Transformation between Two Types of Spherulitic Growth: Tuning the Morphology of Spherulitic Nitroguanidine in a Gelatin Solution

Abstract

Spherulitic growth, categorized as central multidirectional growth and unidirectional growth via small-angle branching, has increasingly been explored as a method to improve the flowability and bulk density of needle-like crystals. However, the formation of two categories of spherulites in solutions is still unclear. In this work, the formation mechanism of two categories of spherulite was studied in a supercooled nitroguanidine (NQ) aqueous solution with a small amount of gelatin. It is proposed that spherulitic growth depends on the initial morphology of the crystallite, wherein the gelatin concentration, temperature, and initial supersaturation play a vital role. Gelatin can significantly inhibit NQ nucleation, promote branching, and modify the morphology of NQ subunits. At high initial supersaturation and low temperatures, the aspect ratio of the crystal precursor increases and branching is accelerated, so that the lateral faces provide more branching sites than the end faces to promote the unidirectional growth. In comparison, high temperatures promoting the multipoint branching should be mainly responsible for the formation of cauliflowerlike spherulites. Furthermore, the bulk densities of the cauliflower-like and compact spherulites of NQ are about triple those of needle-like crystals and their evolutions were observed. Compared with the reported methods, the macromolecule-induced spherulitic growth of NQ without an organic solvent is a green method and will have a bright future for the design and fabrication of other organic spherulites.

Simultaneous control of polymorphism and morphology via gelatin induction for concomitant systems: case study of sulfathiazole

“…In the high gelatin concentration region above 0.50 g per 100 g H 2 O, the ST obtained under different initial supersaturation has almost no difference in morphology, only some changes in particle size. Studies have shown that high crystallization driving force is a necessary condition for spherulites, 43 but within the scope of this work (S = 9.0-17.3), the only triggering condition for ST morphology modification is gelatin. How, why and under what conditions gelatin promotes ST spherulite is the subject of this section.…”

“…42 Gelatin is non-toxic and low-cost, which can transcend the limitations of most polymorph control methods. 43 In this work, ST was chosen as the model substance to investigate the effect of additive/gel of gelatin on both ST polymorphs and morphology in aqueous solution.…”

“…42 Gelatin is non-toxic and low-cost, which can transcend the limitations of most polymorph control methods. 43…”

Preparation and Characterization of Ultrafine Nitroguanidine with Different Aspect Ratios

“…In recent years, the main ways to improve the mechanical properties and thermodynamic stability of NQ have been through physical and chemical methods, with ultrasonic pulverization, grinding refinement, and impact crushing refinement as the main physical methods and solvent–nonsolvent recrystallization refinement and microemulsification refinement as the main chemical methods. − The use of physical methods for pulverization suffers from the shortcomings of safety, energy consumption, and the difficulty of controlling the crystal size distribution and the regularity of the crystal shape. The recrystallization of NQ by chemical methods increases the unsafe factor due to the volatility and combustion of organic solvents such as DMF, NMP, and acetone, as well as the consumption and recycling costs of solvents and new sources of pollution.…”

Spherulitic Growth Strategy for Agitation-Induced Formation of Spherical Amoxicillin Sodium Products

“…For tablet pharmaceuticals, spherical crystals could be directly tableted without the granulation stage, which reduces manufacturing costs and time. , Spherical crystals also improve the crystal form stability of some pharmaceuticals and avoid caking of foods and fertilizers . Therefore, great efforts have been made to exploit the approaches in industrial crystallization to obtain spherical crystals. − …”