The effects of adsorbed water on tensile strength and Young's modulus of moldings determined by means of a three-point bending method

Young's moduli (E) of three representative tableting excipients and their m il powders were measured for compressed rectangular beam specimens over a r ange of porosities using a three-point bending technique. We also examined the effects of the amount of water adsorbed on the tensile strength of thes e specimens. The maximal tensile strength (sigma(max)) decreased with incre asing water vapor adsorption for microcrystalline cellulose (MCC) and mixed powders of lactose and MCC, sigma(max) increased with increasing compressi on stress and specimen weight for all samples. sigma(max) of an alpha-lacto se and cornstarch mixture with a ratio of 7 : 3 showed a large value. Young's modulus (E) and the crushing energy (CE) of MCC were larger than th ose of the other samples. Young's modulus of specimens decreased as the pro portion of alpha-lactose increased. Disintegration time (DT) of tablets comprised of lactose and MCC mixture wa s much faster than those of tablets comprised of individual powders, This a ppeared to demonstrate the effect of MCC swelling on the disintegration tim e of the tablet, The disintegration time of the lactose/cornstarch series i ncreased only when Young's modulus increased sharply.