Bio-based PA56 modified by PA66 and its supercritical CO₂ foaming behaviour

Bio-based polyamide 56 (PA56) foams, characterised by ultrahigh compressive strengths and expansion ratios, were prepared using supercritical CO₂ intermittent foaming technology. Chain-extended PA56/PA66 [CE(PA56/PA66)] was synthesised through the use of a chain extender (ADR, epoxy-based). An investigation was conducted into the influence of ADR and PA66 content on the rheological behaviour, mechanical properties, thermal properties, and foaming performance of the CE (PA56/PA66). The non-isothermal crystallisation behaviour of CE(PA56/PA66) was analysed using the Jeziorny, Mo, and Kissinger methods. The results demonstrated that the branched structure considerably improved the viscoelasticity and foaming properties of PA56, thus improving its cellular morphology. The addition of PA66 increased the crystallisation rate of the system and reduced its activation energy. PA66 promotes melt enhancement, crystallisation nucleation, and cell nucleation in the CE(PA56/PA66). At a foaming temperature of 255 °C, the foams produced from the branched PA56 with 20 phr PA66 exhibited smaller cell diameter (140 μm) and higher cell density (4.7 × 10⁶ cells/cm³). The compressive strength of the PA56 foam with 4 phr CE and 20 phr PA66 (0.68 MPa) was 119% higher than that of pure CEPA56 foam. This study provides an effective method for preparing a high expansion ratio and compressive strength of bio-based PA56 foam and an essential theoretical reference for its processing and moulding technology.