In order to improve the melt foaming properties of thermoplastic polyamide elastomers and reduce the shrinkage rate of foamed materials, acid anhydride chain extenders SMA (styrene maleic anhydride copolymer) are used in this paper to in situ reactive blending thermoplastic polyamide elastomers (TPAE) and polyamide 6 (PA6). The rheological and crystalline properties of the modified samples were characterized by a rotational rheometer and differential scanning calorimeter, and the melt batch foaming experiment with CO 2 as the foaming agent was carried out. The results showed that the melting enthalpy of modified TPAE reduced with the addition of content of PA6, which implied that the crystallinity of the hard phase of the system was depressed. Nevertheless, the reduction of crystallinity was beneficial to improve the penetration of gas and reduce the effect of the pressure difference inside and outside the cell on foam shrinkage. Additionally, the microcross-linked structure formed with the increase of PA6 content enhanced the storage modulus of modified TPAE, which could accelerate recovery of strain. The foaming temperature zone and recovery performance of all modified TPAE samples were significantly improved. The overall shrinkage rate was reduced to less than 10%, the maximum expansion ratio could reach 11–13 times with a more complete and uniform cell structure, and the resilience was improved by about 12%.

In order to improve the flame retardancy of poly(ethylene terephthalate) (PET) and maintain its excellent foamability, nanosilica (nano-SiO2), and zinc diethyl hypophosphite (ZDP) were selected as synergistic flame retardants, and pyromellitic dianhydride (PMDA) was used as a chain extender to carry out flame retardant and chain extension modification of PET simultaneously. The flame retardancy and flame-retardant mechanism of modified PET were characterized by limiting oxygen index, vertical combustion test, thermogravimetric analysis, and SEM. Dynamic rheological test and DSC were used to analyze the rheological and thermal properties. The foaming ability was also studied by batch foaming experiments. The test results indicated that nano-SiO2 and ZDP had a synergistic effect, which could significantly improve flame retardancy of PET. The vertical combustible grade of modified PET reached V-0 grade, and the limiting oxygen index increased from 21% to about 30%. The role of nano-SiO2 on the flame retardancy of PET was mainly to increase compactness and strength of the carbon layer, which could block combustible gas produced by the pyrolysis of PET and resist dripping behavior. At the same time, the addition of nano-SiO2 increased the crystallization temperature and crystallinity of PET. Otherwise, nano-SiO2 could act as a bubble-nucleating agent and improve the foaming ability of modified PET. When the addition amount was 1 wt%, not only did the maximum foaming ratio increase but the foaming temperature zone was also widened from 225°C-235°C to 225°C-250°C. Finally, a flame-retardant PET system with good foaming property was proposed.