Environment‐friendly chemical recycling of aliphatic polyurethanes by hydrolysis in a CO₂‐water system

Abstract

In order to develop a chemical recycling system of polyurethanes (PUs), environment‐friendly hydrolysis of two types of aliphatic PUs was studied under pressured CO2 in water, in which the carbonic acid generated from CO2 acted as an acid catalyst. Two PUs, namely H‐PU or I‐PU, were synthesized starting from 1,4‐butanediol and 1,6‐hexamethylene diisocyanate or isophorone diisocyanate, respectively. The hydrolysis of PUs depended on the experimental conditions, such as the temperature and CO2 pressure. As a result, 98% of H‐PU and 91% of I‐PU were successfully hydrolyzed under the typical conditions of 190 °C for 24 h at 8.0 MPa CO2. The reaction mixtures afforded 1,4‐butanediol and diamines without the formation of any byproducts. Both of these raw materials generated from the originated PUs by selective hydrolytic cleavage of the urethane linkages, and they were easily isolated in high yields simply by evaporation of the water‐soluble components within the reaction mixture. By comparing the results of the two aliphatic PUs with those of an aromatic PU (M‐PU), the hydrolyzability was found to decrease in the order H‐PU, I‐PU, and M‐PU. The difference can be ascribed to the hydrophilicity of the aliphatic or aromatic groups connected to the urethane moieties at the terminals of PUs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45897.

Polyurethane Foams: Past, Present, and Future

“…Suguru Motokucho et al [ 162 ] recycled two types of aliphatic PUs (namely H-PU and I-PU which were synthesized from 1,4-butanediol and 1,6-hexamethylene diisocyanate or isophorone diisocyanate, respectively) by hydrolysis under pressured CO 2 in a water system. The hydrolysis of PUs was dependent on the temperature and CO 2 pressure.…”

Degradation and stabilization of polyurethane elastomers

“…These hydrolysis conditions normally show little-to-no effect, however, if the acidity or alkalinity is high, the rate of hydrolysis of the PU will be increased, with the temperature playing a large part in the increased rate [445]. For example, Motokucho et al [497,498] showed that degrees of hydrolysis up to 98% for PUs based on either HDI, IPDI, or 4,4′-MDI could be achieved at 190 °C for 24 h at 8.0 MPa CO2 pressure (which generates carbonic acid). In addition, strong acids have different forms of attack.…”

Preparation of monosultap‐polyurethane microcapsules in an inverse emulsion through interfacial polymerization

“…And the time for cumulative release above 98% is 120, 100, and 60 days at 25, 35, and 45 °C, respectively. The reason why the microcapsules have faster release when pH is 5 compared to pH is 7 at the same temperature is that hydrolysis of a polyurethane material is more easily in the acidic condition than that in the neutral condition . As illustrated in Figure (c) (pH = 9), in 30 days, the cumulative release is already 99.2% at 45 °C.…”