‘Non-solvent’ heat resistant binders: rheology of blends of oligoimides with liquid oligomers

Abstract

The rheology of binders based on blends of powdery oligoimides with liquid epoxy and acrylic oligomers was studied for a broad interval of concentrations, temperatures and shear rates. It was shown, that prehistory of blends, phase organization of a system and the extent of approaching the equilibrium state determine the rheological behavior of blends. At equilibrium, depending on the state variables, the investigated blends can be single-phase or two-phase. Furthermore, the coexisted phases are not uniform and are characterized by a complex supermolecular structure of composites. In some cases the original blends have not sufficient time to reach the equilibrium state by the beginning of the rheological test, and the system structure evolution to the equilibrium occurs during the experiment. In terms of rheology some structural transformations act in the same direction and the others act in the opposite direction promoting simultaneously both an increase and a decrease in viscosity, affecting the rheological behavior of the system. The experimental dependence of rheological parameters can be explained within the framework of the following conception: structural transformations have thermodynamic nature, they are kinetically controlled and, depending on external factors, can proceed sequentially and/or simultaneously, at the molecular, supermolecular, phase and morphological levels. The resulting data allowed determination of the most perspective compositions of binders based on oligoimides and liquid ‘temporary’ plasticizers as well as the optimal processing conditions.