Nanocellulose: a 'super material' from nature

In the exploration of materials science, scientists are always looking for new materials with excellent performance and environmental sustainability. In recent years, a substance called nanocellulose has gradually come into public view. With its unique physical and chemical properties and broad application prospects, it has been hailed as 'the most potential green nanomaterial in the 21st century.'

What is nanocellulose?

Nanocellulose is a nanoscale functional material extracted from natural cellulose. Natural cellulose widely exists in plants, bacteria and even some marine organisms. It is the most widely distributed and abundant natural polymer organic matter in nature. when we treat cellulose through chemical, physical or biological methods to reduce its diameter to between 1 and 100 nanometers and its length from hundreds of nanometers to several micrometers.Nanocellulose is obtained

According to different structures and preparation methods, nanocellulose is mainly divided into three categories:

1. Cellulose Nanocrystal ( CNC) : The amorphous region in cellulose is removed by strong acid hydrolysis, leaving the high-purity crystalline region. The finished product is in the shape of a short rod with extremely high crystallinity, strong rigidity, good transparency, and uniform size. It is suitable for use in optical materials, high-strength coatings, and precision composite materials.

2. Cellulose nanofibers ( CNF) : They are mostly prepared by high-pressure homogenization, micro-jet, TEMPO catalytic oxidation or enzyme-assisted methods. They retain the alternating structure of cellulose crystal regions and amorphous regions. They are elongated fibers with a large aspect ratio, excellent flexibility, easy to form a three-dimensional network structure, excellent film formation and dispersion, and a wider range of applicable scenarios.

3. Bacterial nanocellulose ( BNC) : It is synthesized by fermentation of specific bacteria (such as acetic acid bacteria). It has extremely high purity and a three-dimensional network structure. It is widely used in the biomedical field, such as artificial skin, wound dressings, etc.

Unique properties of nanocellulose

Nanocellulose has attracted much attention because of its many excellent properties:

· High strength and high modulus : The strength of nanocellulose can reach 1-2 GPa, and the Young's modulus can reach 100-150 GPa, which is an order of magnitude higher than conventional wood pulp fibers and is equivalent to high-strength fibers such as Kevlar. Its weight is only about 1/5 of steel, but it has 5 times the strength of steel. It is an ideal reinforcement phase for building high-performance composite materials.

· High specific surface area : The specific surface area of ​​nanocellulose can reach 100-300 m²/g, which gives it unique advantages in the fields of adsorption, catalysis and sensing. For example, it can efficiently adsorb heavy metal ions or dye pollutants in water, and can also be used as a catalyst carrier to improve the efficiency of catalytic reactions.

· Good biocompatibility and degradability : Nanocellulose is non-toxic and non-irritating, and bacterial cellulose has excellent compatibility with human tissues, has no immune rejection, and can be directly used in the field of biomedicine. At the same time, it is completely biodegradable in the natural environment, does not produce microplastic pollution, and meets the requirements of carbon neutrality and circular economy.

· Transparency and processability : Nanocellulose has good transparency and can be made into transparent films for use in food packaging, flexible electronic devices and other fields. It is also easy to process and shape, and can through papermaking, coating, 3D printing and other processes.be used to prepare various functional products

Preparation method of nanocellulose

There are various methods for preparing nanocellulose, mainly including mechanical methods, chemical methods, biological methods and combined methods.

· Mechanical method : Through the action of strong external force, the cellulose fibers are gradually disassembled and refined to the nanometer scale. Common methods include high-pressure homogenization, micro-jet, mechanical ball milling, high-intensity ultrasound and refining. For example, the high-pressure homogenization method is to pass the cellulose suspension through high-pressure homogenization equipment, so that it passes through a narrow channel and is dispersed into nano-sized particles under high-speed shear and collision.

· Chemical method : Using the unique properties of various reagents to achieve precise conversion of cellulose. Commonly used chemical preparation methods include acid hydrolysis, TEMPO oxidation and deep eutectic solvent method. The acid hydrolysis method uses strong acids such as concentrated sulfuric acid or hydrochloric acid to selectively hydrolyze the amorphous region of cellulose, retaining the structure of the crystalline region, and producing cellulose nanocrystals. The TEMPO oxidation rule is to oxidize the hydroxyl groups on the cellulose surface into carboxyl groups under mild conditions to improve fiber dispersion.

· Biological method : Mainly rely on the fermentation of microorganisms such as Acetobacter and Agrobacterium to synthesize nanocellulose. This method has significant advantages such as low energy consumption and no pollution, but it has a long production cycle, high raw material costs, and low yield. It is currently mostly used in laboratory research and development.

· Combined method : organically combine mechanical, chemical, biological and other methods to achieve complementary advantages. For example, the yield and quality of nanocellulose can be improved by first removing impurities and amorphous areas in cellulose through chemical pretreatment, and then using mechanical methods to further refine it.

Wide range of applications of nanocellulose

With its unique properties, nanocellulose shows great application potential in many fields:

· Biomedical field : Nanocellulose can be used to make biodegradable medical supplies, such as dressings and bandages, which can help with wound healing. Bacterial cellulose dressing can create a moist healing environment, promote wound repair, and has both breathability and antibacterial properties. It can also be used as a tissue engineering scaffold to support cell growth and be used for tissue repair such as cartilage and cornea. In addition, after functionalization, nanocellulose can be used as a drug sustained-release carrier to improve the solubility and bioavailability of drugs.

· Food industry : Nanocellulose can be used as a food additive to improve the texture, stability and taste of food. It can be used as a thickener, stabilizer and emulsifier in drinks, sauces and baked goods to improve food quality. At the same time, nanocellulose can also be used to prepare food packaging materials, such as degradable cling film, which has excellent oxygen and oil barrier properties, extending the shelf life of food and reducing white pollution.

· Environmental protection field : Nanocellulose's high specific surface area and rich surface active groups make it an excellent adsorption material, which can be used for sewage treatment to remove heavy metal ions, dyes and other harmful substances in water. In addition, it can also be used for air filtration to purify particles and harmful gases in the air.

· Materials engineering field : As a reinforcing phase, nanocellulose can significantly improve the mechanical properties of composite materials. By adding nanocellulose to plastics, rubber, coatings and other materials, high-strength, lightweight bio-based composite materials can be prepared for use in automobile interiors, home appliance casings, packaging materials, etc., reducing the carbon footprint of products. It can also be used to prepare transparent conductive films, flexible electronic devices and optical sensors, promoting the development of the electronics industry in a green and flexible direction.

· Papermaking and printing fields : Adding nanocellulose in the papermaking industry can improve the strength, density and printing performance of paper and reduce the amount of wood pulp. Nanocellulose can also be used to prepare high-strength, high-heat-resistant 3D printing consumables, expanding the application scope of 3D printing technology.

Looking to the future

Although nanocellulose has broad prospects, it still faces some challenges, such as the high cost of large-scale production and environmental pollution problems in some preparation methods. In the future, with the development of green chemistry and nanotechnology, scientists will continue to optimize the preparation process of nanocellulose, reduce costs, and improve production efficiency. At the same time, through functional modification, the application fields of nanocellulose are further expanded, allowing it to play an important role in more scenarios.

As a 'super material' derived from nature, nanocellulose is leading materials science into a new era with its unique charm and huge potential. We have reason to believe that in the near future, nanocellulose will play an irreplaceable role in improving human life and promoting sustainable development.