Biobased Polyamide 5652 with α-Crystal Form: Characterization and Low Moisture Absorption
Yanping Wang, Changlei Yang, Bingxue Guo, Tingting Kuang, Yufei Liu, Min He, Shuhao Qin, Jie Yu
Abstract
Biobased polyamide 56 (PA56) is recognized for its low-carbon footprint and environmental sustainability, yet its application in engineering is constrained by high moisture absorption. In response to this problem, our study presents a breakthrough with the development of PA5652 achieved through solid-state polymerization, featuring an α-crystal form morphology. Integrated analyses through molecular dynamics (MD) simulations, Fourier-transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy reveal strong intermolecular trans doubly hydrogen-bonded interactions in PA5652. These trans-double H-bonds induce the formation of the α-crystalline phase in PA5652, while variable-temperature infrared spectroscopy and X-ray diffraction (XRD) confirm the reversible Brill transition of its α-crystalline phase at elevated temperatures. Crystalline superstructures exhibit characteristic negative birefringence under polarized optical microscopy, indicative of a well-ordered lamellar packing. The melting point ( T m ), crystallization temperature ( T c ), degree of crystallinity ( X c ), and saturation moisture absorption rate ( M t ) of PA5652 are 270 °C, 241 °C, 48.3%, and 5.8%, respectively. Compared to PA56, the T m, T c, and X c have increased by 8%, 14.7%, and 39.2%, while the saturation M t has decreased by 79.4%. This study mitigates the moisture absorption of biobased PA by regulating the crystalline structure, providing a new pathway for research in this field.