Open Collections

Abstract

Super-black materials absorb more than 99% of UV and visible light. They are attracting considerable scientific and industrial attention. Super-black materials traditionally have been made by etching metal alloys or creating a surface consisting of vertically aligned carbon nanotubes. But super-black materials have not been made from wood even though there are many natural super-black materials such as wing patches in birds and butterflies. This material, which was made by plasma etching transverse basswood (Tilia americana L.) surfaces has reflectivity averaging 0.68% (300 to 700 nm). Understanding this novel material is the focus of this thesis. A series of experiments were carried out to understand how plasma etching reduces the reflectivity of basswood, whether super-black wood can be made from species other than basswood and how plasma etching alters the properties of basswood. Plasma modification of surfaces was carried out using an inductively coupled oxygen plasma at various power levels. Reflectivity and colour measurements used a UV-Vis-NIR spectrophotometer and a colour spectrophotometer. Scanning electron microscopy and X-ray micro-computed tomography were used to examine the structural changes at plasma-etched surfaces and FTIR-spectroscopy was used to examine chemical changes. Experiments show that high-energy (500 W, 30 min) plasma etching of transverse basswood surfaces creates a lignin-enriched surface with deep pits, columns and tangled fibrils. Most of these features were also found in plasma-etched jelutong (Dyera costulata (Miq.) Hook.f.) and European lime (Tilia vulgaris Hayne Mill.) and their reflectivity was similar to that of basswood. Species lacking these characteristics were not super-black following plasma etching. Super-black colouration of transverse wood surfaces was retained when they were coated with a gold vanadium alloy indicating structural colouration. Super-black basswood surfaces were hydrophobic but fragile and susceptible to UV degradation. These limitations were overcome by treating the surface with a penetrating epoxy polymer, potentially expanding the applications of super-black wood. Plasma etching of radial longitudinal basswood surfaces enhanced ray-fleck figure, an important visual feature. Overall, high-power inductively coupled oxygen plasma modification is a promising, liquid free technology for modifying wood to create novel sustainable materials such as super-black wood.