Method for preparing nanocellulose dispersion into powder

The method of preparing nanocellulose dispersion into powder mainly involves removing solvents in the dispersion while retaining the structure and functionality of nanocellulose. Here are a few common methods:

1. Freeze-drying (Lyophilization)

• Principle : Freeze-drying removes the solvent by quickly freezing the dispersion into solids, and then converts the moisture in the solid directly into water vapor by sublimation under low temperature and vacuum conditions, thereby removing the solvent and leaving the dried powder.

• Advantages : Freeze-drying can maintain the original form and structure of nanocellulose , prevent particles from agglomerating or structure collapse, and is suitable for thermally sensitive materials.

• step :

1. Pour the nanocellulose dispersion into the tray of the freeze-dryer.

2. Quickly freeze the dispersion to low temperature (usually -40°C to -80°C).

3. Sublimate the moisture in a vacuum environment until a dry powder is obtained.

2. Spray Drying

• Principle : Spray drying atomizes the dispersion into tiny droplets, and then quickly evaporates the solvent in the droplets through a high-temperature airflow to obtain dry nanocellulose powder.

• Advantages : Suitable for large-scale production, fast drying speed, and can control the particle size and morphology of the powder by adjusting process parameters.

• step :

1. Inject the nanocellulose dispersion into the atomizer of the spray dryer.

2. Disperse the liquid into tiny droplets through a nebulizer.

3. Hot air passes through the mist droplets and quickly evaporates the solvent to form a dry powder.

4. Collect the dried nanocellulose powder.

3. Hot Air Drying

• Principle : The solvent is evaporated by heating the dispersion, leaving behind the dried nanocellulose powder.

• Advantages : Simple operation, low cost, suitable for small-scale production.

• step :

1. Apply the nanocellulose dispersion evenly onto a flat tray.

2. Evaporate the solvent through hot air at controlled temperatures.

3. After completely drying, scrape the formed nanocellulose powder.

4. Supercritical Drying

• Principle : Use supercritical fluids (such as carbon dioxide) to replace liquid solvents, and directly gasify the supercritical fluid by reducing the pressure, thereby avoiding the existence of the liquid-gas interface and preventing the collapse of the nanocellulose structure.

• Advantages : It can maintain the porous structure of nanocellulose, suitable for the preparation of high-performance powder materials.

• step :

1. Place the nanocellulose dispersion in a container containing supercritical carbon dioxide.

2. Remove moisture by solvent replacement.

3. Release pressure to vaporize supercritical carbon dioxide, leaving behind dry powder.

5. Solvent Exchange Drying

• Principle : Use a volatile organic solvent (such as ethanol or acetone) to replace the moisture in the dispersion, and then evaporate the organic solvent to obtain a nanocellulose powder.

• Advantages : Reduces agglomeration during drying and is suitable for maintaining nanostructures of nanocellulose.

• step :

1. Mix the nanocellulose dispersion with the volatile organic solvent and replace the solvent.

2. After multiple replacements, remove the organic solvent by low temperature evaporation or vacuum evaporation.

3. Collect the formed dry powder.

6. Precipitation Method

• Principle : The nanocellulose is precipitated by adding poor solvents (such as salt solution or ethanol) to the dispersion , and then centrifuge, filter and dry.

• Advantages : Simple and effective, suitable for small-scale preparation of nanocellulose powder under laboratory conditions.

• step :

1. Add poor solvent to the nanocellulose dispersion to precipitate the cellulose.

2. Separate the precipitate by centrifugation or filtration.

3. Dry the precipitate to obtain nanocellulose in powder form.

Each method has its advantages and disadvantages, and the choice of the appropriate method depends on the application requirements of the desired powder, the availability of the equipment, and the scale of preparation.