Nucleating effect and crystal morphology controlling based on binary phase behavior between organic nucleating agent and poly(l-lactic acid)

Abstract

A new kind of nucleating agent for poly(l-lactic acid) (PLLA), N,N'-bis(benzoyl) hexanedioic acid dihydrazide (BHAD), was synthesized. Differential scanning calorimetry (DSC), polarization optical microscopy (POM), wide-angle X-ray diffraction (WAXD) and rheometer were used to study the crystallization behavior and crystal morphology of PLLA nucleated by BHAD. In order to ensure the same thermal history of the samples characterized by DSC, POM and XRD, these samples were all thermally treated by DSC. In nonisothermal crystallization, BHAD showed excellent nucleating ability to PLLA. However, it was different from the traditional heterogeneous nucleation mechanism. POM observation showed that morphologies of PLLA crystals varied with the concentration of BHAD and can be classified into three types. Through the systematic investigation of DSC, POM and rheological analysis, it was clearly demonstrated that BHAD had solubility in PLLA matrix, depending on its concentration and processing temperature. Consequently, a highly schematic binary phase diagram of the PLLA/BHAD system was presented, accompanied with a reasonable mechanism of how the PLLA crystal morphologies controlled by BHAD.