Viscosity: a key factor in the diffusion and longevity of fragrances

Encapsulation process in the cosmetics industry

Encapsulation is a key industrial process in the cosmetics sector. It involves enclosing an active substance (solid, liquid, or gaseous) in a matrix or protective envelope in order to protect it, control its release, or improve its properties. 

Among the many critical parameters that must be controlled to ensure the quality and effectiveness of the final product, viscosity plays a key role.  

In perfumery, microencapsulation processes make it possible to control the release of the active substance and prolong the longevity of the fragrance. 

What is Viscosity? Definition

Viscosity characterizes a fluid’s resistance to flow. It is a major parameter in several stages of the encapsulation process. Often described as the thickness or fluidity of a liquid, viscosity depends on several factors: 

• The chemical nature of the fluid (polymers, solvent, surfactant, etc.) 

• Temperature 

• Solids or solutes concentration 

• The shear rate for non-Newtonian fluids (strain rate applied to the fluid) 

In encapsulation processes, the viscosity of the solutions or dispersions used (polymers, emulsions, gels, etc.) directly impacts capsule formation, size, morphology, stability, and even functionality. A Precise control of this parameter is therefore essential to ensure the reproducibility, efficiency, and profitability of encapsulation processes. 

Role of viscosity in encapsulation processes 

The most common encapsulation processes (coacervation, extrusion, spray drying, emulsification, etc.) are based on the manipulation of fluids. Thus, viscosity has a direct influence on: 

• Droplets or particles formation: excessively high viscosity can prevent the formation of fine droplets, while excessively low viscosity can lead to coalescence or instability. 

• Emulsion stability: Adjusted viscosity stabilizes the interfaces between phases, preventing sedimentation. 

• Matter transfer: The diffusion of active substances or solvents is affected by the viscosity of the medium. 

• Final product’s quality: The size, particle size distribution, porosity, mechanical strength, and controlled release depend on the viscosity of the phases involved. 

Impact of viscosity on various encapsulation processes

Coacervation

Coacervation is a process based on the phase separation of a polymeric system. Viscosity of the polymeric solution is crucial: 

• Coacervate formation phase: Excessively high viscosity can prevent the formation of homogeneous microdroplets. 

• Gelification phase: Viscosity influences the gelation kinetics and the size of the capsules formed. 

Example: In the encapsulation of fragrances or flavors, poorly controlled viscosity can result in irregularly sized capsules, affecting the controlled release of the active ingredient. 

Spray-drying

Le spray-drying is a widely used technique for encapsulating active ingredients in a polymer matrix. The viscosity of the solution to be atomized is a key parameter: 

• Atomization: Excessively high viscosity can clog nozzles or produce particles that are too large. 

• Drying: Viscosity influences crust formation and particle porosity. 

Example: In the pharmaceutical industry, inappropriate viscosity can lead to non-homogeneous particles, affecting the bioavailability of the drug.  

Extrusion 

Extrusion is often used to encapsulate liquids or solids in gels or polymers. The viscosity of the gel or polymer solution must be carefully controlled to: 

• Enable smooth extrusion without breakage/leakage. 

• Ensure good retention of the active ingredient. 

• Facilitate the formation of uniformly sized capsules. 

Example: In the food industry, encapsulating essential oils by extrusion requires precise viscosity to prevent leaks or deformed capsules. 

Emulsification 

Emulsification is a key step in many encapsulation processes. The viscosity of the oil and aqueous phases, as well as that of the final emulsion, influence: 

• The droplet size. 

• The emulsion stability. 

• The ease of separation or subsequent solidification. 

Example: In cosmetics, an emulsion that is poorly stabilized due to unsuitable viscosity can lead to phase separation or premature release of the active ingredient. 

Consequences of improper viscosity control 

Inadequate viscosity control can lead to numerous problems, affecting the quality of the final product and the profitability of the encapsulation process: 

• Capsules heterogeneity: Uncontrolled size, shape, and distribution. 

• Emulsions unstability: Phase separation, coalescence, sedimentation. 

• Difficulties to process: Clogged nozzles, poor material transfer, extended drying time. 

• Release related issues: too rapid or too slow release of the active ingredient. 

In process viscosity monitoring 

In-line: Sofraser viscometers 

The MIVI is a versatile viscometer with a wide range of configuration options and accessories (depending on process conditions) or mounting options (e.g., reactor, piping) that allow it to be adapted to all installations and processes.  

Sofraser viscometers provide continuous viscosity measurement in real time without interrupting the manufacturing process. It allows the operator to adjust the fluid composition manually or automatically to ensure a stable and optimized process. 

MIVI’s vibrational technology improves efficiency and control in your manufacturing process. It guarantees compliance with the sanitary/hygienic conditions required in the cosmetic and pharmaceutical industries.  

Thanks to their integration into encapsulation processes, the viscosity meters ensure complete control over the manufacturing stages and the quality of the final products. 

Versatility and flexibility for optimization

Maintaining optimal viscosity ensures the quality of the final product and can be achieved by implementing one or more strategies: 

• Temperature Control: Viscosity generally decreases as temperature increases. 

• Concentration adjustment: Dilution or concentration of polymer solutions. 

• Use of additives: Thickeners, surfactants, or rheology control agents. 

• Automation: Integration of sensors and real-time control systems. 

Example: In the pharmaceutical industry, online viscometers enable continuous adjustment of the viscosity of encapsulation solutions, ensuring consistent quality. 

Conclusion

Viscosity control is a critical parameter in encapsulation processes, influencing both the quality of the final product and the efficiency of the process.  

Manufacturers must therefore invest in appropriate measurement and control tools and integrate viscosity control into the design of formulations and processes. Technological innovations, particularly in sensors and modeling, are opening up new possibilities for even more precise and automated control.  

In short, viscosity is not just a physical parameter, but a strategic lever for innovation and competitiveness in the field of encapsulation. Encapsulation is a key industrial process in many sectors: pharmaceuticals, food processing, cosmetics, chemicals, and many others. 

In the pharmaceutical industry, the MIVI sensor is used to control the viscosity of gelatin in encapsulation processes. To read the dedicated article, click on the following link : How versatile viscometers optimize encapsulation processes?