Stearic acid crystals stabilization in aqueous polymeric dispersions

Abstract

In wet granulation processes, coatings or binders generally consist of mixtures of various raw materials that confer or enhance specific properties to the final product. Typically, a coating solution is composed of water, film forming polymer (such as hydroxypropyl-methylcellulose, HPMC) and filler (such as stearic acid, SA).One of the important issues in wet granulation processes is the stability of the aqueous coating (or binder) dispersion. An unstable dispersion results in the agglomeration of the colloidal particles, thereby affecting the film coating properties and eventually the coating process.In this study, we use dissipative particle dynamics (DPD) to elucidate the structure of aqueous colloidal formulations. DPD is a coarse-grained molecular dynamics simulation method where the materials are described as a set of soft beads interacting according to the Flory–Huggins (1942) model. The DPD simulation results are compared to experimental results obtained by Cryogenic-SEM and particle size distribution analysis.It is shown from the DPD simulation results that the HPMC polymer is able to form a layer that covers SA particles and thus produces stable colloids. Microcrystalline cellulose (MCC) also covers SA agglomerate but it is not able to diffuse inside its inner core. The agglomerate structure is characterized via the density distribution and the polymer chain end-to-end distance.Experimental results show similar trends; particle size distribution analysis shows that in the presence of HPMC, the majority of SA particles are below 1μm in diameter, also MCC is able to prevent the formation of big SA agglomerates and may be a better stabilizing agent than HPMC. SEM images reveal that HPMC surrounds SA agglomerates with a hatching textured film and anchors on their surface.