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