In this work, the hydroxyl reactivity of two kraft lignin grades towards 4,4′-diphenylmethane diisocyanate (MDI) was investigated. 31P NMR allowed the monitoring of the reactivity of each hydroxyl group in the lignin structure. FTIR spectra revealed the evolution of peaks related to hydroxyl consumption and urethane formation. These results might support new PU developments, including the use of unmodified lignin and the synthesis of MDI-functionalized biopolymers or prepolymers. |
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| Keywords: | lignin-based polyurethanes chemical reactivity hydroxyl group |
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