Crystallization, mechanical, and electromagnetic properties of conductive polypropylene/SEBS composites

Polypropylene (PP) and styrene-ethylene-butylene-styrene triblock copolymer (SEBS) are blended with a weight ratio of 70/30 to serve as the matrices. The prepared polymer blends were evaluated by tensile, flexural, and Izod impact tests, as well as by differential scanning calorimetry (DSC), optical microscopy, and scanning electron microscopy. The optimal PP/SEBS matrices were then combined with graphene nanosheets (GNs) and carbon fibers (CFs) by a melt compounding method to form conductive polymer composites. The crystallization properties, tensile properties, conductivity, and electromagnetic interference shielding effectiveness (EMISE) of the composites were evaluated by DSC and tensile strength and conductivity tests. In PP/SEBS blends, the SEBS acted as the nucleating agent of PP, thereby increasing the crystallization temperature and accelerating the crystallization rate, without significant influence on the degree of crystallinity. An increase in SEBS loading is inversely proportional to the tensile strength, tensile modulus, flexural strength, and flexural modulus of the PP/SEBS blends, but is highly proportional to the impact strength. In addition, the tensile strength of the conductive PP/SEBS/GN conductive composites decreased with the increase in the amount of GNs, with a percolating threshold of approximately 1.6 vol%. A distinct synergistic effect of the GNs and CFs on the conductive PP/SEBS/GN/CF composites was not achieved until the total loading level was 15 wt%. Optimal conductivity and EMISE of the conductive PP/SEBS/GN/CF composites were achieved at GN/CF ratios of 10/5 wt% and 5/10 wt%, respectively.