Tunable crystallization behavior, memory effect, and thermo-mechanical properties of biobased polyamides PA5X

To reduce carbon dioxide emissions, the development of sustainable bio-based polyamides with performance advantages has become the focus of widespread attention. 1,5-Pentanediamine (PDA) is a renewable monomer produced by decarboxylation of lysine, which can be used as a sustainable alternative to traditional petroleum-based diamines and play a crucial role in the synthesis of bio-based polyamides. Herein, a series of bio-based aliphatic polyamides (PA5X) synthesized from PDA and aliphatic diacids with different methylene groups were successfully prepared via melt polycondensation. Their chemical structures were characterized, and the effects of diacid chain length on crystallization behavior, memory effect, and thermo-mechanical properties were emphatically investigated. The results show that the melting and crystallization temperatures of PA5X decrease with increasing diacid chain length. Meanwhile, the PA5X exhibits high thermal stability, with T_d,5 % exceeding 380 °C. Unlike the even-even polyamide, the crystalline form of PA5X is γ-form, and the crystallization behavior and spherulitic morphology change significantly with diacid chain length, which is attributed to the complex entanglement effects. More particularly, the correlation between the diacid chain length and the melt memory effect is explored. PA56 with shorter methylene groups exhibits stronger melt memory effects due to the memory effects being directly affected by segmental chain interactions. Moreover, PA5X exhibits comparable or even superior tensile strength and ductility compared with hexamethylenediamine-based polyamide (PA6X) and reported fully bio-based PA11. This work provides a comprehensive investigation into the structure-property relationship of the bio-based polyamide PA5X, demonstrating great potential for application in high-performance eco-friendly materials.