Research on thickening mechanism, rheological properties and application of nanocellulose

In many water-based industrial systems such as coatings, daily chemicals, food, and biomedicine, thickeners are core functional additives that regulate the viscosity of the system, stabilize the dispersion state, and optimize the feel of use. Traditional organic thickeners and inorganic thickeners generally have shortcomings, such as high additive content, easy stickiness, poor salt and temperature resistance, standing delamination, and weak shear stability, making it difficult to meet the development needs of high-end fine chemicals and functional materials. As a new type of nanofunctional material derived from natural plants and bacterial biomass, nanocellulose relies on its unique one-dimensional nanofiber structure, ultra-high specific surface area and multiple interface mechanisms to demonstrate extremely excellent thickening, suspension, and rheology control properties. It has become a new generation of high-performance green thickening substrates, effectively breaking through the industry pain points of traditional thickening systems that ' thickening is prone to viscosity and flow is prone to instability . This article will focus on an in-depth explanation of the thickening core advantages, mechanism of action, rheological properties and industrial application of nanocellulose.'

1. Structural basis for nanocellulose to adapt to efficient thickening

Nanocellulose is mainly divided into three categories: cellulose nanofibrils ( CNF ), cellulose nanocrystals ( CNC ) and bacterial cellulose ( BC ). Among them, cellulose nanofibrils ( CNF ) are the category with the best thickening performance and the most widely used. Its structural characteristics are the core prerequisite for achieving efficient thickening. Different from traditional granular and polymer chain thickeners, CNF presents an ultra-long one-dimensional nanofilament structure, with a fiber diameter of only 5–50 nm , a length of hundreds of nanometers to several microns, and an aspect ratio far exceeding that of conventional thickening materials.

This high aspect ratio structure gives it two core advantages: First, a complete spatial network can be constructed with a very low addition amount. The addition amount of conventional polymer thickeners is generally 1%–3% . , and CNF only needs an ultra-low dosage of 0.1%-0.5% to significantly increase the viscosity of the system and achieve efficient and lightweight thickening; secondly, the surface of the fiber is rich in hydroxyl groups, which can form abundant hydrogen bonding sites in the aqueous system. At the same time, the nanocellulose modified by carboxylation and sulfonation has a uniform charge on the surface, which can superimpose electrostatic repulsion and steric hindrance effects, providing structural support for a stable three-dimensional network structure and long-term water-locking and thickening. Compared with short rod-shaped CNC ，CNF, the longer fiber segments can form stronger physical entanglements, giving the system higher viscosity and elastic modulus at the same concentration, and the thickening effect is more prominent.

2. Core thickening mechanism of nanocellulose

The thickening effect of nanocellulose is not a single physical stack, but the result of the synergistic effect of four major mechanisms: physical entanglement, hydrogen bond cross-linking, electrostatic repulsion, and steric hindrance. It realizes system thickening and stability in multiple dimensions, which is the core reason why its performance far exceeds that of traditional thickeners.

1. Nanofiber physical entanglement dominates skeleton thickening

In the water-based dispersion system, the uniformly dispersed nanocellulose fibrils will spontaneously build a continuous, uniform, three-dimensional three-dimensional network skeleton structure through the intertwining and overlapping of their own ultra-long chain segments. This network is like a intertwined with countless ultra-fine fibers ' microscopic scaffold ' , which can greatly restrict the free flow of water molecules, directly increase the static viscosity of the system, and achieve a basic thickening effect. This physical network structure has extremely strong structural stability and will not collapse due to slight environmental fluctuations. It is the core skeleton of the long-term thickening of the system.

2. Hydrogen bond cross-linking strengthens network stability

The large number of hydroxyl groups on the surface of nanocellulose can form dense intermolecular hydrogen bonds with water molecules and polar additives in the system. On the one hand, the nanofiber network is closely combined with the aqueous system, firmly locking in water, and preventing water leakage and delamination of the system; on the other hand, secondary cross-linking is formed between the fibers, further strengthening the three-dimensional network structure, improving network density and structural strength, giving the thickening system higher static viscosity and anti-settling ability, and effectively solving the problem of sedimentation failure of powders and particles in suspended systems.

3. Electrostatic repulsion and steric hindrance optimize thickening uniformity

The surface of modified nanocellulose carries a uniform negative charge, and a stable electrostatic repulsive force is generated between fibers, which can effectively avoid the agglomeration and flocculation of nanofibers, ensure their uniform dispersion in the system, and make the thickening effect uniform across the entire area without local thickening or agglomeration. At the same time, the polymer chain segments on the fiber surface can produce steric hindrance effects, further blocking fiber aggregation, maintaining the regularity of the network structure, and making the system thickened delicately and transparently, without the gelatinous and heavy feeling of traditional thickeners.

3. Core rheological properties: shear thinning and thixotropic reversible thickening

Compared with the single thickening effect of traditional thickeners, the most valuable advantage of nanocellulose is its controllable rheological properties , which perfectly solves the contradiction between ' stable standing ' and ' smooth use ' and is also its core competitiveness for high-end applications.

1. Typical shear thinning characteristics

The nanocellulose thickening system has excellent shear thinning properties: when the system is left standing or in a low-shear state, the fiber network stretches completely and has extremely high viscosity, which can firmly suspend solid particles, oil droplets, and active ingredients in the system, achieving long-term stability and preventing settling, stratification, and oil-water separation. When subjected to shear external forces such as stirring, smearing, and spraying, the intertwined nanofiber network quickly stretches, slips, and unwounds. The viscosity of the system drops significantly instantly, the fluidity is significantly improved, and the system becomes thin and smooth.

This feature completely overturns the shortcomings of traditional thickeners that ' thickening makes them sticky and flowing makes them thin .' It not only ensures product storage stability, but also optimizes the construction and use experience, without problems such as stickiness, mud rubbing, and wall hanging.

2. Reversible thixotropy and yield stress characteristics

The nanocellulose dispersion system has good thixotropy and yield stress characteristics. The yield stress value is stable and the system's anti-flow and anti-settlement capabilities can be accurately controlled. When the external shearing force is removed, the disentangled nanofibers can be quickly re-entangled and cross-linked, and the three-dimensional network structure is restored instantly. The viscosity of the system rebounds quickly, returning to a high consistency and high stability state. This reversible rheology characteristic can be recycled repeatedly and has long-lasting stability. It will not cause thickening failure or system instability due to multiple shearing effects. It is suitable for industrial operation scenarios such as repeated stirring, spraying, and coating.

4. Performance comparison between nanocellulose and traditional thickeners

Traditional mainstream thickeners each have obvious shortcomings, and nanocellulose has achieved all-round upgrades in thickening efficiency, stability, user experience, and environmental protection, with significant comparative advantages. The addition amount of organic polymer thickeners is high, the cost is high, and the salt resistance and temperature resistance are poor. In high-salt and high-temperature environments, it is easy for viscosity to drop suddenly, system demulsification and stratification, and the finished product is sticky and thick; inorganic bentonite, fumed silica and other thickeners are easy to agglomerate, have uneven fineness, insufficient thickening fineness, and are prone to graininess and turbidity problems, affecting the product texture.

Nanocellulose requires only a very low amount of addition to achieve efficient thickening. It has excellent salt resistance, temperature resistance, acid and alkali resistance, and can be adapted to complex formula systems. The thickening texture is fine and transparent, without a heavy and sticky feeling, and the rheological properties are controllable. At the same time, the raw material is derived from natural biomass, is biodegradable, non-toxic and harmless, and is green and environmentally friendly. It is fully in line with the current development trend of lightweight, functional and green materials, and is a high-quality upgraded substitute for traditional thickeners.

5. Core application scenarios based on thickening characteristics

Relying on the ultimate thickening, suspension, and rheological control properties, nanocellulose has been applied on a large scale in many high-end fields, giving full play to its unique functional value.

1. Daily cosmetics field

In skin care products and makeup systems such as essences, gels, lotions, and facial masks, nanocellulose serves as a green thickening rheology agent and can replace traditional carbomer and xanthan gum. A low addition amount can stabilize the formula system, prevent the functional ingredients and powder from settling and stratifying, and extend the shelf life of the product; at the same time, relying on the shear thinning characteristics, it can achieve a high-end skin feel of ' thick and stable when left standing, light and smooth on the skin ' , without stickiness, mud rubbing, and stuffy skin problems, and is suitable for the formulation needs of pure skin care and high-end makeup.

2.Coating and ink industry

In water-based coatings and printing ink systems, the thickening and thixotropic properties of nanocellulose can effectively regulate the viscosity of the coating, prevent the coating from settling during storage and sagging during construction, improve the uniformity of spraying and coating, and make the paint film and ink layer smooth and delicate. At the same time, its nano-network structure can improve the density and adhesion of the coating. While achieving rheological control, it also takes into account the optimization of material mechanical properties and is suitable for the production of high-end water-based environmentally friendly coatings.

3. Food industry field

As a natural food-grade thickening stabilizer, nanocellulose can be used in ice cream, yogurt, sauces, drinks and other products. It stabilizes the food system structure through thickening and suspension, inhibits the growth of ice crystals, prevents sauce layering and precipitation, and optimizes the taste and texture of food. At the same time, it has no chemical additions, is safe and biodegradable, and is in line with the development direction of green and healthy food.

4. Biomedicine and functional gels

In systems such as medical gels, sustained-release ointments, and biological dressings, the precise thickening and rheological properties of nanocellulose can regulate the gel molding effect to ensure uniform application and good adhesion of the ointment. At the same time, it stabilizes the active ingredients of the drug and achieves long-term sustained release. It has excellent biocompatibility and is non-irritating, adapting to the stringent requirements of high-end medical materials.

6. Summary and Outlook

Nanocellulose relies on its unique one-dimensional nanostructure and multiple thickening mechanisms of physical entanglement, hydrogen bond cross-linking, electrostatic and steric hindrance synergy to achieve high-quality thickening effects of low dosage, high efficiency, high stability, and controllable rheology , completely solving many application pain points of traditional thickening materials. Its unique comprehensive advantages of shear thinning, reversible thixotropy, weather resistance and stability, and green environmental protection make it not only a simple thickening additive, but also a multi-functional rheology control substrate, covering high-end application scenarios in daily chemicals, coatings, food, biomedicine and other fields.

Currently, with the continuous maturation of nanopreparation technology and the continuous optimization of surface modification processes, the thickening efficiency and system adaptability of nanocellulose will be further improved, and the cost will be gradually reduced. a domestic high-tech enterprise Nanjing Tianlu Nanotechnology Co., Ltd., , is deeply involved in the field of nanocellulose, focusing on the research and development, large-scale production and application of various nanocellulose products. Relying on mature modification and preparation processes, it continues to optimize the thickening and rheological stability of materials, effectively promoting the industrialization and implementation of high-performance nanocellulose materials. In the future, nanocellulose is expected to fully replace traditional high-energy-consuming, low-performance chemical thickeners and become the core rheological functional material in the field of green fine chemicals and new functional materials, promoting the iterative upgrade of formula systems in various industries toward lightweight, high-end, and green.