From Mechanism to Practice: A Review of Charring Agents for Polypropylene With Detailed Performance Analysis and Selection Guidance

Polypropylene (PP) is one of the most widely produced synthetic polymers globally, with an annual production exceeding 80 million metric tons and a market value projected to reach approximately USD 118 billion by 2032. Its excellent mechanical properties, chemical corrosion resistance, and low density have made it indispensable in automotive components, electronic appliances, packaging materials, and building construction. However, its high flammability and molten droplets are easy to ignite other materials, so flame-retardant modification is needed to improve the fire safety of PP materials. Existing reviews have focused primarily on the classification of flame retardants and the synergistic effects between various additives; they have largely overlooked the critical role of charring agents—their molecular design, charring mechanisms, and selection criteria. To address this gap, this review systematically surveys the literature published from 2010 to 2026. Systematically analyzes existing flame-retardant polypropylene formulations with a particular emphasis on recent advances in charring agents. A selection paradigm was simultaneously established for charring agents applicable to various flame-retardant polypropylene systems. According to the thermal decomposition behavior and carbon layer formation mechanism of various charring agents, the advantages and disadvantages of different charring agents were summarized according to different charring mechanisms and synergistic flame retardant mechanisms. The key role of charring agents in different formulations is deeply analyzed, which provided comprehensive theoretical guidance and technical support for the design and development of efficient, environmentally friendly, and multi-functional charring agents for a new generation of polypropylene flame retardant materials.