MECHANICAL PROPERTIES OF CELLULOSIC MATERIALS AT MICRO- AND NANOSCALE LEVELS
Authors: Siqun Wang, Seung-Hwan Lee and Qingzheng Cheng
Abstract: This chapter provides an overview of the mechanical properties of cellulosic materials at micro- and nano-scale levels, covering micro- and nano-mechanics, the relevant theory, the methodology, and potential applications for recent developments in the cellulose field. Firstly, we discuss nano-indentation as an approach for measuring modulus, hardness, and creep behavior. Nano-indentation is a very promising tool for measuring the submacro and nanoscale mechanical properties of biomaterials. With nanoindentation and atomic force microscope (AFM), we have been able to characterize a wide range of natural fibers that have the potential to be used as natural reinforced materials. Both regenerated cellulose fibers and pulp fibers have been studied. Using regenerated cellulose fiber as a model material, we have investigated the relationship between nanoindentation-based modulus and nano-tensile-based modulus. Ten hardwood species were tested to investigate the characteristic nanomechanical cell-wall properties of each species. Secondly, we describe the nano-three-point bending technique for measuring the bending modulus of single cellulose fibrils. Thirdly, we provide a method for measuring the compression strength of cellulosic materials through a micro-pillar compression test. Further, we discuss the fracture behavior of cellulosic materials, as well as the elastic modulus of wood cell walls as measured by an in-situ bending technique. Fourthly, we discuss the mechanical properties of the S1 and S3 layers in cell walls as detected by advanced tools. Finally, we will show how these mechanical properties are influenced by processes and environmental conditions such as molecular composition, thermal aging, and refining.
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