Structural and Physical Changes in Phenol−Formaldehyde Resol Resin, as a Function of the Degree of Condensation of the Resol Solution

Abstract

The structural and physical differences of phenol−formaldehyde resol resins collected during a resin synthesis were studied, as a function of the degree of condensation of the resin. The structural and physical properties of the resins were analyzed using nuclear magnetic resonance (NMR) spectroscopy, viscosity and refractive index measurements, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), solids content analyses, and contact angle determinations on wood veneer. As a result of the condensation reactions, the amount of methylol groups and free reactive sites of phenolic species decreased, while the amount of methylene bridges increased, as a function of the degree of condensation. The changes in the resin structure resulted in an increase in the viscosity, refractive index, and average molar masses, and a decrease in reactivity, with increasing degrees of condensation. The wetting of the surface of the wood veneer was reduced as the viscosity and average molar masses of the resin solution each increased.