Study On The Preparation And Properties Of TPU Foaming Material

Thermoplastic polyurethane(TPU)is a block copolymer consisted of soft segments and hard segments in the molecular structure. TPU is sorted into polyester and polyether types based on soft segments. TPU can be used in many fields because of its excellent performance. It shows high flexibility and processibility. Due to the porous structure, the TPU foaming material is much lighter and costs less. In addition, its resilience and cushioning properties also do a better job than others. Currently, the production and application of the foamed beads(expanded or expandable) are very hot in researching area. There are only few research on the expanded TPU(ETPU). So the ETPU preparations were carried out by batch foaming with supercritical carbon dioxide in this study. The TPU raw materials were polyester TPU-1#(DP3070A) and polyether TPU-2#(Elastollan1170A). The surface morphology, foaming structure and melting/crystallization characteristic of ETPUs prepared in different saturation pressure, temperature and time were investigated, in order to find out the optimum foaming process conditions.The study on TPU-1#(DP3070A) bead foams indicated that: the temperature of preparing DP3070 A foamed beads was from 80℃ to 95℃. With the increase of saturation temperature or saturation time, the initial and final expansion ratio of the foamed beads increased and the cell density decreased. With the increase of saturation pressure, the initial and final expansion ratio, cell density all increased. However, it would result in severe contraction of the foamed beads and deterioration of the beads skin, if the pressure and temperature was too high. So the optimum processing condition of DP3070 A bead foaming was 85℃-12MPa- 2hours.The ETPU beads manufactured under the condition possessed a final expansion ratio of 4.2-fold, smooth and dense skin. The double melting peak of DP3070 A raw material disappeared after the foaming process. The melting point of the ETPU beads increased with the increase of saturation pressure, and the melting enthalpy increased with the increase of saturation time.The study on TPU-2#(Elastollan1170A) bead foams indicated that: the temperature of preparing Elastollan1170 A foamed beads was from 105℃ to 120℃. With the increase of saturation temperature or saturation time, the initial expansion ratio of the foamed beads increased significantly, and the final expansion ratio increased a little. With the increase of saturation pressure, the initial expansion ratio and cell density increased significantly, and the final expansion ratio changed little. However, it would result in severe contraction of the foamed beads and deterioration of the beads skin, if the pressure and temperature was too high. So the optimum processing conditions of DP3070 A bead foaming were 105℃-10MPa-3hours and 105℃-12MPa-2hours. The ETPU beads manufactured under the conditions possessed the final expansion ratio of 4.08-fold and 4.12-fold, smooth and dense skin both. The double melting peak of Elastollan1170 A raw material disappeared after the foaming process. With the increase of saturation temperature or aturation time, the melting point and melting enthalpy of the ETPU beads increased.The study about the new foaming process of two-step depressurization and gas mixture indicated that: Compared to one-step depressurization, the ETPU beads manufactured under the two-step depressurization process(10→7→0MPa) possessed greater expansion ratio and cell density, and the cells were still closed-pore structure. So the optimum processing condition was 105 ℃-1hour-(10 → 7 → 0)MPa. The ETPU beads manufactured under the condition possessed a final expansion ratio of 4.06-fold, smooth and dense skin. Compared to beads foaming with pure carbon dioxide, the ETPU beads manufactured under gas mixture foaming process possessed smaller expansion ratio and shrinkage,but larger cell diameter. The optimum processing condition was 115℃-8MPa-2hours. And the mass ratio of N2 and CO2 was 1:27. The ETPU beads manufactured under the condition possessed a final expansion ratio of 5.33-fold, but slight rough skin.