Publication Type:Book Chapter
Source:International Conference on Wood Adhesives , Forest Products Society, Lake Tahoe, Nevada, p.338-342 (2009)
Solution-state nuclear magnetic resonance spec- troscopy (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 sys- tem 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 sin- gle-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 forma- tion between wood and pMDI is not controlled by ure- thane formation.