Toughening mechanism of PP/EPR/SiO2 composites with superior low-temperature toughness

Abstract Although it has been shown that the brittle-ductile transition temperature (Tbd) of rubber-toughened thermoplastics can be effectively reduced by introducing nanoparticles, the toughening mechanism is still unknown. In this work isotactic polypropylene/ethylene propylene rubber/silica nanoparticles (iPP/EPR/SiO2) composites with excellent low-temperature toughness were prepared. It was found that Tbd could be regulated synergistically by EPR and SiO2. The phase morphology showed that as silica content increased, the interface area between PP matrix and EPR dispersed phase gradually became larger. Moreover, Tbd continued to decrease with the increase of the area of EPR relaxation peak which was due to the expansion of the interface area. According to the results of impact fracture surfaces of the composites, it was found that for composites with greater EPR relaxation peak area, yielding deformation of their matrices was more intense after low-temperature impact test. Thus, a toughening mechanism for iPP/EPR/SiO2 composites at low-temperature was proposed: the internal friction loss induced by the increased phase interfacial area between EPR and iPP matrix attenuated the velocity of the impact force, as a result, compelling high-elastic deformation occurred in iPP matrix which ultimately made the composite to behave as ductile fracture at low temperatures.