Low-molecular weight aliphatic amides as nucleating agents for poly (L-lactic acid): Conformation variation induced crystallization enhancement

Two kinds of low molecular weight aliphatic amides, N, N′-ethylenebis (12-hydroxystearamide) (EBH) and N, N′-ethylenebisstearamide (EBSA), have been selected in present study to mediate the crystallization behavior of poly (L-lactic acid) (PLLA). The results showed that the crystallization rate of PLLA was significantly improved with the addition of EBH and EBSA, and EBH presented a stronger nucleating efficiency. The correlation between the variation of chain conformation during the early stages of isothermal crystallization and the enhancement of crystallization rate for pure PLLA and its mixtures was investigated by time-resolved FTIR. The formation of interchain conformational-ordered structure and intrachain 103 helix structure for amide-doped PLLA preceded that for pure PLLA, suggesting a stimulatory nucleating effect of EBH and EBSA. In the case of PLLA/EBH, the interchain interactions of –(COC + CH3) and –CH3 groups were faster than the –(CH3+CC) intrachain interactions, while the interchain interactions and the intrachain 103 helix formation were nearly synchronous for PLLA/EBSA. The hydrogen bond interaction between hydroxyl groups in EBH and the carbonyl groups in PLLA was proposed to be an important factor influencing the conformation variation during isothermal crystallization of PLLA.