Great improvement of low‐temperature impact resistance of isotactic polypropylene/ethylene propylene diene monomer rubber blends by traces of carbon nanotubes and β‐nucleating agents

Abstract

In this work, a considerable low-temperature toughness enhancement of isotactic polypropylene (iPP) was achieved by adding 30 wt% ethylene propylene diene monomer rubber (EPDM) as well as traces of β-nucleating agent (β-NAs) and carbon nanotubes (CNTs). The impact strength of the iPP/30 wt% EPDM blend with 0.1 wt% β-NAs reached 6.57 kJ/m 2 at −20°C, over 2.5 times of pure iPP. A slightly improved impact strength was further found in the β-nucleated iPP/30 wt% EPDM at the presence of 0.05 wt% CNTs. The presence of traces of CNTs, β-NAs, and EPDM displayed synergistic low-temperature toughness reinforcement effect on the iPP blends. The underlying toughening mechanism was attributed to the formation of a great amount of voids and plastic deformation of iPP matrix affected by CNTs, β-NAs, and EPDM.Our work provided a feasible strategy to significantly increase the low-temperature toughness of iPP. methods. The addition of β-nucleating agents (β-NAs) proved to be the most effective method to induce many β-crystals in iPP. Copious amounts of studies have revealed that the introduction of β-NAs can only significantly improve the room-temperature toughness of iPP. 12-15 For instance, Grein et al 16 found that the sole addition of β-NAs was insufficient to enhance the low-temperature toughness of iPP, and the fracture behavior is susceptible to the crystalline structure only when the test temperature exceeded the glass transition temperature. Likewise, the tensile strength and modulus of β-iPP were also deteriorated, due to the loosely stacking crystal structure of β-crystals. The rigid nanofillers like calcium carbonate (CaCO 3 ) and carbon nanotubes (CNTs) were usually acted as the reinforcement fillers for polymers. 17-20 Liu et al 21 observed that the tensile strength and Young's modulus of iPP/CNT nanocomposites with 3 wt% CNTs were improved by 72 and 37%, respectively, as compared with pure iPP. Interestingly, the rigid nanofillers also showed the potential to enhance the impact toughness of iPP. Wang et al 22 reported that iPP nanocomposites with 0.5 wt% CNTs demonstrated the improved impact strength by 27% compared with the pure iPP. As a matter of fact, either one aforementioned factors is not enough to significantly improve the low-temperature toughness of iPP. Thus, a few studies were carried out to incorporate two of above factors. Kotek et al 23 investigated the synergistic effect of ethylenepropylene copolymer (EPR) and β-NAs on the low-temperature toughness of iPP and found that the elongation at break of the β-nucleated iPP/EPR blends was increased by 121% at a low temperature (−40°C). Hu et al 24 observed that the iPP blends containing β-NAs and ethylene-octene copolymer exhibited excellent low-temperature impact toughness compared with pure iPP and revealed the combined effects of matrix crystalline structure and the amorphous chain mobility on the low-temperature toughness of the blends. Nonetheless, there are only a few publication focused on the low-temperature toughness of iPP, not even to mention t...

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