Crystallization behavior and crystallite morphology control of poly(L-lactic acid) through N,N′-bis(benzoyl)sebacic acid dihydrazide

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. (c) 2012 Society of Chemical Industry