Application of a piperazine pyrophosphate intumescent flame retardant in thin‐walled glass fiber‐reinforced polypropylene materials

Abstract To overcome the “candlewick effect” caused by glass fibers (GFs), a novel intumescent flame retardant (IFR) system (FR‐1420) composed of piperazine pyrophosphate (PAPP) and melamine polyphosphate (MPP) is used to induce flame retardancy in GF‐reinforced polypropylene (PP/GF). The thermal stability, combustion behavior, char formation, and flame‐retardant mechanism of the IFR‐PP/GF samples are investigated by thermogravimetric analysis (TGA), the limiting oxygen index (LOI), UL‐94 test, cone calorimeter test, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. When the FR‐1420 content is increased to 25 wt%, the 0.8 mm UL‐94 V‐0 grade is achieved and the LOI increases to 39.0%, overcoming the “candlewick effect” caused by GFs in the thin‐walled PP composite. The IFR‐PP/GF composite creates a continuous and compact char layer after combustion. It is concluded that the charring of FR‐1420 greatly weakens the candlewick effect of the GF. Moreover, the carbon layer wrapped on the surface of the GF is beneficial for the formation of a more continuous and compact carbon layer throughout the combustion zone, consequently protecting the PP composites during combustion, and resulting in better flame retardancy of the IFR‐PP/GF composite than the PP/GF composite.