P o s t g r a d u a t e S c h o o l s of Pharmacy a n d *Powder T e c h n o l o g y U n i v e r s i t y o f B r a d f o r d , BRADFORD, W. Y o r k s h i r e , BD7 l D P , U . K . Summary. -S i n c e i n t e r a c t i o n b e t w e e n w a t e r and p a r t i c x l a t e solid is a major f a c t o r in formulation, processing and product performancc:.of pharmiiceuticals, t h e inoisture sorption properties of four g r a d e s of microfine c4ellulose (MFC) and t h r e e g r a d e s of microcrystalline cellu'lose (MCC) w e r e investigated.All t h e powders investigated exhibited t y p e iI BDDT sorption isotherms, fro% which t h e monolayer c a p a c i t y and s u r f a c e a r e a could be evaluated.The h e a t of sorption (-AHa) a n d immersior, l(-AHi) of water-vapour w e r e d e t e r m i n e d by b a t c h and flow rnicrocalorimetry, which t o g e t h e r with t h e w a t e r sorption isotherms g a v e t h e integral (-AH) a n d differential h,eats (--CH), f r e e 2 1 7 1 Copyright 0 1986 by Marcel Dekker, Inc.Drug Dev Ind Pharm Downloaded from informahealthcare.com by UB Wuerzburg on 11/01/14For personal use only.

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The technique of inercury porosimetry is usually regarded as a method for the determination of surface areas and the evaluation of pore size distributions in porous solids. With fine non-porous or microporous materials the initial lowpressure region of a mercury penetration graph can be used to determine the inter-particle spaces or voids in an assembly of discrete particles.A determination of the particle size and distribution of three powders, in the one micrometre and sub-micrometre size range, has been obtained from mercury porosimetry breakthrough and intrusion pressures. The mercury intrusion particle diameters and distributions are compared with values obtained by gravitational and centrifugal sedimentation methods and electron microscopy counts for particle size measurement.

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The progress of the compaction process to produce from an assembly of particles a coherent mass can be achieved by the application of shear and normal stress. The achievement of a densified coherent mass necessitates, together with the yielding of material, the movement of particles over and between each other. In uniaxial compaction the angle of internal friction, δE, is a projection of the unique critical state line which divides a three dimensional relationship between volume change (V), shear stress (ϕ) and normal stress (σ) into yield domains and surfaces. There is one region for failure and flow (the Hvorslev surface) and another region for failure and consolidation (the Roscoe surface). In this paper the concepts of the Roscoe and Hvorslev surfaces together with the Coulomb yield criterion have been applied to the uniaxial compaction, over a range of compactable stresses, of titanium dioxide (20–2000 kPa). The characteristics of applied and shear stress, angle of internal friction (δE), angle of shearing resistance (ϕ) and surface area (SBET) were measured and correlated with the compaction stress (σc) and diametral strength (σf) of the compacts to investigate the phenomena of uniaxial compaction.