Synthesis, characterization, crystallinity, mechanical properties, and shape memory behavior of polyurethane/hydroxyapatite nanocomposites

Herein, polycaprolactone diols with diverse molecular weights were synthesized by ring-opening method. Then, polyurethanes were synthesized through two-step pre-polymerization method by polyaddition of hydroxyl and -NCO groups. Afterward, a set of polyurethanes/hydroxyapatite nanocomposites were synthesized through solution casting as well as in situ polycondensation methods. The exact nominal molecular weights of the synthesized polycaprolactones were determined by proton nuclear magnetic resonance (hydrogen-1 nuclear magnetic resonance). Hydrogen bonding index of ester and urethane carbonyl groups (HBI(C = O)) of samples was determined through Fourier-transform infrared spectroscopy. Results showed that the incorporating of the hydroxyapatite nanoparticles has reduced HBI(C = O). X-ray diffraction patterns and differential scanning calorimetry thermographs confirmed the barrierity and nucleation performance of hydroxyapatite nanoparticles, and the variation of phase mixing degree of polyurethane's hard and soft segments has altered the crystals size and degree of crystalline in polyurethane/hydroxyapatite nanocomposites. Field emission scanning electron microscope images showed that hydroxyapatite nanoparticles have been uniformly dispersed through in situ polymerization method. Mechanical properties were studied in the terms of HBI(C = O), hydroxyapatite nanoparticles content, and degree of crystallinity. Two different programming procedures were used to evaluate shape fixity and recovery ratios of samples at room temperature and 60 degrees C.