Thermal cure monitoring of phenolic resole resins based on in situ fluorescence technique

Abstract

AbstractThe thermal curing reaction of two phenolic resole resins is monitored using the fluorescence technique. The intrinsic fluorescence can be used as an indicator for cure monitoring for the first resole. As the thermal curing proceeds, the intrinsic fluorescence intensity of the resole resin decreases and exhibits a few nanometers of redshift. The fluorescence intensity of the emission maxima is correlated with the conversion measured by differential scanning spectroscopy. A linear correlation is found at three different temperatures. The intrinsic fluorescence cannot always be used for monitoring the curing process of phenolic resole resins. Thus, three intramolecular charge transfer compounds and two organic donor–π‐acceptor salts are selected and applied for the cure monitoring of the second phenolic resole resin. As the curing reaction proceeds, the fluorescence emission spectra of the probes exhibit a blue spectral shift and the intensity changes because of environmental changes. An intensity ratio method is applied in which the ratios of the low‐ to high‐intensity changes in the emission bands are used to determine the degree of the curing process. There is a smooth correlation between the intensity ratio method and the degree of cure. The method enables one to follow the changes in the polymer structure at low and intermediate degrees of the curing process (below 70%) and obtain comparable results from different types of probes during the same curing process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1773–1780, 2002