Research progress of flame retardant modified polycarbonate/acrylonitrile butadiene styrene alloys: a review

Rationale, scope, and target audience

Polycarbonate/acrylonitrile butadiene styrene alloys (PC/ABS alloys), as a class of widely utilized modified engineering plastics, combine the advantageous properties of polycarbonate (PC)—such as high impact strength, transparency, and heat resistance—with the excellent processability, cost-effectiveness, and toughness of acrylonitrile-butadiene-styrene (ABS) (Fig. 1). This synergy makes them indispensable in demanding applications across electronics (e.g., laptop housings, mobile phone components), automotive interiors (e.g., dashboards, trim pieces), and electrical enclosures. However, a critical limitation hindering their broader application, particularly in sectors with stringent fire safety regulations (e.g., IEC 60332-1 for wires/cables, FMVSS 302 for automotive interiors, UL standards for consumer electronics), is their inherent flammability. Unmodified PC/ABS exhibits a low limiting oxygen index (LOI), achieves only an HB rating in the Underwriters Laboratories 94 Vertical Burning Test (UL-94 vertical burning test), produces significant heat release, Peak Heat Release Rate (PHRR) is approximately 800–1,000 kW/m², and generates toxic gases (HCN, CO) and flaming droplets upon ignition, posing substantial fire hazards.

Consequently, enhancing the flame retardancy (FR) of PC/ABS alloys is not merely an academic pursuit but a critical industrial necessity driven by safety regulations, environmental concerns (phasing out halogenated FRs), and market demand for safer, high-performance materials. Research into flame-retardant modified PC/ABS has surged, exploring diverse FR systems from traditional halogens to advanced phosphorus, silicon, and synergistic combinations. This review aims to synthesize the current state of knowledge in this rapidly evolving field.

Literature search methodology

To ensure a comprehensive, unbiased, and up-to-date coverage of the literature on flame-retardant modified PC/ABS alloys, a systematic search strategy was employed. This systematic approach aimed to gather a representative body of high-quality literature, enabling a critical synthesis of the current research status, key findings, challenges, and future directions in flame-retardant modification of PC/ABS alloys. Through the comprehensive search strategy described above, a total of 120 relevant records were initially identified. The flow diagram of the literature screening and selection process is presented in Fig. S1 (PRISMA flow diagram).

Background on PC/ABS and flame retardancy need

In modern production and life, polymer materials covering plastics, rubber, fibers and other categories could be found everywhere in industry, agriculture and daily life, and they had become an indispensable part of daily life, from cutting-edge technology in national defense to key industries such as electricity, construction and transportation (Tang et al., 2017; Tang et al., 2013). Flame retardants, as a functional modification additive, were widely used in natural or synthetic polymer materials, and their use was second only to plasticizers (Wang, Yang & Guo, 2023). It had the ability to transform flammable polymers into a flame-retardant or even non-flammable state, thus effectively reducing the huge loss of life and property caused by fire (Sadeghzadeh et al., 2024; Zylstra et al., 2023; Liang, Neisius & Gaan, 2013; Realinho et al., 2014).

PC excelled in the field of material science by virtue of its excellent mechanical properties such as high toughness and high strength (Song et al., 2022), good electrical insulation and relatively high glass transition temperature (Moslan et al., 2021). ABS had good impact resistance, toughness and processability (Li et al., 2020). However, its weathering and flame-retardant properties were not as good as they should be (Huang et al., 2018). Therefore, the alloy obtained by blending PC and ABS resin combined the advantages of PC and ABS resin (Reby Roy et al., 2022). The resulting PC/ABS alloy had an improved melt flow rate and better processability than PC (Zuo et al., 2025). Due to the presence of the ABS component, the flame retardant performance of PC/ABS alloys is significantly inferior to that of pure PC (Huang et al., 2018; Realinho et al., 2018; Rahbari et al., 2018). This has made improving their flame resistance through modification a valuable and widely researched topic, attracting significant attention from both industry and academia. Cone calorimetry tests confirm that its peak heat release rate (PHRR) reaches 800–1000 kW/m², and the fire hazard is 2–3 times that of the flame-retardant modified system. These characteristics make it difficult to meet the mandatory flame retardant standards in the fields of electronic appliances (such as IEC 60332-1) and automobiles (FMVSS 302), and urgently requires flame retardant modification to enhance safety (Table S1).

Overview of flame-retardant modification for PC/ABS

Flame retardants are substances that impart flame retardancy to flammable polymers and reduce the risk of fire. It is found that there are two main types of flame-retardant modification of PC/ABS alloys: intrinsic flame-retardant modification method and additive modification method (Liu et al., 2021).

The additive modification method, which involves directly blending flame retardants with the substrate, is widely adopted due to its operational simplicity, cost-effectiveness, and suitability for large-scale industrialization. Consequently, extensive research has been conducted on various flame retardants, each with its own distinct advantages and limitations, as none are without drawbacks.

Halogenated flame retardants

Halogenated flame retardants were once extensively applied because of their remarkable flame-retardant efficiency, excellent thermal stability, abundant raw materials, and affordable prices (Liu et al., 2019; Abd El-Wahab, 2015; Badea et al., 2016). Halogenated flame retardants released a refractory gas, H-X, during combustion, and it was more dense (Hu et al., 2011; Liu et al., 2024). It was able to coat the surface of the material, thereby serving as a barrier against heat and oxygen. Moreover, only a small quantity of halogenated flame retardant needed to be added to endow the material with excellent flame-retardant properties.

Seddon & Harper (2001) conducted a study examining how Tetrabromobisphenol A (TBBPA) and Sb₂O₃ affected the properties of ABS. The study showed that the notched impact strength of ABS increased when the Sb₂O₃ particle size approached 0.1 µm. Petsom and other scholars (Petsom et al., 2003) chose 1,2-bis(2,4,6-tribromophenyl) ethane for the flame-retardant treatment of ABS. The results indicated that the flame retardant exerted a substantial influence on the notched impact strength and heat deflection temperature of ABS. However, it had a negligible impact on the tensile and flexural strengths (Wang et al., 2025). While applying halogenated flame retardants to PC/ABS alloys could yield relatively good flame-retardant outcomes (Wang et al., 2015), these flame retardants produced toxic gases during combustion. Such gases posed risks to both the environment and human health (Ullrich et al., 2022). Previously, the use of halogenated flame retardants was being phased out (Table S3) (Lee et al., 2022; Aznar-Alemany et al., 2019).

Flame-retardant modification of PC/ABS using phosphorus-based flame retardants

Previously, among flame retardants, phosphorus-based flame retardants were the most widely used in the market besides halogenated ones (Badea et al., 2016). They were more environmentally friendly than their halogen-based counterparts, emitting less smoke and exhibiting lower toxicity (Aznar-Alemany et al., 2019; Han et al., 2023; Chen et al., 2022).

Silicon flame retardants

Silicone-based flame retardants have gained increasing attention due to their excellent flame retardancy, high mobility, good mechanical properties (notably excellent low-temperature impact strength), and advantages of low smoke and toxicity. They can be classified into organic and inorganic types. Although they excel in environmental protection, low toxicity, and low smoke emission, silicone-based flame retardants remain in the early R&D stage, with scarce market products that are costly (Camino, Lomakin & Lageard, 2002; Camino, Lomakin & Lazzari, 2001).

Synergistic flame retardants

While single-flame retardants often impair mechanical and processing properties at high loadings, combining different types can create a synergistic effect. This enhances efficiency, reduces required dosage, and ultimately improves both the cost-effectiveness and performance of the composite.

Comprehensive performance comparison of flame-retardant systems

The minimum modification conditions and key performance metrics of flame-retardant systems to achieve UL94 V-0 rating are compared in Table S4. Organophosphorus flame retardants (e.g., BDP) achieve the target UL94 V-0 rating at the lowest loading of 10wt%, exhibiting 1.5 × higher efficiency than halogenated systems while maintaining 85% impact strength retention—significantly superior to phosphorus-nitrogen synergistic systems (55–65%) (Greco & Sorrentino, 1994). Silicone-based flame retardants, leveraging flexible Si-O-Si chain structures, minimize impact strength loss (>85% retention) at merely 8 wt% loading. However, their flame-retardant efficiency (LOI: 32–40%) is constrained by dispersion homogeneity (Iji & Serizawa, 2025; Wei et al., 2009). Phosphorus-silicon synergistic systems (e.g., RDP + 5% nano-SiO₂) demonstrate optimal balance: at 14 wt% total loading, LOI reaches 29–32%, peak heat release rate (PHRR) decreases by 70% (vs. unmodified), and melt dripping is completely eliminated, establishing them as the preferred solution for electronic device housings (Qiao et al., 2019). Future efforts should focus on surface modification of nano-SiO₂ or developing reactive phosphorus-silicon compounds to reduce additive costs and enhance process stability.

The incorporation of flame retardants substantially alters the mechanical properties of PC/ABS alloys (Table S5): Organophosphorus systems (e.g., BDP, 10 wt%) demonstrate optimal balance—85% impact strength retention (38.2 kJ/m²) with only 9.8% tensile strength loss (52.3 MPa), attributed to plasticizing effects mitigating matrix embrittlement (Pawlowski & Schartel, 2007). Silicone-based retardants (8 wt%) achieve the highest impact retention (>85%, 41.3 kJ/m²) via stress dissipation through flexible Si-O-Si chains, though tensile strength decreases by 4.1% due to interfacial weakening (Wei et al., 2009). High-loading systems cause severe degradation: Phosphorus-silicon compounds (DPA-SiN, 30 wt%) reduce impact strength by 50% (22.5 kJ/m²) via phase separation, while phosphorus-nitrogen systems (APP/PER, 30 wt%) incur 36.4% tensile strength loss (36.9 MPa) (Zhong et al., 2025). Industrial selection guidelines are: organophosphorus for electronics housings (balanced performance), silicone for automotive interiors (high toughness), and avoidance of P-N/P-Si compounds in structural parts (>30% strength reduction).

Significance of the study

The study of flame retardant-modified PC/ABS composites is of great significance, both academically and for promoting materials science and engineering (Table 1).

Safety is a prime concern. By applying suitable flame retardants, the fire-resistant properties of PC/ABS composites are enhanced. This reduces fire accidents, safeguards lives and property. The products can meet or exceed strict international standards like UL94 and IEC, ensuring market access. Their applications extend beyond consumer electronics to public transportation and medical equipment, sectors with strict safety regulations. Economically and socially, advances in flame retardant modification technology boost innovation and upgrading in the new materials industry while driving related industrial chains, generating employment and economic benefits, thus creating a positive feedback loop for society and the economy. A key focus of future research is the development of eco-friendly flame retardants. Though effective, traditional halogenated flame retardants pose environmental and health risks. So, there is a growing body of research on halogen-free alternatives like those based on silicon, nitrogen, and phosphorus, which are both efficient and eco - friendly.

In summary, developing and applying flame retardant-modified PC/ABS composites enhances safety, greener, and more efficient modern industrial system, promoting the coexistence of environmental protection and technology.

Future prospects

The future of flame retardant modified PC/ABS composites is highly promising. Research will focus on developing efficient, eco-friendly non-halogenated flame retardants such as phosphorus-based, nitrogen-based, silicone-based, and bio-based options from renewable resources. For instance, a recent study demonstrated that a novel DOPO-derived phosphaphenanthrene compound significantly enhanced flame retardancy in PC/ABS blends while maintaining mechanical performance. Combining various flame retardant types, like phosphorus-based and nitrogen-based ones, can achieve synergistic effects. A representative example is the use of ammonium polyphosphate (APP) with melamine cyanurate (MC), which has been shown to form an intumescent char layer that effectively inhibits heat and mass transfer during combustion. Nanomaterials like nanoclay and nanosilica can enhance both mechanical and flame retardant properties. Future flame retardants also need to have additional functions like antistatic, antibacterial, and weatherability to expand the application fields of PC/ABS composites (Watanabe et al., 2009), such as in battery shells of new energy vehicles, high-speed train interiors, and building cable sheathing. For example, a multifunctional composite integrating zinc oxide-based antibacterial agents and silicone-based flame retardants has been developed for use in high-touch public transport interiors.

With the growth of application areas, it’s crucial to establish unified international standards and test methods to regulate the market and ensure product quality and user safety. As countries tighten material flame retardant requirements, research must keep up with regulatory changes. Despite the high development costs of advanced flame retardants, process optimization and production scale-up can reduce costs and enhance competitiveness. Promoting the recycling of these composites is essential for resource recycling and environmental protection. Recent advances in chemical recycling techniques, such as aminolysis of PC/ABS blends, have shown promise in recovering high-purity monomers for reuse. From the perspective of Technology Readiness Level (TRL), various technologies for flame-retardant modification of PC/ABS are currently at different stages of development. Traditional halogen-based flame retardants, although technologically mature (TRL 9), are being phased out due to environmental concerns; organophosphorus flame retardants (e.g., BDP, RDP) have reached commercial application levels (TRL 8-9), while most silicon-based, phosphorus-silicon synergistic, and bio-based flame retardants are still in the laboratory research and pilot stages (TRL 3-6). In the future, efforts should focus on accelerating the industrialization process of high-TRL green flame retardant systems to promote the transition from laboratory innovation to large-scale application.

In the future, the development of flame retardant modified PC/ABS composites will focus on environmental friendliness, high performance, multifunctionality, and sustainability. This will contribute significantly to creating a safer, greener, and more efficient modern industrial system, providing better products and a better future for society.