Mechanical behavior of multi-phase clay-modified polypropylene blend systems

This research focuses on the toughening and strengthening mechanism in multi-phase polypropylene (PP) blends with clay at different locations. Two main categories of PP blends, based on the toughener phase used, are studied: PP/Noryl/clay blend and PP/rubber/clay blend. For PP/Noryl/clay blend, clay location can be controlled via sequential mixing technique. For PP/rubber/clay blends, clay/rubber morphology is mainly determined by rubber characteristics and the interactions between rubber phases and clay.; For PP/Noryl/clay blend system, it is found that clay can maintain the rigidity of polymer comparing with the one without clay. But the clay location has little effect on the stiffness. This may be due to the low clay concentration in the blends. It is shown that clay location has great effect on toughening mechanisms in different PP blends. Toughness is decreased dramatically in the blend with clay at interface. Debonding mechanism is found to be a third toughening mechanism other than crazing and shear yielding in this blend. It is believed that debonding suppresses effective energy dissipation process, i.e., crazing.; For PP/rubber/clay blend system, stiffness is increased in PP/styrene-ethylene-propylene/clay (PP/SEP/clay) in which clay resides in the matrix. Pre-mixing of SEP and clay is helpful for obtaining small clay particle size and good particle dispersion, which are crucial for strengthening PP. For PP/styrene-butadiene-styrene/clay (PP/SBS/clay) system, clay is encapsulated within SBS rubber particles. Rubber/clay particles act like rubber particles in all. Therefore, stiffness is decreased and toughness is increased. Rubber cavitation is found to be the main toughening mechanism in this system.