Blends of styrene-butadiene-styrene triblock copolymer and isotactic polypropylene. Reinforcing effect of polypropylene at high temperatures

Blends of styrene-butadiene-styrene (SBS) triblock copolymer with isotactic polypropylene (iPP) or maleic anhydride-grafted polypropylene (MAP) were p repared in a twin-screw extruder. Static and dynamic experiments at room te mperature in previous works showed that the added homopolymers have a signi ficant influence in the improvement of the general mechanical properties of the SBS when the homopolymer is the dispersed phase. Our aim was to study the reinforcing effect as a function of temperature. When the glass transit ion of the polystyrene blocks in the SBS is approached (40 degreesC-50 degr eesC in static experiments), there is a significant worsening of the failur e properties, as well as a profile change in the stress-strain plot. If a r einforcing hard phase is added, these changes can be decreased. The tempera ture dependence of the reinforcing effect of the added homopolymer was eval uated with the analysis of tensile experiments in terms of various theoreti cal models. A modified activation energy model with temperature-dependent p arameters was used to describe the nonlinear regime and quantitatively comp are the properties of the different blends with those of pure SBS.