Boron-Based Polyphosphazene-Functionalized Mxene Nanosheets for Polypropylene Composites with Improved Mechanical Properties and Flame Retardancy Applications
Wei Liu, Lin Wang, Longlong Ding, Congwu Zhang, Weiye Yang, Dongli Liu, Weizhao Hu
Abstract
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 (Ti 3 C 2 T x @PPD) for functionalizing Ti 3 C 2 T x 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 Ti 3 C 2 T x exhibited excellent catalytic char-forming performance compared to others in the literature. Only 2% of incorporated Ti 3 C 2 T x @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 Ti 3 C 2 T x @PPD inhibited deterioration of the mechanical properties of the composite. In addition, the pyrolysis path of Ti 3 C 2 T x was revealed under a special environment. This study lays the foundation for the functional design of Ti 3 C 2 T x nanomaterials that can be used in various applications that require high-performance resins.