Effect of Nucleation Mechanism on Complex Poly(L-lactide) Nonisothermal Crystallization Process, Part 2: Crystallization Kinetics Analysis Andrea Martinelli, Massimo Calı`, Lucio D’Ilario, Iolanda Francolini, Antonella Piozzi Dipartimento di Chimica, Sapienza Universita ` di Roma, P.le A. Moro 5, Roma 00185, Italy Received 30 October 2010; accepted 4 May 2011 DOI 10.1002/app.34833 Published online 31 August 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: In the first part of this article, we reported the crystalline memory effect on the nonisothermal crystallization of poly(L-lactide). The experiments were carried out by using polymer single crystals growth from dilute solution as standard starting material. In this article (Part II), we have analyzed in detail the effect of the melting condition on the overall crystallization kinetics by applying the Nakamura-Avrami model to DSC results. The absence or the low concentration of foreign infusible heterogeneous nuclei in our system allowed us to exalt the self-nuclei role in polymer crystal- lization, to follow their concentration decrease during the melting process and to find the limiting melting tempera- ture for their disappearance. Below such a temperature, a stable equilibrium number of self-nuclei was observed, probably deriving from ordered structures, persisting in the melt, and originated from the single crystals thick- ening process during the polymer dynamic melting in the DSC. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2697–2705, 2012 Key words: poly(L-lactide); crystallization; melting conditions; nucleation; memory effects; differential scanning calorimetry (DSC) INTRODUCTION The nucleation mechanism involved in poly(L-lactide) (PLLA) crystallization is a widely studied issue. In fact, PLLA is characterized by a slow crystallization kinetics and, under the high cooling rate usually used in molding processes, the crystallization could not takes place and glassy amorphous material is obtained. On the other hand, the dispersion of nucle- ating agents in the polymer melt represents wide industrial practice that enables the reduction of the crystallization induction period, the increase of the solidification rate and temperature, the control of the spherulite density and mean size and the final product crystallinity. Studies on different nucleating agents for PLLA, including poly(D-lactide) (PDLA), 1,2 modified clays, 3 talc, 2 ethylene bisstearamide (EBS), 4 1,3,5-Benzenetricarboxylamide derivatives, 5 hydra- zide compounds, 6 polyglycolide, 7 and self- nuclei, 2 were reported in literature. In particular, Schmidt and Hillmyer, 2 , according to the method proposed by Fillon et al. 8 , compared the efficiency of heterogeneous nucleating agents with that of self nuclei, obtained by subjecting PLLA to different melting conditions. They found that the nucleation efficiency of stereocomplex crystallites formed in PLLA/PDLA blends, containing low con- centrations of PDLA, was largely dependent on the thermal treatment of the melted sample. The effect of the melting condition on the subse- quent nonisothermal melt-crystallization was also studied by Wang and Mano 9 , who related the dou- ble crystallization process, observed by DSC analy- sis, to the different nucleation mechanisms activated at different temperature. Other studies evidenced the presence of crystallization nuclei in the quenched amorphous PLLA. From isothermal and nonisother- mal cold-crystallization experiments, it was found that their concentration depends on the cooling rate from the melt 10 and on annealing processes the amorphous polymer undergoes just above or below its glass transition temperature 11 . In general, it was observed that the presence and the concentration of heterogeneous nuclei or self- nuclei directly affect the crystallization process and, thus, the morphological mechanical, thermal, optical properties of the polymer products. In the Part I of this article, we showed that the concentration of athermal nuclei directly influences the nonisothermal crystallization behavior of PLLA and indirectly the polymer structure. 12 By modulat- ing the thermal treatment of the polymer in the melt state, we were able to vary the concentration of residual crystals fragments (self-nuclei) coming Correspondence to: A. Martinelli (andrea.martinelli@ uniroma1.it). Journal of Applied Polymer Science, Vol. 123, 2697–2705 (2012) V C 2011 Wiley Periodicals, Inc.