Morphology and Rheological Behavior of Maltene_ polymer Blends. I. Effect of Partial Hydrogenation of Poly(styrene-block-butadiene-block_styrene-block)- Type Copolymers

摘要

Because of the importance of the maltene_ polymer interaction for the better performance of polymermodified asphalts, this article reports the effects of the molecular characteristics of two commercial poly(styreneblock- butadiene-block-styrene-block) (SBS) polymers and their partially hydrogenated derivatives [poly{styreneblock[( butadiene)1x_(ethylene-co-butylene)x]-block-styreneblock} (SBEBS)] on the morphology and rheological behavior of maltene_polymer blends (MPBs) with polymer concentrations of 3 and 10% (w/w). Each SBEBS and its parent SBS had the same molecular weight and polystyrene block size, but they differed from each other in the composition of the elastomeric block, which exhibited the semicrystalline characteristics of SBEBS. Maltenes were obtained from Ac-20 asphalt (Pemex, Salamanca, Mexico), and the blends were prepared by a hot-mixing procedure. Fluorescence microscopy images indicated that all the blends were heterogeneous, with polymer-rich and maltene-rich phases. The rheological behavior of the blends was determined from oscillatory shear flow data. An analysis of the storage modulus, loss modulus, complex modulus, and phase angle as a function of the oscillatory frequency at various temperatures allowed us to conclude that the maltenes behaved as pseudohomogeneous viscoelastic materials that could dissipate stress without presenting structural changes; moreover, all the MPBs were more viscoelastic than the neat maltenes, and this depended on both the characteristics and amount of the polymer. The MPBs prepared with SBEBS were more viscoelastic and possessed higher elasticity than those prepared with SBS.