Reinforcement for polypropylene via self-assembly of β-form nucleating agent: new insight on the perpendicular orientation of lamellae

In this work, the reinforcing mechanism of β-form hybrid shish-kebabs induced by β-form nucleating agent (NA) on polypropylene (PP) tapes was revealed. The results showed a hierarchical orientation of fibrous crystalline profile and well-organized β-form PP lamellae existing in the β-form hybrid shish-kebabs, which exhibited remarkable reinforcing effect on the PP tapes in the orientated direction where the tensile strength increased from 44 to 54.7 MPa compared with isotropic one. However, when the tapes were strained perpendicular to the initial orientation, the tensile strength of NA-modified PP tapes decreased to 32.1 MPa. Theoretical analysis was conducted, and a new model was established to interpret this phenomenon. We suggest that specific layer structure constructed by well-organized lamellae and the tie molecules within the β-form hybrid shish-kebabs be responsible for the reinforcing effect due to the promoted fibrillation which stabilizes the crazing zone.