The Relationship Between Timber Chemical Compositions and Mechanical Properties Qiushi Peng A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy The University of Sheffield School of Architecture August 2019 Acknowledgements Throughout the conducting of the research, I have received a lot of support and assistance. I would like to thank my lead supervisor Dr Wen-Shao Chang, who provide a valuable support for my research by his wealth of knowledge in timber materials, rich experiences of experimentation and patient guidance. I would also like to thank Dr Graham Ormondroyd, Dr Morwenna Spear and Dr Simon Curling, who provided an advanced lab for my research. Their deep understanding and abundant experience supported me and gave me confidence in the experimental period. I would also like to thank Prof Richard Harris, Dr Martin P. Ansell and Mr Gervais Sawyer, who supported my research by their distinctive knowledge in timber industry. I would like to thank my parents for their unconditional support whilst studying abroad, I could not have finished my PhD without their sympathetic ear and wise advice. Last but not least, I would like to thank all my friends, Dr Henry Wu, Raymond Shih, Fang- Yu Liin, who shared their research experiences. I would also like to thank my flatmates, Yu-Ting Hung and Yingqi Liu, who supported me all the time in the hardest period. I II Abstract Timber is widely used both in modern and historic construction, with ageing being the most serious risk in the structural mechanical strength. A non-destructive test to predict timber mechanical properties is urgently needed and many studies indicated that chemical compositions have close relationships to the mechanical properties. Hence, this study focusses on the relationships between timber chemical composition and the corresponding mechanical strength, providing contributions to the non-destructive testing of timber mechanical properties. Non-destructive testing has a wide prospect both in evaluation of modern timber construction and historic timber framed building conservation. Heat treatment is a method to cause changes in timber, whilst FTIR is the technique for analysing its chemical compositions. Static and dynamic mechanical properties were tested by a 3- point bending and a dynamic thermal mechanical analysis (DMTA) facility, respectively. The changes of timber mechanical properties are the results of various combined chemical compositions. In general, condensation and cross-linking reactions play an essential role in timber strength improvement. The static bending mechanical properties, modulus of rupture (MOR) and modulus of elasticity (MOE) increase, whilst in the dynamic mechanical properties and Tan δ decrease, which indicates an increase in elasticity and/or decrease of viscosity. Pyrolysis reactions in hemicellulose and lignin, lead to a decrease in the timber static mechanical properties and increase in Tan δ of the dynamic ones. Both static bending mechanical properties (MOR and MOE) and dynamic bending mechanical properties (storage modulus, loss modulus and Tan δ) can be predicted by the peak areas of the normalised FTIR spectrum. The coefficients of determination (R-square) of all the regression models are between 0.62 and 0.9, which indicates that the models are functional. In studies of timber accelerated ageing, the changes of each peak area during heat treatment are regressed by a model where temperature and treatment period as independent variables. The model shows that new pine can be treated in a two-steps heat treatment, which involves an air and a vacuum step to obtain similar chemical compositions of 580 years old real timber by heat treatment. The R-square of the model is more than 0.7 and thus, shows effective regression. III IV Contents ACKNOWLEDGEMENTS..................................................................................................... I ABSTRACT ...................................................................................................................... III LIST OF TABLES ............................................................................................................... IX LIST OF FIGURES ............................................................................................................. XI CHAPTER 1 INTRODUCTION ............................................................................................. 1 1.1 Background and Motivation .................................................................................................. 1 1.2 Objectives ............................................................................................................................. 4 1.3 Outline of the thesis .............................................................................................................. 5 CHAPTER 2 LITERATURE REVIEW...................................................................................... 7 2.1 Timber composition .............................................................................................................. 8 2.1.1 Timber Cell Composition ................................................................................................... 10 2.1.2 Relationship between Chemical composition and Mechanical Bonding ........................... 17 2.1.3 Moisture Content and Environment Temperature ........................................................... 20 2.1.4 Summary ........................................................................................................................... 25 2.2 Changes of Timber Chemical Composition ........................................................................... 26 2.2.1 Chemical Composition Analysis Method ........................................................................... 27 2.2.2 Chemical Composition Changes During Natural Ageing .................................................... 37 2.2.3 Chemical Composition Changes from Artificial Treatment ............................................... 47 2.2.4 Mass Loss and Colour Change during Heat Treatment ..................................................... 55 2.2.5 Summary ........................................................................................................................... 60 2.3 Changes in Timber Mechanical Properties ........................................................................... 64 2.3.1 Static Mechanical Properties of Natural Aged Timber. ..................................................... 64 2.3.2 Static Mechanical Properties of Heat-Treated Timber ...................................................... 67 2.3.2 Dynamic Mechanical Properties of Timber ....................................................................... 70 2.3.3 Summary ........................................................................................................................... 76 2.4 Conclusions ......................................................................................................................... 77 CHAPTER 3 MATERIALS AND EXPERIMENT PLAN ............................................................ 81 3.1 Materials ............................................................................................................................. 81 3.2 Experiment Design .............................................................................................................. 85 V 3.3 Experiment Process and Facility .......................................................................................... 89 3.3.1 Heat treatment .................................................................................................................. 89 3.3.1 Chemical Analysis .............................................................................................................. 92 3.3.2 Static Mechanical Properties ............................................................................................. 93 3.3.3 Dynamic Mechanical Properties ........................................................................................ 93 3.4 Peak Fitting of FTIR ............................................................................................................. 94 CHAPTER 4 CHEMICAL COMPOSITION CHANGES DURING HEAT TREATMENT ................. 99 4.1 Mechanism of Chemical Composition Changes of the Timber Molecule ............................. 99 4.2 Chemical Composition Change of the Natural Ageing Process ........................................... 108 4.3 Equilibrium Moisture Content Change During Heat Treatment ......................................... 110 4.3.1 EMC Changes of New and Old pine .................................................................................110 4.3.2 Moisture Content Related to FTIR ...................................................................................114 4.4 Mass Loss of New and Old Timber During Heat Treatment ............................................... 115 4.5 New Timber Chemical Composition Changes During Heat Treatment ............................... 121 4.5.1 New Samples in Vacuum Treatment ...............................................................................121 4.5.2 New Samples in Air Treatment ........................................................................................128 4.5.3 Summary ..........................................................................................................................134 4.6 Old Timber Chemical Composition Changes