The Oriented Structure of Lignin and its Viscoelastic Properties Studied by Static and Dynamic FT-IR Spectroscopy

Summary In order to define the role of lignin for stress transfer in the fiber wall, its orientation and mechanical interaction with other cell-wall components were investigated. Polarized infrared spectra of oriented thermomechanical pulp fiber sheets were used to determine the molecular orientation, and dynamic infrared spectroscopy was used to study the rheology of lignin in the cell wall. The results indicate that there is a preferred orientation of the phenyl-propane units of lignin along the fiber axis in spruce tracheids. This implies there is an ordered structure of lignin in the secondary wall of tracheids analogous to that of the cell-wall polysaccharides. The dynamic IR-spectra also indicated that lignin exhibits a much more viscoelastic behavior than do the carbohydrates, a knowledge of importance in the interpretation of transverse fiber properties.