Heterogeneous nucleation and self-nucleation of poly(p-dioxanone)

The changes in nucleation behaviour upon addition of Boron Nitride (BN), Ta lc and Hydroxyapatite (HA) to poly(p-dioxanone) (PPDX) were monitored by DS C and Polarised Optical Microscopy (PM). Self-nucleation DSC studies eviden ced the existence of the usual three self-nucleation domains depending on t he self-nucleation temperature (T-s) employed. By far the best nucleation a gents for PPDX were its own self-nuclei and this result was independent of the presence or absence of any of the other nucleating agents employed; onc e Domain II was reached, self-nucleation dominated the nucleation process. BN and Talc were able to nucleate PPDX, thereby increasing its nucleation d ensity, its dynamic crystallisation temperature upon cooling from the melt (T-c) and its enthalpy of crystallisation (Delta H-c). BN was a better nucl eating agent than talc. HA on the other hand caused an "antinucleation" eff ect on PPDX characterised by a decrease in its nucleation density, a decrea se in its T-c and in Delta H-c. Isothermally crystallised PPDX exhibited la rge banded spherulites whose morphology changed as a function of crystallis ation temperature from single banded structures with a very clear Maltese c ross to double banded spherulites. PPDX also shows a change in growth regim e upon increasing crystallisation temperature (from Regime III to Regime II ) according to the kinetic interpretation of growth rate data. BN did not c ause any significant modification of the spherulitic growth kinetics (in Re gime II) except for a small decrease in surface free energy of PPDX crystal s (sigma(e)). On the other hand HA was found to increase the spherulitic gr owth rate and the overall crystallisation rate of PPDX, this increase was c aused by a degradation process experienced by the polymer during the treatm ents involved in isothermal crystallisation that was only present in the sa mples with HA. It is postulated that the interaction between the phosphate groups on the surface of HA and the ester groups of PPDX are responsible fo r both the antinucleation effect and the catalysis of the hydrolytic degrad ation of PPDX. (C) 2000 Kluwer Academic Publishers.