Thermal stability of UPy-based polyurethane in granular FDM 3D printing

Abstract

Granular fused deposition modeling (GFDM) 3D printing is a convenient and effective fabrication technique for personalized polyurethane scaffolds. The residence time of polyurethane in the heating chamber is crucial to its thermal stability. In this work, a biodegradable shape memory polyurethane containing a soft segment of poly(D,L-lactic acid) and a hard segment with pendant 2-Ureido-4[1H]-pyrimidone (UPy) units (UPy-p-PDLLA-SMPU) was successfully printed at 130°C by using GFDM 3D printing. Subsequently, the effects of residence time at 130°C chamber on the thermal stability of UPy-p-PDLLA-SMPU were investigated by using 1H NMR, WAXD, ATR-FTIR, GPC and DSC. It is found that the urethane and urea groups demonstrate divergent thermal stability with a dependence on the steric hindrance. Specifically, the urethane groups and the urea groups with negligible steric hindrance first start thermal degradation after a residence time of 1 h, resulting in an initial degradation ratio of 7.9% and 4.1%, respectively. After 3 h residence, they further thermally degrade to reach a degradation ratio of 25.2% and 14.6%, respectively. Correspondingly, the Mn decreases from 48 kDa to 42 kDa after 1 h residence and then to 31 kDa after 3 h residence. In brief, it is acceptable to finish the GFDM 3D printing of UPy-p-PDLLA-SMPU within 1 h at 130°C. These findings provide a guidance to select appropriate parameters for the GFDM 3D printing and add new thermal degradation mechanism to UPy-based supramolecules.