Determination of spherulite growth rates of poly(L-lactic acid) using combined isothermal and non-isothermal procedures

A combination of isothermal and non-isothermal methods was used to measure spherulite growth rates (G) Of poly(L-lactic acid) (PLLA). G was determined during cooling at a constant rate by monitoring the growth of a spherulite radius as a function of temperature. Coupling with a self-nucleation proce dure permitted to highly enlarge the temperature range where G data can be obtained within a single experiment. Very good agreement existed between da ta gained with the proposed procedure and those obtained with the tradition al isothermal method. Further enlargement of the temperature range was prov ided by using tailored temperature programs. After the first growing crysta ls had appeared, the samples were quenched in liquid nitrogen to stop cryst al growth, then a conventional isothermal measurement was performed. Again the thermal treatment imposed on the sample did not affect the measured val ue of G. The use of combined isothermal and nonisothermal methods coupled w ith self-nucleation permitted to obtain G data of PLLA in a very wide tempe rature range. Spherulite growth rates of PLLA were analyzed with the Hoffma n and Lauritzen theory, which allowed to detect a regime II-III transition at 120 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.