SEM characterization of the cell walls in glow discharge plasma-treated wood: current and future applications

Arash JAMALI¹ and Philip D. Evans²

1. Plateforme de Microscopie Electronique, Université de Picardie Jules Verne, Amiens, France
2. Department of Wood Science, University of British Columbia, Vancouver, British Columbia, Canada

Many macroscopic properties and qualitative characteristics of wood, as a biomaterial with hierarchical structure, originate from its cell wall composition and organization at microscopic and molecular levels. The ultrastructure of wood can be modified to remove restrictions on its potential end-uses.
Cold plasmas, including glow discharge plasma, are reactive mixtures of charged particles that can be tailored to modify the surface characteristics of wood without producing unwanted waste. In this research, we undertook a comprehensive scanning electron microscopy (SEM) study to show the ability of plasma in modifying the cell wall’s ultrastructure and its effects on surface performance of wood.

Our results revealed that glow discharge plasma was able to etch the surface of both softwoods and hardwoods, and to create voids by etching pit membranes and borders as well as cell wall material. Furthermore, our SEM observation, supplemented with chromatic confocal profilometry, wet chemistry and FTIR analyses, revealed a preferential etching of holocellulose by plasma and enrichment of lignin at wood surfaces, making it possible to more easily see the distribution of lignin in cell walls. We show how such an increased porosity could be beneficial for greater accessibility of chemical reagents to wood surfaces, such as bleaching agents or wood coatings.

We also present an example of extension of plasma treatment to other biological materials, such as seeds, and show the effect of plasma-modified cell walls on seed imbibition using in situ environmental Scanning Electron microscopy (ESEM).

Acknowledgment:
The authors acknowledge the financial support of “Région Hauts-de-France” and Canadian strategic network ForValueNet-NSERC.

References:
[1] Jamali, A. and Evans, P.D. (2022). Chemical and morphological modification of softwood and hardwood surfaces by an oxygen glow discharge plasma. Journal of Wood Chemistry and Technology, 42(5): 381-394.
[2] Dauwe, R., Roulard, R., Ramos, M., Thiombiano, B., Mesnard, F., Gontier, E., Jamali, A. (2021). Etching of the seed cuticle by cold plasma shortens imbibitional leakage in Linum usitatissimum L. Industrial Crops and Products, 167. 113536.
[3] Jamali, A., Evans, P.D. (2020). Plasma treatment reduced the discoloration of an acrylic coating on hot-oil modified wood exposed to natural weathering. Coatings, 10(3), 248.