Knowledge Bank

Infrared absorption spectra of oriented cellulose fibers have been observed using polarized radiation. Natural fibers are in general too thick but swelling them in NaOH solution followed by pressing and drying is an effective way of obtaining a suitable thickness in the $900-1100cm-1$ and $3100-3600cm-1$ regions. The dichroism observed for the bands which can be assigned agrees well with tha: predicted from the crystal structure1, e. g. the CH stretching bands are polarized perpendicular to the fiber axis. In the region of CH and OH deformation frequencies ($1200-1500cm-1$) nine bands are observed, of which four are polarized parallel and five, perpendicular to the fiber axis. Probable assignments will be given for these bands. In the region of CO and CC stretching frequencies ($800-1200cm-1$) all the bands are polarized parallel to the fiber axis. Observations were also made on deuterated cellulose i.e. cellulose which had been swelled in NaOD. Of the six OD stretching bands observed, five show parallel dichroism, indicating that the OH bands in cellulose are arranged predominantly parallel to the fiber axis. The deuteration of amorphous cellulose will also be discussed.