The Preparation And Characterization Of Nano Hydroxyapatite (nHA) And Its Organic Composites

Hydroxyapatite (HA) is widely used in fields of biomaterials, biotechnology, additive and functional materials, due to its special component, structure and properties, especially the good biocompatibility based on its similarity to inorganic component of bone. In the researches on preparation methods of HA, biomimetic nano hydroxyapatite (nHA) is emphasized and highlighted since 1980's. People have synthesized rod-like and needle-like HA crystals with nano size. Such nano crystals provide excellent properties and special function for composite biomaterials.The dissertation designs a novel solution system, using ethylene glycol (EG) as the solvent of calcium hydroxide, i.e. Ca(OH)2-EG-HsPO4 system, to synthesize needle-like nHA crystals, which has a B type CO32- substitute. The morphology and component of nHA are similar to bone apatite. The ethylene glycol solvent influences the formation of nHA crystals in following aspects: 1) The ethylene glycol as chelating reagent offers the reaction an ionic level calcium; absorbs the hydrogen ions of orthophosphoric acid, which is benefit to the preparation of fine and homogenic nHA crystals in the weak alkaline circumstance. 2) The ethylene glycol acts as crystal seed growing factor to control nHA to grow in c-axis direction and form needle-like crystals. 3) The low surface tension of ethylene glycol can avoid the rigid reunion of nHA crystals, keeping them in dispersive distribution.The study prepares two kinds of composites consisting of nHA and polyamide, i.e. nHA/PA66 and nHA/PA6. A few bonding modes are present between nHA and PA, such as ligand bonding of COO" and Ca2+, hydrogen bonding of-NH and -OH,C=O and -OH as well as -NH and PO43-. The content of nHA in the composites can be adjusted in the range of 10-70 wt% and nHA crystals disperse uniformly in PA. The destruction of hydrogen bonds in PA polymer chains breaks the symmetrization of PA molecule structure and decreases the crystallizing ability. However, the crystallinity decrease of nHA/PA66 is not as obvious as nHA/PA6, because nHA crystals as nucleus also increase the crystallinity of PA66 in the composite. The mechanism of PA crystal transformation is established. PA66 is transformed from a type predominated to a mixture of more P type and less a type, and PA6 is transformed from y type predominated to a more a type mixture.