Synthesis and supercritical CO2 foaming of thermoplastic polythiourethanes with different hard segment content

Abstract

The reprocessing of polyurethane elastomers into foams using supercritical CO2 offers an interesting opportunity to increase interest in the recycling of polyurethane materials. The significance of the chemical structure of the starting polymers in supercritical foaming is not entirely understood, so it is important to thoroughly comprehend this process. For that reason, in the present work, the influence of the hard segment content on the foaming process using supercritical CO2 will be explored. To carry out this work, three films with different hard segment contents (23 wt%, 33 wt%, and 43 wt%) were synthesized, characterized, and foamed. After characterization, it was confirmed that no bands in the wavenumber corresponding with isocyanate (2250 cm−1) or thiol (2540 cm−1) appeared after reaction, corroborating that all reagents have reacted completely. In addition, during the chemical characterization, it was also observed a change in the intensity of the peaks related to nonbonded and H-bonded CO (1712 cm−1 and 1640 cm−1 respectively), which is related to an increase in the crystalline phase of the polymer with the increase in hard segment content. On the other side, once the foaming tests were performed, a shift in the temperature foaming window was seen with the increase in the hard segment content. In addition, it was also observed that there was a better compromise between the expansionability and shrinking after 24 h in the case of the polymer HS_43%, as despite the fact that this polymer achieved the lower values of expansion ratio, it was also the polymer with the lower values of shrinking. Finally, it is also remarkable that, in some cases (for example, HS_43% at 65 ºC and 10 and 15 MPa or HS_3% at 50 ºC and 15 MPa), it was possible to obtain foams with average cell sizes lower than 35 µm, which make them susceptible to being employed in insulation applications.