Santiago-Calvo Mercedes, Naji Haneen, Bernardo Victoria, Martín-de León Judith, Saiani Alberto, Villafañe Fernando, Rodríguez-Pérez Miguel Ángel
Cellular Materials Laboratory (CellMat), Condensed Matter Physics Department, Faculty of Science, University of Valladolid, 47011 Valladolid, Spain.
Department of Chemical Engineering, Faculty of Engineering, University of Babylon, Hilla 51001, Iraq.
Polymers (Basel). 2021 Sep 17;13(18):3143. doi: 10.3390/polym13183143.
A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and rheology. Then, these materials are foamed by a one-step gas dissolution foaming process and the processing window that allows producing homogeneous foams is analyzed. The effect of foaming temperature from 140 to 180 °C on the cellular structure and on density is evaluated, fixing a saturation pressure of 20 MPa and a saturation time of 1 h. Among the TPUs studied, only that with 50 wt.% HS allows obtaining a stable foam, whose better features are reached after foaming at 170 °C. Finally, the foaming of TPU with 50 wt.% HS is optimized by varying the saturation pressure from 10 to 25 MPa at 170 °C. The optimum saturation and foaming conditions are 25 MPa and 170 °C for 1 h, which gives foams with the lowest relative density of 0.74, the smallest average cell size of 4 μm, and the higher cell nucleation density of 8.0 × 109 nuclei/cm. As a final conclusion of this investigation, the TPU with 50 wt.% HS is the only one that can be foamed under the saturation and foaming conditions used in this study. TPU foams containing 50 wt.% HS with a cell size below 15 microns and porosity of 1.4-18.6% can be obtained using foaming temperatures from 140 to 180 °C, saturation pressure of 20 MPa, and saturation time of 1 h. Varying the saturation pressure from 10 to 25 MPa and fixing the foaming temperature of 170 °C and saturation pressure of 1 h results in TPU foams with a cell size of below 37 microns and porosity of 1.7-21.2%.
采用预聚物法合成了一系列具有不同硬段（HS）含量（40、50和60 wt.%）的热塑性聚氨酯（TPU）。通过邵氏硬度、凝胶渗透色谱（GPC）、差示扫描量热法（DSC）、广角X射线衍射（WAXD）、动态热机械分析（DMTA）和流变学对这些合成的TPU进行了表征。然后，通过一步气体溶解发泡工艺对这些材料进行发泡，并分析了能够生产均匀泡沫的加工窗口。在固定饱和压力为20 MPa和饱和时间为1 h的情况下，评估了140至180 °C的发泡温度对泡孔结构和密度的影响。在所研究的TPU中，只有含50 wt.% HS的TPU能够获得稳定的泡沫，在170 °C发泡后具有更好的性能。最后，通过在170 °C下将饱和压力从10 MPa变化到25 MPa，对含50 wt.% HS的TPU的发泡进行了优化。最佳饱和和发泡条件为25 MPa、170 °C下1 h，得到的泡沫具有最低的相对密度0.74、最小的平均泡孔尺寸4 μm和较高的泡孔成核密度8.0×10⁹个核/cm。作为本研究的最终结论，含50 wt.% HS的TPU是唯一一种能够在本研究使用的饱和和发泡条件下进行发泡的材料。使用140至180 °C的发泡温度、20 MPa的饱和压力和1 h的饱和时间，可以获得泡孔尺寸低于15微米且孔隙率为1.4 - 18.6%的含50 wt.% HS的TPU泡沫。在170 °C的发泡温度和1 h的饱和时间下，将饱和压力从10 MPa变化到25 MPa，得到的TPU泡沫泡孔尺寸低于37微米且孔隙率为1.7 - 21.2%。
