Advances in the Application of CNF in Water-Based Coatings and Inks
Why CNF Is of Interest in Water-Based Systems
As coatings and inks continue to shift toward water-based, low-VOC formulations, the challenge is to achieve a balance among storage stability, application and leveling performance, and high-shear processability. With its high aspect ratio and abundant surface hydroxyl groups, CNF can form a three-dimensional network in water through fiber entanglement, hydrogen bonding, and interparticle interactions. As a result, even at relatively low addition levels, CNF can significantly modify the low-shear viscosity and yield behavior of the formulation.
This makes CNF particularly suitable for addressing issues such as pigment and filler sedimentation, phase separation during storage, sagging during spraying or printing, and thixotropic formulations that require the system to remain stable at rest while flowing readily under shear.
From Thickening Agents to Rheology-Structure Modifiers
Traditional thickeners are primarily designed to increase viscosity, whereas the distinctive feature of CNF lies in its ability to form a fibrillar network structure. With an appropriate formulation, the system exhibits a relatively strong network at low shear rates, thereby enhancing suspension stability. Under high shear generated during mixing, pumping, coating, or printing, the network is partially disrupted, resulting in a decrease in viscosity. Once shear is removed, the network gradually rebuilds.
Therefore, CNF should not be evaluated solely based on viscosity measured at a single fixed rotational speed. More informative rheological parameters include flow curves, yield stress, thixotropic loops, and three-interval thixotropy tests (3ITT) for structural recovery, together with sedimentation behavior during storage and actual application performance.
Surface Functionalization Broadens the Formulation Window
Carboxylated CNF, owing to its negatively charged surface and improved water dispersibility, can provide effective network formation and suspension performance in many water-based systems. Unmodified or hydroxyl-functionalized CNF, by contrast, is more dependent on the specific matrix and dispersion process. Salts, pigments, electrolytes, surfactants, and resin emulsions within the formulation can all affect the CNF network. Therefore, the optimal CNF dosage must be determined through systematic concentration-gradient testing.
For inks, additional factors such as filterability, inkjet nozzle compatibility, particle size, and fiber length must also be considered. CNF is not necessarily suitable for all fine-inkjet systems; however, it offers considerable potential for rheological control research in screen printing, flexographic printing, functional coating inks, and high-solids water-based formulations.
A New Role in Functional Coatings
Beyond rheological modification, CNF can also serve as a film-forming auxiliary network and a carrier for functional fillers. By incorporating conductive materials, pigments, inorganic nanosheets, or bio-based polymers, CNF can further enable the development of barrier, conductive, crack-resistant, or functional surfaces. Future research will focus on achieving a stable rheological processing window at low CNF loadings, improving interfacial compatibility with emulsions and pigments/fillers, and optimizing the rate of structural recovery during continuous coating and printing processes.
Small-Scale Evaluation Approach
For water-based coatings and inks, it is recommended to first establish a CNF concentration gradient of 0, 0.10%, 0.25%, and 0.50% (based on total dry solids), while keeping all other formulation parameters unchanged. The samples can then be evaluated systematically for dispersion quality, low-shear viscosity, rheological recovery, sedimentation during storage, application and leveling performance, and the final film properties. The objective is not to maximize viscosity, but rather to identify an optimal formulation window that balances storage stability with practical application performance.
Sources and Further Reading
• 本文结合近年来纳米纤维素流变、涂层与复合材料研究趋势整理。CNF在具体水性配方中的效果高度依赖树脂、颜填料、电解质和分散工艺，需通过小试验证。
• Goetten de Lima, G. et al. Enhancing Barrier and Antioxidant Properties of Nanocellulose Films for Coatings and Active Packaging: A Review. ACS Applied Nano Materials, 2025.
• Habib, A. et al. Recent advancements in nanocellulose reinforced biopolymer hybrid composites: A review. Journal of Cleaner Production, 2025.
Note: This article is intended for technical exchange and discussion within the industry and is based on publicly available research and technological developments. The specific properties and performance of the materials may vary depending on raw materials, surface chemistry, dispersion state, formulation, and processing conditions. Actual applications should be validated through laboratory-scale testing. For applications involving food, medical, or other regulated fields, applicable regulations and compliance requirements for the end products must also be satisfied.