Rotational viscometry for the study of urea-formaldehyde resins

Abstract

Rotational viscometry as a generally recognized method for rheological measurements of non-Newtonian liquids was used for the study of commercial urea-formaldehyde resins. The measurement results were analysed using the power law function with evaluation of the consistency and flow indices. The resins were observed during their storage until alkali-promoted poly-condensation led to gelation. It is suitable to differentiate two periods in the course of the poly-condensation process-the initial period of slow viscosity growth and the following period of fast structuration. Regularity in the change of values of the flow index, calculated from data obtained with two rotational viscometer models, permits to characterize the flow behaviour of urea-formaldehyde resins in the initial period of polycondensation. The results of the rheokinetic study were compared with the data obtained with standard methods. In the relationships trends were found, which are consistent with conceptions about the formation of the resin structure and processes, occurring during the initial period of polycondensation.