Polypropylene‐based in situ fibrillation‐reinforced ternary composite foams with improved filler‐phase dispersion

In Situ Nanofibrillar Polypropylene-Based Composite Microcellular Foams with Enhanced Mechanical and Flame-Retardant Performances

With the increasing demand for plastic components, the development of lightweight, high strength and functionalized polypropylene (PP) from a cost-effective and environmentally friendly process is critical for resource conservation. In situ fibrillation (INF) and supercritical CO2 (scCO2) foaming technology were combined in this work to fabricate PP foams. Polyethylene terephthalate (PET) and poly(diaryloxyphosphazene)(PDPP) particles were applied to fabricate in situ fibrillated PP/PET/PDPP composite foams with enhanced mechanical properties and favorable flame-retardant performance. The existence of PET nanofibrils with a diameter of 270 nm were uniformly dispersed in PP matrix and served multiple roles by tuning melt viscoelasticity for improving microcellular foaming behavior, enhancing crystallization of PP matrix and contributing to improving the uniformity of PDPP’s dispersion in INF composite. Compared to pure PP foam, PP/PET(F)/PDPP foam exhibited refined cellular structures, thus the cell size of PP/PET(F)/PDPP foam was decreased from 69 to 23 μm, and the cell density increased from 5.4 × 106 to 1.8 × 108 cells/cm3. Furthermore, PP/PET(F)/PDPP foam showed remarkable mechanical properties, including a 975% increase in compressive stress, which was attributed to the physical entangled PET nanofibrils and refined cellular structure. Moreover, the presence of PET nanofibrils also improved the intrinsic flame-retardant nature of PDPP. The synergistical effect of the PET nanofibrillar network and low loading of PDPP additives inhibited the combustion process. These gathered advantages of PP/PET(F)/PDPP foam make it promising for lightweight, strong, and fire-retardant polymeric foams.

The Injected Foaming Study of Polypropylene/Multiwall Carbon Nanotube Composite with In Situ Fibrillation Reinforcement

This paper explored the injection foaming process of in situ fibrillation reinforced polypropylene composites. Using polypropylene (PP) as the continuous phase, polytetrafluoroethylene (PTFE) as the dispersed phase, multi-wall carbon nanotubes (MWCNTs) as the conductive filler, and PP grafted with maleic anhydride (PP-g-MA) as the compatibilizer, a MWCNTs/PP-g-MA masterbatch was prepared by using a solution blending method. Then, a lightweight, conductive PP/PTFE/MWCNTs composite foam was prepared by means of extruder granulation and supercritical nitrogen (ScN₂) injection foaming. The composite foams were studied in terms of rheology, morphological, foaming behavior and mechanical properties. The results proved that the in situ fibrillation of PTFE can have a remarkable effect on melt strength and viscoelasticity, thus improving the foaming performance; we found that PP/3% PTFE showed excellent performance. Meanwhile, the addition of MWCNTs endows the material with conductive properties, and the conductivity reached was 2.73 × 10^-5 S/m with the addition of 0.2 wt% MWCNTs. This study's findings are expected to be applied in the lightweight, antistatic and high-performance automotive industry.