**3.2 Proton conductivity in chitin system**

Regarding the proton conductivity in chitin and chitosan, which have already revealed, these values in sheet specimens show approximately 10−4 ~ 10−1 S/m [1]. The proton conductivity of the chitin system sheet increases monotonically with increasing humidity, and the value of chitin is tens of times higher, especially when the relative humidity is changed from 60% to 100%. In the case of chitosan, its value changes approximately 10 times higher. Further, we focused on acetyl group in chitin, and have revealed that relationship between proton conductivity in chitin system and the deacetylation by using Fourier transform infrared spectrometer (FT-IR). **Figure 5** shows the FTIR spectrum of chitin used in the experiment [10]. It was found that the acetyl group plays important role for appearance of proton conductivity in chitin system because the degree of deacetylation gave conductivity of anomalous behavior [10].

Furthermore, we have approached the proton conductivity in chitin system by using measurement of water contents and comparing chemical component. First, we have used sheet and fiber specimen of chitin, and measured the degree of swelling by microscopic observation after immersion experiment in water. As a result, it was confirmed that the sheet specimen was isotropically swelled in both the cross section and the in-plane, and the fiber specimen was anisotropically swelled by approximately 20% in both the fiber cross section and the fiber direction. From the above, it was clear that the chitin system introduced water molecules, so we made a comparison based on the water content and chemical component. The results obtained by these researches indicated that injection of water molecule and existence of acetyl group for promotion it, that is necessary to appearance of the proton conductivity in chitin system. However, it has not been completely understood that water molecule how to behave in chitin system yet.
