Maintaining modulus of polypropylene composites with ultra-high low temperature toughness by synergistic branched polyethylene and nucleating agents

Abstract

In this work, the synergistic effect of highly branched polyethylene (HBPEs, s = 1, 2) elastomers featuring dendritic structure and α-type nucleating agents (NA1, NA2) on the toughness and stiffness of block polypropylene (PP–B) was investigated. Blends of PP-B/HBPE/nucleating agent ternary systems were prepared, yielding materials with exceptionally high low-temperature toughness and minimal stiffness loss. The results indicate that HBPE enhances the low-temperature impact strength of the system but leads to a reduction in modulus. After the addition of the nucleating agent, both the low-temperature toughness and stiffness of the blend are improved simultaneously. The PP-B/HBPE2/NA2 (90/10/0.2) blend achieves the optimal balance between low-temperature toughness and stiffness, with its low-temperature impact strength increasing by a factor of 7 compared to PP-B, reaching 56.9 kJ/m2, and a bending modulus of 1110 MPa, nearly identical to PP-B. Dynamic mechanical properties and phase morphology results indicate that HBPE reduces the glass transition temperature of the rubber phase in the blended system and exhibits good compatibility with PP-B. Analysis of the crystallization behavior reveals that the significant increase in the crystallization temperature of PP-B and the substantial reduction in the size of spherical particles observed in PP-B/HBPE/NA blends are facilitated by NA1 and NA2. Additionally, NA1 and NA2 promote the transformation of the PP-B matrix into α-type crystals and enhance the crystallinity of PP-B.