On October 19, the "2020 National Flame Retardant Academic Annual Conference" was successfully held in Zhuhai. The conference was organized by the Flame Retardant Materials Committee of the China Petroleum and Chemical Industry Federation, the Flame Retardant Committee of the China Ordnance Society, and the National Engineering Research Center of Flame Retardant Materials at Beijing Institute of Technology. Attendees included universities, research institutions, and leading enterprises engaged in flame retardant material research and production. Experts from the industry gathered to discuss the development of flame retardants and materials, sharing scientific achievements. Hundreds of professional papers from various industries were presented at the conference.

At the opening ceremony, 11 individuals were recognized as "Outstanding Workers in the Flame Retardant Industry for 2020" and awarded plaques and certificates. Mr. Zhou Kan, General Manager of Pusaifu, was honored with the title of "Outstanding Innovative Worker in Flame Retardant Industry - 2020 National Flame Retardant Academic Annual Conference." Mr. Zhou Kan's pragmatic, exploratory, and innovative spirit has made outstanding contributions to the flame retardant industry.

Moving forward, Pusaifu will continue to pursue technological innovation, focusing on the research and development of new environmentally friendly halogen-free flame retardants. We will collaborate with outstanding enterprises in the industry, share resources and research findings, and create value for our customers while prioritizing the safety of society and public property. We remain committed to advancing the halogen-free flame retardant industry.

Two of Pusaifu's research papers—*"Halogen-Free Intumescent Flame Retardant System for Polypropylene Meeting UL94 5VA Standards"* and "Comparative Study of Two Flame Retardants in High-Gloss Polypropylene Materials"—were selected for the conference proceedings, contributing to academic exchange and promoting progress in the flame retardant field.
 

Halogen-Free Intumescent Flame Retardant System for Polypropylene Meeting UL94 5VA Standards

Liu Huaxia, Chen Zhizhao, Zhou Kan(Pusaifu Phosphorus Chemical Co., Ltd., Qingyuan)

Abstract

This study evaluates three halogen-free flame retardants representing two typical systems - ammonium polyphosphate-based (EPFR-100D) and piperazine pyrophosphate-based (EPFR-100DM, 110D5VA) - in polypropylene (PP) composites. Experimental results demonstrate that at loading levels of 45%, 42%, and 38% respectively, all formulations achieve UL94 5VA rating at 2mm thickness. The 110D5VA-modified PP system exhibits optimal mechanical properties among the tested samples.

Keywords

Polypropylene, Flame retardant, UL94 5VA, Performance

Introduction

Polypropylene (PP), as one of the five major general-purpose resins, finds extensive applications in injection molding, film production, and fiber manufacturing. However, its inherent flammability necessitates flame-retardant modification. While halogenated flame retardants offer high efficiency at low loadings, they generate toxic fumes during combustion, failing to meet increasingly stringent environmental requirements. Conventional halogen-free alternatives, though environmentally preferable, typically demonstrate inferior flame retardancy compared to halogen-based systems via radical quenching mechanisms - particularly for demanding applications like new energy vehicle components, heater housings, and microwave enclosures. Such high-performance applications often require multicomponent synergistic formulations.

The UL94 standard represents the most widely adopted flammability test protocol for plastics, with its 5VA classification being the most rigorous - requiring specimens to withstand five 5-second flame applications without perforation (for plaques) or flaming drips (for bars), with after-flame time under 60 seconds. While achieving UL94 5VA certification has become the benchmark for premium PP products, this performance typically comes at the expense of mechanical properties. Our research therefore focuses on developing optimized halogen-free synergistic systems that meet UL94 5VA requirements at reduced additive loadings while preserving material integrity.
 

1 Experimental Section

1.1 Materials

Flexural strength 22 MPa; Flexural modulus 876 MPa; Notched impact strength 610 J/m Halogen-free intumescent flame retardants: Ammonium polyphosphate system (EPFR-100D)

Piperazine pyrophosphate system (EPFR-110DM)

110D5VA

(All from Pusaifu Phosphorus Chemical Co., Ltd., Qingyuan) Antioxidants Lubricants Anti-dripping agents  
 

1.2 Equipment
UL94 vertical burning tester Universal testing machine (Model CMT4204, Shenzhen New SANS Materials Testing Co., Ltd.) Melt flow indexer (Model XRL-400A, Chengde Precision Testing Machine Co., Ltd.) Izod impact tester (Model ZBC-25B, Shenzhen New SANS Materials Testing Co., Ltd.)  

1.3 Experimental Procedures

1.3.1 Sample Preparation

PP resin was dried at 90°C for 3 hours. The dried PP was then uniformly mixed with flame retardants and additives according to the formulation, followed by extrusion and pelletization using a twin-screw extruder. The pellets were dried and injection-molded into standard test specimens and plaques for evaluation.

1.3.2 Performance Testing
Tensile properties: ASTM D638 Flexural properties: ASTM D790 Notched Izod impact strength: ASTM D256 Melt flow index: ASTM D1238 Flammability: UL94 standard

2 Results and Discussion

2.1 Mechanical Properties

As shown in Table 2, phosphorus-nitrogen based halogen-free flame retardants significantly reduce the mechanical properties of polypropylene. This is primarily attributed to their poor compatibility with PP due to substantial polarity differences. The flame retardants disrupt the continuity of the PP matrix, consequently deteriorating its mechanical performance.

2.2 Flame Retardancy (UL94 5VA Test Method)

Table 4 results demonstrate that 110D5VA exhibits the highest flame retardant efficiency, followed by the piperazine pyrophosphate system, while the ammonium polyphosphate system shows relatively lower efficiency in UL94 5VA tests. This occurs because the intense flame in 5VA testing cannot be sufficiently blocked by the char layer formed solely through ammonium polyphosphate or piperazine pyrophosphate systems. The excessive heat causes melting on the non-flame-exposed side, inducing severe PP molecular chain movement that tears the molten polymer (Figure 3).

Figure 3 UL94 5VA test specimen showing top-side tearing

110D5VA contains synergistic components that not only stabilize the char layer but also provide structural reinforcement within the matrix, effectively preventing top-side tearing (Figure 4).

Figure 4 UL94 5VA test specimen performance

3 Conclusions

(1) Phosphorus-nitrogen halogen-free flame retardants demonstrate poor compatibility with PP, leading to reduced mechanical properties;

(2) The piperazine pyrophosphate system shows higher flame retardant efficiency in PP than ammonium polyphosphate systems;

REFERENCES

[1]  Silva K D , Ray S , Taylor M , et al.Synergistic Effects of Nano-Fillers on Halogen-Free Fire RetardantPolypropylene Composites[M]// TMS 2015 144 th, Annual Meeting & Exhibition.Springer International Publishing, 2015.

[2]  Zhu Changjiang. Preparation of novel halogen-free intumescent flame retardants and their application in polypropylene[D]. 2018.  

[3]  KURODA,Shintaro. The Development of FlameRetardant Polypropylene : UL94 CLASS 5VA[C]// 2011.

[4]  Wei K , Jianpeng G , Xiaolong Z , et al.Though Properties of Halogen-free Flame-retardant Long-glass-fiber-reinforcedPolypropylene[J]. China Plastics, 2015.

[5]  Luo Jiyong, Zhang Daohai, Tian Qin, et al. Research progress on halogen-free flame retardant polypropylene synergized with inorganic nanoparticles[J]. Materials Reports, 2019(S1).

[6]  Tao Siping, Lu Zhanquan, Xiao Peng. Study on high-performance halogen-free flame retardant polypropylene technology[J]. China Plastics Industry, 2012(03):118-121.

[7]  Cui Zhe. Preparation and properties of polypropylene/ethylene-propylene-diene monomer/intumescent flame retardant/layered double hydroxide nanocomposites[D]. University of Science and Technology of China, 2009.

Halogen-freeintumescent flame retardant system is used in UL94 5VA level polypropylene

Abstract In this paper, two types offlame retardants of ammonium polyphosphate system (EPFR-100D) and piperazinepyrophosphate system (EPFR-100DM, 110D5VA) are used in polypropylene. Theexperimental results show that: when EPFR -100D, EPFR-100DM, 110D5VA when theaddition

amount reaches 45%, 42%, and 38% respectively, the flame retardantgrade of polypropylene can reach 2mm thickness UL94 5VA, and the polypropylenesystem using 110D5VA has relatively best physical and mechanical properties.

Key words Polypropylene, Flameretardant, 5VA, Performance