Hydrogen bonding and crystalline structure of bio-based PA56.

PA56 is a newly commercialized bio-based polyamide with excellent thermal, mechanical and processing properties. However, its hydrogen bonds and crystalline structures are not well investigated yet. In this study, PA56 films with γ form and α-like form crystalline phases were successfully prepared by melt-crystallization and solution casting, respectively. The hydrogen bond and crystalline structure were systematically studied with solid-state 13C NMR, variable temperature-FTIR and dynamic oscillatory rheological tests. 13C NMR and variable temperature-FTIR results indicate that the hydrogen bond strength of PA56 in α-like form crystal is higher than that in γ-form, while both are lower than that of PA66 in α-form. The chemical shifts of carbons in diamine units are highly dependent on the crystalline forms due to the molecular chain of PA56 adopts different conformations in γ-form and α-like form. The curve-fitting of variable temperature-FTIR spectra reveals that the melt crystallization results in γ-form regardless of the crystal form before melt. Dynamic oscillatory rheological tests demonstrate that the stronger hydrogen bond interactions endow α-like form of PA56 a higher dynamic storage modulus and complex viscosity than γ-form. [Display omitted] • The hydrogen bond strength and crystalline structure of PA56 were investigated. • The hydrogen bond strength of PA56 in α-like form is highe than that in γ form. • Melt crystallization results in γ-form regardless of the crystal form before melt. • The relationship between crystal structure and rheology property was clarified. [ABSTRACT FROM AUTHOR]