Yingtai: Factors Influencing The Freeze-Drying Curve

Yingtai: Factors Influencing the Freeze-Drying Curve

The factors influencing the freeze-drying curve are numerous. The freeze-drying curve records the changes in sample and shelf temperatures, condenser temperature, and vacuum over time. Since the sample temperature is influenced by the shelf temperature (usually differing by 3–5°C), the shelf temperature versus time curve is commonly used to represent the process. Various factors affect the freeze-drying curve, including the sample composition, properties, concentration, fill volume (liquid level height), sublimation area, eutectic point, heat transfer medium and method, condenser temperature, condenser area, cooling capacity, system vacuum, and equipment performance. Consequently, different samples will have distinct freeze-drying curves under varying conditions.

1. Sample Type: Different samples have varying eutectic points, influencing the required freezing temperature and the corresponding shelf temperature. Products with low residual moisture content require longer freeze-drying times, while those with higher moisture tolerance have shorter times. Additionally, some large molecule compounds may deform at specific temperatures, affecting heat transfer and causing defects.

2. Sample Fill Volume: The fill volume impacts both the total amount of material in the freeze-dryer chamber and the quantity in each container. Larger volumes generally require longer drying times. If the liquid level in containers exceeds 2 cm, it may be difficult for moisture to sublimate, leading to potential layering issues, especially with colored samples.

3. Type of Sample Container: Containers with flat or thinner bottoms conduct heat better, while those with uneven or thicker bottoms have poorer heat transfer and require longer drying times. Metal containers generally have good thermal conductivity. Tray-dried samples can be challenging due to large bottom areas and potential deformation.

4. Performance of the Freeze-Dryer: The performance of the freeze-dryer directly affects the freeze-drying curve. High-performance machines have smaller temperature differences between layers, low condenser temperatures, high ice capacity, minimal vapor flow resistance, and fast vacuum pumps. Different machines, even for the same sample, can produce varying process curves.