Nonisothermal melt‐crystallization behavior of calcium phosphate/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) nanocomposite microspheres

Microspheres consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) polymer matrix and calcium phosphate (Ca-P) nanoparticles were made using the solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique. Amorphous Ca-P nanoparticles with the calcium to phosphate ratio of 1.5 were relatively well distributed in microspheres. The nonisothermal crystallization behavior of Ca-P/PHBV nanocomposite with different Ca-P contents (0–20%) was studied through differential scanning calorimetry using different cooling rates. During nonisothermal crystallization, the presence of Ca-P nanoparticles resulted in an increase in crystallization rate and the nucleation activity of the nanocomposite also increased with increasing Ca-P content. Various models were applied to investigate nonisothermal crystallization kinetics. All approaches, except for the Ozawa model, could successfully describe the nonisothermal crystallization behavior of PHBV and Ca-P/PHBV nanocomposite. The effective activation energy for nonisothermal crystallization was calculated using the differential isoconversional method proposed by Friedman. The morphology of PHBV spherulites in nanocomposite was also studied using polarized optical microscopy. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers