Emulsifiers are a type of substance that can form a stable emulsion from the mixture of two or more insoluble components. The working principle is that during the emulsification process, the dispersed phase is dispersed in the form of micro droplets (micrometer level) in the continuous phase. The emulsifier reduces the interfacial tension of each component in the mixed system and forms a relatively strong thin film on the surface of the micro droplets or forms a double layer on the surface of the micro droplets due to the charge provided by the emulsifier, preventing the aggregation of micro droplets and maintaining a uniform emulsion. Polyglycerol-10 Oil Liquid for Personal Care, Polyglyceryl-10 Monostearate in Cosmetics, Polyglycerol-4 decanoate for personal care Xi'an Hersoncare Bio-Tech Co., Ltd , https://www.hersoncarebio.com
Freeze drying is a sophisticated dehydration process that relies on the principle of sublimation. In this method, the material is first rapidly frozen at low temperatures, turning the water within it into ice. Then, under controlled vacuum conditions, the ice directly transitions into vapor without passing through the liquid phase, allowing the moisture to escape. The resulting product is known as a lyophilized substance, and the entire process is referred to as lyophilization.
During freeze-drying, the material remains in a frozen state throughout the process, ensuring that ice crystals are evenly distributed. This prevents issues like foaming or oxidation that can occur during traditional drying methods. The final product has a porous structure, retains its original shape, and dissolves quickly in water. It also preserves the biological and chemical integrity of the material to a large extent.
A freeze dryer consists of several key components: a refrigeration system, a vacuum system, a heating system, and an electrical control unit. These systems work together to maintain the necessary conditions for sublimation. The material is first pre-frozen, then placed in the drying chamber where sublimation occurs. Afterward, it is packaged in a controlled environment.
To achieve high-quality results, it's essential to understand the three main stages of lyophilization: pre-freezing, primary drying (sublimation), and secondary drying (removal of bound moisture). Proper control of temperature and pressure is crucial to prevent melting and ensure efficient drying.
The freezing rate significantly affects the crystal structure of the material. Faster freezing leads to smaller, more uniform ice crystals, which improve drying efficiency. Slower freezing produces larger crystals, which may hinder the sublimation process. The choice of freezing method—whether simultaneous cooling of the product and chamber or pre-cooling of the shelf—also impacts both the quality and speed of the process.
Supercooling can be a challenge during freezing, as the solution may remain liquid below its eutectic point. To avoid this, the freezing temperature should be set below the eutectic point and maintained long enough for complete solidification.
During sublimation, the vacuum system plays a critical role by maintaining low pressure, allowing water vapor to escape efficiently. The condenser captures the vapor, preventing it from re-entering the system. The heating system provides the energy needed for sublimation, while the refrigeration system ensures proper cooling of the condenser and drying chamber.
The temperature range for sublimation typically falls between -25°C and -50°C, creating a significant pressure difference that drives the vapor toward the condenser. Without adequate heat input, the sublimation process would slow down or stop entirely.
Throughout the drying cycle, careful temperature management is required to avoid melting, especially in the later stages when the remaining moisture is more tightly bound. Residual moisture includes chemically bound and physically adsorbed water, which requires additional time and care to remove.
Finally, the freeze-drying curve—a graphical representation of temperature changes over time—helps monitor and optimize the process. Adjustments in shelf temperature during the second stage depend on the product’s properties, with safety always being a priority to protect the integrity of the final product.