Performance of supercritical methanol in polyurethane degradation

Abstract

Polyurethane is a group of block copolymer which is composed of diisocyanate, chain extender, and polyol, including polyurethane foam, polyurethane elastomer, waterborne polyurethane, etc. This research focused on thermoplastic polyurethane elastomer (TPU) which is formed with 4,4′-diphenylmethane diisocyanate(MDI), poly(1,4-butanediol-hexanedioic acid) diolpolyester(PBA) and extended with 1,4-butanediol(BDO). The degradation of TPU was carried out with the help of methanol as the supercritical solvent. The SEM of the reaction residues revealed the process of the depolymerisation. The products were measured by GC-MS and found out to be PBA, BDO and 4,4′-methylene diphenyl carbamate (MDC) which is the methylate of MDI. GC-FID, HPLC-UV and GPC were used to further analysis. The experimental results showed that supercritical methanol performed outstandingly in TPU recycling, it needed lower temperature and shorter time than regular methods. At 230°C/70min, over 90% raw materials of TPU could be recovered.