Atomic Layer Deposited TiO2 on a Foam-Formed Cellulose Fibre Network - Effect on Hydrophobicity and Physical Properties

Climate change and plastic pollution challenge us to develop alternatives for fossil-based plastics, and cellulose-based materials are excellent candidates for this. Foam forming technology for cellulose fibre products increases process efficiency, widens the raw materials base, and enables low-density structures from fibres. Low-density cellulose-based materials can be used, for example, for packaging, insulation, and construction materials. However, to achieve optimal performance, the resistance against moisture and mechanical compression ought to be enhanced. In this research, the effect of atomic layer deposited (ALD) titanium dioxide on four foam-formed cellulose-based structures was studied. The hydrophobicity of these materials was analyzed with water contact angle measurements. Moisture content and mechanical properties were tested at high humidity (50% RH and 90% RH) by analyzing moisture uptake and compression strength. Furthermore, the morphology and microstructures were evaluated with scanning and transmission electron microscopy (SEM and TEM). ALD treatment changed the hydrophilic materials to hydrophobic with 5 cycles of TiO2 for all four substrates. The effect on moisture content was milder but was observed strongest with unrefined and partly refined samples at 50% RH. A clear trend between moisture content and mechanical strength was detected since the compression strength increased with decreasing moisture content.