Home » Application » Elastomers » Why Is TPE Flame Retardancy So Difficult? These 7 Reasons Explain It.

Why Is TPE Flame Retardancy So Difficult? These 7 Reasons Explain It.

Views: 39 Author: Yinsu Flame Retardant Publish Time: 2026-07-07 Origin: www.flameretardantys.com

Inquire

Why is TPE flame retardancy so difficult? These 7 reasons explain it.

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 plastics mainly consist 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.

However, TPE thermoplastic elastomer formulations contain numerous components, and due to the structural and property differences among these components and unclear mechanisms, flame retardant treatment presents considerable difficulty. There are also significant safety hazards during use, which imposes certain limitations on TPE product applications. So, what difficulties might be encountered in TPE flame retardant treatment?

Difficulty in flame retardant selection

Flame retardants have poor compatibility with the substrate. When the addition amount of flame retardant in the elastic system is slightly high, especially in halogen-free flame retardancy, the elastic modulus, flexibility, mechanical properties, and wear resistance of TPS decrease significantly. Melt flowability becomes poor, making the elastomer difficult to mold, and flame retardant migration tends to occur on the surface, causing environmental pollution.

Unclear flame retardant mechanism

The TPS system mainly consists of a multiphase mixed structure of rubber, polyolefin resin, plasticizer, and filler. Although halogen-free flame retardancy for polyolefin resins has relatively mature formulations and examples, the flame retardant mechanisms of SEBS and polyolefins such as PP and PE are actually different. It is quite difficult for one flame retardant to simultaneously flame retard multiple plastic components.

Plasticizers reduce flame retardancy

To reduce hardness and achieve a softer hand feel, TPE plastics often require the addition of plasticizers (white oil), typically mainly four types: No. 26, No. 32, and No. 70 white oils. Due to the differences in limiting oxygen index and flowability among these four oil types, and the inherent flammability of oil substances, the flame retardancy of elastomers is greatly reduced. Therefore, how to resolve the relationship between plasticizers and flame retardancy when producing low-hardness products, and how to select the type of white oil, is crucial.

Based on the above potential difficulties, what practical problems might be encountered during the processing of flame-retardant TPE, and what are the corresponding solutions?

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.

Summary

Flame-retardant TPE/TPU plastics are 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.