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Spherically agglomerated crystals of ascorbic acid for direct tableting were successfully prepared by the spherical crystallization technique. This agglomeration dramatically improved the micromeritic and compaction properties of the original ascorbic acid crystals. The dominating mechanisms that improved compaction properties of the spherically agglomerated crystals depended on their fragmentation and plastic deformation during compaction. Support for this mechanism existed because the compacted agglomerated crystals had higher stress relaxation and lower elastic recovery than the original crystals. Spherically agglomerated crystals were tableted directly without capping by using a single-punch tableting machine under dynamic compaction, although the tensile strength of tablets with spherically agglomerated crystals decreased when the compression speed increased. * 5-6-1 Mitahorahigashi, Gifu, 502-8585 Japan TEL: +81-58-237-3931 (ext. 244) FAX: +81-58-237-6524 † This report was originally printed in J. Soc. Powder Technology, Japan. 38, 160-168 (2001) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan. cle diameter of 425 μm, made by Takeda Chemical Industries, Ltd.). A control for both assessments was commercially available granulated ascorbic acid for direct tableting (hereinafter, “C97 granules,” average particle diameter of 422 μm, made by Takeda Chemical Industries, Ltd.). C97 granules are produced in a f luidized bed with 3% starch added as a binder. As the model drug for plastic deformability we used potassium chloride (Japanese Pharmacopoeia, hereinafter written “KCl,” average particle diameter of 650 μm, produced by Yamazen Corporation). 2.2 Preparation of Ascorbic Acid Agglomerated Crystals for Direct Tableting Ascorbic acid was dissolved in 50°C purified water (a good solvent) to prepare a 0.4 g/ml saturated solution. A pipette was used to quickly drop a prescribed amount of the solution into a 500 ml cylindrical agitator tank containing 300 ml of ethyl acetate (a poor solvent, maintained at 5°C) while stirring with a fourbladed propeller-type agitator at either 300 or 800 rpm. By choosing a water-to-ethyl acetate volumetric ratio of either 1:100 or 4:150, we prepared spherical agglomerated crystals of ascorbic acid by two different crystal agglomeration mechanisms: spherical agglomeration (SA), and emulsion solvent diffusion (ESD). We inserted baff les in the agitator tank to promote granulation with SA, but with ESD we let granulation occur without using baff les so as to prevent the breakdown of emulsion droplets. After stirring for 20 min the crystal agglomerates obtained were suction filtered, washed with a small amount of methanol, and dried under reduced pressure for at least 24 h. We used the agglomerate fraction in the 125 to 500 μm range, obtained by classifying with a screen to bring them into line with the C97 granule particle size range. This fraction’s yield was good at 70 to 80%. 2.3 Measuring Physical Properties of Agglomerated Crystals A scanning electron microscope (JTM-T330A, JEOL., Ltd.) was used to observe the particle form of the original crystals (100 mesh product), coarse crystals (FG product), and C97 granules, and the surface property and cross sections of the two types of spherically agglomerated crystals (SA and ESD products). Sample f lowability was measured and assessed by using the pouring method to make them pile, then measuring their angle of repose. Sample packability was assessed by analysis of the tapping process with the Kawakita [2] (Eq. 1) and Kuno [3] (Eq. 2) methods, and using the parameters a, b, and k in the equations. (n/C) (1/ab) (n/a), C (V0 Vn)/V0 (1) ρf ρn (ρf ρ0)exp( kn) (2) Where: a is the degree of volume reduction when the tap number is infinity, b and k are constants for the apparent packing rate, V0 and Vn are the volume in the initial loosely packed and the nth tapped state, and ρ0, ρn, and ρf are the apparent density in the initial state, the nth tapped state, and the most densely packed state. 2.4 Tablet Preparation A screen was used to classify the test samples into a 125 to 500 μm fraction. We placed 150 mg of each sample into a die with diameter of 8 mm, and used an AUTOGRAPH (Instron type press) (AG5000D, Shimadzu Corporation) to tablet the samples at a constant rate of 10 mm min 1 and at various compression pressures between 50 and 300 MPa 5%. Assuming commercial production, we mixed 1% magnesium stearate into each sample and used the universal tensile compression tester and a single-punch tableting machine (TabA11, Okada Seiko Co., Ltd.) to produce tablets under a constant compression pressure of 200 MPa 5% and at various compression speeds. The compression speed of single-punch tableting machine was calculated from the displacement rate of upper punch when compressing. 2.5 Compression Behavior Analysis 2.5.1 Heckel Analysis [4, 5] We used Heckel’s equation (Eq. 3) to analyze the compression process of agglomerated crystals, and assessed their compactibility. 1n [1/(1 D)] KP A (3) Where: D is the relative density of the tablets under compression pressure P (MPa; the ratio of tablet density to the powder’s true density), K is the slope of the straight portion of the Heckel plot, and the reciprocal of K is the mean yield pressure (Py). Eq. 4 gives the intercept obtained by extrapolating the straight portion of the plots. A 1n [1/(1 D0)] B (4)

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Development of Agglomerated Crystals of Ascorbic Acid by the Spherical Crystallization Technique for Direct Tableting, and Evaluation of Their Compactibilities [Translated]<sup>†</sup>

Development of Agglomerated Crystals of Ascorbic Acid by the Spherical Crystallization Technique for Direct Tableting, and Evaluation of Their Compactibilities [Translated]†

Development of Agglomerated Crystals of Ascorbic Acid by the Spherical Crystallization Technique for Direct Tableting, and Evaluation of Their Compactibilities [Translated]^†