Polyurethane, as a polymer material widely used in many fields, is produced by the reaction of isocyanates (commonly MDI and TDI) with polyether polyols. As a core raw material for the polyurethane industry, China has become the world's largest supplier and consumer of isocyanates.

Among the large family of isocyanates, 1,6-hexamethylene diisocyanate (HDI), as a typical representative of aliphatic diisocyanates, is gradually becoming the focus of industrial development due to its unique properties and broad application prospects. Especially with the breakthrough in domestic technology for producing HDI from hexamethylenediamine, it brings new development opportunities and transformative momentum to the HDI industry and even the entire polyurethane industry.

1. HDI: A Specialty Isocyanate with Superior Performance and Huge Market Potential

HDI, or 1,6-hexamethylene diisocyanate, belongs to the category of aliphatic diisocyanates. Its derivatives include HDI trimer and HDI biuret. HDI and its derivatives are mainly used in the production of polyurethane coatings, elastomers, adhesives, and textile finishing agents.



Compared to aromatic isocyanates such as MDI and TDI, HDI does not contain a benzene ring in its molecular structure. This structural difference endows HDI-derived polyurethanes with many excellent properties. In terms of color retention, HDI-derived polyurethanes can maintain bright and stable colors over long periods without fading; their light retention performance ensures that the surface gloss lasts, maintaining a good appearance even when exposed to outdoor environments for a long time; anti-chalking performance ensures that the surface does not easily chalk during use, extending the service life of the material. Additionally, it has outstanding oil resistance and wear resistance, making it suitable for applications requiring high wear and oil resistance, such as industrial flooring and mechanical components.

One of the most significant advantages of HDI-derived polyurethanes is their excellent yellowing resistance. In applications where color stability is highly required, such as high-end furniture coatings, outdoor plastic products, and automotive OEM paints, HDI-derived polyurethanes can effectively resist yellowing caused by ultraviolet rays, oxidation, and other factors, maintaining the aesthetics and quality of the product. In contrast, aromatic isocyanates may perform relatively poorly in these areas, especially under outdoor UV exposure or high-temperature steaming conditions, where they might undergo chemical reactions to produce carcinogenic aromatic amines, posing certain safety hazards.

China already has globally leading capabilities in the production of traditional isocyanate products such as MDI and TDI. However, HDI, as a specialty isocyanate, had its production technology and raw materials long monopolized by foreign companies. Due to technological blockades and high production costs, the price of HDI products remained high, limiting its application primarily to some high-end areas, such as high-end coatings and high-performance elastomers, which greatly restricted the release of market demand.

There exists a substitutable relationship between HDI and traditional isocyanates like MDI and TDI. If domestic breakthroughs in HDI production technology can reduce production costs and bring HDI prices to an acceptable level for downstream enterprises, the market demand for HDI will be significantly expanded, potentially replacing traditional isocyanates in more fields.Polyurethane, as a polymer material widely used in numerous fields, is generated by the reaction between isocyanates (commonly MDI and TDI) and polyether polyols. As the core raw material for the polyurethane industry, China has already taken the lead globally in both supply and consumption capacity of isocyanates.

Within the large family of isocyanates, 1,6-hexamethylene diisocyanate (HDI), as a typical representative of aliphatic diisocyanates, is gradually becoming the focus of industrial development due to its unique properties and broad application prospects. In particular, with the breakthrough in domestic technology for producing HDI from hexamethylenediamine, this has brought new opportunities for development and transformation to the HDI industry and even the entire polyurethane industry.

1. HDI: A Special Isocyanate with Outstanding Performance and Huge Market Potential

HDI, or 1,6-hexamethylene diisocyanate, belongs to the category of aliphatic diisocyanates, and its derivative products include HDI trimer, HDI biuret, etc. HDI and its derivatives are mainly used in the production and manufacturing of polyurethane coatings, elastomers, adhesives, and textile finishing agents, among others.



Compared to aromatic isocyanates such as MDI and TDI, HDI does not contain a benzene ring in its molecular structure. This structural difference endows polyurethanes derived from HDI with many excellent properties. In terms of color retention, polyurethanes derived from HDI can maintain their bright and stable colors over long periods without fading; their gloss retention ensures that the surface remains lustrous, even when exposed to outdoor environments for extended periods, maintaining a good appearance; anti-chalking performance prevents the surface from chalking during use, extending the service life of the material. Additionally, its outstanding oil resistance and wear resistance make it suitable for applications requiring high wear and oil resistance, such as industrial floors and mechanical parts.

One of the most significant advantages of polyurethanes derived from HDI is their excellent yellowing resistance. In application areas where color stability is extremely critical, such as high-end furniture coatings, outdoor plastic products, and automotive OEM paints, HDI-derived polyurethanes can effectively resist yellowing caused by factors like ultraviolet radiation and oxidation, preserving the beauty and quality of the product. In contrast, aromatic isocyanates may be inferior in these aspects, especially under conditions of outdoor UV exposure or high-temperature steaming, where they might undergo chemical reactions to produce carcinogenic aromatic amines, posing certain safety risks.

China has already developed world-leading capabilities in the production of traditional isocyanate products such as MDI and TDI. However, HDI, as a special isocyanate, had its production technology and raw materials monopolized by foreign companies for a long time. Due to technological blockades and high production costs, the price of HDI products remained persistently high, limiting its application primarily to some high-end areas, such as premium coatings and high-performance elastomers, which significantly constrained the release of market demand.

HDI has a substitutable relationship with traditional isocyanates such as MDI and TDI. If domestic production technology for HDI can be improved, reducing production costs to a level acceptable to downstream enterprises, the market demand for HDI will greatly expand, potentially replacing traditional isocyanates in more fields, promoting the polyurethane industry towards higher-end and greener development.

2. Hexamethylenediamine (HMDA) to HDI: Technology Pathway and Localization Challenges

Currently, one of the main methods of producing HDI is through the reaction between hexamethylenediamine and phosgene. As an important raw material in this process, hexamethylenediamine is primarily produced by hydrogenation of adiponitrile. However, for a long time, the global adiponitrile market has been highly monopolized by a few companies, with extremely high technological barriers. This directly leads to a persistent tight supply situation for adiponitrile/hexamethylenediamine, severely restricting HDI production.

The production technology of adiponitrile is complex, with strict process requirements involving multiple key steps and technical difficulties. For example, during the synthesis of adiponitrile, precise control of reaction conditions, selection and use of catalysts, etc., require accurate operations and advanced technical skills. Due to the blockade of core technologies by foreign enterprises, China has long faced significant challenges in the research and development of adiponitrile production technology.

As a downstream product of adiponitrile, the supply of hexamethylenediamine is also affected by the adiponitrile market. Under the condition of a tight supply of adiponitrile, the price of hexamethylenediamine remains high, further increasing the cost of HDI production. Moreover, since the production technology of hexamethylenediamine is also controlled by a few foreign companies, Chinese enterprises not only face price pressures when acquiring hexamethylenediamine raw materials but also the risk of unstable supplies.

In the production of HDI, the phosgene method is currently the primary production approach and the most competitive industrial production technology on the market. Phosgene, or carbonyl chloride, is an important organic intermediate, but it is itself a highly toxic gas, having intense suffocating properties. Phosgene is synthesized from carbon monoxide and chlorine under the catalytic action of activated carbon, with its toxicity being about 10 times that of chlorine. Inhalation of high concentrations can lead to pulmonary edema and even suffocation death.

Given the high toxicity of phosgene, China has implemented strict control measures on phosgene projects. As early as 2014, the State Administration of Work Safety clearly required strict restrictions on new projects involving phosgene and phosgenation, and strict control over new phosgene distribution points. This means that in the development of HDI production technology, China must not only overcome the bottleneck of hexamethylenediamine raw material supply but also address safety and environmental issues associated with the production and use of phosgene.

3. Breakthrough in Domestic Technology: Corporate Practices and Industry Transformation

With the continuous development of China's chemical industry and the improvement of innovation capabilities, some enterprises have begun to actively explore and practice the localization of HMDA-to-HDI technology, achieving significant results.

Wanhua Chemical, as a leading enterprise in China's chemical industry, has invested substantial resources and efforts into the research and development of HDI production technology. After years of effort, Wanhua Chemical successfully broke through the key technologies of HDI production, achieving localized production of HDI. Currently, Wanhua Chemical has an annual HDI capacity of 80,000 tons, accounting for approximately 21% of the global total capacity, becoming the second-largest HDI supplier globally. The breakthrough in HDI production technology by Wanhua Chemical not only breaks the technological monopoly of foreign enterprises but also lays a solid foundation for the development of China's HDI industry.

Mery New Materials Co., Ltd. has also played a significant role in the localization process of HDI. In August 2021, Mery New Materials and Hebi Coal Chemical Co., Ltd. jointly established Mery Technology (Henan) Co., Ltd.; in June 2022, the environmental impact assessment for Mery Technology's integrated polyurethane project was announced, marking the company's official entry into the special isocyanate market. The main product of this project is HDI, which is the primary raw material for special TPU.

Mery New Materials has invested heavily in R&D funds for HDI production technology, continuously optimizing production processes and improving product quality. As of December 2023, the project has cumulatively invested 860 million yuan. The first phase of the Henan project will build the world's largest single-unit capacity HDI facility, expected to start production in the first half of 2024, at which time Mery New Materials will become the second domestic manufacturer capable of producing HDI after Wanhua Chemical.

Mery New Materials' HDI project not only enables the company to supply some of its core TPU raw materials internally, breaking foreign monopolies, reducing production costs, and enhancing the company's profitability, but it will also have a positive impact on the entire HDI market. The additional capacity will increase the market supply of HDI products, alleviating the tight supply-demand situation; large-scale production will generate economies of scale, lowering product prices, allowing more downstream enterprises to use high-performance HDI products, promoting the application of HDI in more fields.

In addition to Wanhua Chemical and Mery New Materials, several other companies are also actively laying out the HDI industry, increasing investment in technological research and development, and continuously advancing the localization technology of HDA from hexamethylenediamine. These companies' efforts and practices will gradually break the monopoly of foreign companies over HDI production technology and markets, promoting the healthy development of China's HDI industry.

4、The Industrial Impact and Future Outlook Brought by Localization Technology

The breakthrough in the localization technology of HDI from hexamethylenediamine has had a profound impact on China's HDI industry and even the entire polyurethane industry.

From the perspective of the HDI industry itself, the realization of localization technology has led to a gradual expansion of China's HDI production capacity. In 2021, China's HDI monomer capacity was about 185,000 tons, an increase of 50,000 tons from 2017, with a year-on-year growth rate of 37.04%, all of which came from Wanhua Chemical. With the successive commissioning of HDI projects by Mery New Materials and other companies, it is expected that by 2025, China's HDI capacity could exceed 300,000 tons. The increase in capacity will effectively alleviate the market supply-demand contradiction, reduce the price of HDI products, and enhance the competitiveness of China's HDI products in the international market.

The breakthrough in localization technology will also promote the technological upgrade of the HDI industry. During the R&D process, domestic companies are constantly exploring new production processes and technical methods, improving production efficiency, reducing production costs, while also focusing on improving product quality and meeting environmental requirements. This will drive the entire HDI industry towards a more green, efficient, and sustainable direction.

For the entire polyurethane industry, the localization of HDI as a special isocyanate will provide strong support for the upgrading of polyurethane products. Polyurethanes derived from HDI have excellent properties, capable of meeting the demands of high-end sectors for polyurethane materials. As the price of HDI decreases and supply becomes more stable, more downstream enterprises will be able to use HDI to produce high-performance polyurethane products, driving the polyurethane industry towards a higher-end direction.

In terms of application fields, with the increase in HDI supply and the decrease in price, its application areas will continue to expand. In addition to traditional high-end coatings, elastomers, and other fields, HDI will also be more widely used in automotive interiors, electronics and electrical appliances, aerospace, and other fields, providing high-quality material support for the development of these industries.