Green and Simple Approaches Towards the Modification of Lignocellulosic Surfaces

Abstract

Aesthetic appearance, the good mechanical properties with regard to its light-weight and especially its natural abundance made wood an important material for the last centuries. However, wood is at the current situation often not the engineering material of choice as it suffers from its inherent drawbacks due to its hygroscopic character, e.g. the dimensional stability, and degradation processes including biological and UV degradation. To tackle the intrinsic drawbacks, numerous chemical modifications have been developed not only to inhibit the drawbacks but also to add new properties to wood such as transparency, magnetism or superhydrophobicity, to name a few. Though the current approaches are promising, they often dependent on reagents, especially solvents, which are hazardous for the environment. Referring to wood as a natural product the utilization of more green approaches would be crucial to make wood an important factor for the global transformation towards sustainable societies. Hence within this thesis, approaches have been developed to show that a chemical wood surface modification can be in agreement with green chemical methods and that modified wood can be used as a material for green engineering applications. A major part of this thesis is focused on the development of green chemical processes for wood modification, which are in agreement with the ’12 Principles of Green Chemistry’. Those principles were postulated by Paul Anastas and are meant to be a guideline but not an obstacle for the development of greener chemical processes. They also help to access the whole chemical procedure and to target the environmental hazardous parts of the process. It follows therefore that in particular solvents were identified as the hazardous part of most of the chemical wood modifications and therefore a process, which is fully in water was proposed by whom wood can be treated to achieve a superhydrophobic surface. Another focus of this thesis is on the role of wood in aspects of green engineering. As the thesis is part of the umbrella project of the ‘Swiss Energy Turnaround’ (NFP70), the utilization of wood for purposes of engineering and construction was put into a new spotlight. Since wood was mostly substituted by steel and concrete in matters of load bearing in construction in the past, the trust in the material has to be reconquered. Therefore, the design of a new ceiling construction was proposed with the objective to fully substitute the steel in the role of a fastener by a fully glued connection. However, there are several drawbacks associated with a fully glued connection, which mostly are due to the hygroscopic behaviour of the wood itself. Thus the thesis is dealing with a wood surface modification, where a priming system was developed based on sol-gel chemistry to facilitate the gluing process and to enhance the reliability of the composite. The developed priming system was shown to be a simple and versatile application as it is convenient with various epoxy based glue systems, and helps to control the amount of glue penetration. Moreover, the control of penetration is ensuring the ideal glue line thickness and in addition to that the primer is also capable of a chemical crosslink with the epoxy functionalities of the adhesive, which leads to a higher load bearing capacity of the composites in 3-point bending and 4-point bending as well as in push-out tests, which may allow to compete with traditional steel fastening systems. In this thesis, it is shown that despite the long history in the field of wood modification, there is still a large potential for the development of greener and especially more environmental friendly methods. It could also been shown that wood itself can be an ideal candidate as a lead material for the green engineering field and that it is important to combine the potential of green chemistry with the highly abundant and renewable resource wood Weniger anzeigen.