Influence of morphology on rheological and mechanical properties of SEBS‐toughened, glass‐bead‐filled isotactic polypropene

The influence of morphology of glass‐bead‐filled isotactic polypropene containing 0–20 vol% thermoplastic elastomers (TPE) on mechanical and rheological properties was investigated. Polystyrene‐ block ‐poly(ethene‐ co ‐but‐1‐ene)‐ block ‐polystyrene(SEBS) and the corresponding block copolymer grafted with maleic anhydrid (SEBS‐ g ‐MA) were used as thermoplastic elastomers, realizing, in the first case, a three‐phase morphology with separately dispersed glass beads and SEBS particles. In the second case, SEBS‐ g ‐MA forms an elastomeric interlayer between glass beads and polypropene matrix, comprising core–shell particles. Young's modulus and tensile yield stress of the hybrid composites decrease with an increase in TPE volume fraction due to low stiffness and strength of TPE. In comparison with the three‐phase morphology of hybrid composites with SEBS, SEBS‐ g ‐MA interlayers effect a reduced stiffness of the hybrid composites but improve interfacial adhesion and, thus, tensile yield stress. Rheological storage and loss moduli increase with an increase in glass bead and TPE volume fraction. Due to improved interfacial adhesion, melt elasticity and viscosity are enhanced by the SEBS‐ g ‐MA interlayer when compared with separately dispersed SEBS. Consequently, the reduced stiffening effect of the glass beads due to SEBS‐ g ‐MA interlayer decreases mechanical elasticity, whereas improved interfacial adhesion, also promoted by the SEBS‐ g ‐MA interlayer, enhances tensile yield stress and melt elasticity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2499–2506, 1998