Polyester Thermoplastic Polyurethane from MDI and Polyester Diol

The process under analysis comprises two major sections: (1) Polyesterification and (2) Extrusion & Finishing.

Polyesterification. Adipic acid and butanediol (BDO) are mixed, together with the catalyst, and fed into the Esterification batch-reactor. The product of Esterification (monomer), BDO, and the catalyst are fed into the Polycondensation Reactor. In this second batch-reactor, monomers and oligomers are condensed in order to form low-molecular weight polybutanediol adipate, releasing BDO, recovered in a distillation column (Butanediol Recovery Column). The light unreacted reagents and side products of esterification and polycondensation – mainly water – are sent to the Butanediol Recovery Column, where they are removed from crude BDO and discarded. BDO is recovered at the bottom and recycled to Esterification. Before being fed into the extruder, polybutanediol adipate is mixed with butanediol in a buffer mixing tank.

Extrusion & Finishing. Methylene diphenyl diisocyanate (MDI) and the polymeric solution from Polyesterification section, as well as other chemicals (e.g., catalyst and additives) are fed into the first section of a three-section extruder (feeding section). Then, in the second section, mixing, they are thoroughly mixed and directed to the last section, extrusion, where the reaction effectively takes place: MDI reacts with the polyester diol, producing Thermoplastic Polyurethane Elastomer. After Extrusion, TPU is sent to Finishing steps, in which it is pelletized, homogenized, and packed.