An Investigation into the Morphology Evolution of Ethyl Vanillin with the Presence of a Polymer Additive

Ethyl vanillin (EVA) is an important synthetic chemical which is widely used in foods, spices, cosmetics, and pharmaceuticals. However, EVA shows a thin platelike habit in various solvents, and such a habit could bring a series of problems to the downstream process. In this paper, a detailed experimental and modeling investigation for the effect of solvent molecules and polyvinylpyrrolidone (PVP) on the morphology of EVA was conducted. The results show that the EVA crystals obtained in an ethanol-water solution with different supersaturations remain aggregated and have a thin platelike morphology. Adding a certain amount of PVP into the solution can not only improve the aggregation but also modify the crystal habit from thin platelike to blocklike. The inhibition ability of PVP is found to have a positive correlation with PVP molecular weight and concentration. In contrast, the morphology of EVA crystals obtained in the presence of PVP monomer and other structurally similar additives did not change. The underlying mechanism of solvent molecules and PVP in morphology changes was investigated by a molecular dynamics simulation. The modeling results reveal that the special pocket structure on the crystal face is also responsible for the thin platelike habit, apart from the interaction between the exposed functional groups on the crystal faces and the solvent molecules. The change in the crystal habit with the presence of PVP is attributed to the preferential adsorption of PVP on the crystal faces, which may affect the attraction and association of solvent or solute molecules and hence hinder the crystal growth process.