Wood has played a crucial role in human history, evolving from its early use as a building material in pre-historic times
to contemporary wooden skyscrapers. Its advantages are remarkable, offering a sustainable supply well into the future
when managed responsibly.
Despite these benefits, the timber industry faces challenges, including conflicting interests among stakeholders and the
impacts of global warming on forests. Coniferous forests, vital for softwood production, are under increasing pressure,
with shifts in climate favouring more temperature-resistant species. This results in a growing demand met by a limited
or decreasing wood supply, necessitating a significant increase in the service life of wood products.
To address the challenges in outdoor wood applications, where service life is often limited by biotic factors, conventional
wood preservation methods that are based on metal salt solutions or creosote have been dominant in the past and
present. However, these conventional preservatives are subject to increasingly strict regulation due to their fungicidal
nature. Novel wood protection methods, categorised as wood modification, are gradually gaining ground. This includes
thermally treated wood, acetylated wood, and wood treated with thermosetting resins like low-molecular-weight
thermosetting phenol urea formaldehyde (PUF) resin, which is the focus of this thesis.
The research in this thesis, initiated by a collaboration with Lignia Wood Company Ltd. in 2020, originally aimed to
explore aspects of upscaling their commercial wood modification process. However, a shift in focus occurred after the
industrial partner went into administration in 2021, leading the research towards more fundamental aspects of wood
modification.
The thesis comprises nine chapters, beginning with an introduction and literature review. It characterises wood species
and the resin used in Chapters 3 and 4. Chapter 5 compares the modification of different wood species with PUF resin,
revealing improved dimensional stability, although the efficiency varies based on factors like wood density and chemical
composition. The primary focus in Chapters 5 and 6 was on the anti-swelling efficiency (ASE) as the main quality criterion
for evaluating modified wood.
Chapter 6 explores process parameters in the modification process, highlighting the influence of curing time, resin
concentration, and resin alkalinity in different wood species. It also emphasises the importance of resin diffusion into
cell wall micropores during the drying stage, a concept that is further detailed in later chapters.
Chapters 7 and 8 delve into chemical interactions between wood and PUF resin, exploring curing reactions, retardation
factors, and resin-wood interactions at different length scales. These chapters utilise techniques such as differential
scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy.
Finally, Chapter 9 provides a comprehensive summary, critically discussing the main results, proposing alternative
experiments, and exploring potential future developments