Preparation and Formation Mechanism of l-Valine Spherulites via Evaporation Crystallization

l-Valine crystallizes in a flake-like shape generally; however, compared with the flake-like products, spherulitic l-valine has better filterability, flowability, and bulk density and has potential for wider industrial applications in the future. In this study, l-valine spherulites have been successfully prepared by an evaporative crystallization method in the presence of no more than 0.5% hydroxypropyl methyl cellulose (HPMC). The spheroidization of l-valine proceeds via a layer-by-layer transformation from an initial flake-like shape to a petal-like form, and then it continues to grow into the final sphere-like shape. Molecular dynamics simulations show that HPMC interacts with hydrophilic (001) faces preferentially and promotes the continuous layer growth process. Only the substituent groups of hydroxypropyl and methyl exist simultaneously within a certain spatial distance and, in a viscosity of 40–50 mPa·s, can promote the formation of l-valine spherulites. The particle size increased with the increase in the HPMC dosage and decrease of temperature or evaporation rate. This effect of HPMC promoting the spherical formation provides a method to enrich the design of spherulites and new insights into the fabrication mechanism of spherulitic growth.