In this work, the effect of the processing conditions on the thermal behavior of a commercial poly(L-lactic acid) (PLLA) was investigated. In particular, PLLA having a very high molecular weight was processed by a discontinuous mixer at different mixing conditions. The molar mass variation was investigated by size exclusion chromatography-multiangle laser light scattering chromatography, and the thermal characteristics were detected by the conventional differential scanning calorimetry and dynamic mechanical thermal analysis. Tensile tests were performed at room temperature and at 60 C. Our attention was essentially focused on the crystallization behavior of the various samples obtained. A modest decline in the molar mass was obtained with two mixing temperatures of 210 and 250 C, but a significant increase in the crystalline phase content was noticed, with a concomitant tremendous increment in the crystallization rate. A correlation was also made between the molar mass distribution and crystallization rate in isothermal conditions, where clearly visible were the effects of the processing temperature on both the molar mass distribution and how the nucleating agents affected the crystallinity of PLLA. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3528-3536, 2011