Microcellular extrusion foaming of long-chain branched polyamide 6 composites

In this study, by introducing the long-chain branched (LCB) structure into the polyamide 6 (PA6) matrix, low-density microcellular PA6 composite foams with favorable cell morphology were prepared using supercritical CO2 extrusion foaming. PA6/talc composites with varying degrees of LCB were prepared using a twin-screw extruder. Rheological tests showed that the LCB-4.0 T sample with an ultra-high LCB degree had more apparent strain-hardening behavior and higher instantaneous elongational viscosity of 4.40 × 108 Pa·s. Isothermal crystallization tests revealed that LCB-4.0 T had lower crystallization rate. The effect of the degree of LCB on the gas solubility of CO2 in the PA6 composites was also examined. The foamability of the PA6/talc composites was verified via continuous extrusion foaming. High-performance PA6 composite foams with an average cell size as low as 66.7 µm, cell density as high as 2.53 × 107 cells/cm3, expansion ratio as high as 11.8, and foaming temperature window as wide as 16 °C were successfully obtained.