In situ formation of core‐shell rubber particles in polypropylene matrix by melt blending and its effects on the toughness and stiffness of the composites

Toughening of thermoplastics with a one‐phase impact modifier generally results in significant reduction in stiffness, whereas core‐shell rubber modifiers have extra structural parameters such as core rigidity and shell flexibility, by controlling which the stiffness and impact toughness of their composites can be better balanced. In this study, three kinds of polyethylene (PE) with different rigidity are used respectively to prepare polypropylene/ethylene–propylene rubber/polyethylene (PP/EPR/PE) ternary composites by melt blending, in which the EPR‐to‐PE ratio is 1:1. Atomic force microscopy‐infrared (AFM−IR) and scanning electron microscopy (SEM) results indicate that core‐shell rubber particles with a PE core and an EPR shell are formed in situ and uniformly dispersed in the PP matrix. Mechanical measurements show that at the same modifier content the PP composites toughened with these core‐shell rubber particles exhibit higher toughness and stiffness than that with EPR alone, and the more rigid the PE core, the greater the effects. These results are in quantitative agreement with a recent theoretical model, providing solid experimental evidence in support of the latter. Furthermore, this work demonstrates an economical approach to toughening PP by partial substitution of the EPR with the much cheaper PE for better performance. The effect of core rigidity and core‐shell structure on the toughness and stiffness of the PP composites was quantitatively studied. The experimental results showed that core‐shell rubber particles toughened PP composites had higher toughness and stiffness than one phase modifier (such as POE, EPR, etc.), and the more rigid the PE core, the greater the effects. These results were in quantitative agreement with the recent theoretical model. More specifically, Partial substitution of EPR with cheaper PE could reduce the cost and improve the toughness and stiffness simultaneously, killing three birds with one stone.