In the past decades, top-down wood modification approaches have improved wood properties as well as endowed it with new functionalities. This has given rise to high quality biocomposites for novel applications. However, preserving wood 3D structure and porosity while maintaining control over its micro- and nano-structure upon modification stills remains a current challenge. Here, a tailored route of chemical wood modification is presented which allowed efficient impregnation and in-situ polymerization of intrinsically conductive polymers, while preserving and exploiting wood hierarchical structure and mass transport system. The wood was treated with sodium sulfite at neutral pH for up to 14h at subcritical conditions. The treatment increased the surface area up to 170 m<sup>2</sup>/g and charged the wood with up to 375 µmol/g of sulfonic groups which favored absorption of both the oxidizer and the monomer during polymerization and acted as dopants and stabilizer of the impregnated polymer phase. This step was followed either by impregnation with prepolymerized PEDOT: PSS or by in-situ oxidative polymerization of pyrrole. PEDOT: PSS uniformly coated the cell wall lumens while polypyrrole efficiently polymerized throughout the cell wall. In both cases sulfonation increased the compatibility with polymers, facilitating and controlling the polymer deposition. With a more compatible and accessible structure, the treated wood samples showed a polymer weight gain up to 35 wt% and an increase of conductivity up to 16 folds compared with the polymer-native wood system. Electrodes obtained from the treated wood samples were also tested in pseudo/super-capacitor setups, proving that this type of materials could be further optimized for efficient use into novel energy storage devices.

In-situ sulfonation of lignin for conductive wood biocomposites

ACS Spring 2022

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