Ng Wai Kiong, Kwek Jin Wang, Tan Reginald B H
Crystallisation and Particle Sciences, Institute of Chemical and Engineering Sciences, Jurong Island, Singapore.
Pharm Res. 2008 May;25(5):1175-85. doi: 10.1007/s11095-007-9497-8. Epub 2007 Nov 29.
To investigate the anomalous phenomenon of particle size shift during post-milling storage.
Crystallised and ball-milled adipic acid were stored under different humidity conditions. Analyses were carried out to characterise changes in particle size distribution (laser diffraction), morphology (SEM), bulk flow properties (annular shear tester), surface adhesion forces (AFM) and crystallinity (PXRD and DVS).
It was observed that the particle size distribution of milled adipic acid can shift to finer fractions, remain unchanged, or even shift to coarser fractions depending on storage conditions. SEM analysis showed that milled adipic acid is composed of agglomerates, which can undergo de-aggregation or further agglomeration via re-crystallisation. Empirical analysis ruled out the effects of electrostatic charges on the particle size shift. In addition, an improvement in powder flow in terms of bulk tensile strength was seen for milled adipic acid stored under high relative humidity but not under low humidity.
Storage of milled adipic acid below the critical relative humidity led to localised disintegration from the agglomerate surface and particle size reduction, which was not influenced by moisture sorption or loss. This evidence supports that "stress relaxation" mechanism behind particle breakage of post-milled particles. Appropriate storage conditions are important in maintaining the stability of milled powders.
研究球磨后储存过程中粒径变化的异常现象。
将结晶态和球磨后的己二酸在不同湿度条件下储存。通过激光衍射分析粒径分布变化、扫描电子显微镜分析形态、环形剪切试验仪分析整体流动性质、原子力显微镜分析表面附着力以及粉末X射线衍射和动态蒸汽吸附分析结晶度。
观察到球磨后的己二酸粒径分布根据储存条件可向更细的粒径范围移动、保持不变,甚至向更粗的粒径范围移动。扫描电子显微镜分析表明,球磨后的己二酸由团聚体组成,这些团聚体可通过再结晶发生解聚或进一步团聚。实证分析排除了静电荷对粒径变化的影响。此外,在高相对湿度而非低湿度条件下储存的球磨己二酸,其整体抗张强度方面的粉末流动性有所改善。
在临界相对湿度以下储存球磨后的己二酸会导致团聚体表面局部崩解和粒径减小,这不受水分吸附或损失的影响。这一证据支持了球磨后颗粒破碎背后的“应力松弛”机制。合适的储存条件对于维持球磨粉末的稳定性很重要。