The creep behavior of semicrystalline carbon nanotube/polypropylene nanocomposite: A coarse-grained molecular study

Polypropylene (PP) is vulnerable to creep under constant loads, which is a serious problem for PP-based applications. By incorporating carbon nanotubes (CNTs), the CNT/PP composite exhibits improved creep resistance, while the CNT aggregation with high contents could limit the improvement. In order to ensure the long-term durability, the creep response of CNT/PP composite with different CNT contents should be carefully characterized. In this paper, the coarse-grained models of CNT/PP nanocomposite with various CNT contents are constructed, which are subjected to constant loads at various levels. It is found that the threshold stress and energy barrier for the initiation of fracture show an initial increase and a subsequent decrease, with the transition at 3 wt%. The decline of creep properties with high CNT contents is related to the limited CNT restriction effect on the PP chain behaviors, which is resulted from the sliding between CNT chains and the accelerated interfacial sliding between CNT and PP due to increased interfacial voids, as observed from the behaviors and interactions of investigated molecules and chains during creep. This study provides insights into the molecular creep behavior of CNT/PP nanocomposite, which contributes to the understanding of degradation of composite materials under constant loads.