Method for Determining Degree of Cure of Phenolic Resin

A simple and rapid spectrophotometric method is described for measuring the degree of cure of phenol-formaldehyde neat resin or glue made from it. Neat resin is a solution of phenol-formaldehyde polymer and sodium hydroxide catalyst. The method makes use of the ratio of absorbance at wavelength of 287 and 302 micromillimeters of water-extractable materials from partially cured neat resin or glue. The effect of wood extractives and glue additives is negligible. The influence of pressing temperature and time on degree of cure of a phenolic plywood glue can be determined by this method. With a curing temperature of less than 110?C, presumably the presence of water in the glue bond interferes with bond formation. The results indicate that quality of glue bond, measured by percentage of wood failure and shear strength of bonds, is very sensitive to the degree of cure as measured by this spectrophometric method.

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