Graessley's theory has been applied to keratin/PEO concentrated aqueous solutions giving qualitative insight to the rheology of these polymer blends in electrospinning. The shear rate dependent viscosity of different blends was compared with that of pure polymer solutions. The characteristic time tau(eta) was calculated by the minimum value of (gamma) over dot at the beginning of the non-Newtonian viscosity behavior. Flow curves of PEO (at concentration from 1.0 to 7.0 wt %) reduce to a single curve by plotting eta/eta(0) against (gamma) over dot tau(eta) Moreover, PEO solutions exhibit a linear proportionality between zero-shear viscosity and the characteristic time eta(0) proportional to tau(eta). Keratin/PEO blend solutions follow the same proportionality at very high and low keratin content, whereas linearity drops when the keratin content range from 50 to 70%. The departure from the theory has been interpreted as a sign of some interaction between the macromolecules of keratin and PEO. It was supposed that keratin displaces solvent molecules and expands the PEO chain coils increasing the relaxation time of the polymer solution. This behavior was correlated with changes in the morphology of the nanofibres produced by electrospinning from these polymer blends. Finally, additive rules to zero-shear viscosity were applied to keratin and PEO solutions, indicating that the experimental eta(0) values were higher than the theoretical ones for all the proportions of the blends, especially for high keratin amount. (c) 2008 Wiley Periodicals, Inc.