Abstract
The iodinated poly(vinyl alcohol) (PVA) powder was prepared from 10 wt% PVA aqueous solution to which 1.5 times of I$_2$/KI (1:2) with respect to PVA had been added, and conditioned under 50, 65, and 80%RH. Using these iodinated PVA powders, the preparation of films on a melt press was attempted at various temperatures. The fine structure of the films before and after deiodination was evaluated by thermogravimetry, X-ray diffractometry, differential scanning calorimetry and density measurement. The preparation of film on a melt-press was achieved in the temperature range of 80-13$0^{\circ}C$, and the achievable minimum temperature was lower with increasing moisture regain of the conditioned powders. The TG curve for melt-pressed films showed three weight loss zones associated with degradation and evaporation of excess I$_2$ molecules and I$_2$ molecules from I$_{5}$ $^{[-10]}$ ions (zone I), partial degradation of OH side groups on PVA and I$_2$ from I$_{3}$$^{[-10]}$ ions (zone II), the degradation of remaining OH groups and partial degradation of main chains (zone III-1), and degradation of the remaining main chains (zone III-2). The char (zone IV) may consist of KI salts. The weight loss of the film in the second zone corresponding to the partial degradation of -OH groups was remarkably little in the case of the film prepared from the powder of the lowest moisture regain (4.4%) at the highest temperature (13$0^{\circ}C$). All the films prepared on the melt-press were amorphous before deiodination, but crystalline after deiodination. The crystalline structure was identical with that of the untreated PVA. The degree of crystallinity of the film prepared from the powder of the lowest moisture regain was remarkably low.
