Effect of micro-aggregation structure on rheological properties of thermoplastic polyurethanes

The effect of micro-aggregation structure on the rheological properties of thermoplastic Polyurethane (TPU) was investigated. The TPU samples prepared by injection molding were annealed at various temperatures from 23 to 120°C for 4 h. Differential scanning calorimetry (DSC) and pulsed NMR measurements revealed that the degree of micro-phase separation of the TPUs became stronger with increasing annealing temperature due to the progress of formation of well-organized hard segment domains. The temperature sweep experiments for molten TPUs indicated that the temperature of critical gel point at intersection between G' and G", increased with increasing annealing temperature. In addition, the TPUs showed the strain hardening of uniaxial elongation viscosity with increasing annealing temperature owing to residual hard segment domains at an operating temperature. It was revealed that the formation of well-organized hard segment domains had a profound effect on the rheological properties of TPUs, in particular on their elongational viscosity.