Intrinsic adhesion properties of poly(vinyl pyrrolidone) to pharmaceutical materials: humidity effect.

Poly(vinyl pyrrolidone) (PVP) is widely used for bioengineering and pharmaceutical applications, and its adhesion characteristics are critical. When used as a binder in pharmaceutical granulation, it covers the resultant granules and governs their surface properties. The intrinsic adhesion forces of PVP toward common hydrophobic (magnesium stearate) and hydrophilic (lactose) pharmaceutical materials have been studied as a function of relative humidity (RH). The effect of RH on adhesion force was more significant for the PVP/hydrophilic material than the PVP/hydrophobic material. Adhesion was lowest between 20 and 40% RH, and it increased at RH above 40% and below 20%. This is likely to be due to the development of capillary and triboelectrification forces, respectively. In a nano-indentation experiment using a silicon tip at room temperature, the PVP surface underwent a glass transition at 70% RH. This result suggests that surface softening contributes to the increased PVP adhesion at RH above 70%. To adjust the adhesion properties of PVP, humidity control should be an essential part of research and development. Effect of humidity on the adhesion forces between PVP and lactose (LT) or magnesium stearate (MS).