Viscosity master curves and predictions of phenolic resin solutions through early aging

Dipping in solutions of phenolic resins is a common practice in obtaining various composite materials. One key control requirement is to identify the degree of aging of resin solutions in the dip tank, which would age inevitably through time. This work systemically studies the early aging of resin solutions, accompanied by the increase of molecular weights, viscosity, and glass transition temperature. Using rheological methods, this work formulates equations relating the viscosity, aging time, aging temperature, and measurement temperature, and provides a master surface. The aging time – aging temperature superposition is also validated. Based on the shifting factor, the unmeasurable slow aging around room temperature can now be predicted. During the early stage of aging, the glass transition temperature of the solution increases significantly. We propose a “viscosity-temperature index”, for instance, the ratio of viscosities at 0 and 30 °C. It can significantly reduce the error due to solution density, concentration, and viscosity measurement, and can be determined by a low-cost Brookfield-like viscometer near the production line. Combing the universal master curve of the viscosity-temperature index, now we can conveniently and precisely identify the aging degree of phenolic resin solutions.