What's the Real Difference When It Comes to Flame-Retardant TPE? 

Let's Break It Down

Thermoplastic elastomer (TPE), also known as artificial rubber or synthetic rubber, combines the excellent properties of traditional crosslinked vulcanized rubber—high elasticity, aging resistance, and oil resistance—with the convenient processing and wide processing methods of ordinary plastics.

TPE mainly consists of two parts: plastic as the continuous phase and rubber as the dispersed phase. Rubber usually requires compatibility with softening oil or plasticizers. Vulcanizing agents and some auxiliary additives are also essential. Additionally, to reduce costs or improve certain properties, some inorganic fillers are added. According to material composition, TPE can be classified into: styrenic types (SBS, SIS, SEBS, SEPS), olefinic types (TPO, TPV), diene types (TPB, TPI), vinyl chloride types (TPVC, TCPE), urethane types (TPU), ester types (TPEE), amide types (TPAE), organic fluorine types (TPF), silicone types, and ethylene types, covering almost all fields of synthetic rubber and synthetic resins. Several common TPE compositions are listed below.

When selecting flame retardants, most approaches involve finding a compromise that satisfies the following basic requirements. According to value engineering principles, a "balance" must be struck to achieve optimal results: 

(1) High flame-retardant efficiency—less dosage required per unit of flame-retardant effectiveness, i.e., high efficacy/price ratio; 

(2) Must meet ecological and environmental protection requirements; 

(3) Good compatibility with the substrate, resistant to blooming, and compatible with plastic processing conditions; 

(4) Sufficient thermal stability; 

(5) Does not excessively degrade the processing performance of the flame-retarded material or the physical, mechanical, and electrical properties of the final product—achieving harmony between flame retardancy and practicality;

(6) Acceptable light stability;

(7) Abundant raw material sources, simple manufacturing processes, moderate pricing, and acceptable to users.

Some commonly used additive-type flame retardants may decompose at higher processing temperatures, which on one hand limits their use, and on the other hand restricts the processing temperature range of polymers. Many additive-type flame retardants are filler-type; to achieve the required flame-retardant specifications or ratings (such as Class A, B1, UL94-V0, etc.), large amounts often need to be added, leading to agglomeration. Poor dispersion reduces the flame-retardant efficiency and effectiveness of the flame retardant.

Another issue with flame retardants is the reduction of light stability in polymer materials. The flame-retardant effect of hindered amine light stabilizers is degraded by halogen-based flame retardants, and inorganic flame retardants also reduce the light stabilization effect of hindered phenols and thioesters. For example, zinc oxide can significantly reduce the thermal aging time of such additives. Although some small systems composed of halogen-based flame retardants and antimony trioxide can impart high OI and UL94 flame-retardant ratings to polymer materials, meeting usage standards for many places with strict fire safety requirements, this system produces large amounts of smoke during thermal decomposition and combustion, along with toxic and corrosive gases. Currently, efforts are being made to reduce the smoke generation of flame retardants during combustion.

Challenges and Strategies in Flame-Retardant TPE Processing

• Uneven Wire Surface
This frequently occurs during TPE wire processing, generally caused by improperly adjusted temperature and uneven mixing of flame retardants. It may also result from incorrect die selection, and of course is closely related to the material formulation. Experienced processors will rule out equipment issues. After repeated debugging, they can find the appropriate temperature. However, selecting suitable materials and specific formulations requires careful consideration by engineers. It is recommended to communicate more with raw material suppliers to understand material properties and processing precautions. Choosing the right material will yield twice the result with half the effort! TPU wire processing is relatively better than TPE wire surface processing.

• Wire Surface Bloom
So far, no material supplier can guarantee completely no bloom. Specific bloom manifestations include: surface whitening, oil bleeding, or fogging. With current technology, this problem has not yet been solved. It is recommended that when selecting materials, customers choose materials with slight surface whitening. This type of bloom will not affect its physical and electrical properties. Materials with surface oil bleeding should not be used, as they are prone to peeling and flaking during use. Additionally, bloom varies in severity. Good materials exhibit slight bloom, and it does not occur easily in the short term. Even if it occurs, it can be easily wiped away with a gentle hand rub.

• Surface Scratching Whitening and Peeling/Flaking
Scratch whitening is caused by the addition of PP and PE components in the material and can be improved. Some manufacturers have achieved products that do not scratch white, but this is more difficult for TPE than for TPU. If peeling and flaking occur, the quality level is quite mediocre. What needs to be emphasized here is: formulation! Process!

• Processing Difficulty
Elastomers exhibit relatively slow processing speeds, approximately 50% slower than PVC. Temperature is difficult to regulate, and considerable material is wasted during machine debugging. Additionally, machine purging is required before production, resulting in significant waste. These are unavoidable. During production, situations sometimes occur where the front-end production runs normally, but problems arise in the back-end processing. It should be noted here that off-grade materials carry risks, and caution is advised when using them.

Flame-retardant TPE/TPU is a very unique material. The flame retardancy challenges of TPE/TPU still require everyone to put more effort into material selection, formulation, and process. Overall, it is recommended to select liquid flame retardants to reduce hardness while improving flame retardancy, and reduce the addition amount of powder flame retardants to improve product transparency. Use compatibilizers to enhance compatibility between flame retardants and the substrate, improve bloom, and significantly enhance mechanical properties. In terms of process, adopt special screw configurations to improve dispersion of flame retardants in the system, enhance flame-retardant efficiency, and improve appearance. Use novel silicone-based flame retardants with a condensed-phase flame-retardant mechanism to form an oxidation-resistant pyrolytic char layer, improving flame-retardant efficiency.

The difference in producing flame-retardant TPE often lies not in the formulation approach, but in the flame retardant itself—choose the right one, and processing is smooth, surfaces are glossy, and properties are stable. Choose the wrong one, and you'll face bloom, scratch whitening, peeling, low efficiency, and endless troubleshooting without finding the root cause. Yinsu Flame Retardant's TE-01 is a phosphorus-nitrogen synergistic halogen-free flame retardant developed specifically for TPE/TPU. Through surface modification technology, it solves the problems of poor dispersion and agglomeration that traditional flame retardants face in elastomers, achieving UL94 V-0 at moderate addition levels. It also offers good thermal stability and minimal impact on physical properties, making it suitable for SEBS, SBS, and polyester/polyether-type TPU systems.