Influence of the binder on the mechanical strength of compacts prepared by modified wet compression method
Résumé
In this work, we aimed at studying formulation and design of powders by modified wet compression method. In order to focus only on the role of the liquid binder in the mechanical cohesion of compacts, glass beads were used as model particles because they do not deform or fragment at the compression pressure used (35kN). The three different binders studied were sugars: fructose, glucose and saccharose, used as solutions. Therefore, compacts were stored at controlled conditions until reaching water activity equilibrium at a fixed temperature of 25 degrees C. Then, the tensile strength of the compacts was determined using a Brazilian test. It was found to be dependent on the water activity. Critical values of Aw were measured (A(w) = 0.23 for the fructose, A(w) = 0.33 for the glucose, and A(w) = 0.44 for the saccharose), beyond which the glass transition phenomenon of the sugars appeared, and resulted in a sharp drop in the mechanical strength of the compacts. The classification of the sugars according to their respective glass transition temperature (Tg(fructose) < Tg(glucose), < Tg(saccharose)) permitted to confirm the role of the glass transition of the sugars as binders in the mechanical resistance of the compacts. Finally, sorption isotherms of the sugars coupled to the tensile strength results showed that the main parameter for predicting mechanical strength of the compact was the amount of sorbed water by the sugar, regardless to his nature.