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Views: 0 Author: Site Editor Publish Time: 2025-07-16 Origin: Site
Nanocellulose is a new green polymer material obtained by nanoscale dissociation treatment using natural cellulose as raw It not only has excellent properties such as light weight, high strength, and large specific surface area, but also has environmentally friendly characteristics such as renewability, biocompatibility and degradability, and has become an important research direction for sustainable high-performance materials. Compared with traditional micro-scale cellulose, material . nanocellulose has performed better in transparency, mechanical properties, suspension stability, etc., and is widely used in many fields such as high-performance materials, biomedicine, food packaging, electronic devices, etc.
Among them, cellulose nanocrystals ( CNC ) are the most widely studied category and are usually prepared by acid hydrolysis. The process is mature and easy to control, and has become one of the key process routes in laboratory and industrial research.
Natural cellulose consists of highly ordered crystalline regions and disordered amorphous regions. The molecular chains of the amorphous region are loosely arranged and are easily hydrolyzed by acids, while the crystalline region is closely arranged and has strong hydrogen bonding, which can better resist acid erosion. The acid hydrolysis method uses this characteristic to selectively remove the amorphous region in cellulose and retain the ordered crystalline region to obtain cellulose nanocrystals with regular morphology, uniform size and high crystallinity. At the same time, the commonly used sulfuric acid in the reaction will introduce sulfate groups on the surface of the cellulose molecular chain to improve the dispersion of the aqueous phase, but may also have a certain impact on its thermal stability.
Preparation of cellulose nanocrystals by acid hydrolysis usually involves the following steps
1. For raw material pretreatment,
cellulose raw materials with high purity and few impurities are selected, such as cotton pulp, wood pulp, bamboo pulp or crop straw. Lignon, hemicellulose and impurities are removed through alkali cooking and bleaching steps to ensure the quality and uniformity of the final product.
2. The commonly used acid solution for acid hydrolysis reaction
is concentrated sulfuric acid, and some processes also use hydrochloric acid or mixed acid. Typical conditions are acid concentrations of 60% to 65% , reaction temperatures of 45°C to 60°C , and reaction time 30to 60minutes. Temperature and time need to be strictly controlled. Too short will lead to incomplete removal of the amorphous region and insufficient crystallinity. Too long will lead to degradation of the crystal region and affect yield.
3. Reaction termination and washing
dilute the acid solution through a large amount of deionized water to quickly reduce the acid concentration, terminate the hydrolysis reaction, and avoid further degradation of the crystallization zone. Subsequently, multiple centrifugation and water washing were performed to remove residual acid and by-products until of the suspension the pH was close to neutral.
4. Ultrasonic dispersion and homogenization
Use ultrasonic treatment or high-pressure homogenization equipment to disperse the hydrolyzed suspension, disperse the agglomerates, and produce a uniformly dispersed and stable cellulose nanocrystal suspension.
5. Post-treatment and drying
can be directly prepared into sol, film or gel according to application requirements, or powdered products can be prepared by freeze-drying or spray-drying processes for easy storage and transportation.
The main factors affecting the preparation effect of acid hydrolysis include acid type and concentration, reaction temperature, reaction time and raw material type.
Different acid species will affect the surface functional groups and dispersion of the product. For example, sulfuric acid can introduce negative charge on the surface to improve dispersion stability, but will reduce thermal stability; nanocrystals hydrolyzed by hydrochloric acid have high thermal stability, but are prone to agglomeration
The temperature and time ratio is crucial for the removal of amorphous zones and the retention of crystal zones. Small changes in process parameters may have a significant impact on product quality.
Different sources, cellulose content and crystallinity of raw material cellulose will also cause differences in the morphology and performance of the final nanocrystals.
Advantages:
Acid hydrolysis method is mature in process, has good repeatability, and is suitable for a variety of cellulose raw materials. Cellulose nanocrystals with regular morphology, uniform size and high crystallinity can be obtained, and has excellent dispersion, suitable for subsequent modification and composite
Insufficient
acid consumption is large, high concentration of acidic waste liquid needs to be treated after the reaction, which increases the pressure of environmental protection and wastewater treatment
, which may retain sulfate groups on the surface of the product, affecting the large-scale production of some high-temperature application scenarios,
still requires optimization of process design, improve acid recovery rate, and reduce production costs.
In view of the shortcomings of acid hydrolysis, current research and industrial development are mainly concentrated in the following directions
Develop a low acid consumption, recyclable green acid hydrolysis process to reduce the impact on the environment
Introduce mechanical or enzymatic pretreatment to reduce the integrity of the amorphous region and reduce the amount of acid
Establish an efficient waste acid recycling system, combine membrane separation and ion exchange technology to improve the resource utilization level of waste liquid
Improve thermal stability and compatibility through surface modification technology and expand the application range of cellulose nanocrystals
Cellulose nanocrystals prepared by acid hydrolysis have shown broad application potential in composite materials, packaging materials, medical biological materials, coatings, electronic devices and other fields due to their excellent mechanical properties, crystallinity and good dispersion.
In the future, with the continuous optimization of green preparation technology and large-scale production processes, nanocellulose will be expected to become an important representative of high-performance sustainable materials, helping more industries achieve green transformation and high-value development.。
