Abstract
The poly(vinyl alcohol((PVA) film was iodinated with 0.1, 0.3, 0.5, 1.0, and 2.0 mol/ι $I_{2}$/KI aqueous solutions. The thermal properties of iodinated films were investigated by thermogravimetery(TG) and differential scanning calorimetery(DSC): With increasing concentration of $I_{2}$/KI, the weight gain increased up to 1.0 mol/ι, and then leveled off. TG curves for both untreated films and films iodinated with an aqueous solution of 2.0 mol/ι $I_{2}$/KI exhibited three distinct zones of weight-loss, but only the curve for the iodinated film indicated a char zone. For the untreated PVA film, the zones appear to result from the evaporation of $H_{2}O$ molecules absorbed (zone I), partial decomposition of the side groups(-OH) on the main-chains (zone II), degradation of the remaining side groups and partial degradation of main-chains (zone III-1), and degradation of remaining main-chains(III-2), respectively. For the iodinated film, evaporative components corresponding to each zone of weight-loss may consist of not only the same ones as for the PVA film but also others related to $I_{2}$/KI, such as excess $I_{2}$ molecules and $I_{2}$ molecules from $I_{3}^{-}$ and/or $I_{5}^{-}$ ions ($I_{5}^{-}{\rightarrow}I_{3}^{-}+I_{2}{\uparrow},I_{3}^{-}{\rightarrow}I^{-}+I_{2}{\uparrow}$) (zone I and II), and the char may consist of KI salts reformed from the excess $I_{2}$/KI solution through drying($I_{3}^{-}{\cdot}K^{+}+H_{2}O{\rightarrow}H_{2}O+I_[2}+KI$) and recovered from $K^{+}$ and $I^{-}$ ions ($K^{+}+I^{-}{\rightarrow}KI$). The starting temperatures of II and III-1 zones were decreased by the ozxidizing action of evolved $I_{2}$. The DSC thermogram for the untreated PVA film exhibited three endothermic peaks at 230, 270, and 37$0^{\circ}C$, corresponding to the melting of crystals, decomposition of side groups, and degradation of main-chains, respectively. But those for the iodinated films indicated two peaks at 145$^{\circ}C$ and 160~17$0^{\circ}C$ corresponding to the melting of crystals and the degradations of mainchains as well as side groups, the decreases in peak temperatures may be due to the roles of the polyiodide ion which disrupts the hydrogen bonding in crystalline region and the iodine molecule which acts as an oxidizer, respectively.
