Detailed explanation of the preparation method of nanocellulose—— Taking the refining method in mechanical method as the core

An introduction

Nanocellulose ( Nanocellulose ) is a cutting-edge green nanomaterial. Due to its high specific strength renewable biodegradability and good mechanical properties , it is widely used in many high-tech fields such as pharmaceutical electronic biopackaging and food additives. Currently, there are many methods for preparing nanocellulose on the market. Among them, mechanical method has attracted much attention due to its advantages such as environmental protection and safety and high product purity . Refining method is a core technical route that is particularly important in mechanical method.

Classification of preparation methods for two nanocellulose

method	principle	Representative technology	Features
Mechanical method	External force peeling fiber	High pressure homogenized grinding ultrasonic wave	Environmentally friendly, safe and high energy consumption
Chemical method	Nanodissociation after modified fibers	TEMPO Oxidative Acid Hydrolysis	Dimensionally controlled chemical residue
Enzyme method	Enzymatic cellulose re-physical treatment	Cellulase + Mechanical Method	Moderate conditions and high cost

Among them, as a typical technology of mechanical method, the refining method shows great potential in the industrial continuous preparation of nanocellulose. This will be systematically analyzed below.

Principles of preparation of nanocellulose by three-slurry method

The pulping method mainly relies on ** Shear force Friction force and compression force ** Disassembly fibers in natural cellulose into nano-scale structures This method imitates the idea of ​​pulping in paper raw materials in the pulp industry, but requires higher strength and precision equipment configuration and process control.

Mechanism of action:

Microfiber bundles are formed by hydrogen bonds between cellulose molecular chains;

The slurry refining equipment continuously acts on the fibers in a wet state, breaking the hydrogen bonds through mechanical energy input, causing the fibers to dissociate into filament-like units that are tens of nanometers wide;

Finally, CNF with a diameter of 20–100 nm and a length of several microns was obtained

Detailed description of typical process flow of four-slurry refining method

Step 1: Raw material selection

Commonly used raw materials:

Bleached chemical pulp (such as broadleaf wood pulp cotton pulp)

Agricultural waste (wheat straw, sugarcane, corn cob, etc.)

Require:

The content of α- cellulose is higher than 85%

Contains less than lignin1%

Low ash impurity content

Step 2: Pretreatment process (optional but recommended)

1. Alkaline treatment

Reaction with 1–5% NaOH solution at room temperature or 60°C for 1–3 hours to remove hemicellulose and residual lignin

2. Beating (refining)

Mechanical refining is carried out in traditional beating machines to increase the specific surface area of ​​the fiber and improve the subsequent refining efficiency

3. Enzymatic lysis (advanced option)

Add 0.5–2% cellulase and incubate at 50°C for several hours to partially degrade the cellulose chain, thereby reducing energy consumption

Step 3: Refining treatment (core link)

Equipment Type:

Disc grinder ( Supermasscolloider ) : Slurry is entrained between two counter-rotating grinders, producing strong shear force;

Nano-slurry system : Some are made of ceramic grinders or high-precision stainless steel, with a speed of up to 1500–4000 rpm

Operation parameters:

parameter	Typical settings
Slurry concentration	1–2 wt%
Grinding disc gap	10–50 µm
Temperature control	<60℃
Number of cycles	5–30 times
Grinding disc speed	1500–3000 rpm

Notes:

Multiple cycles of slurry refining can gradually reduce gaps and prevent structure damage at one time;

Keep the system cool and avoid heat-induced fiber degradation;

Small amounts of surf modifiers such as CTAB or CMC may be added to reduce agglomeration

Step 4: Dispersed dilution and stable treatment

Ultrasonic treatment : Use a 20 kHz ultrasonic probe to effectively interrupt agglomeration;

Added co-dispersant : 0.1–0.3% CMC PEG , etc.;

Formation of stable colloids : obtain transparent or translucent suspension, with significantly increased viscosity (common viscosity 200–5000 mPa·s )

Step 5: Dehydrate and dry (select according to the purpose)

Centrifugal concentration : Prepare 3–10 wt% colloidal product;

Freeze-drying : made into spongy or powdery nanocellulose;

Spray drying : industrial large-scale dehydration scheme

Five quality control and characterization methods

Testing items	method	illustrate
Particle size /morphology	TEM/SEMAFM	Observe length and diameter
Crystal structure	XRD	Determine whether it is cellulose type I
Viscosity	Rheometer	Judge dispersion and concentration
Thermal stability	TGA/DSC	Evaluate thermal processing performance
Surface charge	Zeta potential	Judge colloid stability

Advantages and challenges of Six-slurry refining

advantage:

Supports a variety of fiber raw materials and has extensive resource utilization

challenge:

High energy consumption, especially in the preparation of high-fine CNF；

Seven typical industrial application cases

industry	Application Products	CNF function
food	Juice ice cream stabilizer	Improve viscosity and stability
medicine	Wound dressing hydrogel	Biodegradable and antibacterial
Package	Green plastic biofilm	Alternative petrochemical materials
coating	Water-based coating ink	Improve strength and wear resistance
electronic	Flexible conductive paper base film	Lightweight and high transparency

Eight conclusions and prospects

As a green process path for the preparation of nanocellulose , the refining method shows great potential in the current development background of ' carbon neutrality ' and ' bio-based materials '. Future development directions include:

Used in combination with chemical modification or enzymatic methods to reduce energy consumption;

Develop new high-efficiency low-loss abrasive equipment;

Build a continuous intelligent production line to achieve large-scale applications;

Develop high-performance functionalized nanocellulose to expand the high-end market (aviation flexible electronic biomedical products, etc.)