NONLINEAR STRESS PROPERTIES OF POLY(STYRENE-BLOCK-BUTADIENE-BLOCK-STYRENE) MELT UNDER ELONGATIONAL AND SHEAR DEFORMATION

Effects of block copolymerized structure on nonlinear stress propertie s under elongational and shear deformation were investigated. Samples used in this study were poly(styrene-block-butadiene-block-styrene) (S BS, weight rate of S/B = 40/60) and polystyrene (PS) as a reference. T ensile stress-strain and shear stress relaxation properties were measu red at the molten state. SBS showed high elasticity after reaching the yield point under elongational deformation at room temperature. PS me lt showed substantial tensile stress increase after the yield point as strain rates increased. However, SBS melt did not exhibit noticeable tensile stress rise at higher elongation, and this property was almost independent of strain rates. Stress relaxation experiments revealed t hat the damping function of SBS melt was more strain-softening than th at of PS melt. The results suggested that the block copoly merited str ucture decreases melt elasticity under elongational and shear deformat ion. A transmission electron micrograph indicated that the lack of mel t elasticity in SBS melt is caused by orientation of the lamellar stru cture toward the stretched direction during deformation. (C) 1995 John Wiley and Sons, Inc.