Thermal analysis and structural characterization of chitinous exoskeleton from two marine invertebrates

Thermomechanical and structural properties of two marine species exoskeletons, Antipathes caribbeana (black coral)and Limulus polyphemus (xiphosure), were studied using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). DMTA curves indicate the viscoelastic behavior and glass transition around 255 °C, black coral presented a second transition (175 °C)associated to the acetamide group attached to the ?-chitin chain. DSC measurements showed a endothermic peak around 100 °C, with enthalpies of 4.02 and 118.04 J/g, indicating strong differences between exoskeletons respect to their water holding capacity and strength water-polymer interaction. A comparative analysis involving DSC and X-ray diffraction showed that lower values ?H in xiphosure correspond to a material with a higher crystallinity (30), in contrast black coral exhibits higher values ?H and a lower crystallinity (19). FTIR confirmed ?-chitin based structure, at higher temperature diminishes the amide bands and a new one appears, related to C-N groups.