Tensile strength and compression of coated pharmaceutical powders

Abstract

A study has been made of the tensile strength and compression of loosely packed beds of lactose, sodium chloride and calcium phosphate powders after they had been coated with small amounts of stearic acid, polyethylene glycols and polyvinylpyrrolidones. The properties of the systems were measured over a range of temperatures. Only when the coatings were continuous and durable did they produce reductions in both tensile strength and resistance to compression. Marked changes occurred in tensile strength at temperatures 20 ° — 40 °C below the conventional melting points of the coatings. The tensile strength results have been expressed in terms of the range and magnitude of the interparticle forces which depend on the surface free energy of the coated powders and on the Brinell hardness of the coating materials employed.