RHEOKINETICS OF UREA-FORMALDEHYDE RESINS GELATION

Rheokinetics of gelation of aqueous suspensions of urea-formaldehyde o ligomers was studied. Experiments were carried out with a rotational v iscometry method using two regimes of deformation: constant stress or constant shear rate. It was shown that a maximum on a viscosity vs. ti me curve is observed and it reflects sedimentation of rather large gel led particles. Then, gelation of a whole system (determined as the poi nt of the unlimited growth, of viscosity) takes place. Experiments car ried out at different temperatures gave us an apparent activation ener gy which depends on the oligomer content in a composition. Characteris tic points of a rheokinetic curve do not depend on the concentration o f a curing agent. The problem of the temperature increase due to heat dissipation is also discussed. It was demonstrated that shear stress i s a kinetic factor influencing the rate of a reaction. A master curve for a rheokinetic curve was constructed, time scale being reduced by t he gel time.