Preparation And Characterization Of Hydroxyapatite Nanorods/Poly(Lactic Acid) Composites

The biological and mechanical properties of poly(lactic acid)(PLA)materials can be improved when compounded with hydroxyapatite(HA).In this paper,calcium oleate was used as the precursor to prepare lipophilic hydroxyapatite nanorods(HA_NRS)by solvothermal method.The morphology and crystal structure of HA_NRS were investigated by testing X-ray diffraction analysis(XRD),transmission electron microscopy(TEM),and X-ray energy spectrum analysis(EDS).The material compositions of HA_NRS were explored by thermogravimetric analysis(TGA),Fourier infrared spectroscopy(FT-IR)and Raman spectroscopy.The influence of hydrothermal temperature and hydrothermal time on the compositions and structure of HA_NRS were analyzed subsequently.The"dispersion-agglomeration"phase diagram of the HA_NRS-PLA-dichloromethane ternary system was drawn,and the dispersion law and dispersion mechanism of HA_NRS were confirmed.The HA_NRS/PLA composites were prepared by the solution blending method and the hot pressing method.Mainly through scanning electron microscopy(SEM),TGA and differential scanning calorimetry(DSC)testing,the composition and microstructure of the composites were investigated.The mechanical properties(tensile test and impact test)of the composites were tested and the structure-activity relationship of the composites was analyzed.Short rod-shaped hydroxyapatite single-crystal nanoparticles(high-temperature particles)were prepared at 180°C,with an average aspect ratio from 7.9 to 9.4,high crystallinity,and 18wt%oleic acid attached to the surface.Prepared at 86°C,long rod-shaped hydroxyapatite single-crystal nanoparticles(low-temperature particles),with an average aspect ratio greater than 20,low crystallinity,and 32wt%oleic acid attached to the surface were acquired.The decomposition temperature of oleic acid is higher than400?.HA_NRS will be fully dispersed in the dichloromethane solution with PLA,this process is irreversible.The upper limit of the effective composite of high-temperature particles and low-temperature particles are 10wt%and 5wt%,respectively.Under the circumstances,HA_NRS was in an ideal homogeneous dispersion state in the PLA matrix,which improved the mechanical properties and crystallization properties of the composites.When the HA_NRS exceeds the upper limit of the effective composite,the interlaced HA_NRS will hinder the structural adjustment of the composites during the cold pressing process,and a large number of pore-like structures will appear in the materials,which can reduce the mechanical properties of composites.The in-situ coating of oleic acid on HA_NRS not only improves the colloidal stability during the synthesis process but also promotes the dispersion of nanoparticles in the PLA matrix.For high-temperature particles,the maximum elongation at break of the composites is 18.19%,which is 186%higher than that of pure PLA,while the tensile strength and Young's modulus remain unchanged.The maximum elongation at break of the composites with low-temperature particles is 16.37%,which is 332%higher than that of pure PLA.In addition,the tensile strength and elastic modulus of 1wt%HA-2/PLA and 2wt%HA-2/PLA composites were significantly improved.HA_NRS will reduce the thermal stability of the composites,decrease the crystallization temperature and increase the melting point.