A STAINING TECHNIQUE FOR EVALUATING THE PORE STRUCTURE VARIATIONS OF MICROCRYSTALLINE CELLULOSE POWDERS

A staining technique was developed for evaluating the pore structure o f microcrystalline cellulose powders. This technique used two direct d yes as molecular probes and was based on the differences between the t wo dyes' molecular size and affinity for microcrystalline cellulose. D irect Blue 1 has a smaller molecular size and weaker affinity for micr ocrystalline cellulose compared to Direct Orange 15, which has a large r molecular size and stronger affinity. We used the ratio of adsorbed Direct Orange 15 to adsorbed Direct Blue 1 after 48 h staining [design ated as (O/B)(48)] as the parameter for evaluating the pore structure variations between different microcrystalline cellulose powders. Seven microcrystalline cellulose samples of three different grades-Avicel P H-101, Avicel PH-102 and Avicel PH-103-were analyzed for their (O/B)(4 8) ratios, and significant differences were found. These differences a re present primarily among different grades and secondly among differe nt batches of the same grade. Among the three grades tested, it was fo und the their (O/B)(48) ratios have the following sequence: Avicel PH- 103 > Avicel PH-101 > Avicel PH-102. This suggested that pore structur e variations are significant among different microcrystalline cellulos es of both different grades and batches, but the degree of variation b etween different batches is less than that between different grades of microcrystalline cellulose. (C) 1998 Elsevier Science S.A. All rights reserved.