Polyurethane Raw Materials (TDI, MDI): Properties and Supply

Polyurethane Raw Materials as an Industrial Category

Polyurethane (PU) is one of the most versatile polymers in modern industry, first synthesised by Otto Bayer in the late 1930s. The key components for its production are aromatic isocyanates such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI), which account for about 95 percent of the global diisocyanate market[reference:15]. The specificity of the category is determined by the fact that TDI and MDI, while possessing similar reactivity, have fundamental differences in physical state, toxicity and application areas, requiring the buyer to have a clear understanding of the properties of each product. TDI at room temperature is a low-viscosity, highly volatile liquid, making it preferred for flexible foam production. MDI, on the other hand, is a solid or high-viscosity liquid with low vapour pressure, which ensures its wider application in rigid polyurethane foams, coatings and elastomers. Both products are hazardous chemicals and require strict adherence to safety measures during handling and transportation.

Chemical Identification and Classification of Grades

TDI is identified by CAS number 26471-62-5 (isomer mixture) or 584-84-9 (2,4-isomer). In international trade, HS code 2929.10 is used for isocyanates. The most common commercial grade TDI 80/20 contains 80 percent of the 2,4-isomer and 20 percent of the 2,6-isomer. The melting point of TDI is about 14 degrees Celsius, so at room temperature it is a liquid, and the molecular weight is 174.20 g/mol[reference:16]. A less common grade TDI 65/35 contains 65 percent of the 2,4-isomer. MDI is identified by CAS number 9016-87-9 (polymeric MDI) or 101-68-8 (monomeric 4,4'-MDI). The melting point of pure MDI is about 38 degrees Celsius, so at room temperature it is a solid[reference:17]. The molecular weight of MDI is 250.25 g/mol. Main commercial forms include monomeric MDI (pure 4,4'-isomer), polymeric MDI (pMDI, a mixture of oligomers with functionality 2.6 to 2.9) and MDI prepolymers. Polymeric MDI is a dark brown liquid with a viscosity of 150 to 250 mPa·s at 25 degrees Celsius and an NCO group content of 31 to 32 percent[reference:18].

Regulatory Framework and Quality Standards

Circulation of isocyanates and articles made from them in Russia and the EAEU is regulated by Customs Union technical regulations, in particular TR CU 005/2011 for packaging, TR CU 021/2011 for food contact, TR CU 007/2011 and TR CU 017/2011 for products in contact with children and skin. The quality of isocyanates is regulated by GOST 26952-86, international standards and suppliers technical specifications. International standards used for identification and control include ASTM D5155 for NCO group content, ISO 14896 for isocyanate group content, ASTM D1638 for viscosity, ASTM D4663 for density. For food contact and medical devices, additional sanitary-chemical and toxicological tests are carried out.

Physico-Chemical Properties and Comparison of TDI and MDI

Key physico-chemical parameters of TDI determine its behaviour during processing. TDI 80/20 is a clear liquid from colourless to light yellow with a pungent odour. The NCO group content is not less than 48 percent, dynamic viscosity at 25 degrees Celsius is about 3 mPa·s, density is 1.22 g/cm3[reference:20][reference:21]. TDI is characterised by high reactivity and low viscosity, ensuring good mixing with polyols and rapid foaming. However, the high volatility of TDI creates increased requirements for ventilation and personal protective equipment. Polymeric MDI (pMDI) is a dark brown liquid with an NCO group content of 30.5 to 32 percent and a viscosity of 150 to 250 mPa·s at 25 degrees Celsius[reference:22]. Unlike TDI, MDI has a significantly lower vapour pressure, which reduces the risk of inhalation exposure but requires heating during processing due to high viscosity. MDI provides higher strength and heat resistance of the final polyurethanes but is less reactive than TDI. Chemical resistance of both isocyanates is high: they react with water, amines, alcohols and acids, so they require storage in sealed containers under nitrogen.

Mechanism of Action and Functional Role

In polyurethane production, TDI and MDI act as the isocyanate component, which reacts with polyols (compounds containing hydroxyl groups) to form urethane linkages. The reaction proceeds by a polyaddition mechanism: the hydroxyl group of the polyol attacks the electrophilic carbon atom of the isocyanate group, forming a urethane linkage[reference:23]. Catalysts play a key role in regulating the balance between the gelation (polymerisation) and gas formation (foaming) reactions. TDI, due to its low viscosity and high reactivity, ensures rapid and uniform foaming, making it ideal for flexible polyurethane foams. MDI, with its higher functionality and low volatility, provides high crosslink density, heat resistance and dimensional stability, which are necessary for rigid foams, coatings and elastomers. To achieve optimal properties, TDI and MDI are often used in blends, for example, in an 80:20 ratio for flexible foam production.

Applications by Industry

Flexible polyurethane foam production remains the largest consumer of TDI. Foam for furniture, mattresses, car seats and packaging is produced mainly from TDI 80/20. MDI is used less frequently in this segment but finds application in high-resilience foams and integral skin foams for the automotive industry. Rigid polyurethane foams for thermal insulation of buildings, refrigerators and pipes in PU insulation are produced from polymeric MDI (pMDI)[reference:25]. Elastomers, coatings, adhesives and sealants are also important application areas. MDI is used for thermoplastic polyurethanes (TPU), cast elastomers, sports surfaces and high-strength adhesives. TDI finds application in the production of urethane rubbers, coatings and artificial leather[reference:26]. Automotive, construction, furniture and footwear industries remain key drivers of demand for both isocyanates.

Comparison with Alternative Materials

Compared to aliphatic isocyanates (e.g., HDI), TDI and MDI have higher reactivity and provide greater rigidity and strength of final products but are inferior in weather resistance and light stability. Aliphatic isocyanates are used for transparent and non-yellowing coatings, while TDI and MDI are preferred for foams, elastomers and adhesives. Compared to TDI, MDI provides higher heat resistance and strength but is less processable due to high viscosity and the need for heating. TDI is preferred for flexible foams and fast processes, MDI for rigid foams and critical structural materials. Blends of TDI and MDI allow a compromise between processability and performance properties.

Common Processing Challenges

The most frequent problems when working with TDI and MDI are:

• Loss of seal and contact with moisture. Isocyanates react with water to release CO2 and form insoluble urea compounds, leading to foaming, turbidity and reduced product quality. Storage must be in sealed containers under nitrogen.
• Failure to observe temperature regime. TDI freezes at temperatures below 14 degrees Celsius, requiring heating before use. MDI requires heating to 40-50 degrees Celsius to reduce viscosity, but overheating above 60 degrees Celsius can cause dimerisation and turbidity.
• Insufficient mixing. Due to high reactivity, TDI and MDI require intensive and rapid mixing with polyols. Insufficient mixing leads to uneven density and foam defects.
• Ignoring toxicity. TDI is highly volatile and can cause respiratory irritation and allergic reactions. MDI is less volatile but also requires protection of skin and eyes. Work must be carried out in well-ventilated areas using PPE.
• Incompatibility with catalysts and additives. Some catalysts and surfactants can cause premature reaction or impair foam stability.

Quality Control and Laboratory Methods

Quality control of isocyanates includes incoming analysis, document verification and laboratory testing. Key parameters for TDI: NCO group content (not less than 48 percent by ASTM D5155), viscosity at 25 degrees Celsius (about 3 mPa·s), density (1.22 g/cm3), colour, hydrolyzable chlorine content, acidity. For polymeric MDI: NCO group content (30.5 to 32 percent), viscosity at 25 degrees Celsius (150 to 250 mPa·s), density (1.23 g/cm3), free monomeric MDI content. For food contact and medical devices, additional tests for isocyanate migration are carried out. Laboratory confirmation is especially important because isocyanate defects (moisture contamination, dimerisation) appear only after reaction with polyols.

Storage and Transportation Conditions

TDI is stored in sealed steel containers under nitrogen at temperatures of 15 to 25 degrees Celsius. At temperatures below 14 degrees Celsius, TDI crystallises, so before use it must be heated to 40-45 degrees Celsius and thoroughly mixed. MDI is stored in sealed containers under nitrogen at temperatures of 20 to 30 degrees Celsius; to prevent crystallisation of monomeric MDI, the temperature must be maintained above 38 degrees Celsius, but for polymeric MDI 20-30 degrees Celsius is sufficient. Transportation is carried out in specialised steel tankers, drums or IBC containers. For export supplies, sea and rail routes are used in compliance with dangerous goods requirements. TDI and MDI are classified as dangerous goods class 6.1 (toxic substances), requiring special marking and accompanying documents.

Analogue Selection and Interchangeability

Isocyanate analogue selection is one of the key services of the portal. We help replace imported grades with comparable alternatives based on NCO group content, viscosity, reactivity and functionality. The algorithm includes analysis of the current grade and its technological parameters, determination of permissible deviations in key parameters, selection of options from available sources (Russia, China, other regions), verification of certificates and laboratory data, and organisation of trial batches for testing on the customer equipment. When selecting an analogue, not only NCO groups and viscosity but also the isocyanate type (TDI or MDI), isomer composition, free monomer content, acidity and compatibility with specific polyols and catalysts are considered. Replacement may require adjustment of the formulation and temperature regime.

Supply Scheme: Worldwide

The portal organises TDI and MDI supplies worldwide. There is no domestic TDI production in Russia, so demand is fully covered by imports. China and the Republic of Korea are the main suppliers of TDI to Russia[reference:27]. The situation with MDI also depends on imports: polymeric MDI is not produced in Russia, and existing projects are at the discussion stage[reference:28]. The largest global isocyanate producer is Wanhua Chemical Group (China), which owns BorsodChem[reference:29]. Each supply is treated as a separate project with an individual scheme covering grade selection, quality verification, logistics and customs clearance.

Logistics and Customs Clearance

Isocyanate logistics includes sea, rail and road routes. TDI and MDI are classified as dangerous goods, requiring the use of specialised tankers and containers, as well as compliance with dangerous goods transportation rules. Customs clearance is supported by the portal broker: document preparation, HS code 2929.10 classification, certification and interaction with control authorities. The logistics scheme is built for the specific route and customer requirements.

FAQ

How does TDI differ from MDI?

TDI is a low-viscosity, highly volatile liquid used for flexible foams. MDI is a solid or high-viscosity liquid with low vapour pressure, used for rigid foams, coatings and elastomers. MDI provides higher strength and heat resistance.

Why does TDI require heating before use?

TDI crystallises at temperatures below 14 degrees Celsius. Before use, it must be heated to 40-45 degrees Celsius and thoroughly mixed to restore homogeneity.

Can TDI be replaced with MDI?

Complete replacement is possible only in some applications, as TDI and MDI have different properties and require formulation adjustments. TDI is preferred for flexible foams, MDI for rigid foams. TDI/MDI blends are used to achieve a compromise.

What documents accompany a supply?

Material safety data sheet (MSDS), quality certificates, declarations of conformity with TR CU, origin documents. For export batches, documents confirming compliance with the importing country requirements.

Are small batches available for testing?

Yes, trial batches from 25 kg are available for most grades. Terms are agreed individually.

Conclusion

Polyurethane raw materials (TDI and MDI) remain the foundation for the production of all types of polyurethanes, from flexible foams to rigid insulation panels and high-strength elastomers. A processor success depends on the correct choice of isocyanate considering its properties and application area, confirmed quality and stable supply. The portal helps select analogues, organise logistics and customs clearance, ensuring supply chain transparency worldwide.

Contact Us

If you are looking for TDI or MDI isocyanates or need advice on grade selection, analogue search and worldwide supply organisation, please contact our team at info@apptrade.ru. We will help you find the right product, verify documentation and organise supply.