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

Abstract

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.

Lightweight and High Mechanical Properties of In Situ Poly(ethylene terephthalate) Reinforced Polypropylene Composite Foams by Chemical Foam Injection Molding

“…This result is consistent with our previous works. 21,27 The immiscible nature of the PET phase and PP matrix, associated with strong elongation flow action during the INF process, are major factors influencing the formation of the fibrillar network. Additionally, the average diameter of PET fibrils in the PP/PET(F)/Talc composite is significantly reduced from 368 to 231 nm when compared with the PP/PET(F) sample.…”

“…26 In addition, during the INF process, the in situ nanofibrillar phase can improve the dispersion and enhance the reinforcing effect of micro/nanofillers. 23 Some studies have indicated that the lightweight, high-strength, and functionalized polymer foams can be fabricated by INF technology with microcellular batch foaming 22,24,27 and injection foaming with supercritical N 2 . 8,15,16,21 Nevertheless, to our best knowledge, there is almost no relevant research about the synergistic effect of the in situ fibrillar phase and fillers on the foamability of PP based on CFIM technology.…”