N,N 0 -Bis(benzoyl) suberic acid dihydrazide (NA) as nucleating agent for poly(L-lactic acid) (PLLA) was synthesized from benzoyl hydrazine and suberoyl chloride, which was deprived from suberic acid via acylation. PLLA/NA samples were prepared by melt blending and a hot-press forming process. The nonisothermal and isothermal crystallization, spherulite morphology, and melting behavior of PLLA/NA with different contents of NA were investigated with differential scanning calorimetry, depolarized-light intensity measurement, scanning electron microscopy, polarized optical microscopy, and wide-angle X-ray diffraction. With the incorporation of NA, the crystallization peak became sharper and shifted to a higher temperature as the degree of supercooling decreased at a cooling rate of 1 C/min from the melt. Nonisothermal crystallization indicated that the presence of NA accelerated the overall PLLA crystallization. In isothermal crystallization from the melt, the presence of NA affected the isothermal crystalline behaviors of PLLA remarkably. The addition of NA led to a shorter crystallization time and a faster overall crystallization rate; this meant that there was a heterogeneous nucleation effect of NA on the crystallization of PLLA. With the addition of 0.8% NA, the crystallization half-time of PLLA/NA decreased from 26.5 to 1.4 min at 115 C. The Avrami theory was used to describe the kinetics of isothermal crystallization of the PLLA/NA samples. Also, with the presence of NA, the spherulite number of PLLA increased, and the spherulite size decreased significantly.

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Adding a nucleating agent is one of the best ways to accelerate the crystallization rate of poly(L-lactic acid) (PLLA) so as to obtain a high degree of crystallinity during the process, which will improve the heat distortion temperature of final products. In the work reported, N, N -bis(benzoyl)sebacic acid dihydrazide (BSAD) was synthesized and used as a nucleating agent for PLLA. Isothermal and non-isothermal crystallization behaviors were investigated using differential scanning calorimetry (DSC). The addition of BSAD successfully enhances the crystallization rate of PLLA. A unique phase separation behavior of PLLA/BSAD blends is found from DSC as well as from polarized optical microscopy, which explains the difference of optimal BSAD concentration between isothermal and non-isothermal crystallization. This is the first recording of a phase separation peak in PLLA/nucleating agent blends using DSC. In thermogravimetric analysis, the enhanced thermal stability indicates that there are strong hydrogen bonds between BSAD and PLLA matrix. BSAD can dissolve in PLLA melt below its melting point through intermolecular hydrogen bonding with PLLA and self-assemble upon cooling, leading to the surface being capable of nucleating PLLA. Different phase separation temperatures can be used to control the morphology of BSAD, which finally determines the crystallite morphology of PLLA.