无定形磷酸钙的硬脂酸表面改性及其改性后的稳定性研究

将硬脂酸溶于热乙醇并以乙醇为反应介质在回流的条件下对无定形磷酸钙(ACP)粉末进行表面改性. 利用活化率、接触角、红外谱图和热分析等研究了ACP的表面改性效果. 结果表明ACP粉末表面有约4wt%的硬脂酸存在, 硬脂酸可以与ACP以-COOCa和HPO₄^2-的形式发生化学作用, 并在ACP粉末表面形成一层硬脂酸憎水层. 通过红外谱图、热分析和X射线衍射等研究了表面改性对ACP稳定性的影响. 发现采用乙醇回流法不会引起ACP的相转变, 改性ACP粉末可存放超过一年而不发生晶相转变, 这表明硬脂酸可以增强ACP的稳定性.

Surface Modification of Amorphous Calcium Phosphates by Stearic Acid and Their Stability

The precipitated amorphous calcium phosphates (ACP) were modified by stearic acid (SA) at about 78℃ for different times, using ethanol as reaction medium in a reflux setup. Modification effects of SA were investigated by activation ratio, contact angle, FTIR and TGA/DTA. The stability of the ACP powders before and after modification was examined by FTIR, XRD and TGA/DTA. The results show that the optimal adding amount of SA is 5 wt%, there are about 4 wt% SA on the surface of the ACP powders, and SA reacts with ACP to form -COOCa and HPO₄^2- groups which leads to a hydrophobic coating form on the ACP surface containing the long alkyl chain of SA. The ethanol mediated reflux method does not induce phase conversion of ACP at about 78℃ for 24h, and the modified ACP powders are still amorphous even after stored in air at room temperature for more than one year. It is proposed that SA existing on the surface of the ACP powders has higher ability to retard conversion of ACP into its crystalline polymorphous than β-CD due to the strong steric hindrance of the long alkyl chain of SA.