Lateral thermal expansion of chitin crystals

Measurements of the thermal expansion coefficients (TECs) of chitin crystals in the lateral direction are reported. We investigated highly crystalline α chitin from the Paralithodes tendon and an anhydrous form of β chitin from a Lamellibrachia tube from room temperature to 250 °C, using X-ray diffraction at selected temperatures in the heating process. For α chitin, the TECs of the a and b axes were αa = 6.0 × 10−5 °C−1 and αb = 5.7 × 10−5 °C−1, indicating an isotropic thermal expansion in the lateral direction. However, the anhydrous β chitin exhibited an anisotropic thermal expansion in the lateral direction. The TEC of the a axis was constant at αa = 4.0 × 10−5 °C−1, but the TEC of the b axis increased linearly from room temperature to 250 °C, with αb = 3.0–14.6 × 10−5 °C−1. These differences in the lateral thermal expansion behaviors of the α chitin and the anhydrous β chitin are due to their different intermolecular hydrogen bonding systems.