ABS, PC, PP... What Flame-Retardant Materials Are Used in Automotive Components?

ABS, PC, PP... What Flame-Retardant Materials Are Used in Automotive Components?

Currently, polymer materials are ubiquitous in automotive components such as under-hood parts and new energy vehicle battery packs. The application of polymer materials in automotive parts and the demand for improving vehicle safety have promoted the development of flame-retardant polymer materials. Currently applied flame-retertant polymer materials are mainly based on PP, PU, ABS, and PC. Composite materials (alloys), PA, PBT, and PMMA are also used based on the specific requirements of automotive components.

1. Flame-Retardant PP
Polypropylene (PP) is the most used polymer material in automotive plastics. It offers excellent chemical resistance, simple processing, and low cost, making it suitable for car dashboards, battery pack housings, door panels, pillars, seat back panels, bumpers, etc. However, PP has poor flammability before adding flame retardants, with a Limiting Oxygen Index (LOI) of 17.8%, making it flammable after ignition. Current research on flame-retardant PP for automotive applications, both domestically and internationally, focuses on modifying the polypropylene matrix. Simultaneously, by adding low-toxicity, halogen-free flame retardants, polypropylene composites with excellent mechanical properties and flame retardant effects are developed to meet the flame retardancy needs of automotive parts.
Flame retardants suitable for polypropylene are mainly additive types. These include halogen-based flame retardants (brominated or bromine-antimony synergists), inorganic filler flame retardants, melamine polyphosphate, melamine cyanurate, phosphazenes, and phosphate esters. With the implementation of stringent environmental policies and the widespread adoption of halogen-free requirements, the shift towards halogen-free flame retardants for polymer materials has become an inevitable trend.

2. Flame-Retardant ABS
ABS is a typical material suitable for automotive painting due to its strong durability and corrosion resistance on plastic surfaces, and it is also used in the production of automotive components. ABS resin contains only C, H, and O elements, resulting in poor stability at high temperatures and easy combustion. The ignition process also produces odorous gases and black smoke particles, posing safety risks if used directly in vehicle parts. Therefore, flame retardancy and heat resistance must be modified before use.
Halogenated flame retardants offer high efficiency, with brominated types generally providing better flame retardancy than chlorinated ones, despite greater environmental concerns. However, relying on their exceptionally outstanding flame retardant effect and low cost, brominated flame retardants remain prominent in some areas with strict flame retardancy standards and materials. Approximately 70% of electronic products use brominated flame retardants, with decabromodiphenyl ethane mainly used for ABS. Nonetheless, with the popularization of environmentally friendly halogen-free requirements, applying halogen-free, phosphorus-nitrogen flame retardants to ABS is also gaining attention.
Melt-blending ABS with polycarbonate (PC) yields PC/ABS composites. This material combines the advantages of both ABS and PC, featuring high heat distortion temperature and stability, while improving processability. PC/ABS alloy is currently the resin alloy with the highest output and fastest growth rate, applicable to car dashboards, battery packs, automotive body parts, and other components. PC resin itself is a flame-retardant, self-extinguishing material with a UL94 V-2 rating. However, its flame retardancy decreases when blended with ABS, necessitating flame-retardant modification before use in automotive parts. Currently, commonly used flame retardants for PC/ABS alloy modification include halogenated flame retardants, phosphorus-based flame retardants, and nano flame retardants.

3. Flame-Retardant PC
As one of the top five engineering plastics, polycarbonate (PC) is used in automotive component production due to its high strength, high impact resistance, heat resistance, and other advantages. Examples include automotive instrument panels, lighting systems, heating panels, defrosters, and bumpers made of PC alloys. With consumption upgrading, the development of new energy vehicles and lightweight trends, domestic demand for PC is also increasing. PC itself possesses certain flame retardancy, offering advantages compared to common polymers like PE and PP, with an LOI of 21%-24% and a UL94 V-2 rating. However, in application areas with relatively high flame retardancy requirements for automotive components, this performance is insufficient, requiring flame-retardant modification.
Brominated flame retardants can significantly improve the flame retardancy of PC, commonly using decabromodiphenyl ether (DBDPO), tetrabromobisphenol A (TBBPA), etc. However, brominated flame-retardant materials are prone to decompose at high temperatures, generating corrosive gases that can damage automotive parts. Additionally, adding brominated flame retardants seriously affects the transparency of PC and does not meet the requirements of environmental policies. Currently, the most widely used phosphorus-based flame retardants in industrialized PC products are mainly TPP (triphenyl phosphate), RDP (resorcinol bis(diphenyl phosphate)), and BDP (bisphenol A bis(diphenyl phosphate)). TPP is solid at room temperature with poor thermal stability, tends to volatilize at PC processing temperatures, and only exerts a gas-phase flame retardant effect. RDP and BDP are liquids at room temperature with good thermal stability, capable of exerting both gas-phase and condensed-phase flame retardant effects. Furthermore, BDP has good compatibility with PC and can act as a plasticizer. Therefore, the PC/BDP system has become a widely used system, with a typical BDP addition ratio of 10%.
Moreover, silicon-containing compounds, as a new generation of environmentally friendly flame retardants, are gradually gaining attention due to their high efficiency, low toxicity, non-polluting characteristics, and minimal impact on the processing and physical properties of PC, such as polysiloxanes. The selection of flame retardants for automotive PC is also leaning towards a halogen-free environment, improving the comprehensive performance of PC by adding various additives or creating composite flame retardants. Additionally, by using composites with ABS, PBT, etc., PC's processability and flame retardancy can also be optimally enhanced.

4. Other Flame-Retardant Polymer Materials
PP, PU, ABS, and PC are currently the main flame-retardant polymer materials applied in automotive component production. Additionally, composite materials prepared by melt-blending two or more polymers are also widely used today. Examples include PC/ABS, PC/PBT, PC/flame-retardant composites, etc.