The expanded polypropylene beads with microcellular structure were prepared by an autoclave-based batch foaming process using non-supercritical CO₂ as the foaming agent. Herein, smaller polypropylene micropellets (∼0.6 mm) were obtained from three kinds of polypropylene resin by underwater micro-pelletizer system. The results from differential scanning calorimetry indicated that the double melting peaks of beads moved to higher temperature with increasing saturation temperature and pressure. The kind of comonomer did not exert noticeable influence on the double melting behaviors. The X-ray diffraction of expanded polypropylene bead revealed that characteristic peaks of α-type crystal did not change compared with that of original polypropylene micropellets. The relationship between cell morphology and saturation temperature/pressure of expanded polypropylene beads are discussed preliminarily by scanning electron microscope.

Due to unique and excellent properties, carbon nanotubes (CNTs) are expected to become the next-generation critical engineering mechanical and energy storage materials, which will play a key role as building blocks in aerospace, military equipment, communication sensing, and other cutting-edge fields. For practical application, the assembled macrostructures from individual CNTs are the common paradigms such as fibers or films. As the main representative, CNT films can not only retain the unique properties of their CNTs components, but also are more likely for mass-production than other macrostructures. Therefore, in this review, we focus on preparation of CNT films and discuss their emerging applications in the field of mechanical and electrochemical energy storage/conversion. Firstly, different preparation processes are systematically summarized. Then we introduce some typical strategies to improve their mechanical performances besides strengthening mechanism. Based on the progress of mass-production and performance optimization, we further discuss their potential utilization in mechanical and electrochemical energy storage/conversion devices. Finally, future perspectives for the development of CNT films in both production and application are proposed. We hope that this review will shed light on the preparation/assembly of CNT films and integrated application of excellent properties from individual to macroscopic dimensions. Moreover, the preparation and crossscale application paradigms of CNT films also offer a good model for other macroscopic ordered assemblies of one-dimensional nanomaterials.