Lignin as part of the moisture-sensitive wood cell wall nanostructure

Antti Paajanen, Aleksi Zitting, Paavo Penttilä

Research output: Contribution to conferenceConference AbstractScientificpeer-review

Abstract

In secondary cell walls of wood, lignin is part of a composite structure together with cellulose microfibrils and hemicelluloses. This moisture-sensitive system swells with the sorption of water, leading for instance to changes in the accessibility of its components to chemical agents. However, the exact morphology and role of the nanoscale lignin domains on these moisture interactions are not well known, in spite of their influence on both the materials properties of wood and fractionation of the cell wall components. It would thus be important to understand how lignin is part of the wood secondary cell walls and how it reacts to moisture.

We utilized a combination of X-ray scattering and molecular dynamics simulations to study the role of lignin in the wood cell wall nanostructure and its moisture behavior. We measured wide-angle and small-angle X-ray scattering (WAXS, SAXS) from delignified spruce wood samples at different moisture contents and compared the results to those from native, unprocessed wood. The WAXS results showed in both cases a similar distortion of the cellulose crystal structure when approaching the dry state, which was also observed in molecular simulations. According to our interpretation of the SAXS data, the removal of lignin from the cell wall led to a sparser packing of the cellulose microfibrils and formation of elongated pores with a cross-sectional diameter of 5-7 nm. The distance between microfibrils increased with the moisture content in both types of samples, and it was larger in delignified wood than in unprocessed wood at all moisture contents.

The results imply that the native wood cell walls contain elongated lignin domains of approximately 5-7 nm in cross-sectional diameter, which possibly restrict the swelling of the microfibril bundles with increasing moisture content. If the lignin is removed by delignification, the microfibril bundles have more freedom to swell by absorbing more moisture, as also evidenced gravimetrically. Nevertheless, the presence of lignin does not have any major effect on the qualitative moisture-induced swelling of cellulose microfibril bundles and deformations of the cellulose crystals by fibrillar aggregation during drying.
Original languageEnglish
Publication statusPublished - 20 Mar 2024
MoE publication typeNot Eligible
EventACS Spring 2024 National Meeting & Exposition - Ernest N. Morial Convention Center , New Orleans, United States
Duration: 17 Mar 202421 Mar 2024

Conference

ConferenceACS Spring 2024 National Meeting & Exposition
Country/TerritoryUnited States
CityNew Orleans
Period17/03/2421/03/24

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