Thermodynamics, crystal structure, and characterization of a bio-based nylon 54 monomer

Nylon 54 is a new type of bio-based polyamide and can be applied to many industrial fields. Its raw materials 1,5-pentanediamine and succinic acid are both from biomass and obtained in bio-refineries. High-quality polymer materials require first high-quality monomers. Crystallization is one of the most popular and effective approaches to obtain good products. In this report, we investigated the solid-liquid equilibrium of nylon 54 salt in different proportions of methanol-water mixtures at different temperatures and correlated the solubilities with temperature and the solvent ratio using the modified Apelblat model, van't Hoff equation, and (CNIBS)/Redlich-Kister model. It has been proved that the solubility of nylon 54 monomer salt increases with the increase of temperature and decreases with the increase of methanol content. Meanwhile, the crystal structural characteristics and thermal behaviors were characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and hot-stage microscopy analysis. The crystallization of nylon 54 monomer salt in different systems was investigated as well, and it was found that the quality of crystals obtained by cooling crystallization in a methanol-water system is relatively better in terms of particle size. These studies help us to obtain nylon 54 monomer salt with better quality for polymerization.