Research subject: In the present study, a series of polyurethane foams were synthesized based on polybutylene succinate (PBS) and hexamethylene isocyanate (HDI) using the salt leaching method. Polymer characterization, thermal behavior, and foam structure were studied. Such biodegradable foams, mostly aliphatic polyesters, could be applied in biomaterial and biomedical fields.
Research approach: PBS-diol was synthesized via a two-step method: esterification and polycondensation. Then, hexamethylene isocyanate (HDI) was added to produce polyurethane. Reaction progress was followed using FTIR spectra. Cerium oxide (CeO2) nanoparticles, 0.1, 0.25 and 0.5 wt.%, were added to the reactor in the final stage of synthesis. On completion of the reaction, NaCl salt, with a size of 170 μm, was added. Consequently, salt leaching was performed to produce foam. Dimethyl formamide (DMF) was added to reduce the viscosity of the mixture. Polymer characterization was performed using spectroscopy, thermal behavior was analyzed via differential scanning calorimetry, and foam structure was examined using scanning electron microscopy. DSC curves reveal the existence of secondary crystallization. SEM images show the produced foam cells.
Main results: The molecular weight of polybutylene succinate was approximately 1800 g/mol. This material, named PBS-diol, and hexamethylene isocyanate (HDI) were reacted to produce polyurethane. Reaction progress was followed using the isocyanate peak at 2265 cm-1, which decreased and diminished at the end of the reaction in the FTIR spectra. The reaction mostly occurred within 60–120 min after HDI addition. Structural variation was studied using HNMR spectra. Inspection of DSC cooling curves shows crystallization peaks for hard and soft segments. Non-isothermal crystallization kinetics were studied using the modified Avrami model. An asymmetric three-dimensional crystal structure was predicted. SEM images show 170 μm cells which are comparable to the initial diameter of the salt.