ABSTRACT:To get more information on the structure of iodinated poly(vinyl alcohol) (PVA), thermal analyses of unoriented and oriented PVA films were conducted. Unoriented and oriented PVA films iodinated with aqueous solutions at selected concentrations were carried out by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG curves for the iodinated film shows four or five weight-loss zones associated with degradation and evaporation of excess I 2 molecules and I 2 molecules from I 5 Ϫ , partial OH side groups on PVA, and I 2 from I 3 Ϫ , the remaining OH groups and the partial main chains, the remaining main chains, and a very small amount of residue from PVA. The char of KI salts remained. By investigating the TG results, it was identified that the amount of I 3 Ϫ ions increased with increasing I 2 /KI up to 65%, but above that weight gain, the rate of increase diminished and the amount of I 5 Ϫ ions from the I 3 Ϫ ions increased. The TG curve for the oriented film was very similar to that for the unoriented film except for its greater weight loss at zone I due to narrow space in amorphous region. The DSC thermogram of iodinated films indicated two peaks at 145°C and 160 -170°C, corresponding to the melting of crystals and the degradations of OH groups and main chains, respectively. The maximum temperatures of peaks were much lower than that of the untreated one.
ABSTRACT:The drawability of poly(vinyl alcohol) (PVA) films iodinated with 0.1, 0.3, 0.5, 1.0, and 2.0 mol/L I 2 /KI aqueous solutions was examined with a tensile tester and a hand-operated drawer at 30 -150°C. The structure of the films drawn to a maximum draw ratio (MDR) and deiodinated was determined by X-ray diffractometry, differential scanning calorimetry, and birefringence. Generally, the improvement of the drawability for the PVA film via iodination was ascertained by the increased breaking strain and decreased yield stress on the stress-strain curves when increasing the I 2 /KI concentration of the aqueous solutions used in the iodination. The MDR was generally increased with the concentration of I 2 /KI and the draw temperature.However, it diminished instead when close to the highest temperature and concentration of I 2 /KI, which was likely due to molecular degradation by the action of iodine as an oxidizer. The variation of the structure of the films drawn and deiodinated seems to be dependent mainly upon the MDR rather than the concentration of I 2 /KI. The greater the MDR was, the higher the degree of crystallinity, birefringence, and initial modulus were but the lower the melting temperature.
The drawability of iodinated at solution before casting (IBC) polyvinyl alcohol films prepared by casting aqueous solutions of 10 wt % PVA containing 15.2, 39.8, 83.2, 117.0, and 140.1% was examined with a tensile tester at 20-608C. The tensile behavior of IBC films showed that the yield and breaking loads were much lower, and the breaking elongation was even higher than those of the unoriented iodinated after casting (IAC) films as well as the untreated PVA films. The maximum draw ratios of the films with the weight gain of 15.2, 39.8, 83.2, 117, and 140.1% were 4.5, 5.5, 8.5, 8.0, and 7.5, respectively, which were achieved at 208C in all. The crystallinity of all films increased by the maximum draw, regardless of crystallinity before drawing. The crystalline structure was recovered to the original PVA crystalline lattice by deiodination. Amorphous orientation and initial moduli increased with the maximum draw ratio, while the orientation of crystals was constant. The orientation and moduli increased up to the weight gain of 83.2%, whose highest draw ratio and initial modulus were 8.5 and of 7.1 GPa, respectively, and then decreased.
The use of remote microwave plasma for the polymerization and deposition of tetraethoxysilane on the surface of polytetrafluoroethylene was investigated using a mixture of Argon and dinitrogen oxide as carrier gas. Layers with thicknesses of 0.5-3 m were obtained, differing in chemical composition, surface energy, and flexibility/ brittleness, depending on the plasma power and both the treatment and aging times. In general, milder treatments and shorter aging times resulted in higher contents of organic structural elements in the layers and greater flexibility and surface energy. Anchoring between the layers and the bulk polytetrafluoroethylene was at least partially caused by fibrils interconnecting the two components. These results were obtained by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, contact angle measurements, and scanning electron microscopy combined with energy dispersive X-ray analysis.
Films iodinated at solution before casting (IBC films) were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing selected quantities of I 2 /KI. The quantity of I 2 /KI was controlled to obtain 15.2, 39.8, 83.2, 117.0, and 140.1%. The Thermogravimetry (TG) curves of the IBC film exhibited three distinct zones corresponding to the evaporation of H 2 O and I 2 molecules (zone I), evaporation of I 2 and partial decomposition of side groups (OOH) (zone II), degradation of the remaining side groups and partial degradation of the main chain (zone III-1), and degradation of the remaining main chain and the char zone corresponding to KI. The crystalline structure of the film with a weight gain of 15.2% was almost the same as that of the pure PVA, and the film with the weight gain of 140% was almost amorphous. The differential scanning calorimetry (DSC) thermograms of the IBC films with a weight gain of 15.2% and 39.8% indicated endothermic single or double peaks at around 180°C, corresponding to the crystal melting and degradation of side groups; those with weight gains of 83.2% and above indicated exothermic peaks at around 170°C, corresponding to crystallization, and broad endothermic peak at around 180 -200°C, corresponding to the crystal melting and degradation of side groups. The dynamic mechanical ␣ a transition of the IBC film with the weight gain of 140.1% appeared at around 20°C. X-ray diffraction and DSC analysis of deiodinated films show that the crystal structure, on deiodination of all the IBC films, regardless of crystallinity, returned to that of the pure PVA.
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