While colorful particles introduced for purely aesthetic purposes still represent a significant share of encapsulated materials used within the cosmetics market, the formulation and delivery of special ingredients and active compounds from cosmetics is becoming an increasingly attractive prospect to manufacturers.
End users are continually seeking products with improved functionality and higher performance profiles. An efficient technology that has the flexibility to process a wide range of different materials is required to meet those needs.
International Specialty Products (ISP) has been working successfully with complex coacervation technology for many years in the production of encapsulated products and has recently added JetCutter technology to its portfolio through an alliance with geniaLab in Germany. So far JetCutter technology has not been used widely for cosmetic products. However, based on experience gained in other applications, it is anticipated that many new cosmetics-based products will emerge shortly.
This paper gives an overview of JetCutter technology, presenting its major advantages and outlining new product developments. It also focuses on the customization of products for special applications and gives guidelines with respect to the use of particles within the end product.
JetCutter technology
Encapsulated beads are produced when component materials are pumped at high velocity as a solid jet of fluid. The fluid jet is then cut into cylindrical segments using the rotating JetCutter tool. Driven by the surface tension, the cut cylindrical segments form spherical droplets and fall into a bath of hardening solution. The resulting chemical reactions process the droplets into encapsulated beads. The whole process is demonstrated graphically in Figsures 1a and 1b.
Droplet generation using the JetCutter technique is based on the mechanical impact of the cutting wire on the liquid jet. The size of the droplets can be adjusted within a range of 200 µm up to several millimeters. The main size-influencing parameters are the nozzle diameter, the flow rate through the nozzle, number of cutting wires, and the rotation speed of the cutting tool.
The cutting process causes a small initial material loss as a cylindrical segment the height of the diameter of the cutting wire is pushed out of the jet, where it can be collected and recycled. If all process parameters are adjusted correctly, these losses can be reduced to 1% or less. This means that more than 99% of the processed fluid is transferred directly into the beads.
Particle size distribution
To achieve uniform bead diameter, a steady jet flow rate and a uniform rotation of the cutting tool are required. As both these parameters can be effectively controlled, it is possible to produce particles within a narrow particle size distribution. Typically, greater than 90% of the processed beads have a diameter which is within +/-10% of the mean diameter size. This makes the finished beads suitable for aesthetic applications where non-uniform bead sizes are not desirable. Figure 2 shows a typical particle size distribution curve.
As the formation of the bead is the result of a mechanical cutting process and the material surface tension, the viscosity of the fluid has no direct influence on the bead formation. JetCutter technology is therefore capable of processing fluids with viscosities up to several thousand mPa·s - i.e. viscosities somewhere between honey and tooth paste. Fluids with high viscosities have been successfully processed into uniform particle sizes as small as 400 µm. Such high viscosities allow the production of very stable particles due to highly concentrated matrices or the addition of high payloads of insoluble materials like waxes, butters, or clay minerals.
The high fluid velocity is a further advantage of the JetCutter technique, allowing high volume throughputs, making the technology suitable for industrial applications. In addition, high velocities of up to 10 m/s allow the production nozzle to be kept free of incrustations and blockages. Other droplet forming technologies, such as vibrating nozzles, often suffer from blockages due to the high payloads of insoluble materials such as pigments or clay minerals.
The materials that are to be encapsulated, such as pigments or active ingredients, have to be mixed into the feed fluid so they are dispersed evenly throughout the volume of the droplet.
Bead formation
While the JetCutter tool is excellent for producing droplets from fluids, solid particles or beads are required for addition to cosmetic formulations. In principle, any fluid that can be solidified instantaneously can be processed and the means to achieve this can be a purely physical reaction (such as a temperature shift to harden a molten material) or a chemical reaction (like the ionic interaction between polymers and counter ions) or a mixture of both. The typical bead matrix consists of a polymer in an aqueous phase resulting in hydrogel particles.
Within the scope of this article we have examined two such materials - calcium alginate and carrageenan. Alginate is a polysaccharide consisting of guluronic and mannuronic acids with a varying molecular order of these building blocks. It is obtained from the cell walls of brown algae and is widely used in food industries as a thickener. Droplets of a sodium alginate solution of typically 1% to 4% (depending on the viscosity and type of alginate, and the required particle strength) are processed into a solution of 2% calcium chloride. Upon entering the collection bath the calcium ions diffuse into the alginate solution thereby hardening the matrix and forming a solid hydrogel system. Maturated beads are harvested from the hardening bath after approximately 48 hours and to avoid microbial spoilage of the products, a suitable preservative such as ISP Rokonsal™ KS4 is usually added.
For carrageenan, derived from red algae as kappa-carrageenan, in this case processing at elevated temperatures is required. Hardening the droplets is achieved by the combined influence of lowering the temperature and increasing ionic strength. In comparison to the above calcium alginate matrix, the resulting hydrogels are usually more susceptible to softening effects caused by interaction with the formulation.
Other successfully tested matrix systems are chitosan (dissolved in acidic and precipitated in caustic), modified cellulose (gelated in the presence of high levels of potassium ions), pectates (gelated by bivalent ions such as calcium and/or high levels of sugars), gellan gum (reacting to ionic strength) or molten butters or fats hardened by cooling. Figure 3 shows three examples of finished bead sizes and materials - white (2500 µm, alginate), red (900 µm, carrageenan) and blue (700 µm, alginate).
Customized solutions
Hydrogel beads from the ISP Captivates™ range represent an open chemical system that is in constant interaction with the cosmetic formulation. Low molecular compounds from the formulation can diffuse into the particles and, similarly, chemicals may be diffused from within the bead. Any of these processes can cause changes to the bead, such as increasing the gel strength or, in contrast, dissolving the bonds of the matrix.
Depending on the final application requirement of the beads, these properties may be desirable or objectionable to the formulator. For example, a massage cream application may require the beads to break upon relatively high shear stress; however, particles in a foam bath application should release the active ingredients upon dilution in hot water. Although the ISP Captivates™ range covers a broad variety of potential applications, the vast majority of microencapsulated materials produced by ISP are tailor-made to exact specifications.
Formulation guidelines
As we have demonstrated, hydrogel beads need to be used in conjunction with a final formulation to achieve a stable system and to provide the desired functionality. Exposure to high levels of chelating agents in the formulation may weaken the bead structure over time. In contrast, a hygroscopic formulation will shrink and fossilize hydrogel beads. In such cases, fat-based beads can be a feasible alternative.
The mechanical properties of the hydrogel bead also need to be considered within the final formulation. While a cream is viscous enough to support even very large beads and keep them evenly distributed, a lower viscosity formulation requires careful consideration. The formulation needs to have sufficient viscosity or structure to support the required particle size. Larger or denser particles require more elaborate formulations for suspension.
The hydrogel bead consists of between 2% and 10% polymer and up to 98% water. Due to the large water content, the density of the bead is affected by any materials dissolved within the formulation. The density of the water phase within the particles will increase to approximately the same level as the suspending fluid.
Recommended applications
Due to the high number of bead variants possible using JetCutter technology, there are very few limitations regarding applications in cosmetic formulations. Provided a formulation has a minimum viscosity and can support particulates, the design of a matching bead should be possible. Product applications include massage creams, liquid soaps or crystal soap bars for hand washing, shower gels and lotions.
Sample formulation
Table 1 shows a formulation for a massage cream with blue pigmented alginate beads
Conclusion
JetCutter technology allows the handling of a broad range of materials. By selecting the right set of chemicals for matrix formation, it is possible to produce a multitude of hydrogel beads that can give products a competitive edge and deliver sensory delights to end users. ISP is committed to helping the formulator find the best product for a given challenge.
Formulation disclaimer
The information contained in this article and the various products described are intended for use only by persons having technical skill and at their own discretion and risk after they have performed necessary technical investigations, tests and evaluations of the products and their uses. While the information herein is believed to be reliable, we do not guarantee its accuracy and a purchaser must make its own determination of a product's suitability for purchaser's use, for the protection of the environment, and for the health and safety of its employees and the purchasers of its products. Neither ISP nor its affiliates shall be responsible for the use of this information, or of any product, method, or formulation or apparatus described in this article. Nothing herein waives any of ISP's or its affiliates' conditions of sale, and we make no warranty, express or implied, of merchantability or fitness of any product for a particular use or purpose. We also make no warranty against infringement of any patents by reason of purchaser's use of any information, product, method or apparatus described in this article.