Viscoelastic features of SEBS TPEs: Novel results in solid and molten states

The viscoelastic behavior of two compression molded poly(styrene)- poly(ethylene-co-butylene)-poly(styene) (SEBS) triblock copolymers were investigated. The investigated samples were synthesized by Repsol-YPF having a polydispersity index of 1.2 and weight average molecular weights of 75,000 g/mol and 200,000 g/mol. The correlation between small amplitude oscillatory flow and industrial processing is observed. The SEBS2 extrudates are found to be very smooth for all of the shear rates, while very severe surface roughening is found in SEBS1 at a shear rate of 10s^-1 and above. The results also show that for the low molecular weight sample, SEBS1, the blocking effect of the PS domain on PEB chains motion is displayed at frequencies below 1 Hz. At high shear rates, an oscillation between entangled and disentangled states of chains to the wall causes the sharkskin phenomena.