How to prepare nanocellulose crystals

Nanocellulose (NFC) is a high-performance material obtained by processing and extraction of natural plant cellulose, and is widely used in green packaging, coatings, medical materials and other fields. Compared with traditional cellulose, nanocellulose has significant advantages in dispersibility, strength, transparency and biodegradability. Preparation of nanocellulose crystals is an important step, especially in the research and application of nanomaterials, the crystallinity of nanocellulose is one of the key factors that determine its performance.

What are nanocellulose crystals?

Nanocellulose crystals are microcrystal structures formed by cellulose molecules arranged in a highly ordered manner. They usually have strong mechanical strength, rigidity, heat resistance and low density. Nanocellulose crystals show a wide range of application potential in a variety of fields, especially in the manufacture of reinforced materials and high-performance composites.

Common methods for preparing nanocellulose crystals

The process of preparing nanocellulose crystals usually involves extracting cellulose from natural plant fibers and processing them through a series of physical or chemical methods to form nanoscale fibers and crystals. Here are several common preparation methods:

1. Acid hydrolysis method

Acid hydrolysis is one of the most common methods for preparing nanocellulose crystals, and is especially suitable for extracting nanocellulose from plant fibers (such as wood, cotton, etc.).。

Principle: Acid hydrolysis method hydrolyzes cellulose through strong acids (usually sulfuric acid), removing the amorphous region, leaving an ordered crystal structure.

step:

1. Choose suitable plant fiber raw materials, such as wood, cotton, etc.

2. Pretreat the cellulose raw material to remove lignin and other impurities.

3. Treat cellulose raw materials with concentrated sulfuric acid (usually 64%-70%) and perform acid hydrolysis.

4. Control the time and temperature of acid hydrolysis to ensure that the hydrolysis reaction is not excessive to avoid damage to the nanocellulose crystals.

5. Neutralize the acid with deionized water to remove the residual acid and finally obtain a nanocellulose crystal suspension.

6. Remove insoluble matter by centrifugation, filtration, etc. to obtain pure nanocellulose crystals.

Advantages: The acid hydrolysis method is simple and easy to operate, and can obtain high-purity nanocellulose crystals, and the reaction time is relatively short.

Disadvantages: It is highly acidic, you need to be careful during operation, and the waste acid produced needs to be treated.

2. Enzyme method

The enzymatic method is to hydrolyze plant fibers through specific enzymes to remove the amorphous regions therein, thereby obtaining nanocellulose crystals.

Principle: Use biological enzymes such as cellulase to selectively hydrolyze cellulose, remove amorphous regions, and leave nanocellulose with strong crystalline properties.

step:

1. Select the appropriate plant fiber raw materials and pretreat.

2. Add specific cellulase, usually hydrolyzed under mild conditions (e.g., temperatures of 50-60°C).

3. After the enzymatic lysis process is completed, the excess enzyme and solution are removed by centrifugation, filtration, etc.

4. Remove dissolved impurities by further washing to obtain nanocellulose crystals.

Advantages: The enzymatic method has high selectivity and can be carried out under mild conditions, avoiding excessive hydrolysis.

Disadvantages: Enzymatic method requires precise control of reaction conditions, and the cost of enzyme is high.

3. Mechanical method

Mechanical methods usually reduce the size of plant fibers to the nanoscale through high-pressure homogenization, ultrasonic treatment, etc., and promote the formation of crystals through physical forces.

Principle: The amorphous region of cellulose is destroyed through powerful mechanical treatment, making the crystal region more concentrated and forming nano-scale cellulose crystals.

step:

1. Select cellulose raw materials and perform appropriate mechanical pretreatment.

2. Use a high-pressure homogenizer or ultrasonic processor to process the cellulose solution to the desired nanoscale.

3. Remove the incompletely depolymerized fibers and impurities by high-speed centrifugation or filtration to obtain pure nanocellulose crystals.

Advantages: Easy to operate, no chemical reagents are involved in the processing process, and is suitable for large-scale production.

Disadvantages: The energy consumption is large, and the crystallinity of the product is lower than that of the acid hydrolysis method.

4. Hydrothermal method

The hydrothermal method uses the special properties of water in high-temperature and high-pressure environments to convert cellulose solution into nanocellulose crystals.

Principle: Under high temperature and high pressure conditions, the solubility of water increases, which promotes the crystallization reaction between cellulose molecules.

step:

1. Dissolve or suspend the cellulose raw material in water.

2. Heat the solution to a certain temperature (usually at 180-220°C) and handle it under high pressure.

3. After the reaction is completed, the solution is cooled and the nanocellulose crystals are extracted by centrifugation, filtration, etc.

Advantages: Hydrothermal method can effectively improve the crystallinity of the crystal without the use of chemical reagents.

Disadvantages: High temperature and high pressure equipment is required, and the energy consumption is high.

Application prospects of nanocellulose crystals

As an important nanomaterial, nanocellulose crystals have very wide application prospects. It not only has potential applications in the paper, textiles, coatings and other industries, but also plays a huge role in environmental protection, medical care, electronics and other fields. With the continuous advancement of preparation technology, the production of nanocellulose crystals will become more efficient and economical.

There are many methods for preparing nanocellulose crystals, each method has its own characteristics and scope of application. Acid hydrolysis, enzymatic methods, mechanical methods and hydrothermal methods are common preparation methods. Choosing appropriate preparation techniques can not only improve the quality of nanocellulose crystals, but also promote their application in industry. In the future, with the development of nanocellulose crystal technology, more innovative applications and preparation methods are expected to emerge.