Toughness enhancement of PP/EVA/LDH composites by controlling β nucleating agent and annealing treatment

Abstract

In order to use polypropylene (PP) more efficiently without destroying its excellent properties, heat treatment after molding is undoubtedly a facile and effective way. In this work, the temperature and time are used as the main treatments for the process regulation of PP/ethylene vinyl acetate copolymer/layered double hydroxide (PP/EVA/LDH) composites with β nucleating agent. The toughness, crystallization behaviors, and crystal morphologies of PP/EVA/LDH composites are investigated by using Izod impact tester, X‐ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimeter (DSC), and polarizing optical microscope (POM). The notched impact strength of the annealed 6PEL2 at 120°C for 12 h reaches 8.0 kJ/m2, which is approximately 186% higher than that of untreated PP (2.8 kJ/m2). The SEM results show that the annealing process‐induced debonding of the phase interface and the enhancement of cavitation enhance the energy dissipation behavior of 6PEL2 under impact loading, which is strongly supported by the increase of folded surfaces on the fracture plane and the pull‐out deformation of the EVA phase. Furthermore, the promising toughening results of 6PEL2 are derived from the secondary crystallization rearrangement of α‐crystals, the reduction of spherical crystal sizes, and the change of crystallization behaviors of β‐crystals.Highlights PP/EVA/LDH composites with nucleating agent are effectively regulated by annealing treatment. Improvement of toughness of polypropylene composites is attributed to the crystalline transformation effect on the crystals and the weak internal stresses. The formation of β‐crystals induced by the nucleating agent greatly absorbs a large amount of energy during the impact fracture.