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Views: 0 Author: Site Editor Publish Time: 2025-04-16 Origin: Site
Nanocellulose refers to nano-scale fibers or crystalline materials extracted from natural cellulose. The diameter is usually between 1 and 100 nanometers ( nm ) and the length can reach several microns or even longer. According to the structure and preparation method, nanocellulose is mainly divided into three categories:
Cellulose Nanofibrils ( CNF, Cellulose Nanofibrils )
It is obtained by mechanical or chemical treatment of cellulose microfibers, and has a high aspect ratio and exhibits a network structure.
It has excellent flexibility and high specific surface area.
Cellulose Nanocrystals ( CNC, Cellulose Nanocrystals )
The amorphous region of cellulose is removed by strong acid hydrolysis, retaining the highly crystalline nanorod-like structure.
Has high intensity, high modulus and unique optical properties (such as liquid crystal behavior).
Bacterial Nanocellulose ( BNC, Bacterial Nanocellulose )
Synthesis of fermentation and synthesization by certain bacteria (such as Acetobacterium leukococcus), has high purity, high crystallinity and three-dimensional network structure.
It is widely used in the field of biomedical science, such as artificial skin, wound dressings, etc.
The main raw material of nanocellulose is natural cellulose, which is widely present in plants, bacteria and even certain marine organisms. There are significant differences in structure, purity, extraction difficulty and applicability of cellulose from different sources.
( 1) Plant source: the widest nanocellulose raw materials
Cellulose in plant cell walls is the main source of nanocellulose, accounting for more than 90% of global production . The cellulose content, fiber length and crystallinity of different plants vary greatly.
① Wood (traditional mainstream raw materials)
Features: High cellulose content ( 40%~50% ), regular fiber structure, easy to process.
Coniferous wood (such as pine and spruce) has long fibers, suitable for the preparation of high-strength CNF；
Broadleaf wood (such as birch and poplar) has shorter fibers, but are more likely to disperse.
Limitations: lignin and hemicellulose need to be removed, the process is complex and may pollute the environment.
Research progress: Develop mild pretreatment techniques such as deep eutectic solvent DES to reduce chemical contamination.
②Agricultural waste (low-cost sustainable choice)
Common ingredients:
Rice and wheat straw: The cellulose content is about 30% to 40% , but the silicon content is high, so additional desiliconization treatment is required.
Sugarcane bagasse: a by-product of the sugar industry, with a high cellulose content (about 40%~50% ) and a low lignin content.
Corn stalk / cotton stalk: China has rich reserves and is suitable for regional nanocellulose production.
Advantages: The cost is extremely low, and it can achieve waste resource utilization, which is in line with the concept of circular economy.
Challenge: There are many impurities (such as wax, ash), and the pretreatment process needs to be optimized.
③ Non-wood plant fibers (special performance requirements)
Cotton: The purity of cellulose is up to 95% or more, and does not require complex purification. It is suitable for the preparation of high-transparency CNF films.
Linen / Hemp: The fiber is long and has high strength and can be used to reinforce composites.
Bamboo: grows fast, with a cellulose content of about 40% to 60% , but the fiber wall is thick and requires stronger mechanical treatment.
( 2) Bacterial source: Biosynthesis of high-purity nanocellulose
Nanocellulose is directly secreted through fermentation of microorganisms (such as Acetobacterium leukococcus and rhizobium), and the product is called bacterial nanocellulose ( BNC ).
①Production principle
Bacteria are metabolized in sugar-containing culture media (such as glucose, coconut water), converting the carbon source into microfiber fibers to form a gel-like membrane (thickness can reach a few centimeters).
② Unique advantages
Ultra-high purity: No need to remove lignin or hemicellulose.
Three-dimensional network structure: more uniform than plant-source nanocellulose, suitable for biomedical applications (such as artificial blood vessels).
Controllability: By changing the strain, culture medium or culture conditions, the fiber diameter and mechanical properties can be controlled.
③Limitations
High cost: sterile environment and precision fermentation equipment are required, and large-scale production is difficult.
Carbon source dependence: Traditional culture media uses glucose, which can combine with agricultural waste (such as sugar cane juice) to reduce costs.
( 3) Animal source: niche but high-value raw materials
The outer skin of certain marine organisms (such as thylakoids) contains natural cellulose.
example:
Tunicate : Its outer cellulose crystallinity is as high as 90% , and it can extract ultra-long CNCs (length up to several microns), with a strength better than plant-source CNCs。
Application potential:
It is used in high-strength composite materials such as aerospace, but due to the sparse raw materials, it is currently only limited to laboratory research.
( 4) Waste recycling: the dual value of environmental protection and economy
The use of industrial or domestic waste to extract nanocellulose is a hot topic in recent years.
Typical raw materials:
Waste paper / cardboard: The cellulose has been partially delectin, and the processing process is simpler.
Textile waste: cotton clothing or gauze can be directly acid-hydrolyzed to prepare CNC。
Food processing residues: such as coffee grounds and fruit peels (citrus peel contains about 20% to 30% cellulose ).
significance:
Reduce landfills and achieve ' turning waste into treasure ' , but it is necessary to solve the interference problem of impurities (such as dyes and oils).
Comparative summary of different raw materials
Future development trends of raw materials
Diversified raw material development:
Explore algal cellulose (such as Ulvar) or fungal mycelium as new sources.
Green pretreatment technology:
Environmentally friendly methods such as ionic liquids and enzyme treatment are used to replace traditional acid / alkali processes.
Mixed raw materials strategy:
Mix wood with agricultural waste to balance cost and performance.
The preparation of nanocellulose usually involves physical, chemical or biological treatments to destroy the macrostructure of cellulose and release nanoscale components.
( 1) Mechanical method
High-pressure homogenization method: The cellulose slurry is sheared through a high-pressure homogenizer to obtain nanofibers.
Grinding method: Mechanically grind cellulose using an ultrafine grinding disc.
Ultrasonic treatment: Use ultrasonic cavitation to separate nanofibers.
( 2) Chemical method
Acid hydrolysis method (for CNC ): Hydrolyze cellulose with concentrated sulfuric acid or hydrochloric acid to remove the amorphous region and retain the nanocrystals.
Oxidation method (such as TEMPO oxidation): The cellulose surface is negatively charged through chemical oxidation, which facilitates dispersion.
Enzyme treatment: Cellulase selectively degrades amorphous regions to assist in nanofiber separation.
( 3) Biosynthesis method (for BNC )
Microorganisms such as Acetobacterium fermented in the culture medium to directly secrete nanocellulose.
Nanocellulose is highly concerned because it has a variety of excellent properties:
( 1) Mechanical properties
High strength: The elastic modulus of CNC can reach 150 GPa , close to Kevlar fiber.
High specific surface area: Due to the nanoscale size, the specific surface area is large, which is suitable for adsorption or composite reinforcement.
( 2) Optical properties
CNC suspensions can form chiral nematic phases (liquid crystal structures) with special optical properties such as polarized light response.
( 3) Biocompatibility and degradability
Originated from natural materials, non-toxic and biodegradable, suitable for pharmaceutical and food packaging.
( 4) Chemical Modification
The surface is rich in hydroxyl groups ( -OH ), which can impart new functions such as hydrophobic and electrical conductivity through chemical modification.
( 1) Composite material reinforcement
Added as reinforced phases to plastics, rubbers or resins to improve mechanical properties and reduce weight (such as automotive lightweight materials).
( 2) Biomedicine
Wound dressing: BNC has good breathability and biocompatibility, promoting wound healing.
Drug carrier: Nanocellulose can be used in sustained-release drugs.
Tissue Engineering Scaffold: Supports cell growth for cartilage or skin regeneration.
( 3) Environmentally friendly materials
Degradable packaging: Replace plastic film to reduce white pollution.
Water treatment: Use high adsorption to remove heavy metals or dye contaminants.
( 4) Electronics and Energy
Flexible electrons: Transparent nanocellulose films can be used in flexible display screens or solar cell substrates.
Battery separator: Improves the safety and performance of lithium-ion batteries.
( 5) Food and cosmetics
As a stabilizer, thickener (such as low-calorie food additives), or as a mask matrix.
Despite the promising prospects of nanocellulose, there are still some challenges:
Large-scale production: High energy consumption (such as mechanical method) or chemical pollution (acid hydrolysis) problems need to be solved.
Cost control: More economical raw materials (such as agricultural waste) and processes are needed.
Performance optimization: How to further improve its water resistance, conductivity, etc. through modification.
In the future, with the development of green chemistry and nanotechnology, nanocellulose is expected to replace petroleum-based materials in more fields and promote sustainable development.
Conclusion
Nanocellulose, as 21one of the most promising bio-based nanomaterials of the century, is changing our perception of traditional materials. It originates from nature, but has properties that surpass many synthetic materials, providing innovative solutions for environmental protection, medical care, energy and other fields. By deeply digging into the characteristics of different raw materials, nanocellulose production can take into account performance, cost and sustainability. With the deepening of research and technological advancement, nanocellulose may become one of the core pillars of future materials science.
