MDI can be divided into three types of products: polymerized MDI, pure MDI and modified MDI. Polymerized MDI mainly produces polyurethane rigid foam and semi-rigid foam products; pure MDI is mainly used to produce various types of polyurethane elastomers.
Modified MDI is a derivative of pure MDI and polymerized MDI products. According to the needs of different downstream application scenarios, the product structure and synthesis process can be improved and designed. At present, the modified MDI products that have been produced on a large scale are mainly：
(1) Carbonized diimide modification, also known as liquefied MDI, consists of 4,4-MDI under the action of catalyst and heating and releases carbon dioxide to form a liquid mixture containing part of the carbonized diimide group (-N=C=N-). The products belonging to this series are Wanhua 100LL, Basf MM103C, Huntsman 2020.
(2) Polyol modification, also known as carbamate modification, is an MDI prepomer formed mainly by the reaction of polyester or polyether polyols with 4,4-MDI and 2,4-MDI.
(3) Blended modification, which is formed by mixing a variety of MDI in a certain proportion. For example, MDI-50 is composed of 4,4-MDI and 2,4-MDI mixed in a ratio of about 50% each.
Modified MDI-In terms of performance, the modified MDI has a low odor, a lower total volatile organic compounds content, more environmentally friendly materials, higher foam hardness, and good flame retardant properties; in terms of storage, the modified MDI has good low temperature storage, is not easy to crystallize, and is more convenient for transportation.
Compared with the TM system (a mixture of TDI and polymerized MDI), the black/white ratio of modified MDI is higher, and the material cost of the two systems will change with price changes.
The downstream consumer markets of pure MDI are mainly white goods, automotive interior and exterior decoration, and building insulation materials; the downstream demand of pure MDI is mainly for the production of TPU, spandex, PU slurry and sole liquid.
In the downstream consumer market of modified MDI, 65% is used in molded foams, 20% is used in the production of soles, 15% is used in elastomers, and 10% is used in adhesives and sealants.