Boron-Based Polyphosphazene-Functionalized Mxene Nanosheets for Polypropylene Composites with Improved Mechanical Properties and Flame Retardancy Applications

Developing high-performance resins with exceptional thermal oxidation stability, flame retardancy, smoke release suppression, and mechanical properties is an important industrial challenge. However, current flame-retardant design strategies often compromise other composite material properties. Especially when using polyolefin, unsaturated polyester, and other noncharred materials, it is usually necessary to add large amounts of flame-retardant fillers. In this study, a nanosynergist (Ti3C2Tx@PPD) for functionalizing Ti3C2Tx nanosheets with boron-based polyphosphazene was designed and adopted for a piperazine pyrophosphate/polypropylene (PAPP/PP) system as an application example. By controlling the chemical environment of cyclotriphosphazene, the condensed phase characteristics of polyphosphazene were preserved, but also an atypical vapor phase flame-retardant mechanism was activated. The combination of P/N/B elements and Ti3C2Tx exhibited excellent catalytic char-forming performance compared to others in the literature. Only 2% of incorporated Ti3C2Tx@PPD reduced the total heat released from the composite by 66.3%, the total smoke released by 71.8%, and the fire growth index by 49.4%. The incorporation of Ti3C2Tx@PPD inhibited deterioration of the mechanical properties of the composite. In addition, the pyrolysis path of Ti3C2Tx was revealed under a special environment. This study lays the foundation for the functional design of Ti3C2Tx nanomaterials that can be used in various applications that require high-performance resins

Innovative Design and Preparation of Hierarchical BP–OH@HAP Structure: Study on Flame Retardancy and Mechanical Characteristics of UPR Nanocomposites

The flammability and brittleness of unsaturated polyester resin (UPR) were two serious problems that limited its application in high-precision fields. Here, the rod-shaped hydroxyapatite (HAP) was anchored on the surface of hydroxylated black phosphorus nanosheets (BP–OH) through a hydrothermal reaction to obtain a highly stable black phosphorus-based nano flame retardant (BP–OH@HAP). Owing to the exposure of many hydroxyl groups, BP–OH@HAP was well dispersed in the UPR matrix, and UPR nanocomposites with 0.5 wt % BP–OH@HAP realized a 71% increase in impact strength. The presence of BP–OH@HAP also greatly inhibited the combustion of UPR nanocomposites. In detail, the UPR composites with 2 wt % BP–OH@HAP achieved a 47.0% decrease in peak heat release rate (PHRR) along with 23.1% reductions in total heat release (THR), revealing the excellent ability of BP–OH@HAP to inhibit polymer combustion. In addition, UPR/BP–OH@HAP 2.0 achieved a 46 s increase in the time to PHRR (tPHRR) and a 62% reduction in the fire growth index (FGI), indicating that the fire spread of UPR/BP–OH@HAP 2.0 was significantly suppressed. Therefore, this work obtained the UPR/BP–OH@HAP nanocomposite with high fire safety through the innovation of inorganic nanotechnology, which provided new research ideas for improving the toughness and flame-retardant properties of UPR-based nanocomposites