Isothermal and non-isothermal crystallization kinetics of a polyglycolide copolymer having a tricomponent middle soft segment

Abstract

• Crystallization behavior of biodegradable segmented copolyesters. • Comparison between isothermal and non-isothermal crystallizations. • Influence of soft segments on equilibrium melting temperature. • Avrami exponents from non-isothermal calorimetric methods. • Secondary nucleation constant from isoconversional methods. Kinetics of isothermal and non-isothermal crystallization studies of a biodegradable monofilament suture constituted by polyglycolide hard blocks and soft segments derived from glycolide, ɛ-caprolactone and trimethylene carbonate have been undertaken by means of calorimetric methods. This segmented polymer was semicrystalline with melting and crystallization characteristics defined by the polyglycolide hard segments. The amorphous phase had a glass transition temperature highly influenced by thermal processing and the random microstructure of the soft segment. Melting process was complex due to the occurrence of lamellae with different degree of perfection. Equilibrium melting point, determined by the Hoffman–Weeks methodology, became slightly lower than reported for polyglycolide and segmented copolymers having a lower soft segment content. A heterogeneous nucleation and a three-dimensional crystal growth were characteristic for isothermal crystallizations performed from the melt state, being the Avrami exponent very close to 3 for all experiments. Secondary nucleation constant was evaluated from the overall crystallization rates and by assuming the validity of Lauritzen–Hofmann approach. Results point out a maximum rate for a crystallization temperature of 131 °C and probably an underestimated nucleation constant. Kinetic parameters for non-isothermal crystallization were deduced by Avrami, Ozawa and Cazé methods. A good agreement with isothermal parameters was only attained with the last methodology, although results from the other ones were appropriate to simulate the crystallization process. Isoconversional analysis was a good methodology to estimate the secondary nucleation constant from a non-isothermal crystallization.