Chain extension of thermoplastic polyamide elastomer and its foaming performance

Abstract Thermoplastic polyamide elastomer (TPAE) foam material has various important applications, including in shoe materials, cushioning packaging, sports, and automobiles, owing to its excellent resilience and anti‐vibration performance. However, owing to its linear molecular chain structure, the melt viscoelasticity of TPAE is low, making it difficult to obtain lower‐density foamed materials. Therefore, it is crucial to improve the melt strength through chain extensions. Given its ability to react with carboxyl and amine groups, multifunctional epoxides were chosen as chain extenders to increase the melt viscoelasticity of TPAE. A rotational rheometer, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used to characterize the rheological properties and crystallization behavior of the modified TPAE. Adding epoxy‐type chain extender KL‐E4370 was conducive for forming the branch structure of TPAE and even a microgel structure, leading to increased melt viscoelasticity and reduced crystallinity of TPAE. Microcellular TPAE foams (cell sizes and densities of 30 μm and 1.5 × 10 8 cells cm −3 , respectively) were successfully fabricated. With increasing concentrations of KL‐E4370, the foaming temperature zone of TPAE widened and the expansion ratio increased from 5.5 to 9 times, leading to a decrease and an increase in cell diameter and density, respectively, and improvement in the rupture and merging of cells.