Although conventional homogenization has served the needs of the dairy industry and other industries for more than a century, the producers of pharmaceutical, personal care, chemical and food products are increasingly turning to high-shear fluid processing when highly precise processing is required. This special class of homogenization applies ultra-high shear force to a product stream to produce extremely small and uniformly sized particles and droplets for particle reduction, emulsification and cell disruption applications. The entire product experiences identical processing conditions as it passes through fixed-geometry micro-channels.
Unlike other homogenization methods, the same results are achieved for multiple systems using the same pressure and micro-channel geometry. Users are assured of achieving identical product results as capacity needs expand from the laboratory testing environment to full-scale production on the manufacturing floor.
Conventional homogenization
The conventional homogenization process was originally designed for processing milk and other dairy products. Auguste Gaulin received a patent in 1899 for a milk homogenization mechanism that reduced the size of fat globules to prevent the formation of a cream layer. It’s a mechanical process that forces milk under pressure through a tiny orifice.
Today, a two-stage homogenization process is typically used for dairy products. The first stage operates at a pressure of 2,500 pounds per sq.in. and reduces the fat globules to a mean size of 0.5 micrometers (with actual size ranging from 0.2 to 2.0 µm). Because the reduced fat globules tend to clump and cluster, a second stage of homogenization is employed. The second-stage valve separates the clusters into individual fat globules that are less likely to form cream during two or three weeks of shelf life.
Limited precision and scalability
Over the past century, more than 100 additional patents have been awarded for improvements on Gaulin’s original design to produce smaller average particle size and achieve higher levels of precision (tighter particle size distribution) than traditionally required by the dairy industry.
For conventional homogenizers, the orifice size, valve geometry and pressure settings apply only to a specific flow rate. When scaling up from a laboratory-size homogenizer to a pilot system, and then from a pilot system to a full-scale production system, completely different valves are used and the pressure may need to be considerably raised or lowered. Sometimes several iterations of equipment design must be tested before an acceptable product is produced or until the specified flowrate is achieved.
High-shear fluid processing
In contrast, high-shear fluid processing is precise and scalable. The method involves the creation of highly-controlled shear rates that are orders of magnitude greater than any other conventional means. Particles and droplets can be reduced to submicron sizes without risk of overprocessing any portion of the product.
The process utilizes an electric-hydraulic system to provide power to one or two single-acting intensifier pumps, which amplify the hydraulic pressure to the selected level and apply that pressure to the product material. Process pressures range from 2,500 to 40,000 pounds per sq.in.
The intensifier pump supplies the desired pressure at a constant rate to the product stream. As the pump travels through its pressure stroke, it drives the product through precisely defined fixed geometry microchannels within an interaction chamber. At the end of the power stroke, the intensifier pump reverses direction and the new volume of product is drawn in. The intensifier pump again reverses direction and pressurizes the new volume of product, repeating the process.
Uniform processing and scalability
The fixed geometry of the microchannels ensures that the processing conditions are identical for all products passing through a single machine. The processing conditions are also identical for all machines using a particular microchannel geometry and pressure setting, regardless of flowrate capacity.
Once a high-shear fluid processor achieves a successful result with a small laboratory system producing only a few hundred milliliters per minute, the same microchannel geometry—in a multislotted approach—and process-pressure specifications can be used in the design of a full-scale production system. Because of the ability to scale-up production seamlessly, many users of high-shear fluid processors can forego the usual pilot plant stage and move directly from the laboratory to full-scale commercial production capacity. There are considerable savings for users that choose this route.
Precision high-shear processing applications
High-shear fluid processors are widely used in two broad categories of applications that require precision processing. The first category is particle reduction and emulsification. For example, drug manufacturers use high-shear fluid processors to make emulsions with high-energy lipids that can be administered intravenously. Uniform droplet sizes well below one micron—smaller than the diameter of the capillaries in the human body—all but eliminate the risk of thrombosis. Many drug manufacturers are moving into therapies that are orally or nasally inhaled. These cases require a precise range of particle size for drug-delivery systems to be effective. Smaller isn’t always better. For example, orally-inhaled particles, if too small, can deposit deep into the lungs. This location may not be the target area desired, as is in the case of many asthma drugs. In most cases, the use of precision high-shear processing can deliver the right particle size range required.
In the chemical industry, the effectiveness and appeal of high-end coatings for aerospace and automotive applications increase as droplet size decreases and particles become more uniformly dispersed. Manufacturers of resins, extenders and additives that are integrated with these coatings use high-shear fluid processors to achieve high-color strength and gloss.
The producers of indoor and outdoor sealants, used for treating wood and other surfaces exposed to the weather, utilize high-shear fluid processors to reduce the amount of volatile organic compounds (VOCs) by increasing water content, allowing these companies to comply with environmental regulations, reduce costs and create a safer environment for their customers. By reducing droplet size, waxes can be more readily dissolved with a lower concentration of solvents.
The makers of high-quality digital inks use a similar process to ensure that all pigment particles are within a tight size tolerance to avoid clogging ink-jet print nozzles. Furthermore, the uniformity of particle size achieves high-formulation stability, enabling longer shelf life. High-shear fluid processors are also used to create precisely-sized pigments for the color liquid crystal display (LCD) screens of computers and portable electronic devices.
The pharmaceutical and cosmetics industries also rely on high-shear fluid processors for creating time-release and depth-release characteristics of lotions and creams. Through uniform micro-encapsulation of active ingredients in liposomes, these products can deliver benefits to specific sites at controlled and predictable rates.
The food industry is using liposomes in nutraceuticals to enable the slow release of nutrients. Increasing the bioavailability of these nutrients in a sustained-release mode adds significant value to the products. High-shear fluid processors enable many other enhancements to the nutritional value, color, taste, and texture of foods and beverages. For example, high-shear processing of soybeans efficiently extracts the soymilk and adds percentages of submicron fiber to the milk. The added fiber increases the market value of the soymilk, while leaving the texture—"mouthfeel"—unchanged for the consumer.
The second category of applications requiring the precision of high-shear fluid processors is cell disruption for the biotechnology industry: precisely-controlled amounts of shear force are applied to bacteria and other cell structures to safely extract high yields of cell contents. These compounds need to be extracted from the living organisms quickly and without damage or contamination. Comparative analysis of precision high-shear processing to conventional homogenization techniques has revealed improved yield and more “active” products such as enzymes, most likely a result of the fixed geometry interaction chamber as compared to the variable geometry homogenization valve. Additionally, high-shear fluid processing provides tight thermal control of temperature-sensitive cellular materials.
Conventional homogenization has served the needs of the dairy and other industries for many years. Today, the development of advanced products utilizing high-fidelity particle reduction, emulsification and cell disruption applications now requires a level of precision, uniformity and predictability that’s often best achieved with high-shear fluid processing.
Add new comment