Nanocellulose crystals ( CNC ) are gradually becoming an important ' nanostructure unit ' in the design of functional composite materials due to their high crystallinity, high strength, biodegradability and rich interface functions . However, in engineering applications, especially thermal stability ，in the field of hot-processed composite materials, has become one of the key performance parameters that restrict the widespread use of CNC .

This paper will systematically analyze the thermal stability characteristics, influencing factors and regulatory methods of CNC based on the molecular structure and thermal degradation mechanism , and will deeply explore its application prospects and challenges in high-performance heat-resistant material systems.

1. Source of thermal stability infrastructure of CNC

1. Thermal inertia in the high crystallization zone

CNC is a rod-shaped nanocrystalline obtained by selectively hydrolyzing the amorphous region of natural cellulose. It has a typical crystallinity of up to 70%-90% , a stable crystal structure and regular molecular chains, making it have relatively good thermal inertia.

High lattice energy and ，strong covalent bond stability between C–O and C–H ;

The hydrogen bond network inside and outside the molecule is closely cross-linked to form a thermal vibration buffer zone;

The crystallization zone is preferred to maintain its complete structure to the frontier of pyrolysis ( T₁₀%~220–250℃ )。

The thermal stability of CNC is mainly reflected in the fact that its initial thermal decomposition temperature is higher than that of natural cellulose raw materials at 30-60℃ , which is better than hydrolyzed untreated wood pulp, starch and other materials.

2. Effect of surface functional groups on thermal stability

The preparation method on the thermal performance has a significant impact of CNC :

The CNC obtained from sulfuric acid hydrolysis method contains sulfate ester groups ( –OSO₃⁻ ), which trigger a catalytic dehydration reaction between 180-220°C , reducing its overall thermal stability;

Hydrochloric acid or neutral enzymatic method has no strong acid group modification, and the CNC produced has better thermal stability, up to about 280-300℃ .

2. Thermal stability measurement parameters and experimental performance

1. Thermogravimetric analysis (TGA)

TGA is the core method for studying the thermal stability of CNC . Common TGA parameters include:

parameter	meaning	CNC typical value (sulfuric acid method)	CNC typical value (neutral method)
T₁₀%	Starting temperature of 10% weight loss	180–210°C	240–280°C
Tmax	Maximum weight loss rate temperature	230–250°C	290–310°C
Residual charcoal	High temperature residual mass ratio	30–40%	15–25%

Thermal cracking of sulfate CNC is usually divided into two steps: ① Surface dehydration → ② Main chain break;

The non-esterified CNC cleavage is concentrated at 250–350°C , and the thermal response is more stable.

2. Differential scanning calorimetry (DSC)

DSC curves were used to analyze the glass transition ( Tg ) and potential thermal deformation characteristics of Since CNC . CNC is a rigid nanocrystal, it has no obvious Tg characteristics , but after introducing composite materials, it can significantly enhance the Tg of the matrix。

For example, adding 2 wt% of CNC can increase the Tg of PLA from 55°C to ~65°C, indicating that it has a 'chain domain' effect.

3. Strategies to improve the thermal stability of CNC

1. Improve the hydrolysis process and reduce thermally sensitive functional groups

Non-sulfonated hydrolysis systems such as hydrochloric acid, enzymatic method, hydrothermal heat；

Low-temperature sustained-release acid treatment to reduce segment degradation;

After surface esterification, wash and remove free SO₄²⁻。

2. Surface crosslinking and coating technology

The with polysiloxane, chitosan, dopamine, etc. CNC surface is physically or covalently coated to form a thermal insulation layer;

Improve the CNC 、heat-resistant shell by cross-linking isocyanates and inorganic oxides (such as SiO₂TiO₂ ) ;

Sol- -gel method to construct CNC- organic and inorganic hybrid structure.

3. Coordinated strengthening of composite systems

Blend with high-temperature polymers such as aromatic polyamide, polyester, polyether ether ketone ( PEEK );

Use two-dimensional layered materials (such as graphene oxides, montmorillonite) to construct a heat-resistant multi-stage composite system。

4. Exploration of practical application in high-temperature composite materials

1. Heat-resistant packaging and coating

CNC is blended with chitosan and polylactic acid ( PLA ) to form a transparent nano film;

It is used in microwave-heated food packaging materials to maintain stability and structural integrity at 120°C ;

In the coating system, CNC can be used as an enhancement phase to impart a higher temperature and permeability to water-based coatings.

2. High temperature sensor and flexible electronic substrate

The after modified CNC TiO₂ coating can be stably used at 250°C ;

The CNC- based flexible substrate has good thermal conductivity and thermal mechanical stability, and is an ideal substrate for wearable temperature sensors .

3. Heat-insulating aerogel and construction materials

CNC is cross-linked with silane by freeze-drying and cross-linking to obtain a light aerogel with thermal conductivity < 0.03 W/m·K , and stable operating temperature > 200℃；

As an environmentally friendly thermal insulation material , it has been initially used in green building interior walls and energy-saving coatings.

5. Research frontiers and future directions

The current research on the thermal stability of CNC is gradually entering the stage of ' multi-scale modeling of -structural regulation -molecular design ' . Future improvement directions include:

Construction of pyrolysis kinetic model : decompose gas components through TG-FTIR 、TG-MS combination analysis and invert CNC pyrolysis path;

Molecular dynamics simulation : Exploring the coordinated response of CNC chain end behavior to thermal stability and composite interface;

Application of in-situ observation technology : synchronous radiation small angle X -ray ( SAXS ) and in-situ AFM reveal the thermal deformation mechanism;

Multifunctional heat-resistant composite system design : such as -thermoelectric dual-response CNC materials, fire self-extinguishing composite materials, etc.

As a natural source structural nanomaterial, nanocellulose crystals have thermal stability not only a basic performance indicator, but also determine their breadth and depth in engineering applications. Through multi-path improvement strategies of structural optimization, surface regulation and composite coordination, CNC is gradually breaking through the traditional thermal performance bottleneck and accelerating its extension to high-end electronic materials, functional coatings, intelligent packaging and other fields. Thermal stability research is no longer a limiting factor, but will become the key driver to empower the high temperature value of CNC material systems.