How To Dry Lactide: The Complete Guide

Have you ever wondered how to dry lactide? Lactide is a biodegradable and bioactive polymer used in various industries, including medical, agricultural, and packaging. However, its hydrophilic nature makes it challenging to dry and use effectively.

Lactide is derived from lactic acid and has become increasingly popular due to its eco-friendly properties. However, its sensitivity to moisture can cause problems during processing, storage, and transportation.

The process of drying lactide is a critical step in its production and use. Without proper drying, lactide can degrade, lose its properties, and become unusable. In this article, we’ll explore the various methods of drying lactide and provide some tips to ensure its proper handling and storage.

Why need to keep lactide dry?

Lactide needs to be kept dry because it is a hygroscopic compound, meaning it readily absorbs moisture from the surrounding environment. When lactide absorbs moisture, it can lead to hydrolysis, which breaks down the chemical structure of lactide and decreases its purity and effectiveness.

In addition, the presence of moisture can also promote microbial growth, which can further degrade lactide. Therefore, it is crucial to keep lactide in a dry environment, such as a desiccator or sealed container with a desiccant, to ensure its stability and quality over time.

How to measure moisture content of lactide?

There are different methods for measuring the moisture content of lactide, which is the amount of water present in the material. 

• Loss on drying: which involves weighing the sample before and after heating it in an oven to remove the water by evaporation. The difference in weight divided by the initial weight gives the moisture content as a fraction or percentage.

• Karl Fischer titration: which involves adding a reagent that reacts with water to produce a color change or an electrical signal. The amount of reagent needed to reach the endpoint of the reaction is proportional to the amount of water in the sample.

• Moisture analyzers, which use infrared or microwave radiation to heat and dry the sample and measure the weight loss

• Water activity meters, which measure the vapor pressure of water in the sample and compare it to pure water.

Each method has its own advantages and disadvantages depending on the accuracy, speed, cost and convenience required.

Drying Methods for Lactide

Drying methods for lactide are techniques that aim to reduce the moisture content of lactide, which is the cyclic diester derived from lactic acid. Lactide needs to be dry before polymerization to avoid hydrolysis and degradation. 

Some of the drying methods for lactide are:

• Vacuum drying: This method involves lowering the pressure around the lactide to decrease the boiling point of water and increase the evaporation rate. Vacuum drying can be fast and efficient, but it requires specialized equipment and high energy consumption.

• Spray drying: This method involves atomizing the lactide into fine droplets and exposing them to hot air in a drying chamber. The droplets lose moisture and form dry particles that are collected at the bottom of the chamber or in a cyclone separator. Spray drying can be scalable and versatile, but it may affect the optical purity of lactide.

• Freeze drying: This method involves freezing the lactide and then sublimating the ice crystals under vacuum. Freeze drying can preserve the structure and quality of lactide, but it is slow and expensive.

• Desiccant drying: This method involves placing the lactide in a container with a desiccant, which is a substance that absorbs moisture from the air. Desiccant drying can be simple and economical, but it may not be effective for very low moisture levels.

Factors Influencing the Drying Process of Lactide

The drying process of lactide is influenced by several factors, such as:

Temperature

The temperature of the drying medium and the ambient temperature affect the rate of evaporation and solidification of lactide. Higher temperatures can increase the drying rate, but also increase the risk of thermal degradation and racemization of lactide.

Pressure

The pressure of the drying medium and the ambient pressure affect the boiling point and vapor pressure of water. Lower pressures can decrease the boiling point and increase the vapor pressure, which can enhance the drying rate. However, lower pressures may also require higher temperatures to achieve sufficient drying.

Catalyst

The catalyst used for the polycondensation and depolymerization of lactic acid to lactide can affect the yield and purity of lactide. Different catalysts have different activities and selectivities for the reactions. For example, tin-based catalysts are more active and selective than zinc-based or acid catalysts.

Material properties

The properties of lactide, such as molecular weight, optical purity, crystallinity, porosity and solubility, can affect the drying behavior and quality of lactide. For example, higher molecular weight and crystallinity can reduce the solubility and diffusion of water in lactide, while higher porosity can increase the surface area and evaporation rate of water.

Material placement

The placement and contact of lactide materials during drying can affect the heat and mass transfer between the materials and the drying medium. For example, spreading the materials in a thin layer or separating them into small particles can increase the exposure and contact area with the drying medium, which can improve the drying efficiency.

Summary

Lactide is an important intermediate for producing PLA, a biodegradable polymer with many applications. Lactide needs to be dried before polymerization to avoid hydrolysis and degradation. 

There are many methods that can be used for drying lactide, each with its own advantages and disadvantages. Depending on the desired properties and quality of lactide, one method may be more suitable than the other.

As the leading supplier for Lactide(L-lactide, DL-Lactide and D-lactide), We have more than 10 years experience in lactide purity and dry process. Contact us directly if you need these material for your project.