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 dioxideon four foam-formed cellulose-based structureswas 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 moistureuptakeand compression strength. Furthermore, the morphology and microstructures were evaluated with scanning and transmission electron microscopy (SEMandTEM). ALD treatment changedthe hydrophilic materials to hydrophobic with 5 cycles of TiO2forall 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 sincethe compression strength increased with decreasing moisture content.