Ecologically friendly wood electronics will help alleviating the shortcomings of state-of-art cellulose-based “green electronics”. Here we introduce iron-catalyzed laser-induced graphitization (IC-LIG) as an innovative approach for engraving large-scale electrically conductive structures on wood with very high quality and efficiency, overcoming the limitations of conventional LIG including high ablation, thermal damages, need for multiple lasing steps, use of fire retardants and inert atmospheres. An aqueous bio-based coating, inspired by historical iron-gall ink, protects wood from laser ablation and thermal damage while promoting efficient graphitization and smoothening substrate irregularities. Large-scale (100 cm2), highly conductive (≥2500 S m−1) and homogeneous surface areas are engraved single-step in ambient atmosphere with a conventional CO2 laser, even on very thin (∼450 µm) wood veneers. We demonstrate the validity of our approach by turning wood into highly durable strain sensors, flexible electrodes, capacitive touch panels and an electroluminescent LIG-based device.

A more extensive use of wood can reduce the environmental and climatic impact of the building industry. However, flammability limits the application of wood in multi-story and high rise timber buildings. Struvite mineralization has been shown to be a green solution for fire-resistant timber, but the influence of struvite minerals on the mechanical and gluing properties of wood as well as the combustion behavior have not been studied yet. In this work, we investigate the mechanical properties of mineralized wood by compression, bending, and tension tests as well as the gluing properties by tensile shear tests. Evolved gas analysis using GC/MSD system is applied to determine the thermal decomposition behavior of the mineralized wood, and Double shot analysis reveals volatile components of mineralized wood during the thermal decomposition process. The results show that the struvite mineralization treatment is a bulk modification technique that improves the fire resistance of wood. The mineralization can significantly influence the thermal decomposition behavior of wood, which results in an enhanced char formation. This char layer is a fire barrier that slows down the heat and oxygen penetration. The heat penetration rate of wood panels fabricated with mineralized wood is 0.6 mm/min during the cone calorimeter test, which is half of that of the wood panels fabricated with native wood. Transverse strength and stiffness under compression were improved, whereas mechanical loading in the longitudinal direction revealed similar or slightly decreased strength and stiffness. The mineralization had a minor impact on the gluing properties of solid wood. Wood mineralization by struvite may enable the more extensive use of wood in the construction sector as a substitute to less eco-friendly building materials.

Abstract. Heterogeneous ice nucleation on dust particles in the atmosphere is a key mechanism for ice formation in clouds. However, the conditions of a particle surface for efficient ice nucleation are poorly understood. In this study, we present results of immersion freezing experiments using differential scanning calorimetry on emulsified mineral dust suspensions, involving the two chemically identical, but morphologically different, kaolin minerals of kaolinite and halloysite. Kaolinite occurs in a platy morphology, while halloysites form predominantly tubular structures. We investigated six different halloysite and two different kaolinite samples. Our results show that, on average, the halloysite samples not only exhibit a higher ice nucleation (IN) activity than the kaolinite samples but also a higher diversity in terms of freezing onset temperatures and heterogeneously frozen fraction. Repeating the freezing experiments after shortly milling the samples led to a decrease in freezing onset temperatures and in the heterogeneously frozen fraction of the halloysite samples, bringing their IN activity closer to that of the kaolinites. To interpret these findings, the freezing experiments were complemented by dynamic vapor sorption (DVS), BET (Brunauer–Emmett–Teller) surface area measurements, pore ice melting experiments with slurries, and transmission electron microscopy (TEM) before and after milling. These measurements demonstrate an increase in surface area and the destruction of tubes by milling and provide evidence for the influence of the tubular structure of the halloysites on their IN activity. We identify the OH–Al–O–Si–OH functionalized edges as being the most likely site for ice nucleation, as the high geometric diversity of the edges best accounts for the high diversity in IN activity of halloysites. We hypothesize that the stacking of layers and the number of stacks in halloysite tubes and kaolinite platelets affect the freezing temperature, with thicker stacks having the potential to freeze water at higher temperatures. The notion that the edges constitute the IN-active part of kaolin minerals is further supported by comparing kaolin minerals with montmorillonites and feldspars, all of which exhibit enhanced IN activity in the presence of ammonia and ammonium-containing solutions. As OH–Al–O–Si–OH functionalized edge surfaces are the only surface type that kaolin particles have in common with montmorillonites and feldspars, the common feature of IN activity enhancement in ammoniated solutions can only be explained by ice nucleation occurring at the edges of kaolin minerals.