Preparation and characterization of surface-modified calcium hydrogenphosphate by hexamethylene diisocyanates

Isocyanate group has been reported as a coupling agent of hydroxyapatite and polymers. The studies showed that the isocyanate would react with hydroxyl groups of hydroxyapatite and form a covalent bond between isocyanate and hydroxyapatite. In the study, hexamethlene diisocyanate (HMDI) was used as coupling agent. Calcium hydrogen-phosphate (CaHPO4, CHP) powders was the candidate ceramic due to higher content of hydroxyl group, which would react with HMDI at the temperature of 30, 40, 50, 60, and 70 degrees C for 4 hours. Dibutyltin dilaurate and hydroquinone were used as catalyst and inhibitor, respectively. The product was analyzed by DTA, TGA, FTIR, XRD, 13C solid state NMR and 31P, 13C liquid state NMR. From the results, we could prove the surface of calcium hydrogen-phosphate has been successfully modified. The largest amount (5.6 wt%) of HMDI could be grafted on the surface of CHP when reacted at 50 degrees C for 4 hours. Some chain extension could be observed and their structure would also be described in the research.