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Title: Anomalous particle size shift during post-milling storage
Authors: Ng, W.K.
Kwek, J.W.
Tan, R.B.H. 
Keywords: Breakage
Milled powders
Particle size shift
Issue Date: May-2008
Citation: Ng, W.K., Kwek, J.W., Tan, R.B.H. (2008-05). Anomalous particle size shift during post-milling storage. Pharmaceutical Research 25 (5) : 1175-1185. ScholarBank@NUS Repository.
Abstract: Purpose. To investigate the anomalous phenomenon of particle size shift during post-milling storage. Materials and Methods. 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). Results. 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. Conclusions. 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. © 2007 Springer Science+Business Media, LLC.
Source Title: Pharmaceutical Research
ISSN: 07248741
DOI: 10.1007/s11095-007-9497-8
Appears in Collections:Staff Publications

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