Determination of the gel point of a polyfurfuryl alcohol resin and characterization of its curing rheokinetics

The determination of the gel point of a resin is a key in order to design and optimize the manufacturing process of composite materials. In this work, the gel point of a biobased polyfurfuryl alcohol (FA) resin has been determined by rheological isothermal tests at different curing temperatures. The obtained gel times using three different amounts of catalyst (2, 4 and 6 % wt.) were correlated to temperature by the Macosko model; to predict the gel time at any temperature within the studied range. Furthermore, the evolution of the complex viscosity of the FA resin after its gel point has been studied as a function of the amount of catalyst and temperature. The rate of viscosity change was compared to the rate of viscosity change during the pre-gel stage, and a clear reduction was observed. Thus, the two different curing stages (pregel and post-gel) can be clearly identified by the rheological behavior of the resin system. The evolution of the viscosity has been modeled using widely used rheokinetic models. Finally, since rheological properties such as viscosity and complex modulus (G*) are highly sensitive to the molecular weight of a polymeric system, and they can be used as indicators of the degree-ofcure of a resin, the measured complex modulus of the FA resin has been used to determine degree-of-cure profiles for FA resins with different amounts of catalyst, and at a range of temperatures.