Effects of Self‐Assembled β‐Crystal Nucleating Agents on Crystallization and Microcellular Foaming Behavior of Long‐Chain Branched Polypropylene

ABSTRACT Long‐chain branched polypropylene (LCBPP) has become the material of choice for foaming due to its high melt strength and excellent strain hardening properties. In this work, different β‐crystal nucleating agents were melt‐blended with LCBPP. The morphology of the nucleating agents, melt strength, and melting crystallization behavior of the mixtures were characterized using POM, rotational rheometer, XRD, and DSC. After selecting the nucleating agent WBG‐II, high‐temperature self‐assembly was performed. The impact strength of the mixture containing 5 phr of the nucleating agent reached 5.36 kJ/m2, which is a 30% improvement compared to pure polypropylene samples. At a foaming temperature of 138°C, with scCO2 as the physical foaming agent, various microcellular LCBPP foams were prepared using the autoclave foaming method. When the content of the self‐assembled nucleating agent increased to 5 phr, the foam expansion ratio decreased from 25 times to about 2 times, the cell size was refined from 142 μm to about 7 μm, and the cell density increased from 2 × 107 to 3.8 × 109 cells/cm3. Simultaneously, the complex structure of the self‐assembled nucleating agent and the induced composite cells synergistically enhanced the compressive strength of the polymer foam.