离子键增强水性聚氨酯/纳米羟基磷灰石复合材料的研究

Improve mechanical properties of waterborne polyurethane/hydroxyapatite nanocomposites through ionic bonds between the two phases

水性聚氨酯/羟基磷灰石（WBPU/HA）纳米复合材料的研究已有报道,但通过离子键增强复合材料的研究却很少见.制备了稳定性良好的带羧酸根的阴离子型WBPU 乳液和带季铵的阳离子型的HA 胶体.其中纳米羟基磷灰石胶体通过合成过程中引入氨乙基磷酸使其带上正电荷.然后加入柠檬酸根将HA胶体转变为阴离子胶体.两种胶体溶液共混,并通过透析去掉柠檬酸根后得到均匀的混合胶体,干燥后得到力学性能良好的WBPU/HA 复合材料.当HA 含量为0-15%（质量分数）时,复合材料力学强度从纯PU 的10.9 MPa 提高到了22.3 MPa,提高幅度达100%.这是由于两相间存在正负电荷的离子键作用.当HA 含量为20%（质量分数）时,由于HA 粒子的团聚导致力学性能下降.提供了一种通过胶体共混来制备离子键增强的纳米复合材料的新方法.

There had been some reports about waterborne polyurethane/hydroxyapatite(WBPU/HA) nanocomposites.Among them,few focused on reinforcement of the composites through ionic bonds.In this paper,we prepared stable hydrocolloids of both anionic WBPU and cationic HA.The latter was synthesized in the presence of aminoethyl phosphate(AEP) that imparted ammonium cations onto the HA particles.This colloid was then transformed into an anionic colloid by adding citrate ions.Thereafter,both the PU and HA colloids were mixed homogenously,followed by removing the citrate ions through dialysis.The dialyzed mixtures were dried to obtain WBPU/HA nanocomposites with good mechanical properties.In parallel with the increase of the HA content from 0 to 15wt%,the tensile strength of the composite increased from 10.9 to 22.3 MPa,corresponding to a 100% gain.This remarkable reinforcement was due to the ionic bonds between the carboxylate groups in the PU chains and the ammonium or calcium ions on the HA nanoparticles.When the HA content was over 20wt%,the mechanical strength decreased due to the severe aggregation among the HA particles,as observed by transmission electron microscopy.This paper provides a new method based on colloidal chemistry to prepare nanocomposites that are reinforced through ionic bonds.