Nowadays, the microfoamed polymer materials [1
] have attracted increasing attention due to their excellent comprehensive properties. Compared with traditional foamed materials, the microfoamed polymer materials possess highly specific properties, including good thermal stability, excellent sound absorption property, low thermal conductivity and dielectric constant, etc. [4
]. As a result, microfoamed polymer materials have been widely used in transportation, the military industry, aerospace, electronics, daily necessities, and so on [7
]. When the microfoamed polymer materials are used as structural materials, the comprehensive properties of the materials need to be higher, especially the mechanical properties, because the foamed materials have a certain weight loss [8
]. Generally, the mechanical properties of the microfoamed polymer structural materials are mainly determined by the morphology of cells in the material, such as the shape, diameter, density, and distribution of the cells [11
]. Therefore, further study of the foaming quality and mechanical properties, such as the impact property of the microfoamed polymer materials, is worthwhile. On the other hand, isotactic polypropylene (iPP), as a widely used semicrystalline polymer, has a considerable commercial importance owing to its numerous advantages, such as low cost, easy processing, recyclability, and excellent mechanical performances [13
]. iPP also has various crystalline modifications, such as α, β, γ, etc. [16
]. Due to its excellent comprehensive properties, it is usually produced into various forms of polymer products [16
Recently, more and more researchers have focused on the research of foamed polymer materials, especially the PP-based materials. Rizvi et al. [17
] fabricated a microfoamed PP/PTFE material, and the formative fibrous PTFE significantly improved the foaming quality with higher bubble density and volume expansion ratio. The foamed PP/PTFE composites exhibited a high sorption capacity to CO2
. Keramati et al. [18
] also studied the effects of nanoclay on the foaming behavior of PP/ethylene–propylene–diene monomer rubber (EPDM). They found that the added nanoclay was dispersed evenly in the PP matrix, and a small amount of nanoclay could hugely increase the cell density and reduce the cell size. Kuboki et al. [19
] have explored the effects of cellulose content and processing condition on the foaming quality and mechanical properties of the PP foamed composites reinforced with fiber by injection molding, and the results showed that the strength, flexural modulus, and notched impact property increase with the increase of cellulose content. Xi et al. [20
] also fabricated a microcellular foamed PP/GF composites, and found that the introduction of GF (glass fiber) could improve the foam structure and mechanical properties of the foamed materials. The above reports aim at the preparation of foamed materials by introducing materials such as nanoparticles, fibers, EPDM, polyolefin elastomer (POE), etc. into a polyolefin material, further studying the effects on the foaming quality and mechanical properties of the foamed materials. These methods of preparing foamed materials mainly focus on the physical foaming, while chemical foaming technology is rarely reported.
In this work, the foamed PP composites are prepared by adding different types of elastomers using the chemical foaming technology. The effects of foaming quality and the impact property of the materials are systematically studied through their structures, crystallization behavior, rheological behavior, low-temperature toughness, and so on.