Ternary blends of high-density polyethylene (HDPE) with atactic polystyrene (PS) and styrene- ethylene/butylene-styrene block copolymer (SEBS) were deformed by plane-strain compression in a channel die. The samples were deformed up to the true strain of 1.8 (compression ratio of 6) at 100 degrees C. Thermal and mechanical properties of the deformed blends were studied in addition to the study of the deformation process. The basic mechanism of plastic deformation is crystallographic slip, the same as that active in deformation of plain HDPE and binary blends of HDPE and PS. This slip is supplemented by the plastic deformation of an amorphous component. In blends of high SEES content, the role of deformation of an amorphous component by shear and flow increases markedly due to reduced overall crystallinity of these blends. In such blends an amorphous component includes a semicontinuous embedding of crystallites, and therefore, the deformation process is dominated by deformation mechanisms active in a more compliant amorphous phase. Consequently, with increasing the content of SEES in the blend, the texture of the oriented blends changes from a single-component (100)[001] texture to a texture with a strong fiber component in addition to a (100)[001] component. In blends with high content of SEES, the crystalline lamellae of polyethylene do not undergo fragmentation up to the compression ratio of 6, while in blends with low and moderate content of SEES, such lamellar fragmentation was detected. (C) 2000 John Wiley & Sons, Inc.