Mechanical Performance Evaluation of Bio‐Based Polyamide 56 and Petroleum‐Derived Polyamide 66 Cord‐Reinforced Rubber Composites for Air Spring Bellows

ABSTRACT Bio‐based polyamide 56 (PA56) cord has attracted increasing attention in recent years, yet systematic studies on its substitution for petroleum‐derived polyamide 66 (PA66) in cord‐reinforced applications remain limited. This study establishes a cross‐scale engineering evaluation framework to provide the first systematic assessment of PA56 as a practical substitution material. An environmentally friendly dipping system based on epoxy/isocyanate synergistic crosslinking was developed to replace conventional resorcinol–formaldehyde treatment while maintaining strong interfacial adhesion. In parallel, a computationally efficient finite element framework incorporating shell–solid coupling was constructed to predict macroscopic mechanical response from homogenized material parameters, enabling engineering‐level performance evaluation. Experimental results show that PA56 composites achieve interfacial adhesion strength reaching 97.1% of conventional PA66 systems, maintain comparable tensile strength, and exhibit enhanced elongation at break. Dynamic mechanical analysis reveals a similar storage modulus across the service temperature range, accompanied by a lower loss factor, indicating reduced hysteretic heat generation. Accelerated thermal aging tests further demonstrate a stiffness evolution trend closely aligned with that of the PA66 baseline. By integrating experimental characterization with multi‐scale computational modeling, this work provides engineering‐level evidence supporting the feasibility of bio‐based PA56 as a sustainable and practically viable substitute for PA66 in cord‐reinforced applications.