Probing the Hydroxymethylated Resorcinol Coupling Mechanism With Stress Relaxation
Keywords:HMR, adhesion, stress relaxation, cooperativity
AbstractThe isothermal stress relaxation of dry wood is well described by the Kohlrausch-Williams-Watts relationship. This provides a direct measurement of the relaxation time and cooperativity for amorphous wood-polymer segments. The insights afforded by this approach are demonstrated for wood treated with hydroxymethylated resorcinol, HMR, coupling agent. HMR significantly stiffens wood against stress relaxation as revealed by large increases in the measured relaxation time and coupling parameter. In contrast, phenol impregnation has no effect on the coupling parameter or the relaxation time. This reveals that the simple bulking of the wood cell wall does not explain the action of HMR. Instead, this suggests that HMR chemically crosslinks the cell wall. Consequently, one aspect of the HMR coupling mechanism may involve covalent crosslinking and stabilization of amorphous regions against water swelling and other mechanical stresses.
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