Making polyvinyl alcohol films iodinated at solution state before casting and its application

This research focused on the manufacture a polarizing film with PVA iodinated at solution before casting (IBC) film, which was prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing boric acid with 0, 0.1, 0.5, and 1.0 mol/L of I₂/KI aqueous solution, and I₂/KI(1:2) with 0, 5, and 10 wt % of PVA. The lights of wavelengths between 450 and 700 nm were polarized in UV analysis. The degree of polarization and transmittance of the IBC polarizing film (10 wt % I₂/KI and 0.5 mol/L boric acid) are 99.9% and 43.2%, respectively. The resistance of the heat and humidity of IBC polarizing films was higher than that of commercial polarizing films, which were elucidated by changing the transmittance of the films. This can be explained by the fact that the interaction between polyiodine molecules and PVA chains as the state of IBC is higher than that of the commercial state. The effect of boric acid may be strengthened for the resistance of heat and humidity. Crosslinking by boric acid improved thermal properties of the IBC polarizing films, resulting from the increases of degradation temperature in DSC and TG analysis. And the unit cell broadening occurred, which was caused by the intrusion of boric acid into PVA chains in X-ray analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polarizer effect and structure of iodinated before and after casting poly(vinyl alcohol) film

Poly(vinyl alcohol) (PVA)/iodine polarizing film was manufactured as follows: PVA iodinated in solution before casting (IBC film) and iodinated again after casting (IBC + IAC film) and then the IBC + IAC film was drawn in boric acid aqueous solution (IBC + IAC polarizing film), to improve the durability of the polarizing film under a humid and warm atmosphere. These effects were examined by investigating the structural and optical properties of the IBC, IBC + IAC, and IBC + IAC polarizing films. In the IBC state, the PVA chain segments that combined boric acid and iodine were regarded as defects of the crystal, the formation of I₃⁻ decreased with respect to weight gain of boric acid. In the IBC + IAC state, the strength of the peak corresponding to I₃⁻ decreased and the I₅⁻ peak increased. The iodine ions penetrated into crystal of the IBC state during the IAC process and formed a new PVA/iodine complex crystal at the 2θ = 20° in the X‐ray diffraction curves. In the IBC + IAC polarizing film state, another type of polarizing film (IBC + IAC polarizing film‐H) containing I₃⁻ ions mainly was manufactured as well as the IBC + IAC polarizing film to compare the effects of the I₃⁻ and I₅⁻ ions on the durability of the polarizing films. The durability of the I₃⁻ ions that were complexed with the PVA chain was higher than the I₅⁻ ions, which could possibly be separated to I₃⁻ and I₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of boric acid treatment method on the characteristics of poly(vinyl alcohol)/iodine polarizing film

Four types of polyvinyl alcohol (PVA)/iodine complex films were made using different boric acid treatments to prepare polarizing films having high durability under humid and warm atmospheres and to identify the effects of the boric acid treatment method on the formation of the PVA/iodine polarizing film. The four types of films were a PVA iodinated film(I), a PVA film that was iodinated and then treated with boric acid(I‐B), a PVA film that was treated with boric acid and then iodinated(B‐I), and a PVA film that was simultaneously treated with iodine and boric acid(I+B). The concentrations of I₂/KI were 0.03, 0.05, and 0.07 mol/L, and the concentrations of boric acid were 0.1, 0.3, and 0.5 mol/L. Comparing four type films treated with 0.05 mol/L I₂/KI and 0.5 mol/L boric acid, the conformation of PVA/iodine complexes for I‐B film were larger than the others. The degrees of polarization (ρ) of all of the films increased to very high levels (99.9%↑). The durability of I‐B was superior to B‐I or I+B, and the change in the ρ was below 5% because the boric acid treated after iodine treatment reduced the molecular mobility of the PVA/iodine complex chains through intracrosslinking, so that the PVA/iodine complex could not easily collapse. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of boric acid treatment on the crystallinity and drawability of poly(vinyl alcohol)–iodine complex films

A film iodinated at solution state before casting (BIBC film) and a film iodinated after casting (BIAC film) were prepared by casting an aqueous solution of poly(vinyl alcohol) (PVA) including I₂/KI and boric acid, and by successively soaking the PVA film in aqueous solutions of boric acid and I₂/KI, respectively. The boric acid-induced and I₂/KI-induced weight gains relative to the PVA were 3, 5, 7, and 10%, and 3, 5, 10, and 20%, respectively. The effects of boric acid and iodine on the crystallinity and drawability of the films were investigated. Although the crystalline structure of the BIAC films was not affected by boric acid, the boric acids in the PVA solution containing I₂/KI may have formed intra-molecular cross-links on the PVA chain to accelerate the formation of the PVA–iodine complex evenly, and subsequently interrupt the PVA crystallization through the BIBC film formation to render the resultant film slightly crystalline or practically amorphous. This occurred even at a much lower I₂/KI-induced weight gain (20%) than the minimum weight gain (125%) at which the iodinated at solution state before casting film without boric acid indicated a practically amorphous state. The maximum draw ratio of the films generally decreased with increasing boric acid content, which was mainly attributed to the increase of the extended segments of the PVA chains in the amorphous region due to the cross-links formed with the boric acids. The maximum draw ratios of the BIBC films tended to decrease more severely than those of the BIAC films.     

On the poly(vinyl alcohol)–iodine complexes

The color development due to the complex formation of poly(vinyl alcohol) (PVA) with iodine increased with increasing syndiotacticity of PVA. Isotactic PVA showed no color development. The color development of syndiotacticity-rich PVA film decreased with increasing annealing temperature for films before complexization, whereas that of atactic (commercial) PVA increased with it. Lower temperatures, the elongation of complex film, and the presence of boric acid enhanced the absorbance at 600 nm due to I^?₅. The complexes are assumed to be made by incorporation of polyiodines into aggregates of syndiotactic sequences in PVA. The polarizability and electric conductivity of complex films are investigated. © 1993 John Wiley & Sons, Inc.     

Role of boric acid in the formation of poly(vinyl alcohol)-iodine complexes in undrawn films

The role of boric acid in the formation of poly(vinyl alcohol) (PVA)-iodine complexes in undrawn films has been investigated by using wide-angle X-ray diffraction (WAXD) and high-resolution solid-state ¹³C NMR spectroscopy. From UV-vis absorption spectroscopy, it is confirmed that boric acid is necessary for the formation of the complexes in films that are treated with I₂/KI aqueous solutions at relatively low I₂ concentrations. The WAXD profiles indicate that, irrespective of the presence of iodine, crystallite sizes perpendicular to the chain axis become smaller by the addition of boric acid in the swelling media. Moreover, small crystallites and surficial parts of larger crystallites may be partially dissolved in the swelling process with water and boric acid suppresses the re-crystallization in the drying process with or without iodine. The ¹³C spin-lattice relaxation time analysis reveals that there exist two components called the mobile and the less mobile components in the films and the latter component, which contains the complexes and the crystalline component, is increased in the fraction by the presence of boric acid. The evaluation of the CH resonance line shows that some of the intermolecular hydrogen bonds are broken by boric acid, which increases the intramolecular hydrogen bonds. The CH₂ lineshape analysis also reveals that the gauche fraction is appreciably increased in the less mobile component by the addition of boric acid. These facts suggest that boric acid may promote the formation of PVA-iodine complexes particularly in the surficial areas of the crystallites probably by reducing the molecular mobility of the PVA chains by causing cross-linking among them.     

Polarization characteristics of poly(vinyl alcohol) films containing metal iodide

The polarization properties of iodine complex layer deposited by oxidation of poly(vinyl alcohol) (PVA) containing metal iodide were investigated. Heat-resistant polarizing films with high polarization efficiency were produced by oxidizing and stretching the PVA containing metal iodide. The results indicate that i) the polarization efficiency of a polarizing film prepared by oxidation of a PVA film containing 1 mmol or more of potassium iodide (KI)/g PVA at 0°C for 120 s in a 10 wt.-% aqueous solution of H₂O₂ and a degree of stretching of 400% is high, ii) the heat resistance of the polarizing film in this experiment is higher than that of a filter prepared from a commercial PVA film.     

Structure and processability of iodinated poly(vinyl alcohol) (III)‐structure of films iodinated in solution before casting

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 I₂/KI. The quantity of I₂/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 H₂O and I₂ molecules (zone I), evaporation of I₂ and partial decomposition of side groups (? OH) (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 α_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. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3497–3502, 2006     

Structure and processability of iodinated poly(vinyl alcohol). II. Drawability of iodinated films

The drawability of poly(vinyl alcohol) (PVA) films iodinated with 0.1, 0.3, 0.5, 1.0, and 2.0 mol/L I₂/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 I₂/KI concentration of the aqueous solutions used in the iodination. The MDR was generally increased with the concentration of I₂/KI and the draw temperature. However, it diminished instead when close to the highest temperature and concentration of I₂/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 I₂/KI. The greater the MDR was, the higher the degree of crystallinity, birefringence, and initial modulus were but the lower the melting temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95:1209–1214, 2005     

Preparation of syndiotacticity‐rich high molecular weight poly(vinyl alcohol)/iodine polarizing film with high water resistance

To enhance durability of poly(vinyl alcohol) (PVA)/iodine polarizing film under humid and warm atmospheres and to identify the effects of syndiotacticity on the polarizing efficiency (PE) and durability of PVA/iodine complex film, we prepared three high molecular weight (PVA)s with similar number‐average degree of polymerization (P_n) of 4000 and with different syndiotactic diad (s‐diad) contents of 53, 56, and 59%, respectively. It was found that syndiotacticity of PVA had a significant influence on the durability of PVA/iodine complex film in warm and humidity conditions (relative humidity of 80% and temperature of 50°C). That is, both desorption of iodine in PVA/iodine film and transmittance of film decreased with increasing syndiotacticity of PVA. In the case of PE, the values of over 99% were obtained at each optimum conditions. The change of PE (durability) of PVA/iodine complex films having P_n of 4000 and s‐diad contents of 56 and 59%, respectively, in warm and humidity conditions was almost zero, whereas those of PVA/iodine film with s‐diad content of 53% and with (P_n)s of 1700 and 4000 were about 60% and 50%, respectively, under same conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Color change of an iodinated poly(vinyl alcohol) film by physical deformation

The color change of an iodinated poly(vinyl alcohol) (PVA) film caused by physical deformation was investigated in this study. The color of a PVA film soaked in an aqueous potassium iodide (KI)/I₂ solution was light yellow, but it turned light blue when the film was physically deformed. The ultraviolet–visible absorption spectrum of the iodinated PVA film extended uniaxially in air was measured at various extension levels. Without deformation, the film showed UV absorption bands at 210, 290, and 360 nm. However, under deformation, the film showed new visible light absorption bands at 440 and 620 nm. From the UV–vis absorption spectra of several iodinated solutions, we found that the absorption wavelength of iodine was affected by the cohesive energy of the solvents. The KI/I₂ diethyl ether solution showed an absorption band at 460 nm, and this provided a clue to understanding the color change of the PVA–iodine complexes caused by physical deformation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43036.     

Conductivity studies of poly (vinyl alcohol)-iodine complex membrane

Summary The conductivities of polymers like poly (vinyl alcohol) (PVA) and its iodine complex membranes are reported here. PVA-iodine complex membrane was prepared by dipping PVA film into an I₂–KI solution. The formation of the complex membrane was confirmed by IR spectra. Conductivities were determined from 30 to 300 °C with a frequency ranges from 42 Hz to 500 KHz in solid state. It was observed that iodine is known to act as a catalyst for dehydration of PVA. A possible mechanism for the dehydration of PVA catalyzed by iodine is also explained.     

Role of adsorbed iodine into poly(vinyl alcohol) films drawn in KI/I2 solution

We have investigated the microstructure of the poly(vinyl alcohol) (PVA) films using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques. The samples were uniaxially drawn in water or KI/I₂ aqueous solution and then dried in an air-oven at 333 K for 1 h prior to SAXS and WAXS measurements. It was found that for the films drawn in KI/I₂ solution PVA chains in the microfibrillar structure are more extended upon the film drawing compared to the case of the films drawn in pure water, which is resulted from the correlation function analysis on the SAXS data. Adsorbed iodines into the film were anticipated to act as junction points between the microfibrils via the formation of the PVA-iodine complexes.     

Structure and properties of poly(vinyl alcohol)–iodine complex formed in the crystal phase of poly(vinyl alcohol) films

The structure and optical properties of the complex formed in the crystal phase of PVA that is caused by soaking at very high iodine concentration are investigated. In the resonance Raman spectra of lightly and heavily iodinated specimens, two Raman shifts appeared at 109 and 161 cm^?1. The 109 cm^?1 peak due to the I mode was much stronger than the 161 cm^?1 peak in a heavily iodinated specimen, whereas the peak was comparable with the 161 cm^?1 peak in a lightly iodinated specimen. The complex formed in the crystal phase is identified as the I mode complex. It has an averaged iodine–iodine distance of 3.2 Å, which is different from the 3.08 Å of the I mode complex formed in the amorphous phase. The effect of KI concentration in the soaking solution on the formation of the complex is also examined. The increased KI concentration in the soaking solutions at a fixed iodine concentration increases the amount of the complex formed in the crystal phase. The change in the hydrogen-bonding state in the crystal phase with the complex formation can be evidenced by IR and NMR. © 1994 John Wiley & Sons, Inc.     

Sorption and permeation of iodine in water-swollen poly(vinyl alcohol) membranes and iodine complex formation

The sorption and the permeation of iodine in water-swollen poly(vinyl alcohol) (PVA) membranes and the formation of PVA–iodine complexes were studied. The logarithms of the permeability and the diffusion coefficient decreased approximately linearly with the increase in polymer volume fraction. When the membrane was soaked in an aqueous I₂–KI solution, it contracted and Young's modulus increased. These findings were explained in terms of the formation of extra junction points due to the PVA–iodine complexes. These changes were reversible and could be recovered by replacing the solution with water. The length of the polyiodine chain increased with the increase in the degree of hydration of the membrane. At a fixed degree of hydration, Young's modulus of an iodine-sorbed membrane was much greater than that of a membrane soaked in pure water. This finding was explained on the basis of a double-network structure. The extension of the membrane promoted the complex formation, and the complex disappeared when the tension was released. The critical strain necessary for the complex formation was independent of the degree of hydration. The length of polyiodine chain increased with strain and became constant at higher strains.     

Study on the structure of nylon 6 films iodinated before forming. II. Investigation of the crystallization behavior through thermal analysis

Two kinds of amorphous nylon 6 films iodinated before forming from the powders iodinated with 0.2N and 1.0N I₂/KI aqueous solutions were prepared by a melt‐press, and isothermally treated at 20 to 80°C for 1 day to 20 days. Thermal analyses were performed to investigate mainly the crystallization behavior on the treatment. The DSC thermograms for the treated films exhibit three temperature‐groups of endothermic peaks at 60 ～ 70°C, 105 ～ 120°C, and higher than 150°C, which may be associated with the melting of the complex crystal, the relaxed γ‐crystal, and the relaxed α‐crystal, respectively. The film containing less I₂/KI and treated at the higher temperature exhibits the peaks associated with the more stable type of crystal. The peak temperature generally increases with the treating temperature and time. On the occasion of there being two peaks associated with the γ‐crystal and the α‐crystals, ΔH for the α‐crystal increases while that for the γ‐crystal decreases with increasing the treating time. The TG curves indicate two temperature‐zones of weight loss by the volatilization of I₂ from I₅^? and the decompositions of I₃^? and nylon 6. With increasing treating temperature, the % weight loss by the volatilization of I₂ decreases, and consequently the temperature of the weight loss by the decomposition of nylon 6 increases. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1062–1069, 2004     

The thermal‐electrical properties of polyvinyl alcohol/AgNO3 films

In this article, one cast technique to fabricate 20–40 wt %AgNO₃‐doped polyvinyl alcohol (PVA) composite films of which electrical resistance sharply dropped (4–5 order) in a certain temperature range was reported. The phase, structure thermal, and electrical resistivity properties of films at different heat treatment temperatures were studied by X‐ray diffraction (XRD), scanning electrical microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that all the AgNO₃ (20–40 wt %) doped PVA films presented an exothermic peak at 182°C. And the temperature of exothermic peak kept constant for various contents of AgNO₃. Meanwhile, the phase composition of the films was greatly affected by the heat treatment temperature. Ag particles were generated during the heat treatment process, and the content of Ag particles increased with increasing the temperature. The resistivity of PVA/AgNO₃ films decreased with increasing the temperature. And a sharp decrease appeared at 155–165°C due to the generation and contact of a mass of Ag particles at this temperature. The thermal‐electrical results suggested the applicability of these materials in temperature sensor, for example, critical temperature resistor thermistor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study on the structure and processibility of the iodinated poly(vinyl alcohol). I. Thermal analyses of iodinated poly(vinyl alcohol) films

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 I₂ molecules and I₂ molecules from I, partial OH side groups on PVA, and I₂ from I, 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 ions increased with increasing I₂/KI up to 65%, but above that weight gain, the rate of increase diminished and the amount of I ions from the I 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. ©2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2407‐2415, 2004     

Role of molecular weight of atactic poly(vinyl alcohol) (PVA) in the polarizing efficiency of PVA/azo dye complex film with high durability

To precisely identify the effect of molecular weight of atactic poly(vinyl alcohol) (a‐PVA) on the durability and polarizing efficiency (PE) of a‐PVA/dye polarizing film, we prepared two (a‐PVA)s with similar syndiotactic diad contents of 54.0%, degrees of saponification of 99.9%, and with different number‐average degrees of polymerization [(P_n)s] of 1700 and 4000, respectively. Through a series of experiments, it was found that molecular weight of a‐PVA had a significant influence on the durability of a‐PVA/dye film in heat and humidity conditions (relative humidity of 80% and temperature of 90°C). That is, both desorption of dye in a‐PVA/dye film and transmittance of film decreased with increasing molecular weight of PVA. The change of PE (durability) of a‐PVA/dye film in heat and humidity conditions was limited to about below 5%. The change of PE of PVA/dye film having P_n of 4000 especially was limited to 1%, whereas that of a‐PVA/iodine film with P_n of 4000, was almost 80% under the same condition. Also, transmittance of the drawn a‐PVA/dye film was far higher than that of the undrawn one. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 967–974, 2005     

Spectroscopic studies on the effect of doping with iodine on metal chloride-treated poly(vinyl alcohol)

The ultraviolet and infrared spectra of films of PVA treated with Co(11), Ni(11), and Cu(11) and then doped with iodine were studied. The spectra of the films preheated in air at temperatures from 25 to 180°C for 2 h were investigated. The obtained data revealed that treatment of PVA with different concentrations of each of the mentioned metal salts causes profound spectral changes. The analysis of UV spectra showed that the intensity of the band at 280 nm decreases with increasing metal concentration. It was also found that doping with iodine results in an appearance of an additional peak at about 360 nm. Careful examination of the infrared spectra indicated that the crystallinity of the samples depends on the concentration of metals and is affected by temperature treatment.