Rapid crystallization of poly(l-lactic acid) induced by a nanoscaled zinc citrate complex as nucleating agent

A nanoscaled zinc citrate complex (ZnCC) was synthesized by the reaction of zinc acetate and citric acid using solution method. As a new eco-friendly nucleating agent, ZnCC was introduced into poly(l-lactic acid) (PLLA) via melt blending. The nonisothermal and isothermal crystallization, melting behavior, crystalline morphology and mechanical properties of the PLLA/ZnCC blends were investigated. It is found that ZnCC exhibits much more prominent nucleation activity on the crystallization of PLLA than conventional nucleating agent talc and commercial zinc citrate (ZnCit). By loading 0.05 wt% ZnCC, PLLA can complete crystallization upon cooling at 10 °C/min, and the crystallization peak shifts to a higher temperature with increasing ZnCC content. In the case of isothermal crystallization from the melt, the addition of ZnCC leads to a shorter crystallization time and a faster overall crystallization rate. Besides, the nucleation density of PLLA increases and the spherulite size decreases significantly in the presence of ZnCC. Epitaxy is the possible mechanism to elucidate the nucleation phenomenon of PLLA/ZnCC system. The tensile results show that ZnCC has a plasticization effect on the amorphous PLLA. Through a short-time annealing procedure, the mechanical properties such as tensile modulus and storage modulus of PLLA are improved by the addition of ZnCC.