Pore structure and surface area of mannitol powder, granules and tablets determined with mercury porosimetry and nitrogen adsorption

Two methods used in pore structure characterisation, mercury porosimetry and nitrogen adsorption, were compared. Pore structure and surface area of mannitol powder, granules produced in wet granulation and tablets compressed with three compression pressures were studied. Greater surface area, more porous structure and greater number of small pores in granules, when compared with powder, increased the compactibility of mannitol granules in tableting. Plastic deformation and fragmentation of powder and granules in compression were observed in volume pore size distributions and surface areas measured with these methods. Pore volume and volume pore size distribution obtained with mercury porosimetry describe densification of mass better than those obtained with nitrogen adsorption. In spite of differences between the methods, the volume pore size distribution curves of samples in the overlapping pore size range had the same shape. The specific surface area of tablets, measured by the nitrogen gas adsorption method described well the deformation under compression. Fragmentation increased the surface area of powder, and plastic deformation decreased the surface area of granules in the pore size range determined. Surface area values measured with mercury porosimetry were larger than those determined with nitrogen adsorption. (C) 1998 Elsevier Science B.V. All rights reserved.