With the rapid development of the automotive industry, long glass fiber reinforced thermoplastic composites (LGF) have been increasingly applied.

Under the trend of automotive lightweighting, “replacing steel with plastics” has become a mainstream approach. By taking full advantage of LGF’s low linear expansion coefficient, high specific strength, high specific modulus, and excellent dimensional stability, its application in lightweight automotive structures effectively reduces vehicle weight, enhances power performance and handling, lowers energy consumption, and improves driving range.

Performance Analysis

1.1 Flame‑Retardant PP‑LGF Materials
Long glass fiber reinforced polypropylene (PP‑LGF) materials offer excellent mechanical properties and dimensional stability, making them widely used across various industrial fields. They can also be designed to exhibit intumescent flame‑retardant or synergistic flame‑retardant performance. These materials are mainly classified into two flame‑retardant types: nitrogen‑phosphorus based and bromine‑based.

The nitrogen‑phosphorus system forms a porous, expanded char layer on the surface of the PP matrix through the action of flame retardants. This char layer acts as a thermal and oxygen barrier, improving the strength and heat resistance of the char, effectively delaying the decomposition and oxidation of the matrix resin, and enhancing the overall flame‑retardant performance of the composite system, thereby achieving flame retardancy for the matrix resin.

Bromine‑based flame retardants primarily rely on the bromine–antimony synergistic effect. During thermal decomposition, they generate inert substances that slow down or terminate combustion. Additionally, the dense HBr produced can dilute oxygen in the surrounding air, is non‑flammable, and can form a protective layer on the material surface to inhibit burning, reduce the combustion rate, or promote self‑extinguishing.

The properties of some typical flame‑retardant PP‑LGF materials currently used in applications are summarized in Table 1.