Characteristics and application prospects of high crystallinity nanocellulose crystals (CNCs)

Cellulose Nanocrystals (CNC) is a class of nanomaterials derived from natural cellulose decomposition, with high crystallinity, high strength, excellent thermal stability and biodegradability. CNC crystallinity is one of its most significant properties, which gives CNC great potential in a variety of high-end applications. This article will deeply explore the high crystallinity characteristics of CNC, including its impact on mechanics, thermal and optical properties, and analyze in detail how this characteristic promotes the widespread application of CNC in composite materials, environmentally friendly packaging, drug delivery and other fields.

1. The crystallinity and importance of nanocellulose crystals

The crystallinity is the ratio of the crystalline region to the non-crystalline region in the cellulose molecule, which affects the mechanical strength, thermal stability, chemical durability and other properties of CNC. Generally speaking, the crystallinity of CNC is as high as 70%-90%, which is much higher than that of natural cellulose (the crystallinity is usually 40%-60%). This high crystallinity imparts CNCs to perform excellent physical properties in multiple applications. Through X-ray diffraction (XRD) technology, researchers found that the crystallization region of CNC is mainly composed of β-glucose units connected by hydrogen bonds, forming a highly ordered crystal structure.

2. Effect of CNC high crystallinity characteristics on performance

The crystallinity of The higher crystallinity makes the molecular chains of CNC more closely arranged and the hydrogen bond interactions are stronger, so it shows excellent tensile strength, compressive strength and toughness. Studies have shown that the tensile strength of CNC can reach 7-10 GPa, several times the strength of conventional cellulose materials. This makes CNC an ideal choice for reinforced composites, nanomaterials and high-performance structural materials.
mechanical properties CNC directly affects its mechanical strength.

Material Type	Tensile strength (GPa)
Nanocellulose crystals (CNC)	7-10
Fiberglass composite material	2-4
Polymer materials (such as PE, PP)	0.5-2

Thermal stability

The high crystallinity of CNC also significantly improves its thermal stability. The ordered structure with a higher crystallization region can effectively inhibit the thermal motion of the molecular chain, so that the CNC can maintain stability at higher temperatures. Experiments show that the decomposition temperature of CNC is usually 280-300°C, which is much higher than that of natural cellulose (200-240°C). This characteristic allows CNC to maintain its physical properties in high temperature environments and is suitable for the fields of heat treatment and high temperature applications.

Optical transparent
CNC has excellent optical properties due to its high crystallinity. The arrangement of crystalline regions allows the CNC to exhibit lower light scattering properties, thereby improving its transparency. For example, the light transmittance of CNC films can reach more than 90%, which has great potential in transparent film and optical coating applications. With the expansion of CNC application fields, its optical performance has also become a hot topic in research and application.

Chemical stability and hydrolysis resistance
CNC with high crystallinity exhibits excellent chemical stability and hydrolysis resistance. The molecules in the high crystallinity region are arranged more closely, and the difficulty of chemical reactions is relatively increased. CNCs show good stability in acid, alkali, brine and other environments, and can maintain their structure in harsh environments. Studies have shown that high crystallinity CNCs can still maintain good stability under extreme pH conditions (such as pH 1-12), while low crystallinity CNCs are prone to hydrolysis and degradation.

3. Factors affecting the crystallinity of CNC

The crystallinity of Natural fibers such as wood cellulose and bamboo cellulose are usually higher in crystallinity, while cellulose from certain herbs are relatively low in crystallinity. The crystallinity of wood cellulose can reach 70%-75%, while the crystallinity of some herbs is less than 50%.
the raw material source CNC is greatly affected by the source of the raw material cellulose.

The preparation method of the preparation process
CNC directly affects its crystallinity. Common preparation methods include acid hydrolysis, mechanical method, enzymatic method, etc., among which acid hydrolysis is the most commonly used method. The study found that by appropriately controlling the acid concentration and hydrolysis time, the crystallinity of CNC can be significantly improved. Generally, when the hydrolysis time is 1-2 hours and the acid concentration is 60%-70%, the crystallinity of CNC can reach 80%-90%.

Hydrolysis time (hours)	Acid concentration (%H2SO4)	Crystalline degree (%)
1	60	80-85
2	70	85-90
3	80	85-90

Temperature and pH
Reaction temperature and pH are important factors affecting the crystallinity of CNC. At higher temperatures (50°C-80°C), hydrogen bonds between cellulose molecular chains can be more fully destroyed, thereby promoting the improvement of CNC crystallinity. At the same time, pH value has a great impact on hydrolysis. Under overacid or overbase conditions, it may lead to a decrease in the crystallinity of CNC. Therefore, maintaining a moderate pH value is crucial to maintaining its high crystallinity.

4. Advantages of CNC high crystallinity characteristics in application

The high crystallinity of high-performance composite
CNC imparts excellent mechanical properties, making it a key component in high-performance composites. When composited with polymers, metals, ceramics and other materials, CNC can significantly improve the mechanical properties, tensile strength and compressive strength of the composite material. For example, CNC-enhanced polymer composites have a tensile strength that can be improved by 50%-100%, and have good toughness and heat resistance.

Environmentally friendly packaging materials
With the increasing strict environmental requirements, CNC, as a biodegradable material, is widely used in the field of environmentally friendly packaging. The high crystallinity of CNC makes it have higher mechanical strength, which can meet the needs of packaging materials during transportation and storage, and has strong biodegradability, and can be completely degraded within 30-60 days after use.

Drug delivery and biomedical material
CNC are widely used in sustained-release drugs and therapeutic nanocarriers as carriers in drug delivery systems due to their excellent biocompatibility, high crystallinity and controllable degradability. Experimental results show that when using high crystallinity CNC as the drug carrier, its drug release control can be stable to release within 72 hours without toxic reactions.

The high crystallinity of the electronic optical material
CNC makes it have good optical transparency and low light scattering properties, and is particularly widely used in transparent films, photoelectric displays and optical coatings. The light transmittance of CNC films can reach more than 90%, and its excellent optical properties make it an ideal choice for high-end optical materials.

V. Conclusion

Nanocellulose crystals (CNCs) exhibit excellent mechanical properties, thermal stability, optical transparency and chemical stability due to their high crystallinity, making them show great application potential in various high-end applications. With the continuous advancement of CNC preparation technology, further improvement in crystallinity will help it to be deeply applied in more fields, such as high-performance composite materials, environmentally friendly packaging, drug delivery systems and electronic materials. Although CNC is high in production costs, with the advancement of industrialization, CNC is expected to become one of the key materials for sustainable development in the future, promoting the innovative application of green technology and new materials.