Choice of dispersants for the nano-apatite filler of polylactide-matrix composite biomaterial

The aim of this study is to compare de-aggregative ability of common organic dispersants for the acicular nano-apatite crystallite with main composition of calcium hydroxyapatite (HA) as a filler of composite containing polylactide (PLA) matrix. Firstly, the acicular nano-apatite powders with an average length of 70–120 nm were synthesized based on traditional chemical co-precipitation and freeze-drying techniques. Common organic dispersants including tetrahydrofuran, acetone, chloroform, N,N-dimethyl formamide (DMF) and ethanol were then employed to disperse synthetic freeze-dried ultra-fine nano-powders. The observations and weight of sediments showed that nano-apatite suspension dispersed by DMF and ethanol presented homogeneous and stable colloid after vigorly stirred for 24 h and then kept still for same time, respectively. Results of particle measurements and viscosity measurement illuminated that a large number of the nano-apatite particles with an average dimension of 297.86 nm and viscosity of 0.8872 cP in DMF suspension could be dispersed up to 91.28 nm by the DMF dispersant and the DMF dispersant could minimize agglomeration between the apatite ultra-fine nano-powders. DMF is a more effective and appropriate dispersant to disperse the apatite nano-fillers than chloroform, tetrahydrofuran, acetone and ethanol, when the nano-apatite/PLA composite biomaterials were prepared.     

Surface analysis, TEM, dynamic and controlled rate thermal analysis, and infrared emission spectroscopy of gallium doped boehmite nanofibres and nanosheets

Ga doped boehmite nanofibres with varying Ga content have been prepared at low temperatures using hydrothermal treatment in the presence of poly (ethylene oxide) surfactant. The resulting nanofibres were characterized by X-ray diffraction (XRD), dynamic and controlled rate thermal analysis and infrared emission spectroscopy (IES), transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDX), N₂ adsorption/desorption. TEM results show that nanotubes are dominant when the doped gallium percentage is no more than 5%; nanosheets and an amorphous phase are observed in 10% and 20% gallium doped samples. N₂ adsorption/desorption analysis reveals a large amount of micropores and mesopores are present in the resultant samples. Similar to iron and yttrium doped boehmite nanomaterials, remarkable larger BET specific area was achieved compared to pure boehmite nanomaterials. Both dynamic and controlled thermal analyses show that the gallium doped boehmite nanomaterials dehydrate at higher temperature than that of pure boehmite. Interestingly, the higher the crystallinity of the resultant nanotubes is, the higher the dehydration temperature. The IES spectra show that dehydroxylation of the resultant gallium doped boehmite nanomaterials starts at 250 °C and is complete by 450 °C, in harmony with the dynamic and controlled rate thermal analysis results.     

纳米晶镁铝水滑石的制备及其热分解机理

研究了无机阻燃剂镁铝水滑石纳米晶的制备及其热分解机理.采用常压下,一步反应的液相法制备镁铝水滑石试样，用XRD和TEM测试试样的相组成和形貌，针状镁铝水滑石纳米晶体的长度约80 nm.依据DSC和DTA-TG测试结果，发现镁铝水滑石纳米晶的热分解由两个阶段组成:第一个吸热峰出现在220 ℃左右，第二个吸热峰出现在380 ℃左右.研究了反应时间对所得镁铝水滑石试样的热分解性能的影响，发现延长反应时间，镁铝水滑石试样的第一次、第二次热分解的起始温度升高,第一次热分解的失重值增大，最后剩余氧化物的量增大，从而增强镁铝水滑石阻燃剂的阻燃性能.根据不同升温速率下获得的DSC测试数据，应用Achar微分法、Šatava-Šesták积分法和Ozawa积分法对镁铝水滑石纳米晶热分解的第二个阶段进行了动力学计算和分析，确定该段的热分解机理函数积分式为(1－α)－1－1.