Self-reinforcing and toughening isotactic polypropylene via melt sequential injection molding

Polymer material exhibits a trade-off between toughness and stiffness, therefore, it remains difficult to develop a strategy that simultaneously realizes improved mechanical strength and toughness. Inspired by the bamboo-like structure, an efficient and simple melt sequential injection molding is proposed to fabricate a controllable skin-core structure of iPP samples with self-reinforcement and toughness. With increasing the melt injection number, the shear layers containing shish-kebabs are progressively thickened, resulting in an effective improvement of mechanical properties. The tensile strength increased from 35.1 to 55.3 MPa for the melt injection number from one to four, meanwhile the toughness was enhanced from 23.1 to 53.6 kJ/m². A simple theoretical model was derived and utilized to describe the experimental data. Theoretically calculated tensile strength of sample with entirely shish-kebabs can even reach 222.9 MPa via this technology, which is much higher than that of most engineering plastics and polymer composites. This work not only provides an efficient way to fabricate high-performance general plastics for engineering purposes but also a new opportunity to understand the fundamental issues about the mechanism of the self-reinforced polymers.