Project
The FAÇADE project proposes to develop a competitive and sustainable bio-sourced anti-UV coating to protect wooden façades, using bio-carbon as UV-absorber. Producing bio-carbon from agricultural and wood wastes is a way to provide added value to low-value by-products. In this project, bio-carbon will be produced from beech wood (Fagus sylvatica L.) and hemp (Cannabis sativa L.). Beech was selected as it is underutilised and of low value in Slovenia (mostly used for heating); moreover, beech wood is likely to increase in availability as changing climate conditions increase its prevalence in regions like Central Europe. Hemp is an annual plant that grows under various climate and soil conditions. Hemp was selected because it is largely undervalued in Slovenia where the plant is grown for cooking and medicinal oil (cannabidiol), products extracted from the seeds and leaves. The hemp stem, including fibres and shives, represents about 70 % of the plant’s dried weight and is likely to end up as low-value products or waste. The developed bio-carbon-based coating will be applied to both larch wood (Larix decidua Mill.), a soft wood usually used for façades without UV protection, and oak wood (Quercus sp.),as an example of hard wood.
The specific objectives of the project are:
– To perform an in-depth analysis of the effect of biomass carbonization processes on the structure and properties of bio-carbon needed for UV protection.
– To develop an efficient and reliable process to convert microscale bio-carbon particles to nanosized carbon particles (CNP) without damaging the inherent structure.
– To manufacture a novel, fully bio-based anti-UV coating and to assess the anti-UV performance on different wood species (larch and oak).
The first step of the FAÇADE project will be the development of nanosized carbon materials from biomass
Two sources of waste from the Slovenian biomass industry will be used for the production of bio-carbon: beech sawmill residue and hemp stalks. This biomass will undergo thermal treatments in a tube furnace that is capable of temperatures up to 1300 °C. Several process parameters will be studied (particle size, gas environment, pyrolysis rate, heating duration and stages, final pyrolysis temperature, chemical and physical activation). The aim of this study will be to understand the relationship between process and bio-carbon structure/properties. To ensure optimal UV protection, size of the carbon particles should be decreased to the nanoscale range. Microwave treatments will be performed on the microscale carbon particles. The properties of carbonized particles produced from thermal and microwave treatments described will be measured. Characterization of the particles includes investigation of the composition and elemental analysis of bio-carbon (moisture, volatile fraction, ash and fixed carbon content, content of C, H, N, S, and O), measure of surface area, pore volume, agglomeration and size distribution of the particles, study of the morphology, crystal structure and optical properties.
The second step of the FAÇADE project will be the development of a homogeneous coating
Within the project, natural drying oils will be considered as film formers for wood protection. Acid composition and viscosity of the film formers will be investigated before incorporation of bio-carbon nanoparticles (CNP) in the coating matrix. The two challenges inherent to the incorporation of CNP in the coating matrix are 1) avoiding the agglomeration of CNP into aggregates and 2) obtaining a homogeneous dispersion of the particles in the matrix. Surface functionalization of CNP can help to uniformly disperse carbon particles into the polymer matrix, nanofibrillated cellulose will be considered if necessary. The prepared coatings will be spread with a bar coater on the two wood species selected for the project (larch and oak). Process parameters influential to the coating process will be identified. Temperature, viscosity, and thickness of the coatings will be assessed.
The third step of the FAÇADE project will be the assessment of the performance of the coatings for wood protection
Analytical, physical and mechanical characterizations of the wood coatings will be performed. Commercial coatings will be incorporated in the study to set up a baseline of minimum physical and mechanical properties needed for the coatings. Uncoated wood (larch and oak), wood coated with commercial coatings, and wood coated with FAÇADE coatings will first undergo artificial weathering in a QUV machine up to 12 weeks as specified in the European standard NF EN 927-6 2018 relative to artificial weathering of wood coatings for outdoor applications. Four intermediary artificial weathering times will be defined, and natural on-site weathering will be conducted simultaneously for a minimal six-month period. A demonstration site will be set up on the roof garden area of the InnoRenew CoE’s new building. Thickness, colour, gloss, surface morphology, hydrophilic behaviour, anti-bacterial effect, UV-resistance, and tensile properties will be investigated for the un-weathered (controls) and weathered coating materials. To understand the UV protection mechanisms of CNP and the influence of CNP structure and/or CNP/matrix interaction on the properties cited above, results will be coupled with near-infrared spectroscopy and microscopical observations. Equivalence between artificial weathering and on-site weathering will be defined to predict the lifespan of the coatings and provide recommendations.
