Preparation technology and application prospects of hydrophobic nanocellulose

As a new bio-based material, nanocellulose has shown broad application potential in many fields due to its inherent advantages such as renewable, degradable, high specific surface area, and excellent mechanical properties. However, the surface of natural nanocellulose is rich in hydrophilic hydroxyl groups, which easily absorbs water and swells, and is difficult to be compatible with non-polar materials, which greatly limits its application in scenarios such as waterproofing, oil-proofing, and oily wastewater treatment. Giving nanocellulose hydrophobicity through scientific modification and preparation processes can effectively expand its application boundaries and achieve high-value utilization of materials. It is also a current research hotspot and industrial development focus in the field of nanomaterials.

The following is a detailed introduction to the core preparation technology, process points and application directions of hydrophobic nanocellulose based on the industry's cutting-edge technology and corporate practical experience, providing reference for technology research and development and industrial applications in related fields.

1. Core principles of preparation

The core of the preparation of hydrophobic nanocellulose is to modify the surface of nanocellulose through physical, chemical or mechanochemical methods, replacing the hydrophilic hydroxyl groups ( -OH ) on the surface with hydrophobic groups (such as methyl, phenyl, silyl groups, etc.), reducing the surface free energy, thereby achieving the transformation of hydrophobic properties. During the modification process, it is necessary to take into account the intrinsic excellent properties of nanocellulose to ensure that the modified material is hydrophobic, mechanically stable and environmentally friendly at the same time to meet the needs of industrial applications.

2. Mainstream preparation methods and process points

At present, the preparation methods of hydrophobic nanocellulose can be divided into three major categories. Each method adapts to different production scenarios and performance requirements. Enterprises can choose the adaptive process according to the actual application direction. The following is a detailed explanation of the core methods:

(1) Chemical modification method (the first choice for the mainstream industry)

The chemical modification method is a chemical reaction between the hydroxyl groups on the surface of nanocellulose and the modifier to achieve covalent grafting of hydrophobic groups. The modification effect is stable and the hydrophobic performance is long-lasting. It is currently the most widely used method in industrial production, and mainly includes silanization modification, esterification modification, urethanization modification, etc.

1. Silanization modification: Using hydrogenated silicone oil, methyltrimethoxysilane, etc. as modifiers, a condensation reaction occurs with the hydroxyl group on the surface of nanocellulose under mild conditions, and hydrophobic silane groups are grafted to quickly control the hydrophobicity. After modification, the water contact angle of nanocellulose can reach more than 120° , and some processes can achieve a superhydrophobic effect of more than 158° . It has excellent weather resistance and solvent resistance, and is suitable for waterproof coatings, oil-water separation materials and other scenarios. Key points of the process: Control the amount of modifier and reaction temperature to avoid excessive reaction leading to nanocellulose agglomeration and ensure uniform grafting of hydrophobic groups.

2. Carbamate modification: Using 3,4 -dichlorophenyl isocyanate as a modifier and dimethyl sulfoxide as a dispersion medium, hydrophobic urethane nanocellulose can be prepared through a one-step mechanochemical method. By adjusting the ball milling time and the amount of modifier, the material morphology and hydrophobic properties can be precisely controlled. The modified material has excellent film-forming properties and adhesion, and can be used in packaging coatings, adhesives and other fields. Key points of the process: Control the ball milling time. Before ball milling for 6 hours , the material will have a loose network structure, and the hydrophobicity will increase with time. After more than 6 hours , the material will defibrate into single fibers, and the hydrophobicity will decrease.

3. Esterification modification: Under the action of acid catalysis, the hydroxyl groups on the surface of nanocellulose are used to undergo an esterification reaction with acids, acid anhydrides or acid chlorides to introduce hydrophobic acyl groups and reduce the hydrophilicity of the material. This method has mild reaction conditions and low cost, and is suitable for large-scale mass production. The modified material can be used in food packaging, biomedical carriers and other scenarios. Key points of the process: Strictly control the reaction pH value and reaction time to avoid catalyst residues affecting material safety.

(2) Physical modification method (green and environmentally friendly)

The physical modification method does not require chemical reactions. Through non-covalent interactions such as electrostatic interactions, hydrogen bonds or van der Waals forces, hydrophobic modifiers such as surfactants and block copolymers are deposited on the surface of nanocellulose, or a hydrophobic network structure is formed. It has the advantages of simple process, environmental friendliness, and no chemical residues. It is suitable for scenarios with high requirements for material purity (such as biomedical use, food packaging).

Commonly used processes include adsorption modification and blending modification, such as blending hydrophobic nanosilica particles with nanocellulose. By controlling the particle content and dispersion method, the hydrophobicity can be further improved. Dispersion by ball milling can make the composite material more stable and transparent. When the mass ratio of silica to nanocellulose is 1.5:1 , the water contact angle of the composite film can reach 158.0° , which can impart superhydrophobic properties to substrates such as paper. Key points of the process: ensure that the modifier is evenly dispersed, avoid agglomeration, improve the adhesion stability of the hydrophobic layer, and make up for the weak physical bonding force.

(3) Mechanochemical modification method (high efficiency and energy saving type)

The mechanochemical modification method combines mechanical force (such as ball milling, ultrasonic) with chemical modification, causing defects on the surface of nanocellulose under mechanical action to promote the reaction between the modifier and hydroxyl groups, thereby achieving simultaneous nanonization and hydrophobic modification. It has the advantages of high reaction efficiency, low energy consumption, and short process flow, and is suitable for large-scale continuous production.

For example, urethanized wood nanocellulose can be prepared by using bamboo powder with part of the lignin removed as raw material, adding modifiers and then ball milling, which not only achieves hydrophobic modification, but also improves the mechanical properties and UV shielding efficiency of the material. After mechanochemical treatment for 12 hours, the UV shielding efficiency of the material can reach 91.8%. Key points of the process: Precisely control the intensity and time of mechanical action, balance the degree of defibration and hydrophobicity of the material, and avoid material degradation caused by excessive mechanical treatment.

3. Key control points in the preparation process

1. Raw material selection: Prioritize the use of nanocellulose raw materials with high purity and good crystallinity (such as bleached softwood pulp, bamboo powder, etc.). The quality of raw materials directly determines the stability and consistency of hydrophobicity after modification. At the same time, it can be combined with the economy of raw material sources to reduce production costs and achieve green and sustainable production.

2. Modifier control: According to the target hydrophobic performance requirements, select the appropriate modifier type and dosage. For example, silane modifiers are suitable for scenarios that pursue high hydrophobic stability, and surfactant modifiers are suitable for low-cost, environmentally friendly needs. Insufficient modifier dosage will lead to a semi-hydrophilic and semi-hydrophobic phenomenon, while excessive dosage may affect the material's mechanical properties and dispersion [5]。

3. Reaction condition control: Strictly control the reaction temperature, pH value, reaction time and stirring speed to avoid excessive temperature causing degradation of nanocellulose and pH deviation affecting reaction efficiency, ensure uniform grafting or adsorption of hydrophobic groups, and improve product batch stability.

4. Post-processing process: The modified nanocellulose needs to be washed, dried, pulverized and other post-processing to remove unreacted modifiers and impurities, control the drying temperature and speed, avoid material agglomeration, ensure product dispersion, and improve application suitability.

5. Environmental control: The experimental and production environment must be kept dry. Excessive humidity will affect the shape of water droplets and the accuracy of hydrophobicity testing. At the same time, avoid the mixing of impurities to ensure product purity and performance stability.

4. Product advantages and application prospects

(1) Core product advantages

1. Green and environmentally friendly: Using renewable natural cellulose as raw material, the modification process can achieve low pollution and degradability, which is in line with the current ' double carbon ' goal and the development trend of green industry. Compared with traditional hydrophobic materials, it is more environmentally friendly [5][3][4]。

2. Excellent performance: It combines the high specific surface area, high strength characteristics and excellent hydrophobicity of nanomaterials. Some products can achieve super-hydrophobicity (water contact angle ≥150° ), and have good film-forming, adhesion and weather resistance, adapting to a variety of application scenarios [2][5]。

3. Wide adaptability: The hydrophobic properties and forms (powder, film, aerogel, etc.) can be adjusted according to different application requirements, and it is compatible with a variety of matrix materials. It can be used in combination with other materials to expand the application boundaries [1][2][3]。

4. Cost controllable: The core raw materials are widely sourced and cheap, and the mainstream preparation process can achieve large-scale mass production. Through process optimization, production costs can be further reduced, and it has strong market competitiveness [4][5]。

(2) Main application prospects

1. Environmental protection field: used for oily wastewater treatment and oil-water separation. The modified nanocellulose aerogel can adsorb engine oil 162up to three times its own weight and can be recycled and reused. It can also be used as an environmentally friendly coating to reduce the adhesion of pollutants [5]。

2. Packaging field: Prepare waterproof and oil-proof packaging materials to improve the barrier performance and moisture resistance of packaging. It can be used in food packaging, industrial packaging, etc. It has environmentally friendly and degradable properties and can replace traditional non-degradable packaging materials [3][5]。

3. New materials field: As a reinforcing agent for composite materials, it is added to non-polar materials such as polylactic acid and rubber to improve the mechanical properties and compatibility of materials, and is used in high-end material fields such as lithium battery separators, flexible electronic devices, and aerogels [4][5]。

4. Other fields: It can be used in biomedical carriers (loading hydrophobic drugs to improve bioavailability), textile waterproof finishing, paper oil-proof coating, etc. With the continuous optimization of preparation technology, application scenarios will continue to expand [1][2][3][5]。

V. Conclusion

The preparation technology of hydrophobic nanocellulose is the key to realizing high-value and diversified applications of nanocellulose. Its green, environmentally friendly and excellent performance characteristics meet the core needs of current industrial upgrading and environmental protection development. Relying on advanced modification technology, the hydrophobic properties of products can be accurately controlled to adapt to the application needs of different industries. At the same time, bio-based materials can be promoted to replace traditional fossil-based materials and help achieve the ' double carbon ' goal [3][4][5]。

In the future, we will continue to delve into the research and development of hydrophobic nanocellulose preparation technology, optimize the process flow, improve product performance, reduce production costs, promote the industrialization of technological achievements, provide efficient, environmentally friendly, and low-cost hydrophobic nanocellulose products and solutions for various industries, and help the high-quality development of the industry.