Browsing by Author "Rautkari, Lauri, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"
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- Antibacterial properties of Scots pine and Norway spruce
School of Chemical Technology | Doctoral dissertation (article-based)(2017) Vainio-Kaila, TiinaWooden surfaces in interior use hold potential for improving human health and wellbeing. The antibacterial properties of wood might reduce the possibility of cross-contamination from surfaces. In order to be able to control the hygienic quality of the wooden surface, the antibacterial effect should be better understood. The main aim of this thesis was to identify and evaluate the antibacterial properties of wood and its components. Different methods were developed and used to study the antibacterial properties of Scots pine and Norway spruce, heartwood and sapwood. The solid wood surface showed clear antibacterial properties, even when the extractives had been removed with acetone. Studies with the extracts showed several human pathogens, including methicillin-resistant Staphylococcus aureus, to be susceptible to pine heartwood and sapwood in particular, and also, to some extent, spruce. Besides extractives, lignin was the only separate wood component showing antibacterial properties. Wood volatile organic compounds (VOCs), which were studied in gaseous form, showed an antibacterial effect against various human pathogens. Several antibacterial compounds were found in all the extracts, however, they did not always explain the order of antibacterial activity between wood species. No single compound could alone explain the effect, hence the antibacterial effect derives either from different mechanisms in different species or from a synergistic effect. α-pinene and limonene could partly explain the antibacterial effect of the VOCs, but other components were also found to have an influence. Wood was found to have various antibacterial parts and a diverse range of bacterial pathogens that were sensitive to it. These results offer a good ground for the exploitation of the hygienic properties of wood and a good starting point for enhancing them further. Additionally, the extracts showed promising qualities and they should be studied further in regard to resistant pathogens. - Interactions between Scots pine heartwood extractives and wood decaying fungi
School of Chemical Technology | Doctoral dissertation (article-based)(2018) Belt, TiinaThe heartwoods of many wood species have natural resistance to degradation caused by wood decaying fungi. Many factors can contribute to the natural durability of heartwoods, but the most significant one is usually the presence of biologically active extractives in the wood material. This thesis investigated the interactions between heartwood extractives and wood decaying fungi in detail, using Scots pine as the wood material. The primary objectives of the thesis were to study the mechanisms of action of extractives and to explore the ways in which the extractives interact with fungi within the structure of wood. The mechanism of action studies focused on the antioxidant activity of extractives and on their ability to inhibit the enzymatic hydrolysis of wood polysaccharides. The antioxidant activity measurements showed that Scots pine heartwood extractives are active antioxidants, which means that they may be able to interfere with the radical-based degradative mechanisms used by wood decaying fungi, particularly brown rots. The extractives could also inhibit the action of hydrolytic enzymes, suggesting that they may be able to prevent the conversion of wood polysaccharides to digestible sugars. However, substantial hydrolase inhibition was only seen with a white rot enzyme preparation, which contained some enzyme(s) capable of modifying the heartwood extractives. The interaction studies used confocal Raman spectroscopy imaging to visualise the cellular level distributions of extractives and other chemical components in intact and decaying heartwood. The studies revealed that the phenolic pinosylvins were present throughout the heartwood tissues, suggesting that they have good ability to interact with fungi and their degradative agents during decay. However, the studies on decaying heartwood showed that pinosylvins were extensively degraded during incipient decay. The hydrophobic resin acids were only detected in the lumens of some tracheids and ray cells, but they were found to have higher resistance to degradation than the pinosylvins. Interestingly, the resin-rich extractives deposits found in tracheid lumens appeared to create local areas of reduced degradation in the decaying heartwood. The results of this thesis provide new information on the ways in which extractives can interact with fungi and contribute to natural durability. The results also increase our understanding of the origins of natural durability in Scots pine, the most abundant wood species in Finland. - Investigating moisture behavior of wood nanostructure using experimental and simulated scattering
School of Chemical Technology | Doctoral dissertation (article-based)(2024) Zitting, AleksiWood is a complex, hierarchical material used in practical applications and as a precursor to bio-based materials. As wood is formerly conductive tissue of a living organism, a tree, it is intrinsically linked with water. In most applications of wood, its interactions with water are important, as almost all of its properties depend on the moisture content (MC). Bulk of the wood structure consists of thick secondary cell walls and thus, many of its properties are fundamentally derived from the nanoscale properties and their moisture interactions. Studying the wood nanostructure in intact cell walls is difficult, thus the exact nanostructure remains elusive. This is especially true for the crystalline cellulose microfibril, despite it being the main structural component of wood. Scattering methods allow for non-destructive characterization of the wood nanostructure and how it responds to moisture in practical, ambient conditions. As scattering methods require prior assumptions about the underlying structure to interpret the results, they need to be supplemented with other methods. One such way are molecular dynamics (MD) simulations which allow recreating cell wall constituents on the atomic scale. By combining these two methods, complementary results on the cell wall nanostructure and how it responds to moisture are created. In this work, X-ray and neutron scattering experiments on Norway spruce were conducted. These were complemented with MD models of aggregated cellulose microfibrils, based on an up-to-date understanding of their structure. Computed scattering was also determined from the models. Neutron scattering of drying wood revealed that the changes in fibril packing depend on the drying region, with much less bundle deswelling during the initial constant-rate drying compared to the later falling-rate drying. MD simulations of fibril bundles revealed two distinct regions of water diffusivity as the system dried. X-ray scattering experiments of wood undergoing a moisture cycle combined with MD models revealed that the models predicted experimentally observed changes well. Both models and experiments showed that fibrillar aggregation below 10-15% MC is a significant factor in changes to cellulose crystallites. These changes remained even after the wood was delignified, with delignification not fundamentally changing the fibril moisture interactions, despite increasing the fibril packing distance. The impact of hemicelluloses and fibril size on computed scattering was investigated with MD models to aid with interpreting experimental data. The results indicated that hemicellulose-coated fibrils produce a notable scattering contribution to the small-angle region and can increase the apparent fibril size seen with scattering methods. Overall, the results of this thesis provide insight into the moisture-related changes inside the wood cell wall and how to interpret experimental scattering patterns from wood.