Characterizing polymeric methylene diphenyl diisocyanate reactions with wood. 1, High-resolution solution-state NMR spectroscopy

Abstract

Solution-state nuclear magnetic resonance spectroscopy (NMR) is a powerful tool for unambiguously determining the existence or absence of covalent bonds between wood components and adhesives. Finely ground wood cell-wall material dissolves in a solvent system containing dimethylsulfoxide-d₆ and N-methyl–imidazole-d₆, keeping wood component polymers intact and in a near-native state. Two-dimensional (2D) NMR experiments, using ¹³C-¹H one-bond heteronuclear single-quantum coherence on non-derivatized cell-wall material from loblolly pine, reveal details about the major cell-wall polymer structures. This technique can detect new covalent bond formation between cell-wall polymers and wood adhesives. A monofunctional model of polymeric methylene diphenyl diisocyanate (pMDI) and also neat pMDI were reacted without catalysts with loblolly pine matchsticks under moisture-controlled conditions to chemically modify the wood cell-wall polymers. The modified matchsticks were ball-milled, dissolved, and characterized via 2D NMR experiments. Results showed that high concentrations of the pMDI model reacted to form carbamate linkages with mannan and lignin sidechain units at 160°C. However, the pMDI reacted matchsticks showed no reactivity at 160°C, thus indicating that the mechanism of durable bond formation between wood and pMDI is not controlled by urethane formation.

Citation

Yelle, Daniel J.; Jakes, Joseph E.; Ralph, John; Frihart, Charles R. 2010. Characterizing polymeric methylene diphenyl diisocyanate reactions with wood. 1, High-resolution solution-state NMR spectroscopy. In: Wood Adhesives 2009 [electronic resource]. Madison, WI : Forest Products Society, c2010. [1 CD-ROM]: p. 338-342. ISBN: 9781892529572: 1892529572. FPS proceedings ; no. 7216-09.