Hierarchical Mechanical Properties of Wood Cell Wall in Microscale and Nanoscale

by Salimeh Saleh
Doctoral thesis
Date of Examination:2021-05-04
Date of issue:2021-09-21
Advisor:Prof. Dr. Cynthia Volkert
Referee:Prof. Dr. Cynthia Volkert
Referee:Prof. Dr. Holger Militz
Referee:Prof. Dr. Andrea Polle
Referee:Prof. Dr. Michael Seibt
Referee:Prof. Dr. Thomas Weitz
Referee:Prof. Dr. Gisela Ohms
Persistent Address: http://dx.doi.org/10.53846/goediss-8827

 

 

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Abstract

English

As one of the remarkable hybrid materials in nature, wood chooses the smartest way to bear mechanical loads by using the least amount of base materials and creates outstanding functional mechanical properties comparable with advanced composite materials. Wood is a cellular biomaterial with a complex multi-component system. The excellent mechanical properties of wood are the consequence of its hierarchical structure at all length scales. Ranging from the meter-scale of the tree trunk, millimeter-scale of growth rings, the microscopic scale of cellular structures such as tracheids, lumens, and cell walls, and the nanoscopic scale of the polymeric components (e.g., cellulose, hemicellulose, and lignin). This hierarchical architecture provides different properties for meeting the tree’s diverse requirements and adapting to climate change. Regarding the hierarchical structure of wood, the key challenge is developing mechanical characterization methods on the micro and nano scales to better understand the smaller scale mechanical properties and uncover whether small-scale architectures have unique properties that can affect the remarkable mechanical functionality of wood. Hence, the micrometer and nanometer analysis were incorporated into this research's original goal by implementing and developing nanoindentation and Atomic Force microscopy techniques. These two methods have been applied in this thesis to detect the ultrastructure and local mechanical properties of wood cell walls. The results allow the fundamental connections between the structure and mechanical response of wood to be revealed, including the important role of the cellulose-lignin interfaces in determining both stiffness and damping.
Keywords: wood cell wall; nanoindentation; atomic force microscopy; thermal treatment; hierarchical structure; mechanical characterization
 
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