Crystallization study on absorbable poly(p-dioxanone) polymers by differential scanning calorimetry

Abstract

An investigation was carried out on the crystallization behavior of p‐dioxanone polymers using differential scanning calorimetry (DSC). Kinetic analyses were performed on data collected primarily during isothermal crystallization. Isothermal data were treated within the framework of the classical Avrami equation. Using this approach, both the Avrami exponent, n, and the crystallization half‐time, t1/2, were evaluated and their implications are discussed for each system studied. It is shown that a small change in the polymer's composition greatly affects the crystallization kinetics, as well as the crystallizability of the materials. Additionally, nonisothermal crystallization under controlled heating and cooling rates was explored. In the case of cooling from the melt, the Ozawa theory and the recently proposed Calculus method were employed to describe the nonisothermal crystallization kinetics. In view of our results, the validity of these two estimation techniques for determining important kinetic and morphological parameters is also discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 742–759, 2001

Study of Non-Isothermal Crystallization of Polydioxanone and Analysis of Morphological Changes Occurring during Heating and Cooling Processes

“…Avrami exponents showed a moderate variation (i.e., between 3.76 and 2.77), with the lowest values being determined for high cooling rates and the average value being close to 3.0. These exponents are lower than those previously reported by Zhang et al [ 24 ] (i.e., 4.26–3.40) and in good agreement with those given by Andjelic et al [ 4 ] for low crystallization rates (i.e., 3.0), although in this case a value of 1.1 was found for high crystallization rates. Isothermal crystallization studies also indicate slightly contradictory values.…”

“…Isothermal crystallization studies also indicate slightly contradictory values. Thus, minimum changes with crystallization temperature were determined by Andjelic et al (i.e., exponents varied between 2.22 and 2.62, with 2.5 being the average value) [ 4 ], but a systematic increase (i.e., from approximately 2 to 3.8) was also reported [ 6 ] for higher isothermal crystallization temperatures (i.e., from 30 to 80 °C). The last behavior was interpreted as a consequence of a change from instantaneous to sporadic nucleation as T c was increased [ 6 ].…”

“…It can be well stated that application of the Avrami equation under non-isothermal conditions merely corresponds to a mathematical fitting that allows appropriate values of the rate constant to be derived [ 26 , 27 , 28 ]. In this case, it should be pointed out that the determined exponents may even have a physical meaning since they suggest three-dimensional spherulitic growth and instantaneous nucleation, as postulated from isothermal studies [ 4 , 6 ]. Furthermore, the sporadic nucleation detected at high isothermal crystallization temperatures [ 6 ] is in agreement with the increase of the exponent observed at low crystallization rates (i.e., 3.76 at 1 °C/min) and supports DSC evidence of the occurrence of two crystallization processes.…”

“…Isothermal crystallization of PDO has been extensively studied by different techniques, including polarized optical microscopy and differential scanning calorimetry (DSC) [3,4,5,6,7,8]. Changes in morphological parameters have also been evaluated by small-angle X-ray scattering [9].…”

“…Non-isothermal crystallization of PDO has been scarcely studied despite the fact that melt-processed samples (e.g., bioabsorbable surgical sutures) are obtained under non-isothermal conditions. However, some non-isothermal melt crystallization analyses have been performed from DSC data and by applying Ozawa [17] and Cazé [18] methodologies to evaluate Avrami exponents [4]. Values calculated by Ozawa were dependent on the temperature, whereas two different values of the Avrami exponent were determined depending on the cooling rate [6].…”