SUPERVISOR: Johannes KONNERTH

PROJECT ASSIGNED TO: Célia LOINTIER

Coating wood is essential to protect it from environmental factors and to enhance its appearance. Often, coatings contain synthetic hazardous compounds, released into the environment upon disposal. The complex composition of coated wood boards complicates the recycling process. Hence, there is a pressing need to develop bio-based, non-toxic and biodegradable alternative coating materials.

A promising approach lies in mimicking nature, particularly the vibrant hues found in certain fruits like that of Pollia condensata, a herbaceous plant native to Africa. These fruits showcase a brilliant blue colour without relying on pigments. Instead, the colour results from the reflection of light at the highly organized cellulosic network within the fruit’s cell wall. 

Biomimicking these nanostructures is replicated by extracting Cellulose Nanocrystals (CNCs) from wood. CNCs are highly crystalline, rod-like nanomaterials known to self-organize into chiral nematic phases in water. Upon drying, the helical structure formed by CNCs is preserved. The chiral pitch, known as the transverse distance over which the CNCs sheets undergo a full 360° twist, compresses during drying to reach dimensions comparable to the wavelength range of visible light. Once the film is fully dried, structural coloration arises. By modifying the pitch of the CNC structure, the reflected wavelength can be tuned, enabling precise control over the color of the surface.

All-wood aims at exploiting the unique optical properties of CNCs for the development of fully biobased wood coatings. The effect of different cellulosic starting materials, CNC preparation approaches, and drying conditions on the optical properties of coated wood surfaces are investigated. Microscopic investigation examines the wood/coating interface providing a deeper understanding into the structure and adhesion of CNC self-assembled coatings. Based on these findings, All-wood explores different application methods such as spray-coating.