Commonly Used Modification Additives for Thermoplastic Polyurethane Elastomers

Commonly Used Modification Additives for Thermoplastic Polyurethane Elastomers

At present, the status quo of the three major types of polyurethane rubber in China is: M-PUR (mixing type polyurethane rubber) shrinking, C-PUR (cast polyurethane rubber) development faster, T-PUR (thermoplastic polyurethane elastomers) momentum steady drive fast. Thermoplastic polyurethane elastomer (TPU) is a variety of polyurethane synthetic materials, usually polymerized from oligomer polyol, isocyanate, chain extender/crosslinking agent and a small number of additives, divided into polyester type and polyether type.

Because of its structure with soft and hard two chain segments, it can be molecularly designed to give the material high strength, good toughness, wear resistance, oil resistance and other excellent properties, it has both the high elasticity of rubber and plastic rigidity, known as “wear-resistant rubber”.Because of its excellent performance and widely used in automotive, construction, mining, aerospace, electronics, medical equipment, sports products and other fields, becoming a very promising synthetic material products.

Auxiliaries are important raw materials in the rubber and plastic industry, the dosage is relatively small, but the role is crucial, polyurethane from the synthesis to the processing and application of auxiliaries are indispensable. At present, additives cover the scope of synthesis, modification and blending, vulcanization and aging, etc. In the process of polyurethane synthesis commonly used additives are catalysts, polymerization blocking agents, chain expanders and chain expanding and crosslinking agents.

It should be noted that the use of catalysts will affect the high temperature performance and hydrolysis resistance of the final product of the elastomer; polymerization blocking agent to acid, chlorides are used more, the acid used most of the hydrogen chloride gas, chlorides are benzoyl chloride, ethyl dichloride, etc.; chain extender refers to the chain growth of the essential compounds of diols and diamines; and the chain extension crosslinking agent refers to the participation in both the chain growth reaction, but also in the formation of the chain between the links of compounds, such as tertiary alcohols and cross-linking points. Crosslinking agent refers to the compounds that both participate in the chain growth reaction and form crosslinking points between the chain links, such as tertiary and quaternary alcohols, allyl ether glycol (not applicable to cast polyurethanes), etc. Generally, low molecular weight aliphatic diols and aromatic diols can be used as chain extenders.

Due to the limited space, this paper only organizes the commonly used additives in the current thermoplastic elastomer blending and modification process for reference.

In the polyurethane elastomer modification blending process using a variety of additives is very much, the main role of the improvement of functional properties, improve the appearance and process, according to the commonly used modification additives are lubricants, wear-resistant agent, filler, matte agent, flame retardant, thermo-oxidative aging agent, coloring agent, mildew agent, and mold releasing agent, and so on.

Lubricants

TPU commonly used lubricants are waxes, such as E wax, montan wax, etc., wax lubricants generally add a relatively small amount; stearic acid and stearate salts, such as calcium stearate, butyl stearate, oleamide, ethylidene bis(stearamide) and so on.

Simply using a lubricant, it is often difficult to achieve the purpose, sometimes need several kinds of lubricants with the use of TPU can also be used as an anti-sticking agent.

According to the relevant information Licocare RBW 102 P VITA is a renewable resource based on medium polarity, good color ester wax, can be applied in the TPU material to play an excellent lubricating effect.

The lubricant should be used in a controlled amount, as excessive amounts can lead to severe surface precipitation.

Abrasion Resistant

Wear-resistant agent is mainly to reduce the surface friction coefficient of TPU, such as silicone oil, molybdenum disulfide, graphite and polytetrafluoroethylene, etc. These modified materials have self-lubricating properties and can be used as bearing bushings and other components.

Silicone oil better brand has a variety of models of Dow Corning, PTFE low molecular weight lubrication wear a little better.

Fillers

TPU with filler materials for the purpose of reducing costs, in addition to improving heat resistance, reduce shrinkage and improve thermal conductivity and other specific requirements, fillers are mainly calcium carbonate, talc, glass beads and glass fibers.

In order to improve the compatibility between the filler and TPU resin, it is best to need the filler for the corresponding surface activation modification, commonly used filler modifiers are aluminate, titanate and silane class.

Matte Finish

Many TPU products require a matte surface, and even require a frosted appearance, according to the different requirements of the matte surface, often use a variety of materials as a matte agent to achieve the desired matte or frosted requirements.

(1) The use of resin-based matte: commonly used resins are EVA, POE, SBS dry glue, TPV and TPEE, etc., the use of compatibility and viscosity differences between the resins can be achieved to achieve different degrees of matte TPU requirements.

(2) Filled matte: commonly used calcium carbonate, talcum powder, silica, wollastonite and glass beads and other inorganic powder materials, according to the fineness of the different, choose the appropriate matte effect.

(3) Alloy-type matte: usually TPU can have some compatibility with a variety of engineering plastics, such as TPU/ABS, PVC/TPU, TPU/PA6, TPU/TPEE and other co-mingled alloy materials.

(4) Resin and filler type can be mixed. Especially the appearance of the wire matte requirements of many types, need different compounding system to achieve the purpose.

Flame Retardant

TPU in order to achieve the requirements of flame retardant, need to add different types of flame retardants, TPU with the main types of flame retardants:

• Halogen flame retardant

1. TPU can be blended with PVC, CPE and other chlorine-containing resins, adding antimony co-efficient to make a flame retardant alloy; it can also be blended with flame-retardant PVC and TPU, using phosphorus-nitrogen halogen-free flame retardant, which can achieve UL94 V0 flame retardant materials.

2. TCPP is also a commonly used flame retardant for TPU, the general additive amount of 10-15%, not excessive, otherwise it is easy to precipitate, such flame retardants are commonly used in casting PU products.

3. In addition, polyurethane elastomers can also be directly halogenated flame retardant decabromodiphenyl ethane and antimony trioxide compounding to prepare various types of flame retardant TPU elastomer materials.

• Halogen-free flame retardant system

1. Inorganic flame retardant system: aluminum hydroxide and magnesium hydroxide as the representative of the inorganic flame retardant, the additive amount is relatively large, the impact on the mechanical properties is fatal.

2. Phosphorus system: phosphate flame retardant, such as BDP, RDP, etc., this kind of liquid phosphate flame retardant, generally used in TPU foaming products more, the main problem is that the addition amount can not be too large, there is an odor, and the risk of precipitation in excess.

Since November 2024 due to TPP has been included in the REACH directive control list, and BDP and RDP contain trace amounts of TPP components, so the use of environmental risks.

Currently can be an alternative program can be used DPK, aryl phosphate ester type halogen-free flame retardants, better temperature resistance, lower odor, and does not contain TPP, tests show that adding 12% in the polyether TPU can reach UL94,1.6mm V0.

3. Phosphorus and nitrogen compounding system: usually use melamine cyanurate (MCA) and aluminum diethylphosphonate (ADP) compounding system, melamine cyanurate (MCA) and aluminum hypophosphite (AHP) compounding system and so on.

Polyester-type TPU flame retardant additive amount is generally 8~12% can reach UL94,1.6mm V0 grade, while the polyether-type TPU needs to add more than 35% to reach UL94,1.6mm V0, if you need to wire flame retardant level of VW-1, the amount of additive needs to be larger, so the impact on the mechanical properties is also very large.

Thermal Stabilizers

• Thermal stabilizers generally refer to antioxidants, such as 1010, 1076, 264 and other main antioxidants, 168, DSTP and other auxiliary antioxidants, and the amount of additive is generally in the range of 0.1~0.3%.

• UV absorbers can significantly improve the UV resistance of aromatic isocyanate polyurethane, commonly used UV absorbers are UV531, UV234, UV329 and so on. The UV absorber UV-326 (trade name) is one of the more representative benzotriazole UV absorbers, with the advantages of stable performance, low toxicity and strong UV absorption.

• Commonly used light stabilizers are hindered amine type GW622, GW944, GW770 and so on. The added amount is generally 0.1~0.3%.

• Anti hydrolysis agent: polyester TPU is particularly easy to hydrolyze in humid environments, so it is necessary to add anti-hydrolysis agent, widely used in the industry is the carbodiimide class of compounds, the market is generally BASF and Vantage Rousse company products.

Colorants

The colorful appearance of polyurethane depends mainly on colorants, of which there are two main types: organic dyes and inorganic pigments.

TPU color material currently the main problem is the stability of UV resistance, color durability, the solution is mainly through the choice of TPU resin and the choice of colorants.

Anti-mold Agent

Polyether-type polyurethane has strong anti-mold ability, for 0~1 level, basically not subject to microbial erosion, and will not grow mold. And polyester type polyurethane in hot and humid and dark environment is prone to microbial erosion and mold growth, this use of environment polyester TPU must be added mold inhibitor.

Commonly used mold inhibitors are 8-hydroxyquinolinone, pentachlorophenol, sodium pentachlorophenate, tetrachloro 4-(methylsulfonyl)pyridine, salicyltiphenylamine, phenylmercury acetate, etc., with an additive fraction of 0.1~1%.

Mold Release Agent

Polyurethane is a strong polar material with strong adhesion to both metals and polar polymers, and will be difficult to release without the use of a mold release agent.

Commonly used mold release agents are silicone, silicone oil, soap and paraffin wax and other additives. In addition, the addition of non-polar materials in the TPU modified materials can also reduce the viscosity of TPU, such as the addition of EVA, TPEE and other resins, can be a solution to the problem of difficult to release TPU injection molding.According to the information introduced by the British Wo Da has a mold release agent Incroslip SL is a special modified amide substances, add 0.3-0.5%, can effectively solve the problem of mold release difficulties.

In addition, there are many kinds of TPU additives, such as antimicrobial agents, chain expanders, antistatic agents, plasticizers and crosslinking agents, etc., the use of other varieties of plastics and similar to the use of this will not go into details.

Conclusion

The polyurethane industry is currently an emerging sunrise industry with excellent cost-performance, especially in fields such as car coatings and new energy vehicles. The consumption of PU in our country is increasing sharply year by year, and the application range of additives is gradually expanding. The variety of additives is rapidly evolving, playing a significant role in various sectors of the chemical industry, with a wide range of types and many of them having high added value.

YINSU Flame Retardant Company, with its efficient flame retardant products developed for PU materials, such as coated red phosphorus powder, red phosphorus paste, and PUP-15 white powder flame retardant, offers halogen-free and environmentally friendly solutions with high flame retardancy.