Exploring the physicochemical nature of PMDI/wood structural composite adhesion

The development of structure/property relationships for wood composites bonded with polymeric diphenylmethane diisocyanate (PMDI) can be achieved by observing the changes in molecular motions and molecular ordering of the wood molecules, which are the two characteristics that define a material’s viscoelastic behavior. These characteristics are easily observed using solid state nuclear magnetic resonance spectroscopy relaxation measurements. In a wood composite, if the number of molecular associations between adhesive molecules and wood molecules is large enough, we should expect to observe changes in at least some of the distributions of molecular mobility or changes in molecular arrangements when comparing the composite to whole wood. Our investigations applied inversion recovery cross polarization measurements to probe the near static motional regimes of aspen wood (Populus tremula) molecules in the presence and absence of PMDI adhesive. These molecular studies were correlated with microscopic dynamic studies obtained via dynamic mechanical analysis. Both the molecular and microscopic dynamics were used to explain the macroscopic properties observed for whole panel composites.

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