Hygroscopicity of a sugarless coating layer formed by the interaction between mannitol and poly(vinyl alcohol) (PVA).

ABSTRACT

A sugarless layer that provides protection against moisture is formed on tablets when a coating solution comprising mannitol and poly(vinyl alcohol) (PVA) is applied. The objective of this study is to investigate the relationship between the formation of such a sugarless layer and the resulting hygroscopic properties in order to derive an appropriate sugarless coating. The hygroscopicity of the sugarless layer is shown to be strongly affected by the addition of PVA, and has the lowest at concentration ratios between 152.5 and 154 (w/w) of mannitol and PVA. The polymorphic form of mannitol is different in formulations with different mannitolPVA concentration ratios. Mannitol occurs in the α-form at mannitolPVA concentration ratios between 151 and 154 (w/w). Moreover, PVA affects the molecular motions in the region associated with the OH stretch, OH deformation, and CH2 wag of mannitol. In particular, the molecular motions change considerably at mannitolPVA concentration ratio of 152.5 and 154 (w/w). In addition, the surface state of the sugarless layer depends on the amount of PVA added, and exhibits the smoothest surface at a mannitolPVA concentration ratio between 152.5 and 154 (w/w). Thus, the hygroscopicity is related to the surface states of the sugarless layer, which, in turn, is affected by the change in the molecular motions of mannitol due to the interactions between mannitol and PVA.