The rising demand for exclusive visual impact in many applications, along with escalating regulatory requirements drive the development of new, environmentally benign, pearlescent materials. Guanine, a common naturally mineralized material, is being used in a variety of products in industries, such as cosmetics, paints and jewelry due to its pearlescence effect. However, the industrial application of guanine crystals is limited since they are extracted from biological sources (mostly fish scales) with limited control over crystals dimensions, morphology and quantity for industrial applications. The main reasons impeding the use of synthetic guanine crystals are guanine insolubility in most solvents and the difficulty of obtaining crystals in the desired morphology. For these reasons, there is a thriving need for the development of a synthetic approach for the formation of well-defined anhydrous guanine crystals with tailor-made properties.
The new technology provides a novel synthetic method for the preparation of highly versatile pearlescent materials, based on guanine crystals, from aqueous solutions. The controllable size and shape of the resulting materials and the sustainability of the method make them suitable alternatives for the existing naturally occurring pearlescent pigments.
· Cost-effective and environmentally-friendly approach
· Control over crystals properties, including size and phase (anhydrous guanine and guanine monohydrate)
· The same technology can be applied for the crystallization of other materials (purines and pteridines)
· Cosmetics and personal care products
· Printing inks and decorative paints
· Automotive paints.
Guanine is practically insoluble in neutral aqueous solutions. However, in aqueous acidic or basic solutions, where the molecules are ionized, guanine is much more soluble. The process involves dissolving guanine powder in either acidic or basic solutions, using HCl or NaOH, respectively, and then inducing crystallization by adjusting the pH of the solution. The crystal morphologies differ significantly when carrying out the crystallization in solutions adjusted to different pH regimes. Using pH induced crystallization, the interplay between the initial guanine concentration and the rate of pH change allow substantial control over the crystallization process and ultimately over the crystal size.