Insight into the Role of Hydroxypropyl Cellulose in Tuning Crystallization Behaviors of dl-Methionine.

Efficient regulation of dl-methionine (dl-met) crystallization behavior remains of great interest since it usually appears in the form of needles or flakes, which is prone to cause problems in downstream processes. In this study, the crystallization process and crystal morphology of dl-met were focused with hydroxypropyl cellulose (HPC) as the tuning additive. The crystallization behaviors of dl-met with HPC were investigated through experiments and theoretical calculations from thermodynamic and kinetic perspectives to understand the mechanism of HPC in the dl-met crystal morphology. It was found that HPC could raise the interfacial energy γ, making nucleation more difficult. Furthermore, the inhibitory effect of HPC on the axial direction growth was much stronger than that on the radial direction, thereby changing the dl-met crystal morphology from rod-like to block-like. Theoretical calculations explained the underlying mechanism of HPC in regulating crystal habits. Due to the structural differences between different crystal surfaces, HPC exhibited a stronger hydrogen bonding with the (111) crystal surface, thus notably hindering its growth, specifically in the axial direction.