It was shown that a solid-state deformation of polypropylene (PP) being in the form of partially disentangled powder is possible by blending with another molten polymer. During mixing of disentangled polypropylene powder with polystyrene at the temperature below melting of polypropylene crystals the shear forces deform powder grains into nanofibers. All disentangled powder particles larger than 0.7 mu m underwent deformation into nanofibers having the mean thickness between 100 and 200 nm. Polypropylene nanofibers got entangled during blending and form a network within polystyrene matrix, reinforcing it. Network of entangled nanofibers can be further deformed with pronounced strain hardening and strength reaching 70 MPa at 135 degrees C. Blending resulted in generation of PP nanofibers and formation of PP nanofibers entangled network, thus formation of all-polymer nanocomposites in one step compounding. The crucial feature for ultra-deformation of PP grains by shearing during mixing is disentanglement of macromolecules. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1983-1994