Molecular modelling approach to fiber hornification: from microfibrils to mesopore

Understanding the effects of drying, thermal and chemical treatments on the fiber wall nanostructure would have a significant impact on the development of tailored fiber materials. In our ongoing research, we use spectroscopy, scattering and thermoporosimetry techniques to systematically study the property and ultrastructure changes in pulp fibers upon such treatments. Particular focus is on the mechanisms underlying hornification. As part of the effort, we use molecular modelling to support the interpretation of the experiments, and to link changes in measurable fiber properties with specific changes in the nanostructure.

We use a novel approach to modelling cellulose microfibril structures, in which an experimentally parameterized packing algorithm is used to create models of the local microfibril network. The resulting structure is then used as a basis for building all-atom (AA) and coarse-grained (CG) molecular models in the 5–10 and 20–100 nm length scale, respectively (Figure 1). The AA models address the effects of drying and temperature on fibril-fibril bonding and local aggregation, as well as water accessibility and diffusivity within the aggregates [1, 2]. The MARTINI 3-based CG models [3] address fibril aggregation on a larger scale, and its relation to mesopore formation. Similar models can also be used to study the formation of lamellar fibril structures.

Our work presents an atomistic simulation approach to studying drying and thermal effects on pulp fiber properties. The multi-scale approach enables us to study structures and mechanisms that are otherwise difficult to address in a molecular model. The joint experimental and computational work aims at improving our control over fiber properties and the performance of new fiber products.

[1] A. Paajanen, A. Zitting, L. Rautkari, J. A. Ketoja, and P. A. Penttilä. Nanoscale Mechanism of Moisture-Induced Swelling in Wood Microfibril Bundles. Nano Letters ,22 (13), 5143-5150, 2022. [2] T. Maloney, J. Phiri, A. Zitting, A. Paajanen, P. Penttilä and S. Ceccherini. Deaggregation of cellulose macrofibrils and its effect on bound water. Carbohydrate Polymers, 319, 121166, 2023. [3] F. Grünewald, M.H. Punt, E.E. Jefferys, P.A. Vainikka, M. König, V. Virtanen, T.A. Meyer, W. Pezeshkian, A.J. Gormley, M. Karonen, and M.S. Sansom. Martini 3 coarse-grained force field for carbohydrates. Journal of Chemical Theory and Computation, 18(12), 7555-7569, 2022.