Infrared spectroscopy has provided valuable insights into the properties of cellulose. Temperature and mechanical strain can cause changes in the vibration frequency of chemical bonds. Frequency shifts in infrared spectra of cellulose induced by temperature indicated a phase transition of the hydrogen bonding pattern as well as the presence of weak C-H…O hydrogen bonds. Frequency shifts induced by mechanical strain allowed insight into molecular mechanics of cellulose. These studies often focused on the mid-range infrared range and pure, ordered cellulose samples. However, the majority of native cellulose is less ordered and accompanied by other polymers forming plant cell walls. This makes interpretation of infrared spectra more challenging as signals broaden and become more numerous. Sample preparation for mid-range spectroscopy is delicate and therefore of limited use for practical applications.<br/>Investigations of temperature dependent changes in mid-range infrared spectra of lignocellulosic materials will be presented. These unpublished observations stem from experiments conducted previously in Prof. Sugiyama’s lab during an exchange visit. Recent insights into the behaviour of pure cellulose now allowed the interpretation of these data. Temperature induced spectral changes of cellulosic materials were comparable to those observed in highly ordered pure cellulose, indicating the dominant contribution of cellulose to this phenomenon.<br/>Furthermore, the recent advances in the understanding of the molecular mechanics of ordered cellulose and the effects of strain on mid-range infrared spectra triggered the exploration of mechanical strain induced changes in near-infrared spectra. Near-infrared spectroscopy has the advantage of simple sample preparation, opening opportunities to use band-shift effects for material characterisation. Mechanically induced band-shifts in near-infrared spectra of wood and paper were observed and correlated linearly to the strain levels in the samples. Furthermore, the results confirmed observations of molecular deformation of cellulose under strain deduced from mid-range infrared spectra. The results suggested that it could be possible to use near-infrared spectroscopy to measure non-destructively internal strain levels in cellulosic materials. The relevance of these fundamental advances in understanding cellulose to solid wood processing of hardwoods will be made.

Temperature and strain induced frequency shifts of infrared signals of cellulosic materials: Fundamental and applied aspects

255th National Meeting (2018)

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