Lateral thermal expansion of cellulose Iβ and IIII polymorphs

Measurements of the thermal expansion coefficients (TECs) of cellulose crystals in the lateral direction are reported. Oriented films of highly crystalline cellulose I-beta and IIII were prepared and then investigated with X-ray diffraction at specific temperatures from room temperature to 250degreesC during the heating process. Cellulose I-beta underwent a transition into the high-temperature phase with the temperature increasing above 220-230degreesC; cellulose IIII, was transformed into cellulose I-beta when the sample was heated above 200degreesC. Therefore, the TECs of I-beta and IIII below 200degreesC were measured. For cellulose I-beta, the TEC of the a axis increased linearly from room temperature at alpha(a) = 4.3x10(-5) degreesC(-1) to 200degreesC at alpha(a) = 17.0x10(-5) degreesC(-1), but the TEC of the b axis was constant at alpha(b) = 0.5x10(-5) degreesC(-1). Like cellulose I-beta, cellulose IIII also showed an anisotropic thermal expansion in the lateral direction. The TECs of the a and b axes were alpha(a) = 7.6x10(-5) degreesC(-1) and alpha(b) = 0.8x10(-5) degreesC(-1). The anisotropic thermal expansion behaviors in the lateral direction for I-beta and IIII were closely related to the intermolecular hydrogen-bonding systems. (C) 2002 Wiley Periodicals, Inc.