Thermal induced crystalline transition of bio-based polyamide 56

Thermal induced crystalline transition of polyamide 56 (PA56) was investigated by DSC, in-situ WAXD, and insitu FTIR spectroscopy. The PA56 alpha-like phase, crystallized from formic acid solution, showed a Brill transition that completed at 200 degrees C (TB) and only gamma phase crystallites were mainly obtained when cooling the PA56 samples to room temperature from molten state. The characteristic absorbance bands of PA56 alpha-like and gamma phases on FTIR spectra were assigned. The strength of the hydrogen bonds in PA56 gamma phase was stronger than those in alpha-like phase, which could be the main reason for the irreversible Brill transition behavior of the PA56 alpha-like phase. Insitu FTIR results indicated that the intermolecular hydrogen bond strength of alpha-like phase reduced during Brill transition before 200 degrees C upon heating. During the melting process, the intermolecular hydrogen bond strength first enhanced and then reduced. The Brill transition of PA56 upon heating was further confirmed by the decrease and increase in the intensity of the band at 1631 cm-1 and 1637 cm-1, corresponding to the vibration band (amide I) of C--O group of alpha-like and gamma phases of PA56, respectively. FTIR results also confirmed the deformation, twisting, and rocking vibrations of CH2 groups were enhanced during the Brill transition procedure.