A new approach to nanocellulose-based coatings could help address one of the long-standing challenges in sustainable surface engineering: how to combine bio-based materials with high water repellency and long-term durability.
Researchers have developed a fluorine-free superhydrophobic coating based on cellulose nanofibrils (CNFs) using a sequential solvent exchange strategy. The resulting coating achieves a water contact angle of more than 155° and maintains its superhydrophobic properties under mechanical abrasion, extreme pH conditions, salt exposure and icing.
The study, published in Progress in Organic Coatings in 2026, provides a potential route toward more durable, PFAS-free surface treatment technologies based on renewable materials.
Why Is It Difficult to Make Durable Nanocellulose Coatings?
Cellulose nanofibrils have attracted considerable interest as a renewable material for advanced coatings and functional surfaces. They are derived from cellulose and offer a combination of high aspect ratio, mechanical strength and abundant surface hydroxyl groups.
The problem appears when the material needs to be processed into a practical coating.
CNFs are naturally hydrophilic and are typically handled as aqueous dispersions. During drying, the fibrils can come into close contact and form strong hydrogen bonds with one another. This causes irreversible aggregation and can destroy the fine nanoscale structure that gives nanocellulose much of its functional value.
For superhydrophobic coatings, this creates an additional problem. High water repellency generally requires both low surface energy and a carefully controlled micro- or nanoscale surface structure.
Simply drying a CNF dispersion therefore does not provide an easy path to a robust superhydrophobic surface.
A Sequential Solvent Exchange Strategy
The research team addressed this processing challenge through a stepwise solvent exchange process involving ethanol and n-butanol.
Potassium acetate was also introduced to disrupt the electrical double layer around the nanofibrils. The treatment helps prevent the fibrils from coming back together through strong hydrogen bonding and creates greater steric separation between them.
Through the sequential exchange process, the CNFs can be transferred from an aqueous dispersion into a stable cyclohexane dispersion without losing the nanoscale framework.
This is an important step from a processing perspective because the resulting dispersion can be used for spray coating, bringing the laboratory-scale material closer to conventional coating application methods.
Rather than modifying the cellulose through extensive chemical transformation, the strategy focuses on controlling how the nanofibrils are dispersed and processed.
Building a Superhydrophobic Surface Without Fluorinated Chemistry
The researchers then combined the nanocellulose framework with polydimethylsiloxane (PDMS), a flexible hydrophobic binder.
A further vapor-phase treatment using methyltrimethoxysilane (MTMS) was used to modify the surface.
The resulting dual-silane system creates two important characteristics at the same time:
- low surface energy;
- a hierarchical micro/nanostructure.
This combination is central to superhydrophobicity. Instead of allowing water to spread across the surface, the textured structure traps air beneath water droplets and promotes a Cassie-Baxter wetting state.
The resulting coating showed a water contact angle of 155.3° ± 1.6°, while the sliding angle remained below 10°. These values indicate a highly water-repellent surface rather than simply a conventional hydrophobic coating.
Durability Under Harsh Conditions
High water contact angles are relatively easy to demonstrate in laboratory experiments. The more difficult question is whether the surface can retain its performance after exposure to real operating conditions.
This is where the new CNF-based coating becomes particularly interesting.
According to the study, the modified coating retained its superhydrophobic characteristics after mechanical abrasion, exposure to solutions ranging from pH 1 to 12, salt solution treatment and freezing conditions.
Durability is a major consideration for practical superhydrophobic coatings. Surface roughness can easily be damaged by mechanical contact, while chemical exposure can alter surface chemistry and cause a loss of water repellency.
The researchers' combination of a nanocellulose framework, flexible PDMS and silane surface modification is designed to address these weaknesses by providing both structural support and a low-energy interface.
Why Fluorine-Free Coatings Matter
Fluorinated compounds have traditionally played an important role in producing highly water- and oil-repellent surfaces. However, concerns surrounding persistent fluorinated substances, including PFAS, have increased interest in alternative surface technologies.
This has created a difficult materials challenge for the coatings industry: replacing fluorinated chemistry without giving up the performance that makes it attractive.
Recent research has explored a range of fluorine-free approaches, including silicone-based systems, silica structures and cellulose-derived materials. CNF-based coatings are particularly interesting because cellulose is renewable and can serve as both a structural building block and a platform for surface engineering.
The latest study takes this concept further by combining bio-based nanocellulose with a scalable dispersion and spray-coating strategy, while targeting durability under demanding conditions.
From Renewable Raw Material to Functional Coating
The significance of the research goes beyond achieving a contact angle above 155°.
One of the biggest barriers for bio-based materials is often not whether they have useful properties in the laboratory, but whether those properties can survive processing and be translated into industrial applications.
The solvent exchange strategy provides a possible solution to this problem.
By preventing irreversible CNF aggregation, researchers can preserve the nanostructure during the transition from water-based processing to an organic dispersion. This makes it possible to use the material in a form that is more compatible with coating technologies.
That opens potential opportunities in areas where water repellency, anti-icing, self-cleaning or corrosion protection are important. Superhydrophobic coatings have been investigated for applications ranging from industrial equipment and transportation surfaces to textiles, heat-transfer components and marine systems.
However, further work will still be needed before laboratory-scale performance can be translated into widespread commercial use. Cost, coating thickness, substrate compatibility, solvent recovery, large-area processing and long-term outdoor stability will all be important considerations.
What This Means for the Coatings Industry
The development highlights a broader direction in materials innovation: high performance and sustainability are increasingly being designed together rather than treated as separate goals.
For coating manufacturers, the opportunity is not simply to replace one ingredient with a bio-based alternative. The more significant challenge is to redesign the material architecture so that renewable components can deliver the required performance.
In this case, the key innovation lies in combining:
Cellulose nanofibrils → controlled solvent exchange → hierarchical surface structure → silicone-based modification → durable fluorine-free superhydrophobicity
This type of materials engineering could become increasingly relevant as manufacturers look for alternatives to fluorinated surface treatments while maintaining performance in demanding environments.
The Next Step for Bio-Based Surface Engineering
The study demonstrates that cellulose nanofibrils do not have to be limited to conventional paper, packaging or reinforcement applications. With appropriate processing and surface engineering, they can become building blocks for advanced functional coatings.
The research also points to an important lesson for sustainable materials development: the performance of a renewable material depends not only on its chemistry, but also on how its nanoscale structure is preserved during processing.
For the coatings industry, that distinction could prove important.
As demand grows for PFAS-free, renewable and durable materials, technologies that combine nanocellulose with practical coating processes may offer a new route toward high-performance sustainable surfaces.
The next challenge will be to determine how effectively these laboratory results can be translated into large-area manufacturing, commercial formulations and long-term field applications.
