2025 AIChE Annual Meeting

(718c) Engineering Anisotropic CNF Alignment Via Wet-Laid Dynamics for Enhanced Mechanical Properties of the Fibrous Sheet

Authors

Akanksha Lakra - Presenter, Georgia Institute of Technology
While designing cellulose-based materials, the orientation of fibrils plays a critical role in their mechanical properties. However, controlling orientation at the nanoscale remains a fundamental challenge due to the unstable and isotropic nature of CNFs in solution during sheet formation. In this study, we focused on controlling the orientation of CNFs to tune the mechanical properties of the prepared sheets using a high-speed Dynamic Sheet Former (DSF). It is expected that a high MD/CD ratio of fibrils will result in the enhancement of the paper sheet. Firstly, we have developed an effective program to quantitatively analyze the orientation of CNFs in sheets based on the optical microscopy images. And then, we studied the correlation between the CNFs’ orientation and DSF parameters, including varying jet to wire speed ratio, CNF and Softwood Kraft pulp fibrils, tracer fibers, drum speed, nozzle pressure, MD/CD ratio, and feedstock concentration. The CNFs’ behaviors caused by these parameters lead to the difference in fibril alignment during the sheet formation process. The results show that when drum speed reaches 1500 meters per minute and nozzle pressure at 1 Bar, CNFs experience strong velocity gradients and shear stresses at the wall interface, leading to preferential orientation along the machine direction. The best aligned structures by the narrowing of the orientation angle distribution are achieved if the wire-to-jet ratio is 1.5. In the optimized conditions, the MD/CD ratio of fibrils could reach the highest value of 6.54, which is over twice that of what is obtained for commercial paper. This work sets up a good example for the study on the correlation between the nanofibril orientation and mechanical properties of CNF sheets, bringing new insights for controlling the anisotropy in CNF-rich material.