Nucleating efficiency and thermal stability of industrial non-purified lignins and ultrafine talc in poly(lactic acid) (PLA)

Poly(lactic acid) (PLA) with D - lactide content of 1.2 wt% has been modified by melt mixing with 3 wt% of lignin (Kraft or Organosolv). Gel permeation chromatography and thermogravimetric analysis were employed to determine the thermal stability of PLA and nucleated PLA compounds during melt blending. The nucleating efficiency of industrial lignins was compared with the nucleation efficiency of ultrafine talc (UT). The feasibility of using industrial lignins and UT as nucleating agents for PLA was investigated by polarized light optical microscopy and differential scanning calorimetry, through non-isothermal and isothermal crystallization, whereas their structure was studied through in-situ synchrotron X-ray diffraction at wide and small angles. Both lignins, as well as UT induced heterogeneous nucleation and their nucleating action in PLA increased the crystallization rate and shortened the overall crystallization half time for isothermal crystallization. All tested nucleating agents increased the degree of crystallinity of PLA. The nucleation efficiency of Kraft and Organosolv lignin and ultrafine talc was 31%, 27%, and 80%, respectively. It was found that the thermal processing window of PLA was not influenced by the addition of lignins or ultrafine talc.