The influence of hydrogen bonding on the deformation micromechanics of cellulose fibers

The influence of the intramolecular hydrogen bonding in regenerated cellulose II fibers, whose orientations have been strictly controlled by processing, is reported. It is shown that for highly oriented fibers chain deformation dominates the micromechanical behavior. However, direct evidence is presented that low orientation fibers are dominated by chain rotation and shear forces between crystalline domains. Using polarized Raman spectroscopy, it is shown that the 1095 cm(-1) band, corresponding to the C-O stretch modes in the cellulose chains, shifts towards a lower wavenumber upon the application of external deformation. This shift is shown to be nonlinear for this particular type of fiber, following the shape of the stress-strain curve. The initial shift rate is also shown to be directly related to the stiffness of the fiber, and subsequent saturation of this shift to the breakdown of hydrogen bonding and the onset of relative molecular motion. It is also shown that the 1414 cm(-1) band, corresponding to side groups (C-O-H) along the chain, and, therefore, is influenced by main-chain hydrogen bonding, also shifts nonlinearly towards a lower wavenumber. Both observed shifts are thought to be a direct result of molecular deformation. However, it is shown that the initial shift in the 1414 cm(-1) band, for fibers with a relatively high orientation, is initally greater in magnitude. Additionally, it is shown that this shift rapdily plateaus with both strain and stress, and this is thought to be due to the breakdown of the hydrogen bonding in the structure, and a potential cause of the yield point in the mechanics of the fibers. The use of Raman spectroscopy is proposed as a method for understanding detailed molecular processes in cellulose polymorphs. Speculative other polymer fibers which are hydrogen bonded, and speculative models for their deformation are also suggested and others reworked from exisiting literature on this subject.