Phase behavior and crystal morphology in poly(ethylene succinate) biodegradably modified with tannin

Abstract

Specific interactions, growth kinetics, and dendritic morphology in poly(ethylene succinate) (PESu) biodegradably modified with various contents of tannic acid (TA) were characterized using differential scanning analysis, Fourier-transform infrared (FTIR) spectroscopy, polarized-light optical microscopy, and atomic force microscopy. Strong interactions and highly retarded growth between PESu and a macromolecular ester with polyphenol groups, TA, interaction-induced highly retarded growth rates for the PESu/TA (80:20) composition are proven to lead to single-crystal-like dendrites when crystallized at high crystallization temperature (T c). At T c = 70 °C, the growth rate for neat PESu is 12 μm/min while it is dramatically depressed to one tenth-fold at 1.5 μm/min with 20 wt.% TA in the blend. Strong specific interactions between the carbonyl group of polyesters and the phenolic hydroxyl group of TA are confirmed by (1) the blend’s glass transition temperature (T g)–composition relationship exhibits a sigmoidal curve, well fitted by the Kwei T g model for miscible blends with large negative q = −90; (2) thermal analysis on crystal melting revealed an interaction parameter χ = −0.64 between PESu and TA; and (3) IR peak shifting analyzed using two-dimensional FTIR technique. A comparative blend of another polyester poly(hexamethylene sebacate) with TA, lacking the specific interactions, does not exhibit such single crystals upon similar melt crystallization.