How do the core mechanical properties affect the toughening of polypropylene with core-shell particles?

Core-shell particles have been extensively used to toughen thermal plastic polymers, in which the core is composed of different thermal plastic polymers such as polypropylene (PP), polyethylene (PE), polystyrene (PS), et al, whereas the shell is composed of rubber or elastomer. However, how the core mechanical properties affect the toughness of core-shell particles toughened polymers has remained unclear up to now. In this article, five kinds of polyethylene (PE) were used to in situ prepare PE-ethylene propylene rubber (EPR) core-shell particles toughened polypropylene (PP) composites. The results show that the PE cores can be yielded during ductile fracture, and the higher the yield stress of PE, the higher the impact toughness is. The notch impact strength increases from 39.2 to 56.7 kJ/m2 with increasing PE yield tress from 10.0 to 28.5 MPa for the composites when the content of PE and PE-EPR core-shell particles in the PP matrix is fixed at 20 wt%. Moreover, it can be well interpreted that the notch impact strength of PP-EPR core-shell particles toughened PP composites is obviously higher than that of PE-EPR core-shell particles toughened PP composites produced by ExxonMobil Chemical Co. because the yielding stress of PP is higher than that of PE [1]. Furthermore, the results show that the notch impact strength increases with increasing PE content. However, excess PE can induce the transition from ductile to brittle fracture of the composites, resulting in a sharp drop in toughness. However, this transition is determined by the modulus rather than the yield stress of the core material. [ABSTRACT FROM AUTHOR]