Masahisa Wada

Polymorphs of cellulose I, III_I, and IV_I have been investigated by X-ray diffraction, FT-IR, and solid-state ¹³C NMR spectroscopy. Highly crystalline cellulose III_I samples were prepared by treating cellulose samples in supercritical ammonia at 140 °C for 1 h, and conventional cellulose III_I samples were prepared by liquid ammonia treatment. The cellulose IV_I sample of highest crystallinity was that prepared from Cladophora cellulose III_I in supercritical ammonia, followed by the sample treated in glycerol at 260 °C for 0.5 h, whereas the lowest crystallinity was observed in ramie cellulose prepared by conventional liquid ammonia treatment followed by glycerol annealing. In general, the perfection of cellulose IV_I depends on the crystallinity of the original material: either of the starting cellulose I or of the cellulose III_I after ammonia treatment. The product thus obtained was analogous to cellulose I_β, which is what it should be called rather than cellulose IV_I. If the existence of the polymorph cellulose IV_I is not accepted, the observations on which it has been based may be explained by the fact that the structure termed cellulose IV_I is cellulose I_β which contains lateral disorder.

Measurements of the thermal expansion coefficients (TECs) of cellulose crystals in the lateral direction are reported. Oriented films of highly crystalline cellulose I_β and III_I were prepared and then investigated with X‐ray diffraction at specific temperatures from room temperature to 250 °C during the heating process. Cellulose I_β underwent a transition into the high‐temperature phase with the temperature increasing above 220–230 °C; cellulose III_I was transformed into cellulose I_β when the sample was heated above 200 °C. Therefore, the TECs of I_β and III_I below 200 °C were measured. For cellulose I_β, the TEC of the a axis increased linearly from room temperature at α_a = 4.3 × 10⁻⁵ °C⁻¹ to 200 °C at α_a = 17.0 × 10⁻⁵ °C⁻¹, but the TEC of the b axis was constant at α_b = 0.5 × 10⁻⁵ °C⁻¹. Like cellulose I_β, cellulose III_I also showed an anisotropic thermal expansion in the lateral direction. The TECs of the a and b axes were α_a = 7.6 × 10⁻⁵ °C⁻¹ and α_b = 0.8 × 10⁻⁵ °C⁻¹. The anisotropic thermal expansion behaviors in the lateral direction for I_β and III_I were closely related to the intermolecular hydrogen‐bonding systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1095–1102, 2002