Elucidating How Wood Adhesives Bond to Wood Cell Walls using High-Resolution Solution-State NMR Spectroscopy

Abstract

Some extensively used wood adhesives, such as pMDI (polymeric methylene diphenyl diisocyanate) and PF (phenol formaldehyde) have shown excellent adhesion properties with wood. However, distinguishing whether the strength is due to physical bonds (i.e., van der Waals, London, or hydrogen bond forces) or covalent bonds between the adherend and the adhesive is not fully understood. Previous studies, where pMDI model compounds were reacted with wood, showed that carbamate (urethane) formation with wood polymers is only possible when: 1. the number of moles of isocyanate is significantly higher than the moles of water molecules in the wood, 2. high temperatures are used, and 3. the isocyanate-based compound is of low molecular weight [1]. A complementary study confirmed that covalent bond formation between a pMDI adhesive and wood does not occur [2]. PF adhesive, like pMDI, has shown strong evidence for wood cell wall infiltration [3-8]. Thus, there is a definite need to discern how wood cell wall polymers interact with PF adhesive on a molecular and Ångstrom scale. This is especially important to understand when attempting to utilize lignin byproducts as PF resin substitutes.

Citation

Yelle, Daniel J. 2013. Elucidating how wood adhesives bond to wood cell walls using high-resolution solution-state NMR spectroscopy. In: Proceedings of the 36th Annual Meeting of the Adhesion Society. 2013 March 3-6; Daytona Beach, FL. Bethesda, MD: The Adhesion Society Inc. 4 p. Available online at http://adhesionsociety.org/program2013/